RU2430083C9 - Method of producing acrylic acid from propane - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: according to the method: A) at least two initial gas streams containing propane, which form the reaction gas A, are fed into a reaction zone A, where one of said gas streams contains fresh propane; the reaction gas A is passed through at least one catalyst layer in reaction zone A in which partial heterogeneously catalysed dehydrogenation of propane results in formation of molecular hydrogen and propylene; molecular oxygen is fed into reaction zone A and oxidises molecular hydrogen in the reaction gas A to water vapour, and a gaseous product A is collected from reaction zone A, said product containing molecular hydrogen, water vapour, propylene and propane; B) the gaseous product A collected from the reaction zone A, while feeding molecular oxygen, is used in reaction zone B to supply at least one oxidation reactor with reaction gas B which contains molecular hydrogen, water vapour, propane, propylene and molecular oxygen, and propylene contained in reaction gas B undergoes two-step heterogeneously catalysed partial gas-phase oxidation in reaction zone B to obtain a gaseous product B containing acrylic acid as the end product, unconverted propane, molecular hydrogen, water vapour and carbon dioxide as by-products, as well as other secondary components with boiling point lower or higher the boiling point of water; C) gaseous product B is output from the reaction zone B and acrylic acid, water and secondary components with boiling point higher than that of water contained therein are separated in a first separation zone I through fractional condensation or absorption, wherein the residual gas I contains unconverted propane, carbon dioxide, molecular hydrogen, secondary components with boiling point lower than that of water, as well as, if necessary, propylene and molecular oxygen not converted in reaction zone B; D) residual gas I undergoes further treatment by washing carbon dioxide contained therein, separation of a partial amount of residual gas I, as well as, if necessary, separation of molecular hydrogen contained in the residual gas I using a separating membrane; E) after further treatment, unconverted propane-containing residual gas I is returned to reaction zone A as at least one of at least two propane-containing initial streams, where in reaction zone A, a certain amount (M) of molecular hydrogen is oxidised to water vapour, which makes up at least 35 mol % but not more than 65 mol % of the total amount of molecular hydrogen produced in reaction zone A and, if necessary, fed into said reaction zone A.

EFFECT: improved method of producing acrylic acid from propane.

22 cl, 1 ex

Description

The present invention relates to a method for producing acrolein, acrylic acid, or a mixture thereof from propane, in accordance with which:

A) - in the first reaction zone A, at least two reaction gas forming A are introduced, containing propane gaseous feed streams, at least one of which contains fresh propane,

- reaction gas A is passed through at least one catalyst bed of reaction zone A, in which molecular hydrogen and propylene are formed due to partial heterogeneously catalyzed dehydrogenation of propane,

- molecular oxygen is introduced into the reaction zone A, which oxidizes the molecular hydrogen contained in the reaction gas A to water vapor, and

- from the reaction zone A, a gaseous product A is selected containing molecular hydrogen, water vapor, propylene and propane,

B) the gaseous product A withdrawn from the reaction zone A, when molecular oxygen is supplied, is used in the reaction zone B to supply at least one oxidation reactor with a reaction gas B containing molecular hydrogen, water vapor, propane, propylene and molecular oxygen, and contained in In the reaction zone B, propylene is subjected to a heterogeneously catalyzed partial gas-phase oxidation in the reaction zone B to obtain a gaseous product B containing acrolein, acrylic acid, or a mixture thereof as the target product a, unconverted propane, molecular hydrogen, water vapor and carbon dioxide as by-products, as well as other by-products with boiling points below and above the boiling point of water,

C) the gaseous product B is removed from the reaction zone B and in the first separation zone I the target product, water and side components contained therein are isolated with a boiling point above the boiling point of water, the residual gas I remaining after their isolation contains unconverted propane, carbon dioxide, molecular hydrogen, side components with a boiling point below the boiling point of water, and, if necessary, propylene and molecular oxygen not converted in reaction zone B,

D) - the residual gas I is subjected in the second separation zone II to an additional treatment 1, which consists in washing the carbon dioxide contained therein and, if necessary, condensing, if necessary, the remaining water in it,

- as an additional processing operation 2, a partial amount of residual gas I is withdrawn from the production process,

- the residual gas I is subjected, if necessary, to an additional treatment 3, carried out in the third separation zone III, consisting in the release of molecular hydrogen contained therein by means of a separation membrane, and

- as, if necessary, the operation of the additional processing 4 is chemically reduced, if necessary, the molecular oxygen contained in the residual gas I,

moreover, the operations of the additional processing 1-4 are performed in random order, and

E) residual gas I containing unconverted propane after completing additional processing steps 1 and 2, and also, if necessary, 3 and / or 4 (circulating gas I) is returned to reaction zone A as at least one of at least at least two propane-containing feed streams.

Acrylic acid is an important chemical, used, in particular, as a monomer for the synthesis of polymers, which, for example, in the form of dispersions in an aqueous medium, are used as binders. In addition, acrylic acid polymers are used as super absorbers of moisture in the field of hygiene and other fields.

Acrolein is an important intermediate used, for example, to produce glutaraldehyde, methionine, 1,3-propanediol, 3-picoline, folic acid and acrylic acid.

A method for producing acrolein, acrylic acid, or a mixture thereof from propane, similar to the method indicated at the beginning of the description, is known, for example, from German patent application DE-A 3313573 and European patent application EP-A 117146.

The method proposed in the invention differs from similar methods described in German patent application DE-A 102004032129, European patent application EP-A 731077, German patent applications DE-A 102005049699, DE-A 102005052923, international applications WO 01/96271 , WO 03/011804, WO 03/076370, WO 01/96270, German patent applications DE-A 102005009891, DE-A 102005013039, DE-A 102005022798, DE-A 102005009885, DE-A 102005010111, DE-A 10245585, DE-A 10316039 and international application WO 03/011804, primarily the absence of an intermediate separation of the gaseous product A taken from the reaction zone A before it is fed to the reaction zone B. Advantage The reason for the absence of such an intermediate separation (primarily during its implementation by thermal methods) consists in eliminating the losses of valuable products and energy that usually accompany it, as well as equipment costs. However, it is not possible to completely abandon such an intermediate separation in the case of using the method indicated at the beginning of the description. On the contrary, like any other technology involving the circulation of gas streams, the method indicated at the beginning of the description requires removing from the production process not only at least one target product, but also at least one side component. Nevertheless, the method indicated at the beginning of the description turns out to be preferable in case of moving the place of separation of side components closer to the place of isolation of the target product, that is, to that area of the production process, in which to achieve the final goal one way or another it is necessary to use material and thermal gradients requiring appropriate energy and capital costs. Such a movement leads to a decrease in the total costs required for the production process under consideration as a whole.

A special side component of this technology with the circulation of gas flows is the molecular hydrogen formed in reaction zone A.

In contrast to exothermic heterogeneously catalyzed oxidative dehydrogenation of hydrocarbons in the presence of oxygen, in which there is no intermediate formation of free hydrogen (hydrogen that is split off from the dehydrogenated hydrocarbon directly forms water), accordingly, free hydrogen cannot be analytically detected under carried out in reaction zone A heterogeneous-catalyzed dehydrogenation refers to "traditional" dehydrogenation, which in The opposite of oxidative dehydrogenation occurs with an endothermic thermal effect (the next stage of heterogeneously catalyzed dehydrogenation can be exothermic combustion of hydrogen in reaction zone A) and at least intermediate formation of free molecular hydrogen. The implementation of such a process, as a rule, requires the use of other reaction conditions and other catalysts than carrying out the above oxidative dehydrogenation.

Thus, in accordance with the technology under consideration, a reaction proceeds in reaction zone A, which is accompanied by the inevitable release of hydrogen. Since molecular hydrogen released in the reaction zone A is not a reagent participating in the target reaction carried out in the reaction zone B, there is no natural hydrogen consumption according to the considered technology with circulation of gas flows. Therefore, the decision on where and in what form the molecular hydrogen generated in reaction zone A (and, if necessary, added to reaction zone A) should be taken out of the production process with circulation of gas flows is completely in the competence of the manufacturers (in the ideal case, a mole of propylene formed in reaction zone A accounts for a mole of hydrogen produced in this case).

According to the publications of the following prior art (see, for example, US patent US 3161670, European patent application EP-A 117146, German patent application DE-A 3313573) in the reaction zone A carry out an operating mode involving the selection of molecular oxygen, a joint filing of the total amount of molecular hydrogen formed as an inert gas to the point after separation zone I, followed by complete heterogeneously catalyzed combustion of hydrogen together with non-converted molecular oxygen in reaction zone B, accompanied by the resulting formation of water, and the return of all formed water to the reaction zone A, and consequently, the release of molecular hydrogen formed in the reaction zone A, carried out only during its second passage through the loop loop and only in the separation zone I in the corresponding oxidized form, i.e. water. This technology suffers from many shortcomings. Firstly, undetected molecular hydrogen complicates the processing of reaction gas B, since it is an explosive component of this gas, characterized by both a special ability to diffuse (some structural materials are capable of passing molecular hydrogen) and a pronounced reduction potential (own studies have shown that the presence of increased amounts of molecular hydrogen in reaction gas B adversely affects the lifetime of the heterogeneously-catalyzed catalysts gas phase oxidation), and secondly, the target product must be separated in separation zone 1 from a small amount of water, which requires a significant energy expenditure, since the target products have an increased affinity for water (increased amounts of water in reaction gas B, as a rule, also reduce the service life of partial oxidation catalysts, usually containing an oxidized form of molybdenum (Mo), since water contributes to the sublimation of molybdenum oxides). In addition, the specified hydrogen combustion after separation zone 1 is accompanied by local release of a very significant amount of heat, which is difficult to optimally local utilization. The problems related to the preferred use of excess molecular oxygen in comparison with the stoichiometry of the target reaction, which is necessary to prolong the service life of the partial oxidation catalysts used in the reaction zone B, are, however, inevitably entail an increased explosion hazard occurring in this reaction zone process (if the target product is acrylic acid and all the necessary amount of molecules is preliminarily added to the reaction gas B ull oxygen, the molar ratio of molecular oxygen contained in the reaction gas B to the propylene contained in it should be at least more than 1.5: 1, taking into account the complete combustion of a small part of the propylene).

According to the prior art, alternatively, process variants are also proposed in which the total amount of molecular hydrogen generated in reaction zone A as such is also sent together to a point after separation zone I. In this case, all propane contained in residual gas I is recommended and separate propylene from all other components of this gas, including molecular hydrogen, and return to reaction zone A only the stream formed as a result of this fission of C ₃ hydrocarbons. However, the disadvantage of this option is the need to first fully transfer the entire amount of C ₃ hydrocarbons to the condensed phase, and then recycle again from the condensed phase to the gas phase.

Another way to solve the above problem according to German patent application DE-A 3313573 is to completely oxidize the molecular hydrogen formed in reaction zone A, carried out in this reaction zone by supplying molecular oxygen to it, and then condensation of at least part of the formed water to the reaction zone B and, therefore, the allocation of this part of the water, or the joint supply of the entire amount of water formed in the reaction zone B. Both of these options have inherent disadvantages. First, condensation of water requires cooling the gaseous product A to temperatures much lower than the temperature required in reaction zone B.

Secondly, an extremely high temperature is subject to reduction, since the combustion of molecular hydrogen is accompanied by the release of an amount of heat, which is almost two times the amount of heat consumed for its formation in the process of dehydrogenation.

In addition, the presence of the entire amount of generated water in the reaction gas, as indicated above, leads to an increase in the cost of its separation in the separation zone I and, as a rule, to a reduction in the service life of the catalyst used in the reaction zone B.

Given the shortcomings of the above prior art, the present invention was based on the task of proposing the method indicated at the beginning of the description, which allows at least partially eliminating these disadvantages.

This problem can be relatively easily solved, thanks to the removal of molecular hydrogen formed in the reaction zone A and the generation of the form of its removal on a longer section of the process chain. When molecular hydrogen is removed in compliance with the specified parameters, carried out exclusively after reaction zone B, and preferred (only) part of molecular hydrogen is removed in the separation zone I in the form of water generated in the reaction zone A during hydrogen combustion, in the separation zone I, the joint water is separated formed in one way or another during partial oxidation in reaction zone B using known methods for isolating the target product and the corresponding effective equipment already available in this zone s.

The specified task according to the invention is solved by a method for producing acrolein, acrylic acid or a mixture thereof from propane, in accordance with which

A) - in the first reaction zone A, at least two reaction gas forming A are introduced, containing propane gaseous feed streams, at least one of which contains fresh propane,

- reaction gas A is passed through at least one catalyst bed of reaction zone A, in which molecular hydrogen and propylene are formed due to partial heterogeneously catalyzed dehydrogenation of propane,

- molecular oxygen is introduced into the reaction zone A, which oxidizes the molecular hydrogen contained in the reaction gas A to water vapor, and

- from the reaction zone A, a gaseous product A is selected containing molecular hydrogen, water vapor, propylene and propane,

B) the gaseous product A withdrawn from the reaction zone A, when molecular oxygen is supplied, is used in the reaction zone B to supply at least one oxidation reactor with a reaction gas B containing molecular hydrogen, water vapor, propane, propylene and molecular oxygen, and contained in In the reaction zone B, propylene is subjected to a heterogeneously catalyzed partial gas-phase oxidation in the reaction zone B to obtain a gaseous product B containing acrolein, acrylic acid, or a mixture thereof as the target product a, unconverted propane, molecular hydrogen, water vapor and carbon dioxide as by-products, as well as other by-products with boiling points below and above the boiling point of water,

C) the gaseous product B is removed from the reaction zone B and in the first separation zone I the target product, water and side components contained therein are isolated with a boiling point above the boiling point of water, the residual gas I remaining after their isolation contains unconverted propane, carbon dioxide, molecular hydrogen, side components with a boiling point below the boiling point of water, and, if necessary, propylene and molecular oxygen not converted in reaction zone B,

D) - the residual gas I is subjected in the second separation zone II to an additional treatment 1, which consists in washing the carbon dioxide contained therein and, if necessary, condensing, if necessary, the remaining water in it,

- as an additional processing operation 2, a partial amount of residual gas I is withdrawn from the production process,

- the residual gas I is subjected, if necessary, to an additional treatment 3, carried out in the third separation zone III, consisting in the release of molecular hydrogen contained therein by means of a separation membrane, and

- as, if necessary, the operation of the additional processing 4 is chemically reduced, if necessary, the molecular oxygen contained in the residual gas I,

moreover, the operations of the additional processing 1-4 are performed in random order, and

E) residual gas I containing unconverted propane after completing additional processing steps 1 and 2, and also, if necessary, 3 and / or 4 (circulating gas I) is returned to reaction zone A as at least one of at least at least two propane-containing feed streams,

characterized in that

in the reaction zone A, a certain amount of (M) molecular hydrogen is oxidized to water vapor, which is at least 5 mol%, but not more than 95 mol% of the total amount produced in the reaction zone A and, if necessary, introduced in it molecular hydrogen.

According to the invention, the amount of M (in all cases calculated as described above) is preferably at least 10 mol.%, But not more than 90 mol.%. The amount of M is particularly preferably at least 15 mol%, but not more than 85 mol%. Even better, if the amount of M is at least 20 mol.%, But not more than 80 mol.%. The amount of M is even more preferably at least 25 mol%, but not more than 75 mol%. Even better, if the amount of M is at least 30 mol.%, But not more than 70 mol.%. The amount of M is also preferably at least 35 mol.%, But not more than 65 mol.%. Even better, if the amount of M is at least 40 mol.%, But not more than 60 mol.%. Best if the amount of M is at least 45 mol.%, But not more than 55 mol.%. The amount of M according to the invention is even more preferably 50 mol%.

A significant advantage of the method proposed in the invention is that propane remains in a predominantly gaseous state of aggregation within the general circuit of its circulation, that is, there is no need to transfer it to the condensed liquid phase. Such an advantage is of particular value given the relatively high cost-intensiveness of the propane condensation process, due to the relatively complete absence of the polarity of this hydrocarbon.

Another advantage of the process of the invention is that the reaction gas B according to the invention necessarily contains a limited amount of molecular hydrogen. Although the presence of molecular hydrogen can lead to the above-mentioned negative phenomena (see German application DE-A 3313573 and European patent application EP-A 117146), molecular hydrogen has a positive feature, which is its chemical inertness in reaction zone B. there is at least 95 mol%, most often even at least 97 mol% or at least 99 mol% of molecular hydrogen passed through reaction zone B remains chemically unchanged.

Another positive feature of molecular hydrogen is its maximum thermal conductivity in a series of gases. According to Walter J. Moore, Physikalische Chemie, WDEG, Berlin (1973), p. 171, measured under normal conditions, the thermal conductivity of molecular hydrogen, for example, is more than ten times the thermal conductivity of carbon dioxide and almost eight times the thermal conductivity of molecular nitrogen, respectively molecular oxygen.

According to the data shown in table I of German patent application DE-A 3313573, the increased thermal conductivity of molecular hydrogen leads to a much lower selectivity for the formation of CO _x in reaction zone B in the presence of molecular hydrogen than in its absence. The increased thermal conductivity of molecular hydrogen leads to accelerated heat removal from the reaction site in reaction zone B, and therefore, lower surface temperatures of the catalyst, respectively, the combustion of only a small part of propylene. First of all, this refers to the case if, in accordance with the method proposed in the invention, the molecular hydrogen having the highest thermal conductivity and the highest thermal capacity is simultaneously involved in heat transfer, providing the corresponding synergistic effect.

According to the invention, fresh propane is understood to mean propane which has not taken part in the dehydrogenation carried out in reaction zone A. As a rule, it is introduced in the form of a component of crude propane, which preferably meets the specifications specified in German patent applications DE-A 10246119 and DE-A 10245585, and also contains minor amounts of components different from propane. Such crude propane can be obtained by the method described, for example, in German patent application DE-A 102005022798. In addition to fresh propane, as a feed stream containing other propane, as a rule, only the residual gas I additionally treated according to the invention is introduced .

According to the method of the invention, the supply of fresh propane is preferably carried out only in the reaction zone A, using it as a component of the initial gas mixture for this reaction zone. However, a partial amount of fresh propane in order to ensure explosion safety can, in principle, also be introduced into the initial gas mixtures for the first and / or second stages of oxidation of reaction zone B.

In a suitable embodiment of the process according to the invention, the reaction gas B sent to the reaction zone B also satisfies the specification given in German patent applications DE-A 10246119 and DE-A 10245585. In addition, according to the invention, it is expedient to carry out between reaction zones A and B the mechanical separation operation described in German patent application DE-A 10316039.

According to the invention, the flow rate of the reaction gas at a particular reaction stage means the volume of gas per hour, expressed in normal liters (nl), of the catalyst layer (for example, a fixed catalyst layer) passed through a liter, the volume expressed in normal liters being the volume that is reaction gas would occupy under normal conditions (at a temperature of 0 ° C and a pressure of 1 bar).

The flow rate of the reaction gas may also relate to only one of its components. In this case, we are talking about the volume of this component expressed in normal liters, passed through a liter of catalyst layer per hour (nl / l · h) (the presence of inert material in the fixed catalyst layer is not taken into account). In the case of using a catalyst layer, which is a mixture of pure catalyst with inert diluting molded bodies, the flow rate of the reaction gas can also relate only to the volume of pure catalyst contained in such a mixture, and the flow rate of the reaction gas in this case is accompanied by a corresponding note.

According to the invention, inert gas is generally understood to mean a component of a reaction gas which, under the conditions of the corresponding reaction, exhibits predominantly inert behavior, more than 95 mol.%, Preferably more than 97 mol.%, Respectively, more than 99 mol.% Of a similar component of the reaction gas, which refers to each of these components.

Typical reaction gases B, which, according to the method of the invention, can be used to feed into reaction zone B, have the following composition:

propylene from 4 to 25 vol.%, propane from 6 to 70 vol.%, water from 5 to 60 vol.%, oxygen from 5 to 65 vol.%, hydrogen from 3 to 20 vol.%

According to the invention, preferred reaction gases B have the following composition:

propylene from 6 to 15 vol.%, propane from 6 to 60 vol.%, water from 5 to 30 vol.%, oxygen from 8 to 35 vol.%, hydrogen from 2 to 18 vol.%

According to the invention, even more preferred reaction gases used for feeding into reaction zone B have the following composition:

propylene from 8 to 14 vol.%, propane from 20 to 55 vol.%, preferably from 20 to 45 vol.%, water from 10 to 25 vol.%, oxygen from 10 to 25 vol.%, preferably from 15 to 20 vol.%, hydrogen from 6 to 15 vol.%

The above preferred average propane contents in reaction gas B are given, for example, in German patent application DE-A 10245585.

The optimum molar ratio V ₁ of the propane content to the propylene content in the reaction gas B for the above ranges of the contents of these components is in the range from 1: 1 to 9: 1 (i.e., the separation of the propane / propylene mixture according to the present invention can preferably be carried out in accordance with international WO 04/094041). The preferred molar ratio V ₂ of the molecular oxygen content to the propylene content in the reaction gas B for the above ranges of the contents of these components is in the range from 1: 1 to 2.5: 1. According to the invention, the preferred molar ratio V ₃ of the propylene content to the molecular hydrogen content of the reaction gas B for the above ranges of the contents of these components is in the range from 0.5: 1 to 20: 1. The preferred molar ratio V ₄ of the water vapor content of the reaction gas B to the total molar amount of propane and propylene contained therein is from 0.005: 1 to 10: 1.

Particularly preferred molar ratio V ₁ in reaction gas B for reaction zone B (starting reaction gas mixture B) is from 1: 1 to 7: 1 or up to 4: 1, respectively, from 2: 1 to 6: 1, particularly favorable from 2 : 1 to 5: 1, respectively, from 3.5: 1 to 4.5: 1. The preferred molar ratio V ₂ in the initial reaction gas mixture B is from 1.2: 1 to 2.0: 1, respectively, from 1.4: 1 to 1.8: 1. The preferred molar ratio of V ₃ in the initial reaction gas mixture B is from 0.5: 1 to 15: 1, respectively from 0.5: 1 to 10: 1, respectively, from 0.5: 1 to 1.5: 1. The preferred molar ratio of V ₄ in the starting reaction gas mixture B is from 0.01: 1 to 5: 1, preferably from 0.05: 1 to 3: 1, preferably from 0.1: 1 to 1: 1, and particularly preferably from 0.1: 1 to 0.5: 1 or up to 0.3: 1.

According to the invention, non-explosive starting reaction gas mixtures B are preferred.

The decisive value for answering the question whether explosive or non-explosive should be considered the initial reaction gas mixture B is due to the fact that a similar mixture under certain conditions (at certain pressure and temperature) is capable of propagating combustion (ignition, explosion) initiated by a local source ignition (for example, hot platinum wire) (see standard DIN 51649 and the results of studies given in international application WO 04/007405). In accordance with the present invention in the case of the spread of combustion, the mixture should be considered explosive. If there is no spread of combustion, the corresponding mixture is considered non-explosive. According to the invention, the absence of explosiveness of the initial reaction gas mixture means the absence of explosiveness and the corresponding reaction gas mixtures resulting from the partial oxidation of a similar initial reaction gas mixture (see international application WO 04/007405).

As a source of molecular oxygen necessary for introducing into the reaction zone B not contained in the gaseous product A, molecular oxygen as such or a mixture of molecular oxygen with a gas behaving chemically inert in reaction zone B (or a mixture of similar inert gases) can be used, for example , a noble gas such as argon, molecular nitrogen, water vapor, carbon dioxide and so on (for example, air). According to the invention, molecular oxygen is preferably introduced in the form of a gas which contains not more than 30 vol.%, Preferably not more than 25 vol.%, Preferably not more than 20 vol.%, Particularly preferably not more than 15 vol.%, Better not more than 10 vol. % and particularly preferably not more than 5% by volume of other (different from molecular oxygen) gases. Particularly favorable is the introduction of pure molecular oxygen into reaction zone B.

The foregoing is in principle equally true for molecular oxygen, which, according to the method of the invention, is to be introduced into reaction zone A through additionally processed, returned to reaction zone A, optionally containing molecular oxygen, residual gas I. However, since the need for the reaction zone And in oxygen is relatively small, in accordance with the method proposed in the invention, primarily for reasons of economy, it can be optimal immediately satisfied thanks to the use of air as an oxygen source.

In accordance with the method of the invention, the additionally treated residual gas I returned to the reaction zone A, as a rule, still contains molecular oxygen unused in the reaction zone B, and its content in the additionally treated residual gas I returned to the reaction zone A can, in principle, be calculated also in such a way that, in accordance with the method of the invention, there is no need for additional supply of molecular oxygen to reaction zone A. However, The additionally treated residual gas I, which is returned to reaction zone A, according to the invention, in principle, does not have to contain oxygen, and in most cases according to the invention, an additional supply of oxygen to this reaction zone is necessary. Pure molecular oxygen or a mixture of molecular oxygen with one or more chemically inert gases, such as molecular nitrogen, water vapor, noble gases and / or carbon dioxide (for example, air), can be used in the reaction zones A and B to do this. According to the invention, it is preferable to use a gas that contains not more than 30 vol.%, Preferably not more than 25 vol.%, Preferably not more than 20 vol.%, Particularly preferably not more than 15 vol.%, Better not more than 10 vol.% And particularly preferably not more than 5 vol.%, respectively, not more than 2 vol.%, different from the molecular oxygen of other gases. In this case, the supply of pure oxygen is also particularly preferred.

The supply of pure oxygen described above both to reaction zone A and to reaction zone B according to the invention is preferred primarily because it does not lead to the accumulation of an excessive amount of inert gas in the circulation system according to the invention, which would require its subsequent removal from the production process.

According to the invention, in the most general case, a typical total content of components other than propylene, molecular hydrogen, water vapor, propane and molecular oxygen in the initial reaction gas mixture B is most often ≤40 vol.%, ≤35 vol.%, ≤30 vol. %, ≤25 vol.% Or ≤20 vol.%, Often ≤15 vol.%, Often ≤10 vol.%. According to the invention, a total content of such components of ≤5% by volume is difficult to implement. Up to 80 vol.% Of the total amount of such components of the initial reaction gas mixture B may be ethane and / or methane. The rest is primarily made up of carbon oxides (carbon dioxide, carbon monoxide) and a noble gas, as well as oxygen-containing side components such as formaldehyde, benzaldehyde, methacrolein, acetic acid, propionic acid, methacrylic acid and so on. Obviously, other ethylene, isobutylene, n-butane, n-butylenes and molecular nitrogen may also be similar other components of the initial reaction gas mixture. However, the fundamental advantage of the method proposed in the invention compared to the method described in European patent application EP-A 293224 is that the initial reaction gas mixture B may contain from 0.1 to 30 vol.%, Respectively, from 1 to 25 or 20 vol.%, often from 5 to 15 vol.% carbon dioxide. The content of carbon monoxide in the initial reaction gas mixture B is usually ≤5 vol.%, ≤4 vol.%, ≤3 vol.% Or ≤2 vol.%, In most cases ≤1 vol.%. However, the initial reaction gas mixture B typically contains ≤20 vol.%, Preferably ≤15 vol.%, Particularly preferably ≤10 vol.% And even more preferably ≤5 vol.% Nitrogen.

Any catalysts for heterogeneously catalyzed partial propane dehydrogenation are suitable for use in reaction zone A, for example, catalysts known from international applications WO 03/076370, WO 01/96271, European patent application EP-A117146, international application WO 03/011804, European patent application EP-A 731077, US patent application US-A3161670, international patent application WO 01/96270, as well as German patent applications DE-A3313573, DE-A 10245585, DE-A 10316039, DE-A 102005009891, DE -A 102005013039, DE-A 102005022798, DE-A 102005009885, DE-A 102005010111, DE-A 102005049699 and DE-A 102004032129.

The reaction zone A, with respect to a single transmission of propane, can have an isothermal structure characterized by targeted heat exchange with fluid (i.e., liquid or gaseous) fluids passing from the outside. With a similar comparison base, reaction zone A can also be adiabatic, that is, the predominant absence of the specified targeted heat exchange with the coolant passed from the outside. In this case, due to the implementation of the technical measures recommended in the aforementioned prior art and the technical measures described below, the thermal gross effect (with respect to a single passage of the initial reaction gas mixture through reaction zone A) can be endothermic (negative), autothermal (mainly zero), or exothermic (positive ) The catalysts recommended in the above publications can also be used to implement the process of the invention. Heterogeneous-catalyzed propane dehydrogenation, regardless of the mode in which it is carried out, adiabatic or isothermal, can, in principle, be performed both in a reactor with a fixed catalyst bed and in a reactor with a moving or fluidized (boiling) catalyst bed (the latter option in connection with the possibility of back-mixing is primarily suitable for heating the initial reaction gas mixture A in the reaction zone A to the reaction temperature due to the combustion present in the reaction gas And hydrogen in the presence of molecular oxygen contained in the circulating gas I).

Partial heterogeneous catalyzed dehydrogenation of propane to propylene typically requires the use of relatively high reaction temperatures. The propane conversion is usually limited by the thermodynamic equilibrium of the dehydrogenation reaction. A typical temperature of the dehydrogenation reaction is from 300 to 800 ° C, respectively, from 400 to 700 ° C. In this case, the dehydrogenation of a mole of propane is accompanied by the formation of a mole of hydrogen. Typical operating pressures in reaction zone A are from 0.3 to 5 or 3 bar. According to the invention, a preferred working pressure in reaction zone A is from 2 to 5 or 4 bar. The working pressure in this reaction zone can also reach 20 bar. In the case of a very high working pressure in the reaction zone A, for example, comprising more than 5 bar, correspondingly in the range from 10 to 20 bar, and the combustion of hydrogen in it in an amount of at least 50 mol.% Of the total amount formed in the reaction zone A of molecular hydrogen, it is preferable to expand the gaseous product A in a turboexpander and use the work done to drive the compressor used to compress the residual gas I before washing the dioxide carbon. At the same time, the gaseous product A is cooled to the temperature necessary for its subsequent processing in reaction zone B. High temperatures and removal of the resulting molecular hydrogen contribute to a shift in the equilibrium of the dehydrogenation reaction proceeding in reaction zone A towards the formation of the target product.

Since the heterogeneously catalyzed dehydrogenation reaction is accompanied by an increase in volume, the degree of conversion of propane can be increased by reducing the partial pressure of the dehydrogenation products. A simple method to reduce the partial pressure is, for example, carrying out dehydrogenation under reduced pressure (however, an increased dehydrogenation pressure tends to prolong the life of the corresponding catalyst) and / or adding predominantly inert diluent gases, such as water vapor, which when dehydrogenated usually behaves like an inert gas. Dilution with water vapor also leads to another advantage, consisting, as a rule, in reduced coking of the catalyst used for dehydrogenation, since water vapor interacts with the coke formed in accordance with the principle of coal gasification. In addition, the heat capacity of water vapor can partially compensate for the endothermic effect of the dehydrogenation reaction.

Limited amounts of water vapor usually stimulate the activity of the catalysts carried out in the subsequent partial oxidation reaction zone B, however, the presence of excessive amounts of water vapor in this reaction zone has a negative effect for the above reasons. In addition, according to the invention, a certain part of the hydrogen is subject to oxidation in the reaction zone A to water vapor. In this regard, according to the invention, it is preferable that the amount of water vapor introduced into the reaction zone A, in terms of the amount of reaction gas A introduced into it, is ≤20 vol.%, Preferably ≤15 vol.% And particularly preferably ≤10 vol.%. However, as a rule, it is usually ≥1 vol.%, Often ≥2 vol.% Or ≥3 vol.% And often ≥5 vol.%.

Other diluent gases suitable for heterogeneously catalyzed dehydrogenation of propane are, for example, nitrogen, noble gases such as xenon, neon or argon, as well as compounds such as carbon monoxide, carbon dioxide, methane and ethane. All of these diluent gases can be used individually or as mixtures with each other. When using a diluent gas generated as a by-product during the implementation of the circulation technology proposed in the invention, or a diluent gas in the form of fresh gas (respectively, a fresh gas component), the corresponding amount of gas according to the invention proposed should be removed from the production process, in connection with which the supply of the corresponding fresh gas according to the invention is less preferred. However, in accordance with the method of the invention, it is possible in principle to introduce into the circulating circuit a predominantly constant amount of diluent gas and make up for the corresponding losses by adding fresh diluent gas.

For heterogeneously catalyzed dehydrogenation of propane, in principle, any dehydrogenation catalysts known in the art are suitable. Such catalysts can roughly be divided into two groups. One of them includes oxide catalysts (for example, chromium oxide and / or alumina), while the other group consists of catalysts containing at least one, as a rule, relatively noble metal (for example, platinum) deposited on the carrier is usually of the oxide type. In particular, any dehydrogenation catalysts of those recommended in international application WO 01/96270, European patent application EP-A 731077, German patent applications DE-A 10211275, DE-A 10131297, international application WO 99/46039, application for US patent US-A 4788371, European patent application EP-A-0705136, international application WO 99/29420, US patent applications US-A 4220091, US-A 5430220, US-A 5877369, European patent application EP-A -0117146 and German patent applications DE-A 19937196, DE-A 19937105, DE-A 19937107. Especially suitable are the catalysts from examples 1, 2, 3 and 4 of German patent application Awning DE-A 19,937,107.

We are talking about dehydrogenation catalysts that contain from 10 to 99.9 wt.% Zirconium oxide, from 0 to 60 wt.% Alumina, silicon dioxide and / or titanium dioxide and from 0.1 to 10 wt.%, at least one element of the first or second main group, the third side group and the eighth side group of the Periodic system of elements, lanthanum and / or tin, provided that the sum of the contents of these components is 100 wt.%.

A particularly suitable dehydrogenation catalyst is also the catalyst indicated in the embodiment of the present invention.

The dehydrogenation catalysts are generally rods with a typical diameter of 1 to 10 mm, preferably 1.5 to 5 mm, and a typical length of 1 to 20 mm, preferably 3 to 10 mm, tablets, the dimensions of which are preferably similar to those indicated rods and / or rings, typical outer diameters and lengths of which are respectively 2 mm to 30 or 10 mm, and a suitable wall thickness is 1 mm to 10, 5 or 3 mm. The catalysts used to carry out the heterogeneously catalyzed dehydrogenation of propane in a fluidized bed (respectively, in a fluidized or moving bed) have a higher dispersion. According to the invention, a fixed catalyst bed is preferably used in reaction zone A.

Dehydrogenation catalysts, primarily used in embodiments of the present invention, as well as those recommended in German patent application DE-A 19937107 (especially those used in embodiments of this invention), are usually prepared in such a way that they are suitable for catalysis as dehydrogenation propane, and the combustion of propane and molecular hydrogen. Moreover, in the case of competition between the reactions of hydrogen combustion and dehydrogenation of propane on such catalysts, hydrogen combustion occurs much faster.

For carrying out heterogeneously-catalyzed dehydrogenation of propane, in principle, any known reactors and technological options are suitable. The latter are described, for example, in all cited prior art publications relating to dehydrogenation catalysts, as well as in the prior art cited at the beginning of the present description.

A suitable dehydrogenation technology of the invention is described in detail relatively also ^{Catalytica ® Studies Division, Oxidative Dehydrogenation and} Alternative Dehydrogenation Processes, Study Number 4192 OD, 1993, 430 Ferguson Drive, Mountain View, California, 94043-5272, USA. As indicated above, a characteristic feature of partial heterogeneously catalyzed dehydrogenation of propane is its endothermicity. This means that the heat (energy) needed to control the required reaction temperature, as well as for the flow of dehydrogenation, should be brought to the reaction gas A before heterogeneously catalyzed dehydrogenation and / or during its implementation. The heat required for the reaction, if necessary, must be given off by the reaction gas A.

In addition, due to the need to ensure a high reaction temperature for the process of heterogeneously catalyzed propane dehydrogenation, the formation of insignificant amounts of heavy boiling high molecular weight organic compounds, up to carbon, which are deposited on the surface of the catalyst and cause its deactivation, is typical. To minimize this negative phenomenon, reaction gas A, which must be passed over the surface of the catalyst in order to heterogeneously catalyze the dehydrogenation of the propane contained in it, as described above, can be diluted with water vapor. Under such conditions, partial or complete removal of carbon deposited on the surface of the catalyst occurs, in accordance with the principle of coal gasification.

Another possibility of eliminating carbon compounds deposited on the surface of the catalyst consists in passing oxygen-containing gas through the dehydrogenation catalyst periodically at an elevated temperature (it is advisable in the absence of hydrocarbons), which leads to quasi-combustion of the deposited carbon. A certain suppression of the process of carbon deposition can also be achieved due to the fact that molecular hydrogen is added to the subject heterogeneously catalyzed dehydrogenation of propane before passing over the catalyst at an elevated temperature.

Obviously, a mixture of water vapor with molecular hydrogen can also be added to the propane to be heterogeneously catalyzed by dehydrogenation. The addition of molecular hydrogen to the heterogeneously-catalyzed propane to be heterogeneously catalyzed also reduces the undesired formation of allen (propadiene), propine and acetylene as by-products.

Thus, in order to form reaction gas A (also referred to in the present invention as the starting gas mixture for reaction zone A or the starting reaction gas mixture A) to be passed through at least one catalyst bed, in the simplest case, only fresh propane and circulating gas I. In this case, the latter may already contain such an amount of molecular oxygen as is required for the combustion of hydrogen in reaction zone A necessary according to the invention. This buslovleno preferred use in the reaction zone in excess of molecular oxygen relative to the stoichiometric amount, the excess oxygen in accordance with the method of the invention is generally mainly in the circulating gas I.

In the aforementioned case, the circulating gas I constantly also contains such a quantity of water vapor, so that the latter together with the water vapor generated during the combustion of hydrogen in the reaction zone A, can ensure optimal efficiency of the overall production process. There is no need to supply other gaseous streams to the reaction zone A in this case. The required degree of propane conversion is achieved by passing reaction gas A once through reaction zone A.

It is obvious that in order to form the reaction gas A to be passed through at least one catalyst bed, in addition to fresh propane and circulating gas I, water vapor and / or molecular hydrogen can be added in addition to ensure optimal efficiency of the process of the invention. The molar ratio of molecular hydrogen to propane in the feed gas mixture for reaction zone A is typically ≤5: 1. The molar ratio of water vapor to propane in the feed gas mixture for reaction zone A can be, for example, from ≥0: 1 to 30: 1, suitably from 0.1: 1 to 2: 1, and optimally from 0.5 : 1 to 1: 1. In addition, additional molecular oxygen (in pure form and / or mixed with an inert gas) and / or additional inert gas can be introduced into the feed gas mixture for reaction zone A, if necessary. The required degree of propane conversion in the reaction zone A in this case can also be achieved by passing the reaction gas A once (initial gas mixture for reaction zone A) without the need for supplying other gaseous streams along the reaction path. In accordance with the present invention, by a reaction path in a reaction zone A is meant a flow path through the reaction zone A of the propane which is introduced into the reaction gas A before first passing it through at least one catalyst bed of the reaction zone A, depending on the degree of conversion of this propane in accordance with a heterogeneously catalyzed dehydrogenation reaction.

A reactor suitable for carrying out such a heterogeneously catalyzed propane dehydrogenation with a single pass of the feed gas mixture through reaction zone A without intermediate gas recharge is, for example, a tubular reactor with a fixed catalyst bed. In this case, the dehydrogenation catalyst is in the form of a fixed layer in one reaction tube or a bundle of reaction tubes. If the parameters of the hydrogen combustion required according to the invention in reaction zone A are calculated so that the gross reaction carried out in this reaction zone proceeds endothermally, it is advisable to heat the reaction tubes according to the invention outside (if necessary, they can also be cooled, of course ) The reaction tubes can be heated, for example, by burning a gas, such as a hydrocarbon such as methane, in the surrounding area. In the best case scenario, such direct heating should be used to heat only the initial sections of the contact tubes, the height of which is from 20 to 30% of the total height of the fixed catalyst bed, and the remaining sections of the contact tubes should be heated to the required reaction temperature, due to the radiant heat released during combustion. In this way, practically isothermal reaction conditions can be provided. A suitable inner diameter of the reaction tubes is from about 10 to 15 cm. The number of reaction tubes of a typical tubular dehydrogenation reactor is from 300 to 1000 or more. The temperature inside the reaction tubes is from 300 to 700 ° C, preferably from 400 to 700 ° C. The feed reaction gas mixture A sent to the tubular reactor is preferably preheated to the reaction temperature. The temperature of the gaseous product A (gaseous mixture) at the outlet of the reaction tube may be lower than the reaction temperature by 50-100 ° C. However, it can also exceed the reaction temperature or be at the same level with it. In accordance with the technology under consideration, it is advisable to use oxide dehydrogenation catalysts based on chromium oxide and / or alumina. In most cases, an undiluted dehydrogenation catalyst is used. To carry out dehydrogenation of propane on an industrial scale, several similarly connected tubular reactors of this type can be used and sent to the corresponding mixture of gaseous products A for processing into reaction zone B. If necessary, only two such reactors can be operated in dehydrogenation mode, while the third the reactor catalyst is subjected to regeneration.

A single pass of the source gas through reaction zone A can also be carried out in a reactor with a moving catalyst bed or in a reactor with a fluidized (boiling) catalyst bed, as shown, for example, in German patent application DE-A 10245585 and the literature cited therein.

According to the method of the invention, reaction zone A can in principle also consist of two sections. The reaction zone A of a similar design is recommended to be used primarily if the source gas for reaction zone A does not contain molecular oxygen (this can occur, for example, in the absence of molecular oxygen in the circulating gas I).

In such a case, in the first section, the heterogeneous-catalyzed propane dehydrogenation itself can be carried out, and in the second section after the intermediate supply of molecular oxygen and / or a mixture of molecular oxygen with an inert gas, the heterogeneous-catalyzed combustion of hydrogen required by the invention is necessary.

In accordance with the method proposed in the invention, in the most general case, it is advisable to operate the reaction zone A in such an operating mode that the degree of dehydrogenation of all propane entering it, in terms of a single passage of the reaction mixture through reaction zone A, is from 5 to 60 mol%, preferably from 10 to 50 mol%, particularly preferably from 15 to 40 mol%, and even more preferably from 20 to 35 mol%. The limitation of the degree of conversion of propane in the reaction zone A to the indicated values according to the invention usually turns out to be sufficient so that the unconverted propane in the subsequent reaction zone B predominantly acts as a diluent gas and can be returned to reaction zone A without significant losses during the implementation of the technology proposed in the invention technology, providing a low degree of conversion of propane, is that with a single pass of the reaction gas And through the reaction onnuyu zone A quantity of heat required for the endothermic dehydrogenation of propane is relatively small, and to achieve sufficient conversion of propane relatively low reaction temperatures.

As indicated above, according to the invention, it may be appropriate to carry out the dehydrogenation of propane in reaction zone A (for example, with a relatively low degree of conversion) in a (quasi) adiabatic mode. This means that the initial reaction gas mixture sent to the reaction zone A is first, as a rule, heated to a temperature of from 500 to 700 ° C, respectively from 550 to 650 ° C, for example, due to direct fire heating of the walls surrounding the mixture. In such a case, the only adiabatic passage of the reaction gas mixture through the catalyst bed is usually sufficient to provide both the required degree of propane conversion and the hydrogen combustion required by the invention, depending on the gross effect determined by the ratio of the amount of heat required for dehydrogenation and the amount of heat generated by the combustion of hydrogen, the reaction gas is heated, cooled, or behaves thermally neutral. According to the invention, an adiabatic mode is preferred in which the temperature of the reaction gas decreases by a factor of about 30 to 200 ° C as a result of a single transmission. Hydrogen generated during propane dehydrogenation, if necessary, can be subjected to heterogeneously catalyzed combustion in the second section of reaction zone A with the intermediate addition of molecular oxygen. Hydrogen combustion can also be carried out in adiabatic mode.

It should be noted that, first of all, when carrying out dehydrogenation in adiabatic mode, it is sufficient to use a single reactor in the form of a shaft furnace as a reactor with a fixed catalyst bed, the mixture of reaction gases through which is passed in the axial and / or radial direction.

In the simplest case, we are talking about a single closed reaction volume, for example, in the form of a tank with an internal diameter of 0.1 to 10 m or 0.5 to 5 m, in which is located on a supporting device (for example, a grate ) fixed catalyst bed. In this case, hot reaction gas A containing propane is passed axially through the reaction volume in which the catalyst is located and which, when carrying out the reaction in the adiabatic mode, is thermally insulated. Moreover, the catalyst may have the form of balls, rings or rods. Since the reaction volume in this case should be made in the form of an extremely economical apparatus, catalysts with any geometrical parameters that cause a particularly low pressure loss are preferred. First of all, these include catalysts with a large free space between particles or structured particles, for example, such as monoliths, respectively, cellular bodies. To conduct a radial flow of propane-containing reaction gas A, the reactor can consist, for example, of two cylindrical grate grids inserted one into the other and placed in a casing with a catalyst embedded in the corresponding annular gap. The casing of the adiabatic reactor, if necessary, can be provided with thermal insulation.

According to the invention, as catalysts for heterogeneously catalyzed propane dehydrogenation, the catalysts described in German patent application DE-A 19937107 (especially all catalysts used in the respective examples), as well as mixtures thereof with geometrically shaped bodies inert under the conditions of implementation, are particularly suitable heterogeneously catalyzed dehydrogenation.

After prolonged use, these catalysts are subjected to a simple regeneration method, which consists, for example, in the fact that, at the first stage, air diluted with nitrogen and / or preferably water vapor is passed through the catalyst bed with a temperature at the inlet of the reactor ranging from 300 to 600 ° C, often from 400 to 550 ° C. In this case, the flow rate of regenerating gas, such as air, passed through the catalyst bed, can be, for example, from 50 to 10,000 h ^-1 with an oxygen content in the regenerating gas from 0.1 or 0.5 to 20 vol.%.

In the next stages of regeneration, carried out under conditions similar to the first stage, air can be used as a regenerating gas. In the technical and industrial relation, it is recommended that the catalyst be purged with an inert gas (for example, nitrogen) before regeneration.

After this, it is recommended, as a rule, to perform additional regeneration of the catalyst with pure or diluted with inert gas molecular hydrogen with a preferred content of the latter in a mixture with an inert gas of ≥1 vol.%, And other similar conditions.

According to the invention, heterogeneously catalyzed dehydrogenation of propane in reaction zone A, accompanied by a relatively low degree of conversion (≤30 mol%), can in all cases be carried out at a flow rate through the catalyst (catalyst bed) of both the entire reaction gas and the propane contained therein similar to the flow rate in variants with high propane conversion (> 30 mol%). The flow rate of reaction gas A can be, for example, from 100 to 40,000 or 10,000 h ^-1 , often from 300 to 7,000 h ^-1 , often from 500 to 4,000 s ^-1 .

A particularly preferred embodiment of the heterogeneously catalyzed propane dehydrogenation carried out in reaction zone A (especially when it is passed once and with a conversion of 15 to 35 mol%) involves the use of a shelf reactor.

Such a reactor contains several layers of dehydrogenation catalyst sequentially arranged in its volume. The number of catalyst layers can be from 1 to 20, suitably from 2 to 8, as well as from 3 to 6. An increase in the number of shelves helps to increase the degree of conversion of propane. The catalyst layers are sequentially ordered, preferably in the radial or axial direction. In production and technical terms, it is advisable to use fixed catalyst beds in such a shelf reactor.

In the simplest embodiment, the fixed catalyst beds are ordered along the axis of the shaft reactor or in an annular gap formed by inserted into each other cylindrical grate grates. The annular gaps may also have the form of segments located one above the other, and the radially transmitted gas flows from one segment to the next, located above or below its segment.

In a suitable embodiment of the design of the shelf reactor, reaction gas A, on the way from one catalyst bed to another, is subjected to intermediate heating, for example, by passing it over the fins of a heat exchanger heated by hot gases, or through pipes heated by hot flue gases (if necessary, also similarly organized cooling of the reaction gas A).

When operating a shelf reactor in adiabatic mode and using catalysts, mainly described in German patent application DE-A 19937107 (in particular, in the corresponding examples), it is sufficient to introduce into the corresponding shelf reactor, the reaction gas mixture, preheated to a temperature of 450 to 550 ° C, and kept inside the reactor at the indicated temperature. This means that the total dehydrogenation of propane should be carried out at extremely low temperatures, which is especially beneficial for the duration of the period of operation of the fixed catalyst beds between two successive regeneration cycles. To ensure higher degrees of conversion of propane to a shelf reactor, it is advisable to direct the reaction gas mixture preheated to higher temperatures (they can reach 700 ° C) and to hold the mixture inside the reactor at the indicated elevated temperature.

In accordance with an even more preferred embodiment, the intermediate heating of reaction gas A described above should be carried out by a direct method (autothermal operating mode is possible). To this end, a limited amount of molecular oxygen, for example, in the form of a component of the circulating gas I, is added to the reaction gas A already before it is passed through the first catalyst bed (in this case, the initial reaction gas mixture A should preferably contain molecular hydrogen added to it) and / or between two successive catalyst beds. This allows a particularly targeted and controlled manner to affect the required according to the invention, as a rule, catalyzed by the dehydrogenation catalysts themselves combustion of a limited amount of molecular hydrogen contained in the reaction gas A generated in the process of heterogeneously catalyzed dehydrogenation of propane and / or added to the reaction gas A [in the production - from a technical point of view, it may also be advisable to load additional catalyst layers into the shelf reactor a, which catalyzes hydrogen combustion especially selectively (similar catalysts are shown, for example, in US patent applications US-A 4788371, US-A 4886928, US-A 5430209, US-A 5530171, US-A 5527979 and US-A 5563314; additional catalyst layers can be alternated, for example, with the layers containing a dehydrogenation catalyst present in the shelf reactor, similar catalysts also suitable for the aforementioned hydrogen combustion in the second section of reaction zone A]. The heat generated in this case, depending on the amount of molecular hydrogen burned, facilitates the heterogeneously catalyzed dehydrogenation of propane in the general exothermic, general autothermal (thermal gross effect is basically zero) or the general endothermic operating mode. An increase in the residence time of the reaction gas in the catalyst bed (it is preferred according to the invention) contributes to the dehydrogenation of propane at a decreasing or essentially unchanged temperature, which, in turn, prolongs the period of operation of the catalyst between two successive regeneration cycles.

The specified oxygen replenishment in the General case should be carried out so that its content in the reaction gas And in terms of the molecular hydrogen contained therein is from 0.5 to 50 or 30 vol.%, Preferably from 10 to 25 mol.%. In this case, pure molecular oxygen (which corresponds to the preferred embodiment of the invention) or molecular oxygen diluted with an inert gas, for example carbon monoxide, carbon dioxide, nitrogen and / or noble gases, and especially air, can be used as an oxygen source. According to the invention, molecular oxygen is preferably used in the form of a gas that contains not more than 30 vol.%, Preferably not more than 25 vol.%, Preferably not more than 20 vol.%, Particularly preferably not more than 15 vol.%, Even more preferably not more than 10 vol.% and particularly preferably not more than 5 vol.% of other gases other than molecular oxygen. Pure molecular oxygen is particularly preferably used for this recharge.

Since during the combustion of one mole of molecular hydrogen with the formation of water, almost twice as much energy is released (about 240 kJ / mol) than is required for the dehydrogenation of one mole of propane with the formation of propylene and hydrogen (about 120 kJ / mol), the autothermal configuration described above reaction zone A in an adiabatic flange reactor is particularly preferred for solving the problem of the present invention, but requires the combustion of about 50 mol.% of molecular hydrogen generated by dehydrogenation OPANAL in reaction zone A.

The advantage of the method proposed in the invention is manifested not only if about 50 mol% of the molecular hydrogen formed in it is burned in the reaction zone A. Rather, it is also shown already in the case, if the reaction zone A is carried out accompanied by the formation of water combustion from 5 to 95 mol.%, Preferably 10 to 90 mol.%, Particularly preferably 15 to 85 mol.%, Even more preferably from 20 to 80 mol.%, more preferably from 25 to 75 mol.%, more favorably 30 to 70 mol.%, more preferably from 35 to 65 mol.%, most preferably from 40 to 60 mol.% or from 45 to 55 mol.% Of molecular hydrogen generated in this reaction zone (preferably in the above-mentioned adiabatic about the reactor).

The above feeding of oxygen should generally be carried out in such a way that its content in the reaction gas A is from 0.01 or 0.5 to 3 vol.% Based on the amount contained in the gas of propane and propylene.

The heterogeneous-catalyzed dehydrogenation of propane in an isothermal mode can be further facilitated by the incorporation of hermetically closed elements (for example, in the form of tubes) into the empty spaces between the catalyst beds of the shelf reactor, which are subjected to a preferred but optional vacuum before installation. Such embedded elements can also be placed in a particular catalyst bed. Inside such built-in elements there are corresponding solids or liquids which, when heated above a certain temperature, evaporate or melt, consuming a certain amount of heat, and condense in the zones of the reactor with a temperature lower than the temperature of their evaporation or melting, releasing heat.

The possibility of heating the initial gas mixture for heterogeneously catalyzed propane dehydrogenation carried out in the reaction zone A to the required reaction temperature also consists in burning part of the propane and / or hydrogen contained in the initial gas mixture in the presence of molecular oxygen contained in it ( for example, by simply bypassing and / or passing this mixture through appropriate specific combustion catalysts) and by using heat combustion to heat the source gas mixture to the temperature necessary for dehydrogenation (as indicated above, a similar technology is advantageously used in a fluidized-bed reactor).

According to the aforementioned embodiment, the reaction zone A of the method according to the invention can be performed as proposed in German patent applications DE-A 102004032129 and DE-A 10200501339, except that a mixture of water is used as the source gas mixture for reaction zone A steam, fresh propane and circulating gas I. In this case, reaction zone A is in the form of a preferably adiabatic shelf reactor, preferably fixed catalyst beds in which are arranged one after the other radially or axially. Such a shelf reactor is preferably provided with three catalyst shelves. The heterogeneously-catalyzed partial dehydrogenation of propane in such a reactor is preferably carried out autothermally. To this end, the feed gas mixture to the reaction zone A after the first in the flow direction (fixed) catalyst bed and between subsequent (fixed) catalyst layers added a limited amount of molecular oxygen, or a mixture thereof with an inert gas. Due to this, the combustion of a limited amount of hydrogen generated in the process of heterogeneously catalyzed dehydrogenation of propane (as well as, if necessary, the minimum amount of propane and / or propylene), which is catalyzed, as a rule, by the dehydrogenation catalysts themselves, takes place, the exothermic effect of which mainly provides the temperature required for dehydrogenation level.

In an expedient embodiment, the conversion of the partially heterogeneous-catalyzed dehydrogenation of propane to be converted is preferably distributed over three shelves with a catalyst so that the total conversion of propane once passed through the reactor is about 20 mol% (according to the method of the invention, the total conversion of propane is obviously may also be 30 mol%, 40 mol% or 50 mol%). The specified degree of propane conversion, as a rule, corresponds to a selectivity of propylene formation of 90 mol%. As the duration of operation of the catalyst increases, the maximum degree of conversion of propane, carried out on separate shelves of the reactor, shifts in the direction of transmission of the reaction gas mixture from the first shelf to the last. The catalyst is typically regenerated before the maximum is shifted to the third shelf. The regeneration is preferably carried out at a point in time, which corresponds to the achievement of the same degree of coking of the catalyst on all three shelves of the reactor.

In the case of partial heterogeneous-catalyzed propane dehydrogenation under consideration, the optimal total flow rate of propane and propylene passed through the total amount of catalyst (i.e., through all catalyst beds) generally ranges from 500 to 20,000 nl / l · h (typical flow rate is from 1,500 to 2,500 nl / l h). In this case, the maximum temperature in the individual fixed catalyst beds is preferably maintained in the range from 500 to 600 ° C or up to 650 ° C. In a particularly preferred embodiment of the considered partial heterogeneously catalyzed dehydrogenation of propane in a shelf reactor, the initial reaction gas mixture A consists only of fresh propane and circulating gas I, which is returned to dehydrogenation from the partial oxidation of propylene and containing water vapor formed at the indicated stage, the amount of which, typically sufficient to provide a satisfactory lifetime for the propane dehydrogenation catalyst.

The disadvantage of the above method is that almost all propane dehydrogenation catalysts simultaneously catalyze the combustion of propane and propylene in the presence of molecular oxygen (i.e., the complete oxidation of these hydrocarbons to carbon oxides and water vapor), and the circulation gas I returned from the partial oxidation stage to the stage of partial heterogeneously catalyzed dehydrogenation of propane, as indicated above, contains molecular oxygen.

According to German patent application DE-A 10211275, this can be counteracted by separating the gaseous reaction product discharged from the dehydrogenation zone into two partial streams of identical composition, one of which is sent as a gaseous product A to the partial oxidation stage, while the other partial stream return to the stage of propane dehydrogenation as a component of the reaction gas A. Molecular hydrogen contained in this circulating gas II formed during the dehydrogenation process, both sintering the protection of propane and, if necessary, propylene contained in the feed gas mixture for reaction zone A, from combustion due to the simultaneous presence of molecular oxygen in the gas mixture. Such protection is based on the predominant combustion of molecular hydrogen (with the formation of water), usually heterogeneously catalyzed by the dehydrogenation catalysts themselves, which is kinetically preferable to the combustion of propane and / or propylene.

According to German patent application DE-A 10211275, it is advisable to circulate the dehydrogenation gas in accordance with the principle of operation of the jet pump (such circulation is also called a loop technique). In addition, this document discusses the possibility of additional introducing molecular hydrogen into the feed gas mixture for reaction zone A as an additional measure of protection against oxidation. In German patent application DE-A 102005049699, it is reported that a certain sequence of dosing molecular hydrogen into the working stream of the jet pump is required.

According to German patent applications DE-A 102004032129 and DE-A 102005013039, the molecular oxygen-containing circulating gas I, which is formed in the heterogeneously-catalyzed partial oxidation stage, is preferably proposed to return the partial heterogeneous-catalyzed propane dehydrogenation stage to a non-original gas mixture. It is more preferable to recycle said gas to reaction gas A formed in reaction zone A, which is carried out only upon reaching a certain degree of propane conversion. In German patent application DE-A 102004032129, before such recirculation, it is also proposed to add additional molecular hydrogen from an external source to the initial gas mixture for reaction zone A. In addition, for the dehydrogenation of propane in the application DE-A 102004032129 it is recommended to use a loop technique. Moreover, exclusively circulating gas I, which is returned from the partial oxidation stage to the dehydrogenation stage, is used as the working stream of the jet pump.

In example II of German patent application DE-A 102005009885 for the dehydrogenation carried out according to the invention in reaction zone A, a loop technique is used, according to which the initial gas mixture for this reaction zone consists of circulating gas I, fresh propane, molecular hydrogen from an external source, the minimum amount of water vapor from an external source and circulating gas II returned from dehydrogenation (you can also refuse to use water vapor from an external source). A mixture of fresh propane, molecular hydrogen from an external source, circulating gas I from the stage of partial oxidation and water vapor from an external source is used as the working stream of the jet pump. In German patent application DE-A 102005049699, recommendations are given regarding a preferred dosing sequence for the components during the formation of said work stream.

According to the invention, the circulating gas I preferably preferably contains not only molecular oxygen and water vapor, but also molecular hydrogen, carbon monoxide and carbon dioxide. Thus, the circulating gas I, as a rule, also contains carbon monoxide. According to the invention, the preferred content of carbon dioxide in the circulating gas 1 is from 5 to 15 vol.%.

According to the invention, the gaseous product A withdrawn from the reaction zone A according to the method of the invention preferably has the following composition:

propane from 25 to 60 vol.%, propylene from 8 to 25 vol.%, hydrogen from 0.04 to 25 vol.%, often up to 15 vol.%, water from 2 to 25 vol.%, carbon dioxide from 0 to 30 vol.%, often up to 15 vol.%

A typical temperature of the gaseous product A is from 400 to 700 ° C, preferably from 450 to 650 ° C.

According to the invention, the pressure of the gaseous product A at the outlet of the reaction zone A is preferably from 2 to 4 bar. As indicated above, it can also reach 20 bar.

According to the invention, the gaseous product A, without intermediate separation of side components, is sent as reaction gas B to at least one oxidation reactor of reaction zone B.

In the preferred embodiment, for this it is enough to add to the gaseous product A the amount of molecular oxygen that is necessary to fulfill the corresponding production goals in reaction zone B. Molecular oxygen can in principle be added in the form of pure oxygen or a mixture with one or more gases characterized by chemically inert behavior in reaction zone B, for example with nitrogen, steam, noble gases, carbon dioxide, that is, for example, in the form of air. According to the invention, molecular oxygen is preferably added to the gaseous product A in the form of a gas containing not more than 30 vol.%, Preferably not more than 25 vol.%, Preferably not more than 20 vol.%, Particularly preferably not more than 15 vol.%, Preferably no more than 10 vol.% And particularly preferably not more than 5 vol.% Or not more than 2 vol.% Of other gases other than molecular oxygen. Even more preferably, pure oxygen is used for addition. The amount of added molecular oxygen generally calculated so that the molar ratio of molecular oxygen contained in the starting reaction gas B contained therein to propylene is in the range from 1: 1 to 3: 1. Before introducing molecular oxygen into the gaseous product A, the latter according to the invention is expediently cooled to a temperature of 250 to 350 ° C, preferably 270 to 320 ° C. According to the invention, such cooling is preferably carried out by indirect heat exchange (heat exchange is preferably carried out by countercurrent, which is generally used in accordance with the present invention, unless otherwise indicated). In this case, the starting reaction gas mixture A intended for reaction zone A is preferably used as a cooling agent, which is likewise simultaneously heated to the temperature required for reaction zone A (provided that the gaseous product A has a sufficiently high initial pressure, it can also be cooled in principle the expansion mentioned above in a turboexpander).

According to the invention, the introduction of molecular oxygen-containing gas into the gaseous product A, preferably subjected to the above-mentioned preliminary cooling, can be carried out as follows: the gaseous product A drives a jet pump consisting of a nozzle, a mixing section, a diffuser and a suction nozzle as a working stream, moving such a nozzle-throttled working gas through the mixing section and the diffuser at the inlet of at least one oxidation reactor ion zone B, as well as the suction effect of the suction pipe, are directed towards the source containing molecular oxygen of the gas, and due to the vacuum created in the suction pipe, the gas containing molecular oxygen is sucked in and moved through the diffuser while mixing with the working stream in the mixing section and the release of the resulting source gas mixture B at the entrance to the second reaction zone B, respectively, at the entrance to at least one oxide reactor reaction zone B. This option is primarily applicable if the pressure of the gaseous product A is from 2 to 5 bar or more, respectively, up to 4 bar.

However, the gas containing molecular oxygen can obviously be mixed also with the gaseous product A sent to reaction zone B in order to form the initial gas mixture for reaction zone B using conventional methods. According to the invention, it may be expedient to carry out between the reaction zones A B a mechanical separation operation in accordance with German patent application DE-A 10316039.

It is known that partial heterogeneous-catalyzed gas-phase oxidation of propylene to acrylic acid by molecular oxygen is in principle carried out in two stages sequentially carried out along the reaction coordinate, the first of which is the synthesis of acrolein, and the second is the conversion of the obtained acrolein to acrylic acid.

The preparation of acrylic acid in two stages successively carried out in time implies the well-known possibility of stopping the implementation of the method of the invention in reaction zone B at the stage of acrolein synthesis (the stage of its primary formation) and isolating the target product at this stage or continue carrying out the proposed invention of the method, until the predominant formation of acrylic acid is completed, and only after that carry out the selection of the target product.

In the process of the invention according to the invention, prior to the predominant formation of acrylic acid according to the invention, a two-stage process is preferable, that is, two successive oxidation steps are carried out, an expedient variant of the process providing for the optimal coordination of the fixed catalyst layers used in the respective steps and preferably other reaction conditions, for example, the temperature layers.

Multimetal oxides based on elements such as molybdenum (Mo), iron (Fe) and bismuth (Bi), which are especially suitable for use as active masses of catalysts of the first oxidation stage (propylene → acrolein), also have a certain ability to catalyze the second oxidation stage (acrolein → acrylic acid), however, for the implementation of the second stage, it is usually preferable to use catalysts, the active mass of which is a multimetal oxide containing at least one of the elements that are molybdenum (M ) And vanadium (V).

Thus, for the partial heterogeneous-catalyzed oxidation of propylene carried out in reaction zone B according to the invention, fixed catalyst beds are suitable, the active mass of which is a multimetal oxide containing at least one of the elements molybdenum (Mo), iron (Fe) and bismuth (Bi ), wherein the partial heterogeneously catalyzed oxidation of propylene is carried out primarily in the form of a single-stage synthesis process acrolein (and optionally acrylic acid) or in a first reaction step, two hundred adium synthesis of acrylic acid.

In this case, the one-stage heterogeneously-catalyzed partial oxidation of propylene to acrolein, and also, if necessary, acrylic acid, respectively, the two-stage heterogeneously-catalyzed partial oxidation of propylene to acrylic acid, using reaction gas B formed according to the invention can be carried out, in particular, in accordance with with European patent application EP-A 700714 (the first reaction stage, carried out as proposed in this document, as well as in the corresponding tubular reactor with flow of salt melt and the initial reaction gas mixture), European patent application EP-A 700893 (the second reaction stage, carried out as proposed in this document, as well as the corresponding counterflow method), international applications WO 04/085369 (in the form of a two-stage process, and this document should primarily be considered as part of this application) and WO 04/85363, German patent application DE-A 10313212 (first reaction step), European patent applications EP-A 1159248 (as a two-step process), EP-A 1159246 (second p promotional stage) and EP-A 1159247 (as a two-stage process), German patent applications DE-A 19948248 (as a two-stage process) and DE-A 10101695 (as a one-stage or two-stage process), international application WO 04/085368 ( as a two-stage process), German patent application DE-A 102004021764 (as a two-stage process), international applications WO 04/085362 (first reaction stage), WO 04/085370 (second reaction stage), WO 04/085365 (second reaction stage) and WO 04/085367 (as a two-stage process), as well as in accordance with European application mi for patent EP-A 990636, EP-A 1007007 and EP-A1 106598.

The foregoing applies primarily to all examples cited in the cited inventions. The embodiments of the present invention can be carried out similarly to the examples from the above-mentioned publications of the prior art, however, in contrast to them, the initial reaction gas mixture used to carry out the first reaction stage (oxidation of propylene to acrolein) is reaction gas B formed according to the present invention. Other parameters are similar examples cited in publications (first of all, this applies to fixed catalyst beds and the corresponding consumption of reagents). In the case of the two-stage execution of examples of the prior art and the secondary oxygen supply between the two stages (the secondary air supply is less preferred according to the prior art), the same is true for the examples of the present invention, however, the secondary oxygen flow rate is set so that the molar ratio of molecular oxygen to acrolein in the gas mixture feeding the second reaction stage corresponded to that used in the example said x art.

According to the invention, the flow rate of the oxygen directed to the reaction zone B is preferably calculated in such a way that unconverted molecular oxygen remains in the gaseous product B, the content of which is expediently greater than or equal to from 0.5 to 6 vol.%, Mainly from 1 to 5 vol. %, preferably from 2 to 4 vol.%. In the case of a two-stage technology, the above contents apply to each of both stages of oxidation.

Multimetal oxide catalysts, especially suitable for carrying out a particular oxidation step, are described in detail and are well known in the art. Examples of such catalysts are given in European patent application EP-A 253409 (on page 5 of the corresponding US patent).

Optimum catalysts suitable for carrying out a particular oxidation step are also given in German patent applications DE-A 4431957, DE-A 102004025445 and DE-A 4431949. First of all, we are talking about catalysts of the general formula (I) given in the two above earlier publications. Particularly preferred catalysts for carrying out a particular oxidation step are given in German patent applications DE-A 10325488, DE-A 10325487, DE-A 10353954, DE-A 10344149, DE-A 10351269, DE-A 10350812 and DE-A 10350822 .

In accordance with the present invention, for any heterogeneously catalyzed gas-phase partial oxidation of propylene to acrolein, acrylic acid or a mixture thereof, any catalysts whose active mass is molybdenum (Mo), bismuth (Bi) and iron (Fe) multimetal oxides are suitable.

This is primarily about multimetal oxide active masses of the general formula (I) from German patent applications DE-A 19955176 and DE-A 19948523, multimetal oxide active masses of the general formulas (I), (II) and (III) from German applications for patent DE-a 10101695, DE-a 19948248 and DE-a 19955168 and about active multimetal masses given in European patent application EP-a-700714 patent.

In addition, multimetal oxide catalysts based on molybdenum, bismuth and iron, suitable for carrying out the indicated reaction steps, are disclosed in document No. 497012 of August 29, 2005, German patent applications DE-A 10046957, DE-A 10063162, DE-C 3338380 and DE-A 19902562, European patent application EP-A 15565, German patent application DE-C 2380765, European patent applications EP-A 807465 and EP-A 279374, German patent application DE-A 3300044, European application patent EP-A 575897, US patent application US-A 4438217, German patent application DE-A 19855913, international WO 98/24746, German patent application DE-A 19746210 (multimetal oxides of general formula (II)), Japanese patent application JP-A 91/294239, as well as in European patent applications EP-A 293224 and EP-A 700714. This primarily relates to examples of the implementation of these inventions, particularly preferred of which are given in European patent applications EP-A 15565 and EP-A 575897, as well as in German patent applications DE-A 19746210 and DE-A 19855913. B In this connection, the catalyst from the European Patent Application EP-A 15565 of Example 1c, as well as alizator which may be prepared in accordance with this example, however, the composition comprises active composition Mo ₁₂ Ni _6,5 Zn ₂ Bi ₁ Fe ₂ P _0,0065 K _0,06 O _x · 10SiO _2. In addition, the hollow cylinder catalyst with dimensions of 5 × 3 × 2 mm (outer diameter × height × inner diameter) from German Patent Application DE-A 19855913 of Example 3, the multimetal oxide mass of which has a stoichiometric composition of Mo ₁₂ , deserves special mention. Co ₇ Fe ₃ Bi _0.6 K _0.083 Si _1.6 O _x , as well as a one-piece multimetal _oxide catalyst of the general formula (II) shown in Example 1 of German patent application DE-A 19746210. In addition, mention should be made of multimetal oxide catalysts described in US patent application US-A 44 38217. Particularly suitable catalysts used in this document are hollow cylinders with dimensions 5.5 × 3 × 3.5 mm, 5 × 2 × 2 mm, 5 × 3 × 2 mm, 6 × 3 × 3 mm or 7 × 3 × 4 mm (respectively, outer diameter × height × inner diameter). Another possible form of such catalysts are rods, for example, 7.7 mm long and 7 mm in diameter or 6.4 mm long and 5.7 mm in diameter.

Most catalysts suitable for carrying out the step of converting propylene to acrolein and, if necessary, acrylic acid, contain multimetal oxide active masses of the general formula (IV):

,

,

wherein

X ¹ means nickel and / or cobalt,

X ² means thallium, an alkali metal and / or alkaline earth metal,

X ³ means zinc, phosphorus, arsenic, boron, antimony, tin, cerium, lead and / or tungsten,

X ⁴ means silicon, aluminum, titanium and / or zirconium,

a means a number from 0.5 to 5,

b means a number from 0.01 to 5, preferably from 2 to 4,

c means a number from 0 to 10, preferably from 3 to 10,

d means a number from 0 to 2, preferably from 0.02 to 2,

e means a number from 0 to 8, preferably from 0 to 5,

f is a number from 0 to 10, and

n means a number, which is determined by the valency and the number of elements different from oxygen in the general formula (IV).

These active multimetal oxide masses can be prepared by known methods (see, for example, German patent application DE-A 4023239), and are usually used in the form of mass-formed balls, rings or cylinders or in the form of layered catalysts, i.e. coated with an active mass inert carrier bodies. As catalysts, obviously, powdered active masses can also be used (for example, in fluidized bed reactors).

The active masses of the general formula (IV) can, in principle, be obtained by a simple method, which involves preparing, from suitable sources of the corresponding elemental components, as thoroughly mixed as possible, preferably finely divided dry mixture of a suitable stoichiometric composition, which is subjected to calcination at a temperature of from 350 to 650 ° C. Calcination can be carried out both in an inert gas atmosphere and in an oxidizing atmosphere, for example, such as air (a mixture of inert gas and oxygen), as well as in a reducing atmosphere (for example, a mixture of inert gas, ammonia, carbon monoxide and / or hydrogen). The duration of calcination is from several minutes to several hours and can be reduced due to the increased temperature of this process. As sources of the elemental components of the active multimetal oxide of the general formula (IV) can be used compounds which are already oxides and / or compounds which can be converted into oxides by heating, carried out in the presence of at least oxygen.

Such starting compounds, along with oxides, can primarily be halides, nitrates, formates, oxalates, citrates, acetates, carbonates, amine complexes, ammonium salts and / or hydroxides (in a thoroughly mixed dry mixture of these components, compounds such as NH ₄ can also be added OH, (NH ₄ ) ₂ CO ₃ , NH ₄ NO ₃ , NH ₄ CHO ₂ , CH ₃ COOH, NH ₄ CH ₃ CO ₂ and / or ammonium oxalate, which are capable of subsequent dissociation and / or destruction accompanied by the formation of gaseous volatilized products and what’s happening zdnee during subsequent calcination of the mixture).

The starting compounds can be thoroughly mixed to prepare active multimetal oxide masses of the general formula (IV), both in dry and in wet state. In the case of mixing in the dry state, the starting compounds are preferably used in the form of fine powders and calcined after mixing and, if necessary, carried out compaction. However, thorough mixing of the wet starting compounds is preferred. In this case, the starting compounds, which are usually the corresponding aqueous solutions and / or suspensions, are mixed with each other. Especially thoroughly mixed in this way, dry mixtures are obtained if they come from sources of elemental components that are exclusively in a dissolved state. The preferred solvent is water. In conclusion, the resulting water mass is subjected to drying, preferably carried out in spray dryers at an outlet temperature of 100 to 150 ° C.

The multimetal oxide active masses of the general formula (IV) can be used to carry out the propylene → acrolein (and optionally acrylic acid) reaction step both in powder form and in the form of a catalyst obtained by molding, particles of which have certain geometric parameters, and molding can be performed before or after the final calcination operation. For example, by compaction of a powdered active mass or a corresponding non-calcined and / or partially calcined initial mass (for example, by tabletting, extruding or extrusion), it is possible to prepare whole catalysts with particles of the desired geometric shape, and if necessary, they can auxiliary agents, for example, such as graphite or stearic acid, can be added (as agents for improving gliding and / or alleviating the mold Ia) and reinforcing agents, such as microfibers of glass, asbestos, silicon carbide or potassium titanate. As recommended in German patent application DE-A 102005037678, instead of the graphite used in the forming, as an adjuvant, may also be added to the boron nitride hexagonal crystal lattice. A suitable geometrical particle shape of the whole catalysts corresponds, for example, to solid or hollow cylinders with an outer diameter and height of 2 to 10 mm. A suitable wall thickness of the hollow cylinders is 1 to 3 mm. Solid catalysts, obviously, can also have the shape of balls, the diameter of which can be from 2 to 10 mm.

Particularly favorable (especially in the case of solid catalysts) is the use of catalysts in the form of hollow cylinders with dimensions of 5 × 3 × 2 mm (outer diameter × length × inner diameter).

Formation of powdered active composition or the corresponding calcined powder nepodvergnutoy and / or partially calcined initial mass may obviously also be performed due to its deposition on the preformed inert carrier. The application of the active mass on the body of the carrier in order to obtain layered catalysts, as a rule, is carried out in a suitable rotating tank, for example, described in German patent application DE-A 2909671 or European patent applications EP-A 293859 and EP-A 714700. it is advisable to subject the powder body to humidification, and after application, drying, for example, with hot air. A suitable thickness of the layer of powder mass deposited on the body of the carrier is from 10 to 1000 microns, preferably from 50 to 500 microns, and particularly preferably from 150 to 250 microns.

In this case, conventional porous or nonporous aluminum oxides, silicon dioxide, thorium dioxide, zirconium dioxide, silicon carbide or silicates such as magnesium silicate or aluminum silicate can be used as carrier body materials. In accordance with the present invention, these materials behave under the conditions of the target reaction in question, as a rule, mainly inert. carrier bodies may be formed into regular or irregular shape, wherein the support bodies are preferred, which have a regular shape (e.g., a form of balls or hollow cylinders) and clearly marked surface roughness. Suitable is the use of having a rough surface, mainly non-porous spherical bodies of the carrier of steatite, the diameter of which is from 1 to 10 mm, respectively, up to 8 mm, preferably from 4 to 5 mm. It is also suitable to use carrier bodies in the form of cylinders with a height of 2 to 10 mm and an outer diameter of 4 to 10 mm. When using carrier bodies in the form of rings that are suitable according to the invention, their wall thicknesses are usually from 1 to 4 mm. The ring-shaped bodies of the carrier to be preferred according to the invention have a height of 2 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. According to the invention, rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter) are also particularly suitable as carrier bodies. Dispersibility of the catalytically active oxide compositions applied to the surface of the support bodies, obviously, should be aligned with the desired thickness formed by this shell (see. European Patent Application EP-A-714 700 patent).

Suitable multimetal active compositions used in stage conversion of propylene to acrolein (as well as if necessary acrylic acid), are also active compositions of the general formula (V):

,

,

wherein

Y ¹ means bismuth or bismuth in combination with at least one of the following elements: tellurium, antimony, tin, copper,

Y ² means molybdenum, tungsten, or a combination of molybdenum with tungsten,

Y ³ means alkali metal, thallium and / or samarium,

Y ⁴ means alkaline earth metal, nickel, cobalt, copper, manganese, zinc, tin, cadmium and / or mercury,

Y ⁵ means iron or iron in combination with at least one of the following elements: chromium and cerium,

Y ⁶ means phosphorus, arsenic, boron and / or antimony,

Y ⁷ means rare earth metal, titanium, zirconium, niobium, tantalum, rhenium, ruthenium, rhodium, silver, gold, aluminum, gallium, indium, silicon, germanium, lead, thorium and / or uranium,

a 'means a number from 0.01 to 8,

b 'means a number from 0.1 to 30,

c 'means a number from 0 to 4,

d 'means a number from 0 to 20,

e 'means a number from> 0 to 20,

f means a number from 0 to 6,

g 'means a number from 0 to 15,

h 'means a number from 8 to 16,

x ', y' mean numbers that are determined by the valency and the number of elements that differ from oxygen in the general formula (V), and

p, q mean numbers whose ratio (p: q) corresponds to the interval from 0.1: 1 to 10: 1,

moreover, these active masses contain three-dimensional areas of chemical composition Y ¹ _{a '} Y ² _b' O _{x '} , which differs from the chemical composition of their local environment, and therefore these areas are delimited from their local environment, and the maximum diameter of such areas (the most a long segment passing through their center of gravity and connecting two points located on their surface (boundary surface) is from 1 nm to 100 μm, often from 10 to 500 nm or from 1 to 50 μm, respectively, from 1 to 25 μm.

According to the invention, multimetal oxide masses of the general formula (V) in which Y ¹ means only bismuth are particularly preferred.

Preferred active masses of this type, in turn, are multimetal oxide masses of the general formula (VI):

,

,

wherein

Z ² means molybdenum, tungsten or a combination of molybdenum and tungsten,

Z ³ means nickel and / or cobalt,

Z ⁴ means thallium, an alkali metal and / or alkaline earth metal,

Z ⁵ means phosphorus, arsenic, boron, antimony, tin, cerium and / or lead,

Z ⁶ means silicon, aluminum, titanium and / or zirconium,

Z ⁷ means copper, silver and / or gold,

a '' means a number from 0.1 to 1,

b "means a number from 0.2 to 2,

c '' means a number from 3 to 10,

d "means a number from 0.02 to 2,

e "means a number from 0.01 to 5, preferably from 0.1 to 3,

f '' means a number from 0 to 5,

g '' means a number from 0 to 10,

h '' means a number from 0 to 1,

x '', y '' mean numbers that are determined by the valency and the number of elements that differ from oxygen in the general formula (VI),

p``, q '' mean numbers whose ratio (p``: q '') corresponds to the interval from 0.1: 1 to 5: 1, preferably from 0.5: 1 to 2: 1,

even more preferred are multimetal oxide masses of the general formula (VI) in which Z ² _{b ″} means (W) _{b ″} and Z ² ₁₂ means (Mo) ₁₂ .

In addition, it is preferable if at least 25 mol% (preferably at least 50 mol% and particularly preferably 100 mol%) in suitable multimetal oxide masses of the general formula (V) (respectively multimetal oxide masses of the general formula (VI)) ) of the total amount of [Y ¹ _{a '} Y ² _b' O _{x '} ] _p ([Bi _a'' Z ² _b'' O _x'' ] _p'' ) are present in the form of three-dimensional regions of chemical composition Y ¹ _a' Y ² _{b 'O x' [Bi a} '' Z ² _{b '' O x '']} , which is different from the chemical composition of their local environment, in connection with which said regions are delimited from their local okra eniya, wherein the maximum diameter of these regions is from 1 nm to 100 microns.

Catalysts with multimetal oxide masses of the general formula (V) are formed similarly to catalysts with multimetal oxide masses of the general formula (IV).

Preparation of active multimetal oxide of the general formula (V) described for example in European patent application EP-A-575897 and in the German Patent Application DE-A 19855913 patent.

The inert carrier materials recommended above, in particular, are also suitable for use as inert materials, diluting and / or delimiting the respective fixed catalyst beds, respectively, for protecting the fixed catalyst beds and / or the formation of bulk layers intended to heat the gas mixture before passing it through catalyst.

As indicated above, as active masses used for the second reaction stage (partial heterogeneously catalyzed gas-phase oxidation of acrolein to acrylic acid), in principle, any molybdenum and vanadium containing multimetal oxide masses are suitable, for example, those described in German patent application DE-A 10046928.

Most catalysts suitable for carrying out this oxidation step (for example, the catalysts described in German patent application DE-A 19815281) contain multimetal oxide active masses of the general formula (VII):

,

,

wherein

X ¹ means tungsten, niobium, tantalum, chromium and / or cerium,

X ² means copper, nickel, cobalt, iron, manganese and / or zinc,

X ³ means antimony and / or bismuth,

X ⁴ means one or more alkali metals,

X ⁵ means one or more alkaline earth metals,

X ⁶ means silicon, aluminum, titanium and / or zirconium,

and means a number from 1 to 6,

b means a number from 0.2 to 4,

C means a number from 0.5 to 18,

d means a number from 0 to 40,

e means a number from 0 to 2,

f means a number from 0 to 4,

g means a number from 0 to 40 and

n means a number that is determined by the valency and the number of elements that are different from oxygen in the general formula (VII).

According to the invention, active multimetal oxide masses of the general formula (VII) are preferred, in which

X ¹ means tungsten, niobium and / or chromium,

X ² means copper, nickel, cobalt and / or iron,

X ³ means antimony

X ⁴ means sodium and / or potassium,

X ⁵ means calcium, strontium and / or barium,

X ⁶ means silicon, aluminum and / or titanium,

and means a number from 1.5 to 5,

b means a number from 0.5 to 2,

C means a number from 0.5 to 3,

d means a number from 0 to 2,

e means a number from 0 to 0.2,

f means a number from 0 to 1 and

n means a number that is determined by the valency and the number of elements that are different from oxygen in the general formula (VII).

According to the invention, even more preferred multimetal oxide masses of the general formula (VII), in turn, have the general formula (VIII):

,

,

wherein

Y ¹ means tungsten and / or niobium,

Y ² means copper and / or nickel,

Y ⁵ means calcium and / or strontium,

Y ⁶ means silicon and / or aluminum,

a 'means a number from 2 to 4,

b 'means a number from 1 to 1.5,

c 'means a number from 1 to 3,

f 'means a number from 0 to 0.5,

g 'means a number from 0 to 8 and

n 'means a number that is determined by the valency and the number of elements different from oxygen in the general formula (VIII).

Suitable multimetal oxide active compounds according to the invention of the general formula (VII) can be prepared by known methods, for example, those described in German patent application DE-A 4335973 or in European patent application EP-A 714700.

Multimetal oxide active materials suitable for carrying out the step of converting acrolein to acrylic acid, especially those having the general formula (VII), can in principle be obtained by a known method involving the preparation of suitable mixed sources, preferably finely divided dry mixtures from suitable sources of appropriate elemental components, preferably stoichiometric composition, which is subjected to calcination at a temperature of from 350 to 600 ° C. Calcination can be carried out both in an inert gas atmosphere and in an oxidizing atmosphere, for example, such as air (a mixture of inert gas and oxygen), as well as in a reducing atmosphere (for example, in a mixture of an inert gas with reducing gases, such as hydrogen, ammonia, carbon monoxide, methane and / or acrolein, or in the gases themselves having a reducing effect). The duration of calcination is from several minutes to several hours and can be reduced by increasing the temperature of this process. The sources of the elemental components multimetal active compositions of the general formula (VII) may be compounds which are already oxides and / or compounds which can be converted into oxides by heating, carried out in the presence of at least oxygen.

The starting compounds can be thoroughly mixed for the preparation of active multimetallic oxide masses of the general formula (VII), both in a dry and a wet state. In the case of mixing the starting compounds in a dry state, it is advisable to use them in the form of fine powders and calcine after mixing and, if necessary, carried out compaction. However, thorough mixing of the wet starting compounds is preferred.

In this case, the starting compounds are usually mixed with each other, which are the corresponding aqueous solutions and / or suspensions. Especially thoroughly mixed in this way, dry mixtures are formed if they come from sources of elemental components that are exclusively in a dissolved state. The preferred solvent is water. Then the resulting water mass is subjected to drying, preferably carried out in spray dryers at an outlet temperature of from 100 to 150 ° C.

The multimetal oxide active masses prepared in this way, primarily the active masses of the general formula (VII), can be used for the oxidation of acrolein both in a powder state (for example, in a fluidized bed reactor) or in the form of a catalyst obtained by molding with particles having certain geometric parameters moreover, molding may be performed before or after the final calcining operation. Thus, for example, by densification of a powdered active mass or a corresponding un-calcined initial mass, carried out, for example, by tabletting, extruding or extrusion, it is possible to prepare whole catalysts of the desired geometric shape, and if necessary, auxiliary agents can be added, for example, like graphite or stearic acid (as a means to improve glide and / or ease molding), and reinforcing additives such as micro window glass, asbestos, silicon carbide or potassium titanate. A suitable geometrical shape of the solid catalyst particles corresponds, for example, to solid or hollow cylinders with an outer diameter and height of 2 to 10 mm. A suitable wall thickness of such hollow cylinders is from 1 to 3 mm. Solid catalysts, obviously, can also have the shape of balls, the diameter of which can be from 2 to 10 mm (for example, 8.2 or 5.1 mm).

The formation of a powdered active mass or a corresponding powdered, non-calcined initial mass, obviously, can also be accomplished by applying it to a preformed inert support for catalysts. The application of the active mass on the body of the carrier in order to obtain layered catalysts is carried out, as a rule, in a suitable rotating reservoir, for example, described in German patent application DE-A 2909671 or European patent applications EP-A 293859 and EP-A 714700.

It is advisable to wet the powder mass applied to the bodies of the carrier, and, after application, to dry it by, for example, passing hot air. A suitable thickness of the powder mass layer deposited on the carrier body is from 10 to 1000 microns, preferably from 50 to 500 microns, and particularly preferably from 150 to 250 microns.

In this case, conventional porous or non-porous aluminum oxides, silicon dioxide, thorium dioxide, zirconia, silicon carbide or silicates such as magnesium silicate or aluminum silicate can be used as the material of the carrier bodies. The bodies of the carrier can be given a regular or irregular shape, with preferred bodies of the carrier of a regular shape with a distinct surface roughness, for example, balls or hollow cylinders with a split supporting surface. It is suitable to use predominantly non-porous spherical carrier bodies of steatite with a rough surface, the diameter of which is from 1 to 10 mm, respectively to 8 mm, preferably from 4 to 5 mm. Thus, suitable spherical bodies of the carrier have a diameter of 8.2 mm or 5.1 mm. It is also suitable to use carrier bodies in the form of cylinders with a height of 2 to 10 mm and an outer diameter of 4 to 10 mm. In the case of an annular shape of the carrier bodies, their wall thickness is usually from 1 to 4 mm. Subject to preferred use, the ring-shaped bodies of the carrier have a height of 2 to 6 mm, an outer diameter of 4 to 8 mm and a wall thickness of 1 to 2 mm. Rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter) are also particularly suitable as carrier bodies. The dispersion of the catalytically active oxide masses deposited onto the surface of the carrier bodies, obviously, should be brought into line with the required thickness of the resulting shell (see European patent application EP-A 714700).

Optimal multimetal oxide active masses suitable for carrying out the step of converting acrolein to acrylic acid are also active masses of the general formula (IX):

,

,

wherein

D means Mo ₁₂ V _{a ''} Z ¹ _{b ''} Z ² _{c ''} Z ³ _{d ''} Z ⁴ _{e ''} Z ⁵ _{f ''} Z ⁶ _{g ''} O _{x ''} ,

E means Z ⁷ ₁₂ Cu _{h ''} H _{i ''} O _{y ''} ,

Z ¹ means tungsten, niobium, tantalum, chromium and / or cerium,

Z ² means copper, nickel, cobalt, iron, manganese and / or zinc,

Z ³ means antimony and / or bismuth,

Z ⁴ means lithium, sodium, potassium, rubidium, cesium and / or hydrogen,

Z ⁵ means magnesium, calcium, strontium and / or barium,

Z ⁶ means silicon, aluminum, titanium and / or zirconium,

Z ⁷ means molybdenum, tungsten, vanadium, niobium and / or tantalum, preferably molybdenum and / or tungsten,

a '' means a number from 1 to 8,

b '' means a number from 0.2 to 5,

c '' means a number from 0 to 23,

d '' means a number from 0 to 50,

e '' means a number from 0 to 2,

f '' means a number from 0 to 5,

g '' means a number from 0 to 50,

h '' means a number from 4 to 30,

i '' means a number from 0 to 20,

x '', y '' mean numbers, which are determined by the valency and the number of elements that differ from oxygen in the general formula IX, and

p, q mean non-zero numbers, the ratio of which (p: q) corresponds to the interval from 160: 1 to 1: 1,

moreover, these active masses can be obtained by a separate preliminary formation of a solid multimetal oxide mass E in a powder state (initial mass 1):

,

,

which then, with the necessary quantitative ratio of p to q, is introduced into an aqueous solution, an aqueous suspension, or a finely divided dry stoichiometric mixture D of molybdenum, vanadium sources, elements Z ¹ , Z ² , Z ³ , Z ⁴ , Z ⁵ , Z ⁶ (initial weight 2) :

,

,

if necessary, the resulting aqueous mixture is dried, and the dry pre-mass is calcined before or after drying at a temperature of from 250 to 600 ° C, obtaining a catalyst with particles of the desired geometric shape.

Preferred are multimetal oxide masses of the general formula (IX), which are obtained by introducing a preformed solid starting mass 1 into an aqueous starting mass 2 at a temperature below 70 ° C. The preparation of catalysts based on multimetal oxide active masses of the general formula (IX) is described in detail, for example, in European patent application EP-A 668104 and German patent applications DE-A 19736105, DE-A 10046928, DE-A 19740493 and DE-A 19528646 .

Catalysts with multimetal oxide masses of the general formula (IX) are formed similarly to catalysts with multimetallic oxide masses of the general formula (VII).

In addition, the multimetal oxide catalysts described in the German patent application DE-A 19815281 are particularly suitable for carrying out the step of converting acrolein to acrylic acid, primarily containing the multimetal oxide masses of the general formula (I).

For the stage of conversion of propylene to acrolein, solid ring-shaped catalysts are preferably used, and for the stage of conversion of acrolein to acrylic acid, ring-shaped layered catalysts are used.

According to the invention, partial oxidation of propylene to acrolein (and also, if necessary, to acrylic acid) using the above catalysts can be carried out, for example, in a single-zone reactor with a large number of contact tubes (tubular reactor) described in German patent application DE-A 4431957 catalyst bed. In this case, the reaction gas mixture and the coolant (heat transfer means) can be passed along the contact tubes of a vertically located reactor in a direct or countercurrent manner.

The pressure of the partial oxidation reaction is usually in the range from 1 to 3 bar, and the total flow rate of reaction gas B through the fixed catalyst bed is preferably from 1500 to 4000 nl / l · h, respectively up to 6000 nl / l · h or higher. A typical propylene flow rate through a fixed catalyst bed is from 90 to 200 nl / l · h, respectively, up to 300 nl / l · h or higher. A particularly preferred propylene flow rate according to the invention is more than 135 nl / l · h, respectively ≥140, ≥150 or ≥160 nl / l · h, since the presence of unconverted propane and molecular hydrogen in the starting reaction gas mixture for reaction zone B causes optimal behavior of this mixture in a hot spot (the above data does not depend on the type of reactor selected with a fixed catalyst bed).

The feed gas mixture is introduced into a single-zone tubular reactor with a fixed catalyst bed, preferably from above. It is advisable to use a molten salt as a heat carrier, preferably consisting of 60 wt.% Potassium nitrate (KNO ₃ ) and 40 wt.% Sodium nitrite (NaNO ₂ ) or 53 wt.% Potassium nitrate (KNO ₃ ), 40 wt.% Nitrite sodium (NaNO ₂ ) and 7 wt.% sodium nitrate (NaNO ₃ ).

As indicated above, the molten salt and the reaction gas mixture can be passed along the contact tubes both in direct flow and in countercurrent. The molten salt moves along the contact tubes, preferably in a tortuous stream.

When passing the reaction gas mixture through the contact tubes in the direction from top to bottom, it is advisable to fill them with the catalyst (in the direction from bottom to top) as follows (when passing the reaction gas mixture in the direction from bottom to top, the reverse sequence of filling the reactor tubes with the catalyst is advisable):

- the lower sections of the contact tubes (from 40 to 80%, respectively up to 60% of their total length) are filled with a pure catalyst or its mixture with an inert material, the content of which in the mixture with the catalyst is up to 30 wt.%, respectively, up to 20 wt.% ( reactor section C)

- sections of the contact tubes located above section C (from 20 to 50%, respectively up to 40% of their total length) are filled with a pure catalyst or its mixture with an inert material, the content of which in the mixture with the catalyst is up to 40 wt.% (reactor section B) , and

- the uppermost sections of the contact tubes (from 10 to 20% of their total length) are filled with an inert material, the loading of which is preferably carried out in such a way as to ensure a minimum pressure drop in these sections (reactor section A).

Preferably, an inert (neat) catalyst undiluted with an inert material is loaded into section C.

The above loading option is especially useful when the reactor is filled with catalysts described in the description of the invention No. 497012 of 08.29.2005, example 1 from the German patent application DE-A 10046957 or in example 3 from the German patent application DE -A 10046957, and as an inert material using rings of steatite with dimensions of 7 × 7 × 4 mm (outer diameter × height × inner diameter). The temperature of the molten salt is similar to the temperature indicated in German patent application DE-A 4431957.

Partial oxidation of propylene to acrolein (and optionally to acrylic acid) in reaction zone B, using the catalysts described above, can also be carried out, for example, in the German patent applications DE-A 19910506, DE-A 102005009885, DE-A 102004032129, DE-A 102005013039, DE-A 102005009891 and DE-A 102005010111 two-zone tubular reactor with a fixed catalyst bed. According to these applications (as well as in the general case according to the present invention), the conversion of propylene with a single pass through a similar reactor is usually ≥90 mol%, respectively ≥95 mol% with an acrolein formation selectivity of ≥90 mol%. According to the invention, the partial oxidation of propylene to acrolein, acrylic acid or a mixture thereof is preferably carried out as described in European patent application EP-A 1159244 and even more preferably as described in international applications WO 04/085363 and WO 04/085362.

The descriptions of the European patent application EP-A 1159244, as well as international applications WO 04/085363 and WO 04/085362 should be considered an integral part of this description.

Thus, partial oxidation of propylene to acrolein (and optionally acrylic acid) in reaction zone B can be particularly preferably carried out at an increased flow rate of propylene through a fixed catalyst bed consisting of at least two temperature zones.

In this regard, reference should be made, for example, to European patent application EP-A 1159244 and international application WO 04/085362.

In the case of two-stage partial oxidation of propylene, the second reaction stage, namely the partial oxidation of acrolein to acrylic acid, can be carried out as described in German patent application DE-A 4431949, for example, in a single-zone tubular reactor with a fixed bed of one of the above catalysts. In this case, the reaction gas mixture and the coolant can be passed along the contact tubes in a direct flow. As a rule, a gas mixture of the products of the preceding partial oxidation of propylene to acrolein carried out according to the invention is generally directed to the second stage (the stage of partial oxidation of acrolein), in principle, as such, i.e., without intermediate isolation of side components (after optional intermediate cooling, which may be indirect or direct, carried out, for example, by supplying secondary air).

Molecular oxygen necessary for the second reaction stage (partial oxidation of acrolein) may already be present in the reaction gas mixture B directed to the stage of partial oxidation of propylene to acrolein. Molecular oxygen can also be partially or completely added directly to the mixture of reaction products in the form of secondary air formed in the first stage (partial oxidation of propylene to acrolein), however, it is preferable to add them in the form of pure oxygen or mixtures of oxygen with an inert gas, the content of which is preferably ≤50 vol.%, ≤40 vol.%, ≤30 vol.%, ≤20 vol.%, ≤10 vol.%, ≤5 vol.% Or ≤2 vol.%. Regardless of the formation, the initial reaction gas mixture, sent to the stage of partial oxidation of acrolein to acrylic acid, preferably has the following composition:

acrolein from 3 to 25 vol.%, molecular oxygen from 5 to 65 vol.%, propane from 6 to 70 vol.%, molecular hydrogen from 0.3 to 20 vol.%, water vapor from 8 to 65 vol.%.

The specified initial reaction gas mixture preferably has the following composition:

acrolein from 5 to 14 vol.%, molecular oxygen from 6 to 25 vol.%, propane from 6 to 60 vol.%, molecular hydrogen from 2 to 18 vol.%, water vapor from 7 to 35 vol.%.

The specified initial reaction gas mixture even more preferably has the following composition:

acrolein from 6 to 12 vol.%, molecular oxygen from 8 to 20 vol.%, propane from 20 to 55 vol.%, molecular hydrogen from 6 to 15 vol.%, water vapor from 11 to 26 vol.%,

moreover, the above preferred compositions are independent of each other, however, the corresponding intervals are preferably carried out simultaneously. The nitrogen content in these mixtures is typically ≤20 vol.%, Preferably ≤15 vol.%, Particularly preferably ≤10 vol.% And even more preferably ≤5 vol.%. According to the invention, the molar ratio of oxygen to acrolein in the initial gas mixture, sent to the second stage of partial oxidation, is preferably usually from 0.5: 1 to 2: 1, often from 1: 1 to 1.5: 1.

The carbon dioxide content in the initial gas mixture sent to the second stage of partial oxidation can be in the range from 1 to 40 vol.%, From 2 to 30 vol.% Or from 4 to 20 vol.%, Or often from 6 to 18 vol. .%.

When carrying out both the first (propylene → acrolein) and the second (acrolein → acrylic acid) reaction stages, the reaction pressure is usually in the range from 1 to 3 bar, and the total flow rate of the (initial) reaction gas mixture through the fixed catalyst bed is preferably from 1500 up to 4000 nl / l · h, respectively, up to 6000 nl / l · h or more. A typical consumption of acrolein through a fixed catalyst bed is from 90 to 190 or 290 nl / l · h or more. Acrolein consumption is particularly preferably greater than 135 nl / l · h, respectively ≥140, ≥150 or ≥160 nl / l · h, since the presence of unconverted propane in the starting reaction gas mixture used according to the invention determines its optimal behavior in a hot spot.

The appropriate conversion of acrolein in terms of a single pass of the reaction gas mixture through the fixed catalyst bed of the second oxidation stage is usually ≥90 mol% with an acrylic acid selectivity of ≥90 mol%.

The feed gas mixture for the second reaction stage is introduced into a one-zone fixed-bed tubular reactor, also preferably from above. Suitably, a molten salt, preferably consisting of 60 wt.% Potassium nitrate (KNO ₃ ) and 40 wt.% Sodium nitrite (NaNO ₂ ) or 53 wt.% Potassium nitrate (KNO ₃ ), is also used as a coolant at this stage. , 40 wt.% Sodium nitrite (NaNO ₂ ) and 7 wt.% Sodium nitrate (NaNO ₂ ). As indicated above, the molten salt and the reaction gas mixture can be passed along the contact tubes of the reactor as a direct flow, and countercurrent. Salt melt washes the contact tubes, preferably in a tortuous stream.

When passing the reaction gas mixture through the contact tubes of a vertically arranged tubular reactor in the direction from top to bottom, it is advisable to fill them with catalyst (in the direction from bottom to top) as follows:

- the lower sections of the contact tubes (from 50 to 80%, respectively, to 70% of their total length) are filled with a pure catalyst or its mixture with an inert material, the content of which in the mixture with the catalyst is up to 30 wt.%, respectively, up to 20 wt.% ( reactor section C)

- sections of the contact tubes located above section C (from 20 to 40% of their total length) are filled with a pure catalyst or its mixture with an inert material, the content of which in the mixture with the catalyst is up to 50 wt.%, respectively, up to 40 wt.% (section B reactor), and

- the uppermost sections of the contact tubes (from 5 to 20% of their total length) are filled with an inert material, the loading of which is preferably carried out in such a way as to ensure a minimum pressure drop in these sections (reactor section A).

A preferably (undiluted) inert material (pure) catalyst is loaded into section C. Similar to the generally heterogeneous-catalyzed gas-phase partial oxidation of acrolein to acrylic acid (primarily with a high consumption of acrolein through the catalyst bed and an increased content of water vapor in the corresponding initial gas mixture), section B can also consist of two successive layers diluted with an inert material ( in order to ensure the minimum temperature in the hot spot and the sensitivity of this temperature) of the catalyst. In this case, a catalyst containing up to 30 wt.% (Respectively, up to 20 wt.%) Inert material is loaded into the lower part of section B, and a catalyst containing from 20 to 50 wt.%, Respectively, up to 40 wt.% Inert, is loaded into its upper part material. In this case, section C preferably contains an inert material undiluted catalyst.

In the case of passing the initial gas mixture through the contact tubes in the direction from the bottom up, it is advisable to reverse the sequence of their filling with the catalyst.

It is advisable to use the above-mentioned embodiment of filling the reactor primarily in the case of catalysts similar to those described in manufacturing example 5 of German patent application DE-A 10046928 or in examples of German patent application DE-A 19815281, and inert materials in the form of rings made of steatite with dimensions of 7 × 7 × 4 mm or 7 × 7 × 3 mm (outer diameter × height × inner diameter). The temperature of the molten salt is similar to that indicated in the German patent application DE-A 4431949. The temperature is usually chosen so that when a single passage of acrolein through the reactor, its conversion in the usual case is ≥90 mol%, respectively ≥95 mol% or ≥99 mol%.

Partial oxidation of acrolein to acrylic acid using the above catalysts can also be carried out, for example, in a two-zone tubular reactor with a fixed catalyst bed, as described in German patent application DE-A 19910508. The degree of conversion of acrolein is similar to the above. Similar to the partial oxidation of acrolein considered above, which is carried out as the second reaction stage of the two-stage oxidation of propylene to acrylic acid in a two-zone tubular reactor with a fixed catalyst bed, it is advisable to directly use the gas mixture of the reaction products of the first partial oxidation stage (propylene → acrolein) , if necessary, after its indirect and direct (for example, due to the supply of secondary air) intermediate cooling REPRESENTATIONS. The oxygen necessary for the partial oxidation of acrolein is used preferably in the form of pure molecular oxygen (if necessary, also in the form of air or a mixture of molecular oxygen with an inert gas, the content of which is preferably ≤50 vol.%, Particularly preferably ≤40 vol.%, ≤30 vol. % or ≤20 vol.%, even better ≤10 vol.%, ≤5 vol.% or ≤2 vol.%) and, for example, add it directly to the gaseous mixture of the products of the first stage (propylene → acrolein) of two-stage partial oxidation . However, as indicated above, molecular oxygen may already be present in the initial reaction gas mixture intended for the implementation of the first reaction stage.

In the case of two-stage partial oxidation of propylene to acrylic acid with the direct use of a gas mixture of products of the first stage of partial oxidation for feeding to the second stage of partial oxidation, as a rule, two single-zone tubular reactors with fixed catalyst beds are connected in series (as in the general case, with a high consumption of reagents through the catalyst, co-current of the reaction gas and the molten salt (coolant) through the tubular reactor) or two dual-zone tubular reactors is preferred Ktorov with fixed catalyst beds. It is also possible mixed series connection of reactors (single-zone / dual-zone or vice versa).

An intermediate cooler may be located between the reactors, which, if necessary, may contain layers of inert material that perform the filtering function. The temperature of the molten salt in tubular reactors used to carry out the first stage of the two-stage partial oxidation of propylene to acrylic acid, as a rule, is from 300 to 400 ° C. The temperature of the salt melt in the tubular reactors of the second stage of partial oxidation of propylene to acrylic acid (i.e., the stage of partial oxidation of acrolein to acrylic acid) in most cases is from 200 to 350 ° C. In addition, the flow rate of coolants (preferably salt melts), passed through the corresponding tubular reactors with fixed catalyst beds, is usually chosen so that their temperature difference at the inlet and outlet, as a rule, is ≤5 ° C. As indicated above, both stages of the partial oxidation of propylene to acrylic acid can also be carried out in one reactor on one catalyst loaded in it, as described in German patent application DE-A 10121592.

It should also be recalled that part of the initial reaction gas mixture B for the first oxidation step (“propylene → acrolein”) may be residual gas I from separation zone 1 and / or residual gas I additionally treated according to the invention.

However, according to the invention, said residual gases I are preferably returned to reaction zone A to heterogeneously catalyzed propane dehydrogenation solely as circulating gas I, which is expediently used solely as a component of the initial reaction gas mixture A. Moreover, for the sake of accuracy, it should be noted that the initial the gas mixture for the first stage of oxidation, and in the original gas mixture for the second stage of oxidation, or only one of these gas mixtures can be entered optional fresh propane. According to the invention, the introduction of fresh propane is not preferable, however, if necessary, it may be advisable, since it eliminates the flammability of the feed gas mixtures.

Thus, a tubular reactor with a catalyst suitably modified in the sections of the contact tubes, which corresponds to the completion of the first reaction stage (transition sections), is the simplest form of conducting both stages of the two-stage partial oxidation of propylene to acrylic acid (similar two-stage processes of partial oxidation of propylene to a single "reactor is described, for example, in European patent applications EP-A 911313, EP-A 979813 and EP-A 990636, as well as in German patent application DE-A 2830765). These transition sections of the contact tubes, if necessary, are filled with an inert material.

However, both oxidation steps are preferably carried out in two series-connected tubular systems. Such tubular systems can be located inside one reactor, and the transition from one bundle of contact tubes to another is formed by an inert material located outside the contact tubes, preferably accessible for passing the reaction gas. The coolant, as a rule, washes only contact tubes, but a transition zone that is not filled with inert material. In this regard, in a preferred embodiment, both bundles of contact tubes are placed in the corresponding spatially separated reactors. In this case, between the two tubular reactors, as a rule, there is an intermediate cooler designed to minimize the observed, if necessary, secondary oxidation of acrolein, which is contained in the reaction product leaving the first oxidation zone of the gas mixture. The temperature of the first reaction stage (propylene → acrolein), as a rule, is from 300 to 450 ° C, preferably from 320 to 390 ° C. The temperature of the second reaction stage (acrolein → acrylic acid), as a rule, is from 200 to 370 ° C, often from 220 to 330 ° C. The pressure in both oxidation zones is suitably from 0.5 to 5 bar, preferably from 1 to 3 bar. The flow rate of the reaction gas through the catalysts used to carry out both reaction steps is often from 1500 to 2500 or 4000 nl / l · h. In this case, the propylene consumption can be from 100 to 200 or 300 nl / l · h, or more.

According to the invention, both oxidation stages can in principle have the design described, for example, in German patent applications DE-A 19837517, DE-A 19910506, DE-A 19910508 and DE-A 19837519.

Moreover, an excess of molecular oxygen in excess of the stoichiometric amount favorably affects the kinetics of the reactions occurring at both stages of the gas-phase partial oxidation, as well as the service life of the corresponding catalysts.

According to the invention, a heterogeneously catalyzed gas-phase partial oxidation of propylene to acrylic acid can, in principle, also be performed in a single single-zone tubular reactor as follows. Both reaction stages are carried out in an oxidation reactor, in which one or more catalysts with a multimetal oxide active mass based on molybdenum, iron and bismuth, capable of catalyzing the reactions occurring in both stages, are loaded. Possible, obviously, is also a continuous or abrupt modification of the loaded catalyst along the reaction coordinate. According to the invention, in a two-stage partial oxidation of propylene to acrylic acid, carried out in the form of two successive oxidation stages, from the gas mixture of the products of the first oxidation stage, if necessary, obviously, it is also possible to partially or completely separate the carbon monoxide contained in it and water vapor, which are formed on of this stage as by-products before directing the gas mixture obtained in this oxidation step to the second oxidation step. According to the invention, a technology that does not provide for such isolation is preferred.

As indicated above, the source of molecular oxygen added between both stages, along with the less preferred air according to the invention, can be pure molecular oxygen, as well as molecular oxygen diluted with an inert gas such as carbon dioxide, carbon monoxide, noble gases, nitrogen and / or saturated hydrocarbons . According to the invention, the oxygen source preferably contains ≤50 vol.%, Preferably ≤40 vol.%, Particularly preferably ≤30 vol.%, Even more preferably ≤20 vol.%, Better ≤10 vol.% Or ≤5 vol.%, Respectively ≤2 vol.%, Different from molecular oxygen gases.

According to the invention, it is also possible to directly cool the gas mixture of the reaction products of the first partial oxidation stage by adding, for example, a cold oxygen source to them before using the specified mixture as a component of the initial reaction gas mixture intended for the second partial oxidation stage.

According to the invention, partial oxidation of acrolein to acrylic acid is preferably carried out in accordance with European patent application EP-A 1159246 and even more preferably in accordance with international applications WO 04/085365 and WO 04/085370. However, in this case, as the acrolein-containing starting reaction gas mixture according to the invention, it is preferable to use a mixture of reaction products formed according to the invention in the first partial oxidation step (i.e., in the step of converting propylene to acrolein), to which, if necessary, so much secondary air is added so that the ratio of molecular oxygen to acrolein in the resulting initial reaction gas mixture in all cases was in the range from 0.5: 1 to 1.5: 1. The descriptions of the European patent application EP-A 1159246, as well as international applications WO 04/08536 and WO 04/085370 should be considered an integral part of this description.

Thus, according to the invention, partial oxidation of acrolein to acrylic acid can preferably be carried out in a fixed catalyst bed comprising at least two temperature zones, with increased consumption of acrolein passed through it.

The two-stage partial oxidation of propylene to acrylic acid is preferably carried out as described in European patent application EP-A 1159248, respectively, international application WO 04/085367 or WO 04/085369.

According to the invention, the gaseous product B after the first and / or second partial oxidation reaction stages mainly contains acrolein, acrylic acid or a mixture thereof as a target product, unconverted propane, molecular hydrogen, water vapor (generated as a by-product and / or present as shared diluent gas), if necessary, unconverted molecular oxygen (to prolong the life of the used catalysts, it is favorable that the oxygen content remains contained in the gas mixture of products of both stages of partial oxidation, was, for example, at least 1.5 to 4 vol.%), as well as other by-products or by-products, the boiling point of which at normal pressure (1 bar) is lower or higher boiling points of water, for example, such as carbon monoxide, carbon dioxide, low molecular weight aldehydes, low molecular weight aliphatic carboxylic acids (e.g., acetic acid, formic acid and propionic acid), maleic anhydride, benzaldehyde, aromatic carboxylic acids slots and anhydrides of aromatic carboxylic acids (e.g., phthalic anhydride and benzoic anhydride), other hydrocarbons if necessary, such as C ₄ hydrocarbons (e.g., butene-1 and other butene isomers), and, if appropriate, other inert diluent gases for example, such as nitrogen.

According to the invention, for separating the desired products contained in the gaseous product B, water and by-products with a boiling point above the boiling point of the water carried out in the first separation zone I, in principle any separation methods known in the art are suitable. A characteristic feature of such methods is that the target product is transferred from the gaseous phase to the condensed phase, for example, due to absorption and / or condensation, and then, with the aim of further isolating the target product, the condensates, respectively absorbates, are subjected to extraction, distillation, crystallization and / or desorption processing. In accordance with the indicated methods, together with the target product and / or following the conversion of the target product to the condensed phase, they are also usually converted to the condensed phase and, thus, water vapor contained in the reaction gas B and side components with a boiling point above the boiling point of water ( according to the invention, steam is preferably converted to the condensed phase in an amount of at least 70 mol%, preferably at least 80 mol%, preferably at least 90 mol% and especially respectfully at least 95 mol.% of the amount produced in the reaction zone in vapor accordingly particularly preferably all contained in the product gas in steam).

Suitable absorbents are, for example, water, aqueous solutions and / or organic solvents (for example, mixtures of diphenyl with diphenyl ether or mixtures of diphenyl with diphenyl ether and o-dimethyl phthalate). In accordance with such “condensation” (isolation) of the target product, water and by-products with a boiling point above the boiling point of the water, usually there remains a residual gas that has not passed into the condensed phase, which contains the relatively difficult to condense (more easily boiling compared to water) components of the gaseous product B Such residual gas usually primarily contains components with a boiling point at normal pressure (1 bar) of ≤ -30 ° C (their total content in the residual gas is usually is ≥60 vol.%, often ≥70 vol.%, most often ≥80 vol.%, but in most cases ≥90 vol.%). Such components primarily include unconverted propane, molecular hydrogen, carbon dioxide, if necessary, unconverted propylene, if necessary, unconverted molecular oxygen, as well as other side components boiling lighter than water, for example, carbon monoxide, ethane, methane, necessary, nitrogen, if necessary, noble gases (for example, xenon, neon, argon and so on). The residual gas may also contain minor amounts of acrylic acid, acrolein and / or water. According to the invention, the residual gas preferably contains ≤10 vol.%, Preferably ≤5 vol.% And particularly preferably ≤3 vol.% Of water vapor. Such a residual gas usually forms at least a major amount (usually at least 80%, respectively at least 90%, or at least 95% or more, based on the propane contained therein) of the residual gas generated in the first separation zone I and in the present description it is called the (main) residual gas I.

First of all, when using an organic solvent to condense the target product by absorption, at least one second residual gas containing unconverted propane and, if necessary, unconverted propylene (its amount in terms of propane contained in it) are usually formed in separation zone I usually much less than the amount of (main) residual gas I and is usually ≤20%, most often ≤10%, ≤5% or ≤1%). This is due to the fact that the resulting condensed phase also absorbs a certain amount of unconverted propane, as well as, if necessary, unconverted propylene.

In the process of subsequent extraction, distillation, crystallization and / or desorption separation of the target product from the condensed phase, this unconverted propane and, if necessary, propylene are usually recycled as a component of at least one other gas phase and are called (by-product) residual gas in the present description I.

In such a case, the sum of the (main) residual gas I and the (secondary) residual gas I is equal to the total amount of residual gas I. In the absence of the formation of (secondary) residual gas I in the separation zone I, the (main) residual gas I will automatically form the entire amount of residual gas I (also called (total) residual gas I).

According to the invention, the target product is transferred from the gaseous product B to the condensed phase, preferably by fractional condensation. First of all, this refers to the case if the target product is acrylic acid. However, in principle, for the isolation of the target product, for example, any absorption and / or condensation methods of "condensation of the target products" and further processing of the "condensate" described in German patent applications DE-A 10213998 and DE-A 2263496, US patent US 3433840 are suitable (the methods described in these publications are recommended to be used primarily for the separation of acrolein), European patent applications EP-A 1388533 and EP-A 1388532, German patent application DE-A 10235847, European patent application EP-A 792867, international patent application WO 98/01415, European standard patent applications EP-A 1015411 and EP-A 1015410, international applications WO 99/50219, WO 00/53560 and WO 02/09839, German patent application DE-A 10235847, international patent application WO 03/041833, German patent applications DE-A 10223058, DE-A 10243625 and DE-A 10336386, European patent application EP-A 854129, US patent application US-A 4317926, German patent applications DE-A 19837520, DE-A 19606877, DE-A 190501325, DE-A 10247240 and DE-A 19740253, European patent applications EP-A 695736, EP-A 982287, EP-A 1041062, EP-A 117146 and EP-A 4308087, as well as in German patent applications DE- A 4335172, DE-A 4436243, DE-A 19924532, DE-A 10332758 and DE-A 19924533. You can also use acrylic acid to isolate e methods described in European patent applications EP-A 982287 and EP-A 982289, German patent applications DE-A 10336386, DE-A 10115277, DE-A 19606877, DE-A 19740252 and DE-A 19627847, European applications EP-A 920408, EP-A 1068174, EP-A 1066239 and EP-A 1066240, international applications WO 00/53560 and WO 00/53561, German patent application DE-A 10053086 and European patent application EP-A 982288. The isolation of the desired products is preferably carried out as described in international application WO / 0196271 (FIG. 7), respectively, in German patent application DE-A 102004032129 and its equivalent legal documents. Suitable isolation methods are also described in international applications WO 04/063138, WO 04/35514 and German patent applications DE-A 10243625, DE-A 10235847. For further processing of the isolated crude acrylic acid, methods described, for example, in international applications can be used. WO 01/77056, WO 03/041832, WO 02/055469, WO 03/078378 and WO 03/041833.

As indicated above, a common distinguishing feature of the above methods for the isolation of the target products is that, for example, in the upper part of the distillation column (equipped with built-in elements increasing the separation efficiency), the lower part of which is introduced after the usual preliminary direct and / or indirect cooling for example, gaseous product B, usually residual gas I remains, mainly containing components of the gaseous product B, the boiling point of which under normal pressure ii (1 bar) below the boiling point of water and in most cases is ≤ -30 ° C (i.e., hardly condensable, respectively volatile components). However, the residual gas I may additionally also contain, for example, components such as water vapor and acrylic acid.

In the lower part of the distillation column, a condensed phase usually accumulates, mainly containing hardly volatile components of the gaseous product B, including the corresponding target product. The condensed aqueous phase, as a rule, is removed from the distillation column through side extraction or cube.

The (main) residual gas I typically has the following composition:

water from 1 to 20 vol.%, propane from 40 to 90 vol.%, oxygen from 0 to 10 vol.%, carbon dioxide from 5 to 30 vol.%, carbon monoxide from 0 to 2 vol.%.

The content of acrolein and acrylic acid, as a rule, is respectively less than 1 vol.%.

The residual gas I formed in the separation zone I according to the invention should be subjected to a certain additional treatment. Moreover, an important circumstance according to the invention is that there is no need for additional treatment of the total amount of residual gas I. Therefore, according to the invention, it may be advisable to additionally treat only part of the total amount of residual gas I (for example, only (main) residual gas I). In this case, the sum of the untreated part of the total amount of residual gas I and the propane-containing residual gas remaining after additional processing of the other part of the total amount of residual gas I, forms the total amount of the additionally treated residual gas I (“new” residual gas I), which according to the invention can be subjected to appropriate other additional processing (the indicated partial amounts may also have different chemical compositions). According to the invention, at least a portion of the total amount of (additionally treated) residual gas I remaining in the unconverted propane containing remaining after completing all, if necessary, additional processing is returned to the reaction zone A according to the invention as at least one of at least two containing propane feed streams. The other part (if necessary, also the portion of the residual gas I, also not subjected to additional processing), if necessary, can be returned to the first and / or second oxidation stages of the reaction zone B, so that using it as a component of the corresponding source gas, it is preferable to ensure the explosion safety of the reaction gas.

However, according to the invention, the amount of residual gas I further treated according to the invention, which is returned according to the invention to reaction zone A as at least one of the at least two propane-containing feed gas streams, is preferably calculated so that the return gas contains at least 80 mol %, preferably at least 85 mol%, preferably at least 90 mol%, at least 92 mol%, at least 94 mol%, at least 96 mol%, or at least 98 mol .% total prop to the outlet from reaction zone B with the gaseous product B. Moreover, the recirculation need not be carried out at the same place in reaction zone A. On the contrary, it can be distributed over several different points of reaction zone A.

The amount of propane contained in the additionally treated residual gas I returned to reaction zone A is at least 90 mol% of the amount of propane contained in the gaseous product B.

According to the invention, an important feature of the technological process discussed above is an arbitrary sequence of additional processing of residual gas I. That is, instead of initially removing from the production process a partial amount of residual gas I and then washing the remaining carbon dioxide, it is also possible, for example, to first wash off carbon dioxide and then remove from the manufacturing process, a partial amount of residual gas washed from carbon dioxide I.

However, in accordance with a preferred embodiment of the invention, the following post-treatment sequence is observed (this is primarily about post-treatment of the (main) residual gas I).

First, a partial amount of residual gas I is removed from the production process (such removal is necessary, first of all, for unloading inert components that enter into it with molecular oxygen introduced from the total production process). In this case, the composition of the partial amount of residual gas I removed from the production process, as a rule, sent to the exhaust gas combustion system, can be similar to the composition of the residual gas I. As a rule, this occurs if the amount of propane contained in the unit removed time residual gas I is ≤30 mol%, preferably ≤25 mol% or ≤20 mol%, respectively ≤15 mol%, preferably ≤10 mol%, particularly preferably ≤5 mol% and even more preferably ≤3 mol% or ≤1 mol% in terms of quantity conduction in the production process per unit time of fresh propane.

If the amount of propane removed from the production process exceeds or is equal to the above values, part of the residual gas I can also be removed by the method, according to which the propane contained in it is preliminarily extracted and, if necessary, propylene, due to which the separated propane and, if necessary, propylene remain a component of the residual gas I further treated according to the invention.

The simple possibility of such a separation consists, for example, in contacting an appropriate amount of residual gas I with a preferably high boiling, preferably hydrophobic organic solvent, for example tetradecane or a mixture of alkanes with carbon numbers from 8 to 20, which in an expedient embodiment has the ability to more preferably absorb propane and propylene than other components of the residual gas I, and the specified contact is carried out, for example, by simply passing the last cut specified absorbent. Due to the subsequent desorption, distillation and / or stripping carried out under reduced pressure with a gas having an inert behavior in reaction zone A (for example, water vapor, molecular hydrogen, molecular oxygen and / or another inert gas (for example, also air), propane and (at if necessary) the propylene is recovered and added to the additionally treated residual gas I. In particular, the absorption separation of propane can be carried out similarly to its separation from the gaseous product A described in German DE-A 102004032129. In the case where, according to the present invention, the isolation described above is carried out, which is less preferred according to the invention, it always applies only to a partial amount of residual gas I, and therefore only to a partial amount contained in propane gas product B. According to the invention, said partial amount of propane is preferably ≤50 mol%, particularly preferably ≤40 mol%, particularly preferably ≤30 mol%, especially sim ilar ≤20 mol.%, even more preferably ≤10 mol.% and in the best case ≤5 mol.%.

After removing a partial amount of residual gas I, at least a portion of this gas in the second separation zone II is washed from the carbon dioxide contained therein. If residual gas I also contains carbon monoxide and oxygen, carbon monoxide can be selectively oxidized to dioxide (while chemical reduction of molecular oxygen is carried out), for example, by passing residual gas I through appropriate catalysts (if necessary, you can also add residual gas I previously molecular oxygen necessary for the oxidation of carbon monoxide). When using the catalysts recommended in the international application WO 01/60738 (complex oxides of stoichiometric composition Cu _x Ce _{1 x} oxygen _-y , in which x means a number from 0.01 to 0.3 and y≥x), this reduction can also be performed in the presence of molecular hydrogen. However, according to the invention, said conversion of carbon monoxide is not preferred. This is due to the fact that at least a portion of the carbon monoxide remaining in the circulating gas I would somehow oxidize within the next loop of the reaction zones A and / or B to carbon dioxide, and therefore would be removed with the above carbon dioxide washing. However, the conversion of carbon monoxide may also be accompanied by the reduction of the oxygen contained in the residual gas I by the hydrogen contained in the residual gas I. Similar recovery can also be carried out separately.

According to the invention, as a rule, it is sufficient to wash only the carbon dioxide contained in the partial amount of residual gas I. In a preferred embodiment, the carbon dioxide is washed at an elevated pressure, typically from 3 to 50 bar, preferably from 5 to 30 bar , preferably from 8 to 20 bar, particularly preferably from 10 to 20 bar, respectively, to 15 bar, and when it is appropriate to use liquids with a basic character (according to Bransted).

Suitable basic liquids are, for example, organic amines, such as monoethanolamine, aqueous solutions of organic amines, for example, such as monoethanolamine, aqueous solutions of alkali metal hydroxides, aqueous solutions of alkali metal carbonates or aqueous solutions of alkali metal carbonates and bicarbonates (see also for example, international application WO 05/05347). According to the invention, an aqueous solution containing potassium carbonate is preferably used to wash the carbon dioxide. As such aqueous solutions, for example, solutions of potassium carbonate in water, solutions of potassium carbonate and potassium hydrogen carbonate in water or solutions of potassium carbonate, potassium hydrogen carbonate and potassium hydroxide in water can be used. The solids content in such an aqueous solution of potassium carbonate is preferably from 10 to 30 or 40 wt.%, Particularly preferably from 20 to 25 wt.%. By adding small amounts of alkali metal hydroxide (e.g. potassium hydroxide) before washing, the alkaline nature of the aqueous solution of alkali metal carbonate can be further adjusted so that, if necessary, minor amounts of carboxylic acids (e.g., acetic acid) contained in residual gas I can be neutralized , formic acid, acrylic acid). The mass ratio of potassium bicarbonate to potassium carbonate in optimal aqueous wash solutions is about 1: 2, and the solids content in these solutions is preferably from 20 to 25 wt.%. The reaction of one mole of potassium carbonate with carbon dioxide and water during the washing process is accompanied by the formation of two moles of potassium hydrogen carbonate (K ₂ CO ₃ + water + CO ₂ → 2KHCO ₃ ).

Instead of washing the carbon dioxide with a liquid with a basic character, the dioxide can also be washed, for example, as described in European patent application EP-A 900121, that is, with the formation of a clathrate carbon dioxide compound.

From a technical and industrial point of view, it is advisable to wash carbon dioxide in a countercurrent wash column. The residual gas I to be washed, as a rule, moves from bottom to top in the wash column, while the wash liquid flows from top to bottom. In accordance with known methods of such washing, the wash column is equipped with internal devices designed to increase the mass transfer surface. As such devices, nozzle bodies that enhance mass transfer (eg, mesh) plates and / or nozzles can be used.

The washed off residual gas I is preferably discharged from the top of the wash column, while, for example, an aqueous solution containing predominantly potassium hydrogen carbonate (or an aqueous solution of a clathrate compound of carbon dioxide) is preferably taken from its cube. The mass ratio of dissolved potassium hydrogen carbonate to potassium carbonate in the solution taken from the cube may be, for example, 2.5: 1.

When hot water vapor is passed through an aqueous solution of potassium hydrogen carbonate, thermal destruction of hydrogen carbonate occurs, accompanied by the formation of carbonate, free carbon dioxide and water. The aqueous solution of potassium carbonate regenerated in this way, after, as a rule, occurring in the process of destruction of the evaporation of condensed water vapor, can be returned to the washing of carbon dioxide described above. Evaporation of condensing water vapor can also be carried out continuously by means of an evaporator integrated in the column. It is also advisable to carry out the above destruction in a column equipped with internal devices to increase the mass transfer surface, for example, in a column with mesh plates, a packed column and / or a column with packed bodies. In this case, countercurrent operating mode is also preferred. Hot water vapor is preferably introduced at the bottom of the column, and an aqueous solution of potassium carbonate is preferably at its top.

Carbon dioxide washing is preferably carried out at low temperatures, while elevated temperatures are preferably used for the destruction of bicarbonate. The destruction of the washing solution, which is part of a set of technological operations, which includes washing carbon dioxide, the destruction of the washing solution and its reuse as a washing liquid, it is advisable to carry out by means of water vapor, the temperature of which is from 130 to 160 ° C, preferably from 140 to 150 ° FROM. The suitable temperature of the solution to be degraded, introduced into the wash column, is from 80 to 120 ° C, particularly preferably from 90 to 110 ° C. According to the invention, the temperature of the residual gas I introduced into the wash column is preferably from 60 to 90 ° C., particularly preferably from 70 to 80 ° C., and the temperature of the wash liquid supplied to it is from 70 to 90 ° C., preferably from 75 to 85 ° C. .

First of all, if carbon dioxide is washed only from a partial amount of residual gas I, it is preferable to compress the residual gas I to the pressure that is preferred for pressure washing, which is carried out in several stages, for example, using a multistage centrifugal compressor with the possibility of taking out compressed gas after each step.

According to the invention, a typical residual gas pressure I at the outlet of separation zone I is from 1 to 2.5 bar, preferably up to 2.0 bar. The pressure of the heterogeneously catalyzed dehydrogenation of propane in reaction zone A is preferably from 2 to 4 bar, preferably from 2.5 to 3.5 bar. According to the invention, the optimum working pressure in reaction zone B is from 1 to 3 bar, preferably from 1.5 to 2.5 bar. The preferred operating pressure in the carbon dioxide washing system is from 3 to 50 bar, respectively from 5 to 30 bar, or from 8 to 20 bar, preferably from 10 to 20 bar, respectively to 15 bar.

From a production and technical standpoint, at the first stage of a multistage compressor, for example, a turbocompressor, in this case also called a compressor for compressing circulating gas I (for example, a centrifugal compressor of type MH4B from Mannesmann DEMAG, Germany), it is advisable to compress the residual gas I to the characteristic of reaction zone A operating pressure, for example, from 1.2 to 3.2 bar. In the event that carbon dioxide is not washed off of the total residual gas I, it is advisable to separate the compressed, as indicated above, residual gas I into two parts of the same composition. Moreover, the amount of each of the parts can be, for example, from 70 to 30% of the amount of residual gas I divided in this way. The portion of the residual gas I not to be washed can be returned directly to reaction zone A. Further compression to the working pressure necessary for washing carbon dioxide, subjected to only another part of the residual gas I. In this case, further compression can be performed only at another stage of the compressor. However, for this, according to the invention, at least two other steps are preferably used. This is due to the fact that the compression of residual gas I is accompanied by an increase in its temperature. Conversely, the throttling (expansion) of the residual gas I washed from carbon dioxide I to a pressure similar to the working pressure in the reaction zone A, which must be performed to return the washed gas to the specified zone, is accompanied by its cooling. In the case of throttling residual gas I in several stages before each subsequent stage, indirect heat exchange of heated compressed uncleaned residual gas I with expansion, cooled, residual gas washed off from carbon dioxide I can be carried out. Such heat exchange can also be used already before the first expansion stage. As a result of indirect heat exchange, condensation of water vapor can occur, in some cases still contained in the residual gas I. It is preferable to carry out the above expansion in production and technical terms in turboexpander (preferably also multi-stage), which allows you to recover the energy expended in compression. The pressure difference at the inlet and outlet of each compression stage, respectively expansion, can be, for example, from 2 to 10 bar.

In separation zone II, typically at least 50 mol%, in most cases at least 60 mol% or at least 80 mol%, often at least 90 vol% or more of the residual gas, are washed I carbon dioxide.

In an expedient embodiment, the amount of washed carbon dioxide corresponds to the total amount of carbon dioxide formed in reaction zones A and B.

In the residual gas washed from carbon dioxide, as a rule, from 1 to 20 vol.%, Often from 5 to 10 vol.% Of carbon dioxide, remains.

The residual gas I washed from carbon dioxide before throttling can be subjected to additional processing carried out in the third separation zone III using a separation membrane, the purpose of which is to isolate at least a partial amount of molecular hydrogen contained in the residual gas I before returning the gas to reaction zone A (similar technical the event is carried out primarily if only a relatively small amount of hydrogen is burned in reaction zone A). Suitable separation membranes are, for example, aromatic polyimide membranes, manufactured in particular by UBE Industries Ltd. First of all, membranes of type A, BH, C or D are suitable. Particularly preferred polyimide membranes from UBE Industries Ltd. are type BN membranes. The rate of hydrogen penetration through similar membranes at 60 ° C is 0.7 · 10 ^-3 [STP · cm ³ / cm ² · c · cm Hg]. Washed residual gas I from carbon dioxide can be passed through a membrane that is permeable only to molecular hydrogen, usually in the form of a pipe (the membrane can also be made in the form of a plate or twisted module). Molecular hydrogen isolated in this way can be used for other chemical syntheses or, for example, together with the residual gas I selected according to the invention, is sent for combustion. Free carbon dioxide can also be involved in the process of such combustion (it can also simply be released into the atmosphere), as well as water condensates formed in the separation zones I and II.

Low-boiling by-products isolated in separation zone I may also be directed to said combustion. Burning is usually carried out with air supply. The combustion process can be carried out, for example, in accordance with European patent application EP-A 925272.

The membrane evolution of molecular hydrogen is also preferably carried out at elevated pressure (for example, from 5 to 50 bar, typically from 10 to 15 bar).

In this regard, it is advisable to carry out the membrane evolution of molecular hydrogen according to the invention either immediately before washing off the carbon dioxide from residual gas I, or (preferably) immediately after its completion, so that a once-increased pressure level is twice useful. In addition to lamellar, twisted or capillary membranes, sleeve membranes (hollow fiber membranes) are suitable for hydrogen evolution. The inner diameter of such membranes can be, for example, several micrometers. For example, a bundle of such tubular membranes is poured at both ends into respective plates, like the contact tubes of a tubular reactor. Outside the tubular membrane, preferably a reduced pressure (less than 1 bar) predominates. Being under reduced pressure (less than 1 bar), the residual gas I is introduced into one of the plate ends of the membrane bundle and pumped through the interior towards the other plate end. As the gas stream moves along a given internal path, molecular hydrogen is released from the permeable membrane outward.

Additionally treated, as described above, the residual gas I (the sum of the additionally treated part and, if necessary, the non-processed part), if necessary, can be recycled to reaction zone A as one of at least two propane-containing feed streams. According to the invention, preferably all of the residual gas I further treated according to the invention is sent to the starting reaction gas mixture A (the starting gas mixture for reaction zone A) I.

According to the invention, the method according to the invention is preferred in which the washing of carbon dioxide from the residual gas I is carried out at the maximum possible operating pressure. As indicated above, this allows the method according to the invention to be carried out using only one compressor (preferably a multistage centrifugal compressor), which must be installed between the zone of formation of residual gas I and the washing system of the carbon dioxide contained therein. It has been found that in accordance with the method proposed in the invention, it is not necessary to use another compressor, primarily between reaction zones A and B. However, this does not exclude the possibility of incorporating such an additional compressor in accordance with the method proposed in the invention.

Another advantage of the method proposed in the invention is that it allows the use of minimal circulation flows. In addition, it is possible to naturally ensure the presence of molecular hydrogen in the reaction gas mixture A sent to the reaction zone A, which protects the hydrocarbons contained in this mixture from combustion occurring in the presence of molecular oxygen simultaneously contained in this mixture. This allows you to provide a relatively high selectivity of the formation of the target product in terms of converted fresh propane. In conclusion, it should be noted that the main feature of the method proposed in the invention is the absence of condensates formed in the separation zones I and II in the inert side components naturally derived from the production process that are formed during the process or feed together with the reaction streams that enter the production process.

Returned to the reaction zone And the circulation gas I has the following typical composition:

propane from 50 to 90 vol.%, carbon monoxide from 0 to 5 vol.%, most often up to 2 or 1 vol.%, hydrogen from 1 to 20 vol.%, carbon dioxide from 1 to 20 vol.%, water from 1 to 20 vol.%, oxygen from 0 to 10 vol.%, more often up to 5 vol.%, propylene from 0 (usually from 0.1) to 5 vol.%.

In conclusion, it should be noted that polymerization inhibitors are always added to the places of the formation of condensed phases in the separation zones I and II. In principle, any known polymerization inhibitors can be used for this. Particularly suitable according to the invention are, for example, phenothiazine and hydroquinone methyl ester. The effectiveness of polymerization inhibitors increases in the presence of molecular oxygen. The acrolein obtained by the process of the invention can be used to convert to the products described in US patent applications US-A 6166263 and US-A 6187963. Examples of such products are 1,3-propanediol, methionine, glutaraldehyde and 3-picoline.

Examples and comparative examples

I. Long-term regime of heterogeneously catalyzed two-stage partial oxidation of propylene to acrylic acid in the absence and presence of molecular hydrogen

A) General design of the experimental reaction unit Reactor of the first oxidation stage

The reactor was a double-walled cylinder made of special steel (a cylindrical guide tube placed in an outer cylindrical tank). The wall thickness at all points of the reactor ranged from 2 to 5 mm.

The inner diameter of the outer cylinder was 91 mm. The inner diameter of the guide tube was about 60 mm.

The double-walled cylindrical reactor at the top and bottom was hermetically sealed with a lid and a bottom, respectively.

The contact tube made of special steel with a total length of 400 cm with an inner diameter of 26 mm, an outer diameter of 30 mm and a wall thickness of 2 mm was placed in the guide tube of the cylindrical tank so that the upper and lower ends of the tube protruded above the lid and bottom, and where it passed through the cover and the bottom were hermetically sealed. The coolant (salt melt, consisting of 53 wt.% Potassium nitrate, 40 wt.% Sodium nitrite and 7 wt.% Sodium nitrate) was located in a closed inner space of a cylindrical tank. To ensure the most uniform boundary thermal conditions on the outer surface of the walls of the contact tube inside the cylindrical tank along its entire length (400 cm), the coolant was circulated by means of a propeller pump.

The necessary temperature of the coolant was regulated by means of an electric heater put on the external tank. Other areas were air-cooled.

Reactor power: Through a vertically located first-stage reactor, direct flow of the salt melt and the initial gas mixture was carried out. The initial gas mixture entered the reactor from below. Its temperature at the entrance to the contact tube was 165 ° C. Saline melt entered the cylindrical guide tube from below at a temperature T ^ein and exited from above at a temperature T ^aus , 2 ° C higher than T ^ein .

The temperature of the salt melt T ^{ein was} controlled so that the degree of conversion of propylene when it was once passed through the reactor of the first oxidation stage was always 97.8 ± 0.1 mol%.

The catalyst was loaded into the contact tube as follows (bottom to top).

Section A: height 90 cm; preliminary bulk layer of steatite balls with a diameter of 4 to 5 mm.

Section B: height 100 cm; a bulk layer of a homogeneous mixture of 30 wt.% steatite rings with dimensions of 5 × 3 × 2 mm (outer diameter × length × inner diameter) and 70 wt.% solid catalyst, similar to that used to fill section C.

Section C: height 200 cm; a bulk layer of solid catalyst in the form of rings with dimensions of 5 × 3 × 2 mm (outer diameter × length × inner diameter) according to example 1 of German patent application DE-A 10046957 (stoichiometric composition [Bi ₂ W ₂ O ₉ × 2WO ₃ ] _0.5 [Mo ₁₂ Co _5.5 Fe _2.94 Si _1.59 K _0.08 O _x ] ₁ ).

Section D: height 10 cm; the final bulk layer of steatite rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter).

Intermediate cooling and intermediate supply of pure oxygen as a secondary gas

For the purpose of indirect indirect cooling by air, a gas mixture of reaction products leaving the reactor of the first oxidation stage was passed through a connecting pipe made of special steel (length 40 cm, inner diameter 26 mm, outer diameter 30 mm, wall thickness 2 mm, wound in increments of 1 cm thermal insulation) with a centered section 20 cm long, filled with an inert bulk layer of steatite rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter), flanged directly to the contact tube of the specified reaction Torah.

The temperature of the gas mixture at the inlet to the connecting tube always exceeded the temperature T ^{1 of the} first oxidation stage, and at the outlet of the connecting tube was from 200 to 270 ° C.

At the end of the connecting tube, molecular oxygen was added to the cooled gas mixture of the reaction products, the pressure of which was identical to the pressure of this mixture. The resulting gas mixture was sent directly to the contact tube of the second oxidation stage, to which the other end of the connecting tube was flanged. The consumption of added molecular oxygen was calculated so that the molar ratio of oxygen to acrolein in the resulting gas mixture was 1.3: 1.

Second Stage Oxidation Reactor

We used a reactor with a stationary layer of a catalyst in the contact tube, the design of which was similar to the reactor of the first oxidation stage. The molten salt and the initial gas mixture were also passed through the reactor by direct flow. The temperature of the salt melt at the inlet to the reactor (T ¹ ) was controlled so that the degree of conversion of acrolein when it was once passed through the reactor of the second oxidation stage was always 99.3 ± 0.1 mol%. The temperature of the salt melt at the outlet of the reactor (T ² ) was 2 ° C higher than its temperature at the inlet (T ¹ ).

The catalyst was loaded into the contact tube as follows (bottom to top).

Section A: height 70 cm; preliminary bulk layer of steatite rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter).

Section B: height 100 cm; a bulk layer of a homogeneous mixture of 30 wt.% steatite rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter) and 70 wt.% layered catalyst, similar to that used to fill section C.

Section C: height 200 cm; a bulk layer of a layered catalyst in the form of rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter) according to example 5 of German patent application DE-A 10046928 (stoichiometric composition of Mo ₁₂ V ₃ W _1,2 Cu _{2, 4} O _x ).

Section D: height 30 cm; the final bulk layer of steatite balls with a diameter of 4 to 5 mm.

C) The results, depending on the composition of the initial gas mixture for the first reaction stage [propylene consumption 150 nl / l · h, the selectivity for the formation of acrylic acid (taking into account both reaction stages and in terms of converted propylene) was constantly ≥94 mol%]

a) The preferred composition of the source gas mixture for the first stage of oxidation:

propylene 7 vol.%, oxygen 12 vol.%, hydrogen 20 vol.%, water 5 vol.%, nitrogen 56% vol.

The temperature at the inlet of the reaction device when using freshly loaded catalyst:

T ^ein (first oxidation step): 320 ° C,

T ^ein (second oxidation step): 268 ° C.

The temperature at the entrance to the reaction device after a three-month period of operation of the catalyst;

T ^ein (first oxidation step): 330 ° C,

T ^ein (second oxidation step): 285 ° C.

b) An advantageous composition of the feed gas mixture for the first oxidation step:

propylene 7 vol.%, oxygen 12 vol.%, water 5 vol.%, nitrogen 76 vol.%.

The temperature at the inlet of the reaction device when using freshly loaded catalyst:

T ¹ (first stage of oxidation): 320 ° C,

T ¹ (second oxidation step): 268 ° C.

The temperature at the inlet of the reaction device after a three-month period of operation of the catalyst:

T ¹ (first stage of oxidation): 324 ° C,

T ¹ (second oxidation step): 276 ° C.

II. The method of producing acrylic acid from propane (stationary operating mode)

The reaction zone A is made in the form of an adiabatic shelf reactor such as a shaft furnace with three fixed catalyst beds sequentially ordered in the direction of gas flow. Each of the fixed catalyst layers is a bulk layer located on a wire mesh made of special steel, which, in turn, consists (in the direction of the gas flow) of a layer of inert material (steatite balls with a diameter of 1.5 to 2.5 mm) in height 26 mm and a layer formed by a mixture of a fresh dehydrogenation catalyst with steatite balls with a diameter of 1.5 to 2.5 mm, with a volume ratio of these components of 1: 3 (in another embodiment, such a bulk layer may consist of a similar amount catalyst without dilution with inert material).

In front of each fixed catalyst bed is a static gas mixer. The dehydrogenation catalyst of the general formula Pt _0.3 Sn _0.6 La _3.0 Cs _0.5 K _0.2 (ZrO ₂ ) _88.3 (SiO ₂ ) _7.1 is an element containing oxidized elements [cesium (Cs), potassium ( K) and lanthanum (La)] an alloy of platinum with tin deposited on the outer and inner surfaces of the carrier rods consisting of a mixture of ZrO ₂ · SiO ₂ oxides (average rod height 6 mm, Gaussian distribution in the range from 3 to 12 mm with a maximum of about 6 mm; diameter 2 mm), and these elements, including the elements contained in the carrier, are in a stoichiometric mass ratio (preparation catalyst and its activation with the formation of the active catalyst is made in accordance with example 4 of the German patent application DE-A 10219879).

The heterogeneously-catalyzed partial dehydrogenation of propane is carried out by directly passing it through said shelf reactor. Propane consumption in terms of the total amount of catalyst located on all shelves (excluding inert material) is 1500 nl / l · h.

62473 nm ³ / h of initial reaction gas mixture A (temperature 438 ° C, pressure 2.92 bar), formed by the following gas streams, is introduced into the first catalyst bed along the way;

- circulating gas I (50870 nm ³ / h) of the following composition:

acrolein 0.01 vol.%, acrylic acid 0.01 vol.%, propane 63.49 vol.%, propylene 0.86 vol.%, hydrogen 14.50 vol.%, oxygen 4.72 vol.%, water 2.05 vol.%, carbon monoxide 1.17 vol.%, carbon dioxide 11.17% vol.

- water vapor (3091 nm ³ / h) and

- crude propane (8512 nm ³ / h) with a basic substance content of more than 98 vol.%.

The temperature of the initial reaction gas mixture A is increased from 80 to 438 ° C due to indirect heat exchange with the gaseous product A, whose temperature is 581 ° C, a pressure of 2.88 bar. The evaporation of crude propane is carried out due to indirect heat exchange with water condensate formed in the separation zone I (acidic water with a temperature of 33 ° C). The cooled condensate can then be used in the separation zone I for condensation of acidic water (for example, as a cooling agent used for its direct cooling). The temperature of water vapor is 152 ° C, pressure 5 bar.

The height of the first bulk catalyst layer (in the direction of transmission of the initial gas mixture A) is chosen so that the reaction gas A formed in this layer (temperature 549 ° C, pressure 2.91 bar) has the following composition:

propane 59.0 vol.%, propylene 5.94 vol.%, hydrogen 10.25 vol.%, water 12.98 vol.%, carbon dioxide 9.97 vol.% And oxygen 0 vol.%.

The maximum temperature in the first catalyst bed is 592 ° C.

The amount of reaction gas formed in the first catalyst layer is 63,392 nm ³ / h. After the first catalyst layer, 986 nm ³ / h of molecular oxygen with a purity of more than 99 vol% is added to reaction gas A.

Oxygen is preheated to 176 ° C. It is throttled to 3.20 bar, due to which the pressure of reaction gas A remains at 2.91 bar after the addition of oxygen.

The height of the second catalyst layer is chosen so that the reaction gas A formed in this layer (temperature 566 ° C, pressure 2.90 bar) has the following composition:

propane 51.91 vol.%, propylene 9.55 vol.%, hydrogen 10.88 vol.%, water 15.38 vol.%, carbon dioxide 9.57 vol.% And oxygen 0 vol.%.

The maximum temperature in the second catalyst bed is 595 ° C.

The amount of reaction gas A formed in the second catalyst layer is 66058 nm ³ / h. To this reaction gas, in front of the static mixer, located in front of the third catalyst bed, 918 nm ³ / h of molecular oxygen (purity greater than 99 vol%, temperature 176 ° C, throttling up to 3.20 bar) is added. The pressure of reaction gas A after the addition of oxygen is maintained at 2.90 bar.

The height of the third bulk catalyst layer is chosen so that the reaction gas A formed therein as the gaseous product A (temperature 581 ° C, pressure 2.88 bar) has the following composition:

propane 47.19 vol.%, propylene 12.75 vol.%, hydrogen 11.38 vol.%, water 17.46 vol.%, carbon dioxide 9.21 vol.%, oxygen 0 vol.%.

The maximum temperature in the third catalyst bed is 612 ° C.

The amount of gaseous product A formed in the third catalyst layer is 68522 nm ³ / h. It is cooled to a temperature of 290 ° C due to indirect heat exchange with the initial reaction gas mixture A.

To the obtained gaseous product A, 13306 nm ³ / h molecular oxygen was added (purity greater than 99 vol%, temperature 176 ° C, throttling up to 3.20 bar). The pressure and temperature of the resulting initial reaction gas mixture B, intended for supplying to the first stage of two-stage partial oxidation (conversion of propylene contained therein to acrylic acid), are 1.75 bar and 283 ° C, respectively.

The first stage of oxidation is carried out in a reactor with a large number of reaction tubes having two temperature zones. The reaction tubes are made of V2A steel (outer diameter 30 mm, wall thickness 2 mm, inner diameter 26 mm, length 350 cm). They are filled with catalyst in the following sequence (from top to bottom).

Section 1: height 50 cm; preliminary bulk layer of steatite rings with dimensions of 7 × 7 × 4 mm (outer diameter × length × inner diameter).

Section 2: height 140 cm; a bulk layer of a homogeneous mixture of 20 wt.% (in another embodiment, 30 wt.%) steatite rings with dimensions of 5 × 3 × 2 mm (outer diameter × length × inner diameter) and 80 wt.% (in another embodiment, 70 wt.%) one-piece catalyst similar to that loaded in section 3.

Section 3: height 160 cm; a bulk layer of solid catalyst in the form of rings with dimensions of 5 × 3 × 2 mm (outer diameter × length × inner diameter) according to example 1 of German patent application DE-A 10046957 (stoichiometric composition [Bi ₂ W ₂ O ₉ × 2WO ₃ ] _0.5 [Mo ₁₂ Co _5.5 Fe _2.94 Si _1.59 K _0.08 O _x ] ₁ ); in another embodiment, you can also use one of the catalysts BVK1-BVK11 according to research report No. 497012 of 08/29/2005 (the units of the numerical values of the specific surface area correctly indicated in the corresponding examples are not cm ² / g, but m ² / g).

The first 175 cm of reaction tubes (from top to bottom) are thermostated due to the countercurrent circulation of salt melt A relative to the reaction gas B. The next 175 cm are thermostated due to the countercurrent circulation of salt melt B relative to the reaction gas B.

The second stage of oxidation is also carried out in a reactor with a large number of reaction tubes having two temperature zones. The reaction tubes are filled with catalyst in the following sequence (from top to bottom).

Section 1: height 20 cm; preliminary bulk layer of steatite rings with dimensions of 7 × 7 × 4 mm (outer diameter × length × inner diameter).

Section 2: height 90 cm; a bulk layer of a homogeneous mixture of 25 wt.% (in another embodiment, 30 wt.%) steatite rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter) and 75 wt.% (in another embodiment, 70 wt.%) layered catalyst similar to that loaded in section 4.

Section 3: height 50 cm; a bulk layer of a homogeneous mixture of 15 wt.% (in another embodiment 20 wt.%) steatite rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter) and 85 wt.% (in another embodiment, 80 wt.%) layered catalyst similar to that loaded in section 4.

Section 4: height 190 cm; a bulk layer of a layered catalyst in the form of rings with dimensions of 7 × 3 × 4 mm (outer diameter × length × inner diameter) according to manufacturing example 5 of German patent application DE-A 10046928 (stoichiometric composition of Mo ₁₂ V ₃ W _1,2 Cu _{2 , 4} O _x ).

The first 175 cm of reaction tubes (from top to bottom) are thermostated due to the circulation of salt melt C carried out by the pump countercurrent with respect to the reaction gas. The next 175 cm of the reaction tubes are thermostated due to the circulation of salt melt D.

Between both stages of oxidation there is a shell-and-tube heat exchanger cooled by means of salt melt, by means of which it is possible to reduce the temperature of the gaseous product formed in the first stage of oxidation. Before entering the second oxidation stage, there is a valve for the supply of molecular oxygen, the purity of which exceeds 99 vol.%.

The propylene flow rate through the catalyst of the first oxidation stage is 145 nl / l · h. The temperature of salt melts (53 wt.% KNO ₃ , 40 wt.% NaNO ₂ , 7 wt.% NaNO ₃ ) at the entrance to the corresponding temperature zones is:

T _A = 324 ° C, T _B = 328 ° C,

T _C = 265 ° C, T _D = 269 ° C.

So much molecular oxygen (176 ° C, 3.20 bar) is added to the gaseous mixture of reaction products obtained in the first stage of oxidation that the molar ratio of oxygen to acrolein in the resulting gas mixture, intended to be supplied to the second stage of oxidation, is 1.25 :one. The consumption of acrolein through the catalyst of the second stage of oxidation is 140 nl / l · h. The pressure at the inlet to the second oxidation stage is 1.61 bar. The temperature of the reaction gas at the outlet of the intermediate cooler is 260 ° C, the temperature of the gas mixture sent to the second stage of oxidation is 258 ° C. The gaseous mixture of the reaction products of the first oxidation stage has the following composition:

acrolein 9.02% vol. acrylic acid 0.61 vol.%, propane 39.5 vol.%, propylene 0.53 vol.%, hydrogen 9.49 vol.%, oxygen 3.90 vol.%, water 25.75 vol.%, carbon dioxide 8.77 vol.%.

The temperature of the gaseous product of the first oxidation stage at the inlet to the refrigerator located after it is 335 ° C.

The temperature of the gas mixture of the reaction products of the second stage of oxidation (gaseous product B) is 270 ° C, a pressure of 1.55 bar; this mixture has the following composition:

acrolein 0.049 vol.%, acrylic acid 9.12 vol.%, acetic acid 0.26 vol.%, propane 39.43 vol.%, propylene 0.53 vol.%, hydrogen 9.52 vol.%, oxygen 2.94 vol.%, water 26.10 vol.%, carbon monoxide 0.72 vol.%, carbon dioxide 9.3 vol.%.

The gaseous product B is subjected to fractional condensation in a tray column (separation zone I), carried out as described in international application WO 2004/035514.

As the first fuel stream, 118 kg / h of low-boiling products [polyacrylic acids (Michael-Addukte) and so on] are sent for combustion. 23577 kg / h of condensate of crude acrylic acid with a temperature of 15 ° C, the content of the main substance of which is 96.99 wt.%, Are taken from the second plate above the supply point of the gaseous product B to the tray column. After adding a small amount of water, the crude acrylic acid is subjected to suspension crystallization described in WO 2004/035514, and the suspension crystallizate is separated from the mother liquor in the hydraulic wash column, which, as described in this application, is returned to the condensation column. The degree of purity of the washed acrylic acid is more than 99.87 wt.%, And it is suitable for the direct production of "superabsorbent" water polymers used in hygiene.

From the third plate above the supply point of the gaseous product B to the condensation column, 18145 kg / h of acidic water condensate that is not returned to the specified column are taken at a temperature of 33 ° C, which has the following composition:

acrolein 0.11 wt.%, acrylic acid 1.30 wt.%, acetic acid 0.95 wt.%, water 95.6 wt.%.

From the upper part of the condensation column, 53379 nm ³ / h of residual gas I directed to separation zone I (temperature 33 ° C, pressure 1.20 bar) is taken, which has the following composition:

acrolein 0.03 vol.%, acrylic acid 0.02 vol.%, propane 61.07 vol.%, propylene 0.82 vol.%, hydrogen 14.02 vol.%, oxygen 4.55 vol.%, water 2.00 vol.%, carbon monoxide 1.13% vol. carbon dioxide 14.36 vol.%.

0.084 vol.% Of residual gas I having the indicated composition is withdrawn from the process as a third fuel stream.

The remaining amount of residual gas I under pressure of 1.20 bar (hereinafter referred to as simplicity called residual gas I for simplicity) is compressed at the first stage of a multistage centrifugal compressor to 3.20 bar, while its temperature rises to 92 ° C. The compressed residual gas I is divided into two halves of identical composition. One of the half of the residual gas I forms a partial amount of the circulating gas I directly returned to the reaction zone A. The other half of the residual gas I, under a pressure of 3.20 bar, is compressed to 5.80 bar in the second stage of the compressor. In this case, the gas is heated to 127 ° C. It is cooled in an indirect heat exchanger to 78 ° C, and cooling is not accompanied by the formation of condensate (the cooling agent is residual gas I at a temperature of 42 ° C under a pressure of 4.25 bar and washed from carbon dioxide, released from molecular hydrogen by passing through a membrane and subsequent throttling in the turboexpander). The temperature of the residual gas I is reduced from 78 to 54 ° C due to indirect heat exchange with air, and cooling is not accompanied by the formation of condensate. At the next compressor stage, the pressure of the residual gas I is increased from 5.80 to 12.0 bar, and the compression of the gas is accompanied by an increase in its temperature from 54 to 75 ° C.

The residual gas I compressed in this way is directed to the lower part of the wash column with packed bodies (separation zone II). 18000 kg / h of an aqueous solution of potassium carbonate with a temperature of 82 ° C. containing phenothiazine as a polymerization inhibitor are fed to the top of the column. Residual gas I with a temperature of 85 ° C, which has the following composition, is removed from the upper part of the wash column, which is washed away from carbon dioxide and is under a pressure of 12.00 bar.

propane 65.94 vol.%, propylene 0.89 vol.%, hydrogen 15.13% vol. oxygen 4.91 vol.%, water 2.16 vol.%, carbon monoxide 1.22 vol.%, carbon dioxide 7.75 vol.%.

The residual gas I washed from carbon dioxide (24528 nm ³ / h) is passed through a bundle of sleeve membranes filled into the plates (polyimide membranes of type B-H from UBE Industries Ltd., external pressure 0.1 bar), at the outlet of which it has the following composition (pressure 12.00 bar, temperature 85 ° C):

propane 66.1 vol.%, propylene 0.89 vol.%, hydrogen 15.03% vol. oxygen 4.92 vol.%, water 2.10 vol.%, carbon monoxide 1.22 vol.%, carbon dioxide 7.73% vol.

The residual gas pressure I (24461 nm ³ / h) decreases in a multi-stage turboexpander from 12.00 to 4.25 bar while reducing the temperature from 85 to 42 ° C. The residual gas I washed off from carbon dioxide and free from molecular hydrogen, due to indirect heat exchange with the residual gas I coming from separation zone I and compressed at the first compressor stage, is heated from 42 to 97 ° C and, together with the other half, the residual gas not washed from carbon dioxide I remaining after fractionating condensation of the gaseous product B is recycled as circulation gas I to the initial mixture of reaction gases A for reaction zone A.

The gas stream (67.2 nm ³ / h), penetrating through the membrane used to isolate molecular hydrogen, has the following composition:

propane 0.12 vol.%, propylene 0.01 vol.%, hydrogen 56.2 vol.%, water 27.2 vol.%, carbon monoxide 0.15 vol.%, carbon dioxide 12.39 vol.%.

It is sent to the common combustion system as a fourth fuel stream.

21846 kg / h of an aqueous solution of potassium bicarbonate with a temperature of 75 ° C is taken from the cube of the column for washing carbon dioxide, which is heated from 75 to 100 ° C and fed to the top of the second column due to indirect heat exchange (using a solution of degraded potassium bicarbonate as a heat carrier) with packed bodies (destruction columns). 26 nm ³ / h of water vapor (144 ° C, 4 bar) are countercurrently introduced into the bottom of this column. The gas stream discharged from the top of the column is subjected to direct cooling using previously formed condensate as a cooling agent, and the aqueous condensate formed upon cooling is returned to the column. Carbon dioxide escaping from the column is sent to the common combustion system as a fifth fuel stream. 14968 kg / h of water is evaporated from the discharge of the destruction column (32968 kg / g). If necessary, the neutralized sodium hydroxide residue is returned as a washing solution to the top of the carbon dioxide washing column.

Fuel streams 1-5 are subjected to co-combustion in an appropriate system, carried out with air supply (17674 nm ³ / h).

Claims (22)

1. The method of producing acrylic acid from propane, in accordance with which
A) - at least two propane-containing gaseous feed streams, at least one of which contains fresh propane, are introduced into the first reaction zone A;
reaction gas A is passed through at least one catalyst bed of reaction zone A, in which molecular hydrogen and propylene are formed due to partial heterogeneously catalyzed dehydrogenation of propane,
molecular oxygen is introduced into the reaction zone A, which oxidizes the molecular hydrogen contained in the reaction gas A to water vapor, and
gaseous product A containing molecular hydrogen, water vapor, propylene and propane is taken from reaction zone A
B) the gaseous product A withdrawn from the reaction zone A when molecular oxygen is supplied is used in the reaction zone B to supply at least one oxidation reactor with a reaction gas B containing molecular hydrogen, water vapor, propane, propylene and molecular oxygen, and contained in the reaction gas Propylene is subjected in the reaction zone B to a two-stage heterogeneously-catalyzed partial gas-phase oxidation to obtain a gaseous product B containing acrylic acid as the target product, rotated propane, molecular hydrogen, water vapor and carbon dioxide as by-products, as well as other by-products with boiling points below and above the boiling point of water,
C) the gaseous product B is withdrawn from reaction zone B and, in the first separation zone I, acrylic acid, water and side components contained therein are separated by fractional condensation or by absorption with a boiling point above the boiling point of water, the residual gas I remaining after their isolation unconverted propane, carbon dioxide, molecular hydrogen, side components with a boiling point below the boiling point of water, and, if necessary, unconverted in the reaction zone In propylene and mol ulyarny oxygen,
D) the residual gas I is subjected to additional treatments
washing out the carbon dioxide contained in the residual gas I,
the removal of a partial amount of residual gas I, and also, if necessary, the release of molecular hydrogen contained in the residual gas I through a separation membrane
E) residual gas I containing unconverted propane, after further treatment, is returned to reaction zone A as at least one of at least two propane-containing feed streams,
characterized in that
in the reaction zone A, a certain amount of (M) molecular hydrogen is oxidized to water vapor, which is at least 35 mol%, but not more than 65 mol% of the total amount produced in the reaction zone A and, if necessary, introduced into it molecular hydrogen. 2. The method according to claim 1, characterized in that the amount (M) of molecular hydrogen oxidized in the reaction zone A to water vapor is at least 40 mol.%, But not more than 60 mol.% Of the total amount produced in the reaction zone A and, if necessary, introduced into it molecular hydrogen. 3. The method according to claim 1, characterized in that the reaction gas B, used to supply at least one oxidation reactor, contains
from 4 to 25 vol.% propylene,
from 6 to 70 vol.% propane,
from 5 to 60 vol.% water,
from 5 to 65 vol.% oxygen and
from 0.3 to 20 vol.% hydrogen. 4. The method according to claim 1, characterized in that the reaction gas B, used to supply at least one oxidation reactor, contains
from 6 to 15 vol.% propylene,
from 6 to 60 vol.% propane,
from 5 to 30 vol.% water,
from 8 to 35 vol.% oxygen and
from 2 to 18 vol.% hydrogen. 5. The method according to claim 3, characterized in that the molar ratio of V ₁ contained in the propane in the reaction gas B to the propylene contained in the reaction gas B is from 1: 1 to 9: 1. 6. The method according to claim 3, characterized in that the molar ratio of V ₁ contained in the propane in the reaction gas B to the propylene contained in the reaction gas B is from 1: 1 to 7: 1. 7. The method according to claim 1, characterized in that the source of molecular oxygen necessary for use in reaction zone B is pure molecular oxygen or a mixture of molecular oxygen with an inert gas containing not more than 10 vol.% Inert gas. 8. The method according to claim 1, characterized in that the source of molecular oxygen necessary for use in reaction zone A is pure molecular oxygen or a mixture of molecular oxygen with an inert gas containing not more than 10 vol.% Inert gas. 9. The method according to claim 1, characterized in that the source of molecular oxygen necessary for use in the reaction zone A is air, and the source of molecular oxygen necessary for use in the reaction zone B is pure molecular oxygen or a mixture of molecular oxygen with an inert gas containing not more than 10 vol.% inert gas. 10. The method according to claim 1, characterized in that the reaction gas B, used to supply at least one oxidation reactor, contains from 0.1 to 30 vol.% Carbon dioxide. 11. The method according to claim 1, characterized in that the reaction gas B used to feed at least one oxidation reactor contains from 1 to 20 vol.% Carbon dioxide. 12. The method according to claim 1, characterized in that the reaction gas B used to feed at least one oxidation reactor contains ≤5 vol.% Molecular nitrogen. 13. The method according to claim 1, characterized in that the reaction zone A is adiabatic. 14. The method according to claim 1, characterized in that the reaction zone A is made in the form of a shelf reactor. 15. The method according to claim 1, characterized in that the additionally treated residual gas I, returned to the reaction zone A, contains molecular oxygen, water vapor, molecular hydrogen, carbon monoxide and carbon dioxide. 16. The method according to claim 1, characterized in that the additionally treated residual gas I, returned to the reaction zone A, contains from 5 to 15 vol.% Carbon dioxide. 17. The method according to claim 1, characterized in that the washing of carbon dioxide from residual gas I is carried out by means of an aqueous solution of potassium carbonate. 18. The method according to claim 1, characterized in that the washing of carbon dioxide from residual gas I is carried out under a pressure of from 3 to 50 bar. 19. The method according to claim 1, characterized in that in the separation zone I from the gaseous product B, water is separated in an amount of at least 70 mol% of the amount of water generated in the reaction zone B. 20. The method according to claim 1, characterized in that in the separation zone I from the gaseous product B, water is separated in an amount of at least 90 mol% of the amount of water generated in the reaction zone B. 21. The method according to one of claims 1 to 20, characterized in that the amount of propane contained in the residual gas I removed per unit time from the production process is less than 30 mol%, calculated on the amount of fresh introduced into the production process per unit time propane. 22. The method according to one of claims 1 to 20, characterized in that the amount of propane contained in the additionally treated residual gas I returned to reaction zone A is at least 90 mol% of the amount of propane contained in the gaseous product B .