RU2285690C2 - Method for preparing acrolein and/or acrylic acid - Google Patents

Abstract

FIELD: organic chemistry, chemical technology.

SUBSTANCE: invention relates to a method for synthesis of acrolein and/or acrylic acid from propane and/or propene. Method involves the following steps: (a) isolating propane and/or propene from gaseous mixture A containing propane and/or propene by their absorption with adsorbent; (b) isolating propane and/or propene from adsorbent to form gas B containing propane and/or propene, and (c) using gas B obtained in stage (b) for oxidation of propane and/or propene to acrolein and/or acrylic acid wherein the heterogeneous catalytic dehydrogenation of propane without feeding oxygen is not carried out. Method shows economy and maximal exploitation period of used catalyst without its regeneration.

EFFECT: improved method of synthesis.

12 cl, 7 dwg, 1 ex

Description

The present invention relates to a method for producing acrolein and / or acrylic acid from propane and / or propene.

Acrolein and acrylic acid are important chemical products. Thus, acrylic acid is used, in particular, as a starting monomer for producing polymers, aqueous dispersions of which are used, for example, as binders. Depending on the scope of these polymers, acrylic acid may be esterified before polymerization. Acrolein is an important intermediate used, for example, to produce glutaraldehyde, methionine, folic and acrylic acids.

According to known methods, the starting products for producing acrolein and / or acrylic acid are propane and / or propene. From the German patent application DE-A 3313573 and the European patent application EP-A-0117146, a two- or three-stage process is known for converting propane to acrolein and / or acrylic acid, in the first stage of which propane is dehydrogenated to propene, and in the second stage, oxidation propene to acrolein. An important feature of this method is that propane is not separated between the first and second stages from the side components formed during its dehydrogenation, for example, from molecular hydrogen. The oxidation of propene is carried out under conditions that exclude noticeable oxidation of hydrogen. In a third step, acrolein can be oxidized to acrylic acid. In addition, it is possible to isolate propane and propene that are not converted in the second or third stage by their absorption and return to the first stage (dehydrogenation stage) after separation from the absorbent.

Japanese patent application JP-A-10-36311 describes a method for producing α, β-unsaturated carboxylic acids, in particular acrylic acid, by gas-phase oxidation of propane in the presence of a metal oxide composite catalyst, moreover, to achieve a high yield of the target product, the propane ratio to oxygen and, if necessary, a gaseous diluent in the composition of the initial mixture is maintained in a certain range, while providing a certain degree of conversion of propane. Unconverted propane can be separated from the reaction products using a selective separator, including a device for adsorption at a variable pressure (Pressure-Swing-Adsorption), and again subjected to gas-phase oxidation.

British patent application GB 1378178 describes a method in which an unconverted hydrocarbon is absorbed by an absorbent, which is subsequently stripped using an appropriate stripping agent, which is added to the hydrocarbon to be isolated in such an amount that the mixture is outside the ignition range.

The objective of the present invention was to create a method of gas-phase catalytic production of acrolein and / or acrylic acid from propane and / or propene, characterized by efficiency and the maximum possible duration of operation of the used catalyst without regeneration.

According to the invention, this problem is solved by absorbing absorbent propane and / or propene from the mixture containing these hydrocarbons, isolating propane and / or propene from the absorbent and using propane and / or propene for subsequent oxidation to acrolein and / or acrylic acid.

Thus, the invention relates to a method for producing acrolein and / or acrylic acid from propane and / or propene, comprising the following steps:

a) the allocation of propane and / or propene from the propane and / or propene-containing gas mixture A by absorbing them with an absorbent,

b) recovering propane and / or propene from the absorbent to produce propane and / or propene-containing gas B and

c) using the gas B obtained in step (b) to oxidize propane and / or propene to acrolein and / or acrylic acid,

moreover, between stages (b) and (c) do not produce heterogeneous catalytic dehydrogenation of propane without oxygen. Preferred embodiments of the invention are given in the description below and in the corresponding drawings.

Since propane and / or propene is released by absorption prior to the oxidation step, gas B typically contains residual amounts of absorbent. It was unexpectedly found that despite this oxidation proceeds without any difficulty. In particular, no significant decrease in the activity of the oxidation catalyst was observed, which could be operated for a long period without regeneration. In addition, there were no problems due, if necessary, to occur at the stage of oxidation of propane and / or propene to the formation of any oxidation products of the absorbent. If the presence of residues of the absorbent material creates certain difficulties, which, as a rule, are absent, if high-boiling hydrocarbons are used as absorbents, the absorbent can be removed, for example, by water quenching or adsorption.

According to German patent application DE-A 3313573, recovered (isolated) by absorption of propane and propene are returned to the stage of heterogeneous catalytic dehydrogenation of propane, during the implementation of which deactivation of the corresponding catalyst can occur, for example, as a result of coking, and therefore dehydrogenation catalysts need frequent regeneration. The presence of an absorbent in the gas stream directed to dehydrogenation does not create any problems, since the absorbent is able to burn together with coking products. The catalysts used for the oxidation of propene to acrolein and / or acrylic acid usually do not regenerate so often, therefore the additional regeneration costs due to the presence of an absorbent in the gas used are more significant than during dehydrogenation. An advantage of the method according to the invention is that the oxidation catalyst can be operated without regeneration for a long time.

The method according to the invention differs from the method according to German patent application DE-A 3313573 in that the propane and / or propene recovered by absorption is sent to the oxidation step. Another difference of the method according to the invention is that between the stages of separation of propane and / or propene from the absorbent and their oxidation to acrolein and / or acrylic acid, heterogeneous catalytic dehydrogenation of propane without oxygen supply is not carried out.

In the framework of the present invention, gas B may also mean a gas mixture.

In step (a), a gas mixture A with any content of propane and / or propene can be used. The preferred molar ratio of propane to propene in gas mixture A is from 0: 100 to 100: 0, in particular from 10:90 to 90:10, often from 80:20 to 40:60.

The gas mixture A preferably contains at least one additional component other than propane and / or propene, the type of which is not subject to any special restrictions and, as a rule, is determined by the origin of the gas mixture. In particular, we are talking about at least one component selected from the group comprising oxygen, hydrogen, carbon oxides, in particular carbon monoxide or carbon dioxide, side components formed during the dehydrogenation of propane, gas-phase oxidation of propene to acrolein and / or acrylic acid or oxidation of propane to acrolein and / or acrylic acid. An additional component is often at least hydrogen, oxygen, carbon monoxide, or a mixture of these gases.

As absorbents used in step (a), in principle, any absorbents capable of absorbing propane and / or propene are suitable. By absorbent is meant preferably an organic solvent, which is preferably a hydrophobic and / or high boiling point compound. Its boiling point (at a normal pressure of 1 atm) is preferably at least 120 ° C, preferably at least 180 ° C, preferably is in the range from 200 to 350 ° C, in particular from 250 to 300 ° C, more preferably 260 to 290 ° C. It is advisable to use solvents whose flash point at a normal pressure of 1 atm exceeds 110 ° C. In general, low-polar organic solvents, for example aliphatic hydrocarbons, which preferably do not contain external polar groups or aromatic hydrocarbons, are suitable as absorbents. In the general case, it is desirable that the absorbent has a boiling point as high as possible and, at the same time, possibly more fully dissolves propane and / or propene. Suitable absorbents are, in particular, aliphatic hydrocarbons, for example alkanes or alkenes with 8 to 20 carbon atoms, aromatic hydrocarbons, for example, middle fractions formed during the distillation of paraffins, ethers with bulky groups attached to an oxygen atom or a mixture of these compounds, their composition can be additionally introduced 1,2-dimethylphthalate, as, for example, described in German patent application DE-A 4308087. In addition, esters formed by benzoic and phthalic acids and unbranched alkanols with 1-8 carbon atoms, in particular n-butyl, methyl or ethyl ester of benzoic acid, dimethyl or diethyl ether of phthalic acid, as well as the so-called oil coolants, in particular diphenyl, diphenyl ether, mixtures of diphenyl with diphenyl ether or the corresponding chlorine derivatives and triarylalkenes, for example 4-methyl-4'-benzyl diphenylmethane and its isomers: 2-methyl-2'-benzyl diphenylmethane, 2-methyl-4'-benzyl diphenylmethane, 4-methyl-2'-benzyl diphenylmethane, as well as mixtures thereof. A suitable absorbent is a mixture of diphenyl and diphenyl ether, preferably an azeotropic composition, in particular consisting of 25 wt.% Diphenyl (biphenyl) and 75 wt.% Diphenyl ether, sold under the trade name diphyl. Sometimes an additional solvent, for example dimethyl phthalate, is added to it in an amount of from 0.1 to 25 wt.% (Based on the total solvent mixture). Particularly suitable absorbents are octanes, nonanes, decanes, undecans, dodecans, tridecans, tetradecans, pentadecans, hexadecanes, heptadecanes and octadecans, with tetradecans being particularly suitable. It is preferable that the absorbent used, on the one hand, have the boiling point indicated above, and, on the other hand, have a not too high molecular weight. Absorbents are preferred whose molecular weight is less than or equal to 300 g / mol. In addition, paraffin oils with 8-10 carbon atoms described in German patent application DE-A 3313573 are suitable. For example, products of the Haplasol i series sold by Haltermann, in particular Haplasol 250/340 i and Haplasol 250/275, are suitable i, as well as PKWF and Printosol oils used in printing inks.

Absorption can be carried out, without any restrictions, using any methods and conditions known to those skilled in the art. Preferably, the contact of the gas mixture with the absorbent is carried out at a pressure of from 1 to 50 bar, preferably from 2 to 20 bar, more preferably from 5 to 10 bar, at a temperature of from 0 to 100 ° C, in particular from 30 to 50 ° C. The absorption can be carried out both in the respective columns and in apparatuses for water quenching with unilateral movement of flows or their countercurrent. Suitable absorption columns are, for example, plate columns with cap and / or mesh plates, columns with structured nozzles (e.g., sheet nozzles having a specific surface area of 100 to 500 m ² / m ³ , in particular Mellapak ^® 250 Y nozzle) and columns filled with packed bodies, such as Raschig rings. In addition, film and spray columns, absorbers with graphite blocks, surface, in particular thin and thick layer absorbers, as well as plate scrubbers, horizontal scrubbers with mechanical stirring and rotary scrubbers can be used. In addition, absorption in a bubble column with or without integrated elements may be preferred.

The separation of propane and / or propene from the absorbent can be carried out by evaporation, flash evaporation (Flashen) and / or distillation.

Propane and / or propene is recovered from the absorbent, preferably by stripping or stripping in step (b) by means of a gas having an inert behavior in step (c) of the invention and / or by means of molecular oxygen (e.g. air). The steaming can be carried out in the usual way, changing the pressure and / or temperature, preferably at a pressure of from 0.1 to 10 bar, in particular from 1 to 5 bar, more preferably from 1 to 2 bar, and a temperature of from 0 to 200 ° C, in particular from 20 to 200 ° C., more preferably from 30 to 50 ° C. Another gas suitable for stripping is, for example, water vapor, but it is preferable to use, in particular, mixtures of oxygen and nitrogen, for example air. If air or oxygen and nitrogen mixtures containing more than 10 vol.% Oxygen are used for steaming, before the steaming or during its implementation it may be advisable to add gas restricting the explosion region. Especially suitable are gases whose heat capacity at 20 ° C exceeds 29 J / mol · K, in particular methane, ethane, propane, butane, pentane, hexane, benzene, methanol, ethanol, as well as ammonia, carbon dioxide and water. Bubble columns with or without integrated elements are particularly suitable for steaming.

Propane and / or propene can also be isolated from the absorbent by distillation, for which columns with nozzles, nozzle bodies or corresponding built-in elements well known to those skilled in the art can be used. The following distillation conditions are preferred: pressure from 0.01 to 5 bar, in particular from 0.1 to 3 bar, more preferably from 1 to 2 bar, temperature in the bottom of the column from 50 to 300 ° C., in particular from 150 to 250 ° C.

If gas is included in gas mixture A, it is preferable to combine absorption with moisture condensation (so-called water quenching, Wasserquench). It is also preferable to perform water quenching after the desorption step, which minimizes the loss of absorbent.

Stage (C) is often carried out immediately after stage (b), that is, without intermediate process steps. However, the possibility of additional isolation of the absorbent between stages (b) and (c), carried out, for example, by water quenching, is not excluded.

The oxidation of propane and / or propene to acrolein and / or acrylic acid can be carried out in step (c) by any method known to those skilled in the art without any restrictions, whereby one or two-stage oxidation of propene to acrolein and / or acrylic acid, oxidation of propane to acrolein and / or acrylic acid or the simultaneous oxidation of propane and propene to acrolein and / or acrylic acid. Heterogeneous catalytic gas-phase oxidation by molecular oxygen is suitable, resulting in a mixture of gaseous reaction products containing acrolein and / or acrylic acid. If necessary, propane and / or propene supplied to the oxidation step is preheated to the temperature necessary for the implementation of this reaction by indirect heat exchange.

A preferred embodiment of step (c) of the process of the invention comprises oxidizing propene to acrolein and / or acrylic acid.

The heterogeneous catalytic gas-phase oxidation of propene to acrolein and / or acrylic acid by molecular oxygen proceeds in two successive reaction steps, the first of which leads to the formation of acrolein, and the second to the formation of acrylic acid. The reaction in two successive stages allows, using, in essence, the known method, to carry out step (c) of the method according to the invention in two successive oxidation zones, and the oxide catalyst used in each of them can be optimized accordingly. So, in the first oxidation zone (propene → acrolein), it is preferable, as a rule, to use a catalyst based on metal oxides containing a combination of molybdenum, bismuth and iron (Mo-Bi-Fe), while for the second oxidation zone (acrolein → acrylic acid ) Preferred are conventional metal oxide catalysts containing a combination of molybdenum and vanadium (Mo-V). The metal oxide catalysts used in both reaction zones have been repeatedly described and are well known in the art. For example, references to relevant US patents are given on page 5 of European patent application EP-A-0253409. Catalysts suitable for use in both oxidation zones are described in German patent applications DE-A 4431957 and DE-A 4431949. These documents refer, in particular, to compounds of the general formula I. The mixture of products formed in the first oxidation zone, sent to the second oxidation zone, as a rule, without intermediate processing.

The simplest form of implementation of both oxidation zones involves the use of a shell-and-tube reactor, and the loading of the catalyst into separate contact tubes at the site of completion of the first reaction step is changed accordingly (see, for example, European patent applications EP-A-0911313, EP-A-0979813, EP -A-0990636 and German patent application DE-A 2830765). For example, in the corresponding part of the tubes instead of the catalyst, if necessary, inert material is charged.

Preferred, however, is the design of both oxidation zones in the form of two series-connected systems formed by bundles of tubes that can be in a common reactor, and the transition zone from one bundle of contact tubes to another forms an inert, outside the tubes, accessible for passage of the reaction components bulk material. The contact tubes, as a rule, are washed by the coolant, while washing away the inert material located outside the contact tubes by it is absent. Therefore, both bundles of contact tubes are preferably placed in spatially separated reactors. An intermediate cooler is usually placed between these reactors in order to minimize, if necessary, the secondary oxidation of the acrolein contained in the mixture of gaseous products leaving the first oxidation zone. Instead of tubular reactors, plate-type heat exchangers with salt and / or evaporative cooling can also be used, for example, those described in German patent applications DE-A 19929487 and DE-A 19952964.

The reaction temperature in the first oxidation zone is typically from 300 to 450 ° C., preferably from 320 to 390 ° C. The reaction temperature in the second oxidation zone, as a rule, is from 200 to 300 ° C, often from 220 to 290 ° C. The pressure in both oxidation zones, it is advisable to maintain in the range from 0.5 to 5 ATM, preferably from 1 to 3 ATM. The rate of transmission of the reaction gas through the oxidation catalysts in both zones of the reactor, measured in nl / l · h, often ranges from 1500 to 2500 h ^-1 or up to 4000 h ^-1 . The transmission rate of propene in nl / l · hour is often from 50 to 300 h ^-1 , in particular from 100 to 200 h ^-1 .

In principle, both oxidation zones can have the design described, for example, in German patent applications DE-A 19837517, DE-A 19910506, DE-A 19910508 and DE-A 19837519. Typically, external temperature control of both oxidation zones, if necessary, included the composition of the multi-zone systems of reactors, by known methods, is brought into accordance with the special composition of the mixture of gaseous reaction products and the loaded catalyst.

According to the invention, it is preferable that, when carrying out the method according to the invention, propane mixed with propene behaves like a gaseous, preferably inert diluent during heterogeneous catalytic oxidation.

The total amount of molecular oxygen needed for oxidation can be immediately added to gas B, however, the possibility of additional oxygen supply at the end of the first oxidation zone is not ruled out.

The molar ratio of propene to molecular oxygen in the first oxidation zone is preferably set in the range from 1: 1 to 1: 3, often from 1: 1.5 to 1: 2. The preferred molar ratio of acrolein to molecular oxygen in the second oxidation zone is from 1: 0.5 to 1: 2.

An excess of molecular oxygen, as a rule, has a preferable effect on the kinetics of gas-phase oxidation in one or the other reaction zone. Since the heterogeneous catalytic gas-phase oxidation of propene to acrylic acid is subject to kinetic control, propene can in principle be used in molar excess with respect to molecular oxygen, which, for example, applies to the first oxidation zone, and an excess of propene actually plays the role of a gaseous diluent.

In principle, heterogeneous catalytic gas-phase oxidation of propene to acrylic acid can also be carried out in a single oxidation zone. In this case, both oxidation stages are realized in one reactor filled with a catalyst capable of catalyzing both oxidation stages, and the catalyst loading along the reaction coordinate can vary smoothly or abruptly. In the embodiment of step (c) in the form of two oxidation zones connected in series, if necessary, it is possible to partially or completely isolate carbon monoxide and water vapor generated as by-products in the first oxidation zone from the mixture of gaseous products leaving this zone before feeding them into the second oxidation zone. Preferably, an oxidation method is selected that does not require such isolation.

In addition to pure molecular oxygen, molecular oxygen diluted with an inert gas, in particular carbon dioxide, carbon monoxide, noble gases, nitrogen and / or saturated hydrocarbons can be used to carry out reaction step (c).

It is advisable to compensate at least part of the need for molecular oxygen by using air as its source. In a preferred embodiment, gas B supplied to step (c) of the method according to the invention essentially consists only of propane and propene, and only air is used as the molecular oxygen source necessary for oxidation. If necessary, by adding cold air to the gas B fed to step (c), direct cooling of this gas can be facilitated.

If the target product is acrolein, it seems impractical to use the second oxidation zone in the implementation of stage (c).

The oxidation of propene to acrolein and / or acrylic acid in step (c) can be carried out as described in European patent application EP-A-0117146, US patents US-A-5198578 and US-A-5183936, or similarly German patent application DE-A 3313573, Canadian patent CA-A-1217502, US patents US-A-3161670, US-A-4532365 and international application WO 97/36849. Suitable propene oxidation processes are also described in European patent applications EP-A-0293224, EP-A-0253409, German patent applications DE-A 4431957, DE-A 4132263 or DE 19508532, in particular, oxidation methods are preferred, involving the use of gaseous diluents.

The oxidation of acrolein to acrylic acid can be carried out in a fluidized bed reactor, as described in international application WO 00/39065.

The oxidation of propene to acrolein and / or acrylic acid can also be carried out in plate heat exchanger reactors described in German patent application DE-A 19952964.

According to another preferred embodiment, step (c) of the method according to the invention is carried out by oxidizing propane to acrolein and / or acrylic acid in one or more steps in the presence of an appropriate catalyst, any methods known to those skilled in the art are suitable, one of which is described, for example, in Japanese Patent Application JP-A-1036311.

Catalysts suitable for the heterogeneous catalytic gas-phase oxidation of propane to acrolein and / or acrylic acid are mixtures of metal oxides of the general formula (I)

in which M ¹ is tellurium (Te) and / or antimony (Sb),

M ² is at least one element from the group consisting of niobium (Nb), tantalum (Ta), tungsten (W), titanium (Ti), aluminum (AI), zirconium (Zr), chromium (Cr), manganese (Mn), gallium (Ga), iron (Fe), ruthenium (Ru), cobalt (Co), rhenium (Rh), nickel (Ni), palladium (Pd), platinum (Pt), lanthanum (La), bismuth (Bi), boron (B), cesium (Cs), tin (Sn), zinc (Zn), silicon (Si) and indium (In),

b is from 0.01 to 1,

c is equal to greater than 0 to 1, preferably from 0.01 to 1,

d is from greater than 0 to 1, preferably from 0.01 to 1,

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

Mixtures of metal oxides whose stoichiometric composition corresponds to formula (I) are known (see, for example, European patent applications EP-A-0608838, EP-A-0529853, Japanese patent applications JP-A 7-232071, JP-A 10 -57813, JP-A 2000-37632, JP-A 10-36311, international application WO 00/29105, Proceedings ISO'99, Sept. 10-11, 1999, G. Centi and S. Perathoner Ed., SCI Pub. 1999, European patent application EP-A-0767164, Catalysis Today 49 (1999), S.141-153, European patent application EP-A-0962253, Applied Catalysis A: General 194-195 (2000), S.479 -485, Japanese patent application JP-A 11/169716, European patent application EP-A-0895809, German patent application DE-A 19835257, Japanese applications and patent JP-A 8-57319, JP-A 10-28862, JP-A-11-43314, JP-A 11-57479, international patent application WO 00/29106, Japanese patent applications JP-A 10- 330343, JP-A 11-285637, JP-A 10-310539, JP-A 11-42434, JP-A 11-343261, JP-A 11-343262, international patent application WO 99/03825, Japanese patent applications JP-A 7-53448, JP-A 2000-51693 and JP-A 11-263745).

Particularly suitable are the mixtures of metal oxides (I), (II) and (III) described below.

In mixtures of metal oxides (I) of the formula (I), M ¹ is tellurium (Te) and / or antimony (Sb); M ² is at least one element from the group consisting of niobium (Nb), tantalum (Ta), tungsten (W), titanium (Ti), aluminum (AI), zirconium (Zr), chromium (Cr), manganese (Mn), iron (Fe), ruthenium (Ru), cobalt (Co), rhenium (Rh), nickel (Ni), palladium (Pd), platinum (Pt), bismuth (Bi), boron (B) and cesium (Cs); b is from 0.01 to 1; s is from 0.01 to 1; d is from 0.01 to 1; n is a number determined by the valency and repeatability of elements different from oxygen in the composition of the mixture (I).

A mixture of metal oxides (I) is preferably prepared as follows. A mixture of sources of elementary constituents of a mixture of metal oxides (I) is subjected to hydrothermal treatment, the newly formed solid product is isolated and converted into the active oxide by heat treatment. Preferred is a mixture of metal oxides (I) of the following composition: M ¹ is tellurium (Te), M ² is niobium (Nb), b is 0.1-0.6, c is 0.05-0.4 and d is 0 , 01-0.6. The temperature of the heat treatment is preferably from 350 to 700 ° C, and the initial stage of heat treatment is carried out, in particular, at a temperature of from 150 to 400 ° C in an oxygen-containing atmosphere, and the final stage at a temperature of from 350 to 700 ° C in an inert gas atmosphere. Suitable stoichiometric compositions of the mixture of metal oxides (I) are similar to those given in European patent application EP-A-0608838, international patent application WO 00/29106, Japanese patent application JP-A 11/169716 and European patent application EP-A- 0962253 compositions.

The hydrothermal preparation of preliminary (inactive) metal oxide mixtures is well known to those skilled in the art (see, for example, Applied Catalysis A: 194-195 (2000) 479-485, Kinetics and Catalysis, Vol.40, No.3, 1999, pp.401- 404, Chem. Commun., 1999, 517-518, Japanese Patent Applications JP-A 6/227819 and JP-A 2000/26123).

By hydrothermal treatment is meant, in particular, the heat treatment of preferably carefully mixed sources of elementary constituents of the desired mixture of metal oxides (I), which is carried out in a pressurized container (autoclave) in the presence of pressurized water vapor at a temperature usually of more than 100 to 600 ° C. The pressure is usually up to 500 atm, preferably up to 250 atm. The temperature can exceed 600 ° C, and the pressure can be higher than 500 atm, however, from a technological point of view, the use of such a regime is not practical. Especially preferred is hydrothermal treatment carried out with the simultaneous presence of water vapor and condensed water. Such treatment can be carried out at a temperature of from more than 100 to 374.15 ° C (critical water temperature) and the corresponding pressure. In this case, it is advisable to use such an amount of water that the complete absorption of the starting compounds by the liquid phase takes place with the formation of a suspension and / or solution.

It is also possible such a method of hydrothermal treatment, according to which a thoroughly mixed mixture of the starting compounds completely absorbs water condensate in equilibrium with water vapor.

The hydrothermal treatment is preferably carried out at temperatures above 100-300 ° C, preferably 150-250 ° C (for example, 160-180 ° C). The content of sources of elementary constituents of the desired mixture of metal oxides (I) in a mixture of water with these sources in an autoclave is usually not less than 1 wt.% And usually does not exceed 90 wt.%. A typical content of sources of elemental components is from 3 to 60 wt.% Or from 5 to 30 wt.%, Often from 5 to 15 wt.%.

Hydrothermal treatment can be carried out both with stirring and without stirring. Suitable starting compounds (sources of elementary constituents of a mixture of metal oxides) for hydrothermal treatment are, in particular, any compounds which, when heated under excessive pressure in the presence of water, are capable of forming the corresponding oxides and / or hydroxides. For hydrothermal treatment, ready-made oxides and / or hydroxides of elemental constituents or only such oxides and / or hydroxides alone can be shared. Sources of elementary components, as a rule, are used in a finely divided state.

Suitable sources of elementary constituents are any compounds which, when heated, if necessary, carried out in the presence of air, can form oxides and / or hydroxides. As such starting compounds, ready-made oxides and / or hydroxides of elementary constituents or only such oxides and / or hydroxides alone can be shared.

Suitable sources of the elemental component containing molybdenum (Mo) are, for example, molybdenum oxides, in particular molybdenum trioxide, salts of molybdenum acid, in particular ammonium heptamolybdotetrahydrate, and molybdenum halides, in particular molybdenum chloride.

Suitable sources of the elemental component containing vanadium (V) are, for example, vanadyl acetylacetonate, vanadium acid salts, in particular ammonium metavanadate, vanadium oxides, in particular vanadium pentoxide (V ₂ O ₅ ), vanadium halides, in particular vanadium tetrachloride (VCl ₄ ), and vanadium oxyhalides, in particular vanadium oxychloride (VOCl ₃ ). As starting compounds, it is advisable to jointly use vanadium-containing compounds in which vanadium has a oxidation state of +4.

Suitable sources of the tellurium-containing elemental component are tellurium oxides, in particular tellurium dioxide, metallic tellurium, tellurium halides, in particular tellurium dichloride (TeCl ₂ ), and telluric acids, in particular orthotelluric acid (H ₆ TeO ₆ ).

Preferred starting compounds containing antimony are antimony halides, in particular antimony trichloride (SbCl ₃ ), antimony oxides, in particular antimony trioxide (Sb ₂ O ₃ ), antimony acids, in particular HSb (OH) ₆ , and antimony oxide ((SbO ₂ ) SO ₄ ).

Suitable sources of the elemental component containing niobium are, for example, niobium oxides, in particular niobium pentoxide (Nb ₂ O ₅ ), niobium oxyhalides, in particular niobium oxychloride (NbOCl ₃ ), niobium halides, in particular niobium chloride (NbCl ₅ ), and complex compounds of niobium and organic carboxylic and / or dicarboxylic acids, for example niobium oxalates and alcoholates. Solutions containing niobium also used in accordance with European patent application EP-A-0895809 are also suitable as a source of niobium.

As for the possible starting compounds containing other elements of M ² , we are talking primarily about the corresponding halides, nitrates, formates, oxalates, acetates, carbonates and / or hydroxides. Suitable starting compounds are often also oxo derivatives, for example tungstates or their corresponding acids, as well as ammonium salts.

Suitable starting compounds are furthermore Anderson type polyanions described, for example, in Polyhedron. Vol.6, No.2, pp.213-218, 1987, which were used to obtain the corresponding metal oxides (I), for example, in Applied Catalysis A: General 194-195 (2000) 479-485, or the polyanions given in the references cited in these publications. Anderson type polyanions are also described in Kinetics and Catalysis. Vol.40, No.1999, pp. 404-404.

Other suitable starting compounds are, for example, polyanions of the Dawson or Keggin type. Preferred are those starting compounds which, at elevated temperatures in the presence or absence of oxygen, are converted to oxides, if necessary, with the release of gaseous products.

To carry out hydrothermal treatment, as a rule, it takes a long time, ranging from several hours to several days. A typical hydrothermal treatment is 48 hours. From a technological point of view, it is advisable to carry out such processing in an autoclave with an internal fluoroplastic lining. The autoclave before hydrothermal treatment can be evacuated, if necessary, with the simultaneous removal of the water mixture contained in it. Before the temperature rises, the autoclave can be filled with an inert gas (nitrogen, noble gas). You can also refuse to implement both of these activities. The aqueous mixture before hydrothermal treatment can be inertized by additional purging with an inert gas. The use of these inert gases may also be expedient from a technological point of view, creating an excess pressure in the autoclave before hydrothermal treatment.

It is advisable to heat-treat the solid product recovered at the end of hydrothermal treatment at a temperature of 350 to 700 ° C, often at a temperature of 400 to 650 ° C or 400 to 600 ° C, and the autoclave can be cooled to room temperature upon completion of hydrothermal treatment temperatures quickly or slowly, that is, over a long period of time (for example, without using forced cooling). Heat treatment can be carried out in an oxidizing, reducing or inert atmosphere. To create an oxidizing atmosphere, for example, you can use ordinary air, as well as air enriched or depleted in molecular oxygen. The heat treatment is preferably carried out in an inert atmosphere, that is, for example, in an atmosphere of molecular nitrogen and / or a noble gas. Of course, it can be carried out under vacuum.

If the heat treatment is carried out in a gaseous atmosphere, the processed product may be in the form of a stationary or fluidized bed.

The total duration of the heat treatment may be 24 hours or longer.

Heat treatment preferably begins in an oxidizing oxygen-containing atmosphere (for example, an atmosphere of air) at a temperature of from 150 to 400 ° C. Or from 250 to 350 ° C. Upon completion of this initial stage, it is advisable to continue the heat treatment, carrying out it in an inert gas atmosphere at a temperature of from 350 to 700 ° C, from 400 to 650 ° C or from 400 to 600 ° C. The heat treatment of the preliminary catalysts obtained as a result of hydrothermal treatment can also be carried out by tableting followed by heat treatment and grinding.

From a technological point of view, it is advisable to grind the solid product obtained as a result of hydrothermal treatment before subsequent heat treatment.

If mixtures of metal oxides (I) are obtained from the starting compounds similar to those used in conventional methods for producing such mixtures, and heat treatment obtained in the usual way, thoroughly mixed dry mixture is carried out similarly to heat treatment of a solid product obtained by preliminary hydrothermal treatment, then all other things being equal under conditions of a mixture of metal oxides (I), subjected to hydrothermal treatment, with heterogeneous catalytic gas-phase oxidation of propane, as a rule, they provide Lee selective yield of acrylic acid and have a higher catalytic activity.

Mixtures of metal oxides (I) can be used as catalysts per se (for example, powdered or ground) or in the form of molded products. Catalysis can be carried out in a stationary, moving or fluidized bed.

The X-ray diffraction pattern of the mixture of metal oxides (I) is generally substantially the same as the corresponding diffraction patterns presented in European patent applications EP-A-0529853, EP-A-0608838 and German patent application DE-A 19835247.

Active mixtures of metal oxides (I) can also be used in combination with finely dispersed, for example, colloidal materials, in particular silica, titanium dioxide, alumina, zinc oxide, niobium oxide, which play the role of diluents.

The mass ratio of diluent to the active mixture can reach 9: 1, that is, it can also be 6: 1 and 3: 1. The active mixture can be combined with a diluent before and after heat treatment (calcination). The diluent is typically administered before hydrothermal treatment. If it is introduced before the heat treatment, it must remain in the calcined mixture, which is also true when the diluent is introduced before the hydrothermal treatment. This condition, for example, is usually satisfied by oxides calcined at high temperatures.

Other suitable catalysts for the oxidation of propane are mixtures of metal oxides (II) having the above formula (I) with diffraction reflections h, i and k in the corresponding X-ray diffraction patterns, the peaks of which lie at diffraction angles (2θ) 2.22 ± 0, 4 ° (h), 27.3 ± 0.4 ° (i) and 28.2 ± 0.4 ° (k), and

- the diffraction reflex h is the strongest in the diffraction pattern and has a maximum half-width of 0.5 °,

- the intensity P _{i of the} diffraction reflex i and the intensity P _{k of the} diffraction reflex k satisfy a ratio of 0.65≤R≤0.85, in which R is the ratio of intensities defined by the formula R = P _i / (P _i + P _k ), and

- the half-width of the diffraction reflections i and k is ≤1.

Preferred is an R value satisfying a ratio of 0.67≤R≤0.75, even more preferably an R value of 0.70-0.75, or R equal to 0.72.

It is preferable to use a mixture of metal oxides (II), where M ¹ is tellurium (Te). In addition, the use of mixtures of oxides (II) is advantageous, where M ² is niobium (Nb), tantalum (Ta), tungsten (W) and / or titanium (Ti). Preferred are mixtures where M ² is niobium (Nb).

The stoichiometric coefficient "b" in mixtures of metal oxides (II) is preferably from 0.1 to 0.6. The preferred range of values of the stoichiometric coefficient "c" is respectively from 0.01 to 1 or from 0.05 to 0.4, and the preferred value of the coefficient "d" is in the range from 0.01 to 1 or from 0.1 to 0, 6. Particularly preferred is the use of such mixtures of metal oxides (II), the stoichiometric coefficients “b”, “c” and “d” are within the above preferred ranges. Other suitable stoichiometric compositions of mixtures of metal oxides (II) are given in the documents cited above, corresponding to the prior art, in particular in Japanese patent application JP-A 7-53448.

A targeted method for producing mixtures of metal oxides (II) is described, for example, in Japanese patent application JP-A 11-43314, according to which such mixtures are recommended to be used as catalysts for the heterogeneous oxidative dehydrogenation of ethane to ethene.

According to the known method described in the documents cited above, corresponding to the prior art, first get a mixture of metal dioxides of the formula (I), consisting of the i-phase and other phases (for example, k-phase). The content of the i-phase in the resulting mixture can be increased, for example, by selecting other phases, for example, the k-phase carried out under a microscope, or washing it with appropriate liquids, which can be, for example, aqueous solutions of organic acids, in particular oxalic, acetic, citric or tartaric, inorganic acids, in particular nitric acid, alcohols and aqueous solutions of hydrogen peroxide. A method for producing mixtures of metal dioxide (II) is also described in Japanese patent application JP-A 7-232071.

Mixtures of metal oxides (II) can be obtained by the method described in German patent application DE-A 198 35247. According to this method, the most carefully mixed, preferably finely divided, dry mixture is obtained from appropriate sources of elemental components, which is subjected to heat treatment at a temperature of 350 up to 700 ° C, from 400 to 650 ° C or from 400 to 600 ° C. Heat treatment can be carried out in an oxidizing, reducing or inert atmosphere. To create an oxidizing atmosphere, for example, ordinary air is used, as well as air enriched or depleted in molecular oxygen. The heat treatment is preferably carried out in an inert atmosphere, for example in an atmosphere of molecular nitrogen and / or a noble gas. Usually it is carried out at normal pressure (1 atm). Of course, the heat treatment can be carried out under vacuum or under reduced pressure.

If a gaseous atmosphere is used for the heat treatment, it can be carried out in a stationary or fluidized bed. Heat treatment may take a total of 24 hours or longer.

Heat treatment preferably begins in an oxidizing oxygen-containing atmosphere (for example, in an atmosphere of air) at a temperature of from 150 to 400 ° C or from 250 to 350 ° C. Upon completion of the initial stage, it is advisable to continue the heat treatment in an inert gas atmosphere at a temperature of from 350 to 700 ° C, from 400 to 650 ° C or from 400 to 600 ° C. Heat treatment of the preliminary catalysts obtained as a result of hydrothermal treatment can also be carried out in the following way. First, they are tableted, if necessary, pre-crushed to a powder state (tabletting is carried out, if necessary, with the addition of 0.5 to 2 wt.% Fine graphite), and then subjected to heat treatment and regrind.

The starting compounds for preparing mixtures of metal oxides (II) can be mixed in a dry or wet state. If dry mixing is carried out, it is advisable to use the starting compounds in the form of a finely divided powder and, after mixing and, if necessary, compaction, calcining (heat treatment). Preferred, however, is stirring in the wet state, with the starting compounds usually being in the form of an aqueous solution and / or suspension. The resulting aqueous mixture was dried and calcined. By an aqueous mixture is preferably meant an aqueous solution or an aqueous suspension. The drying is preferably carried out immediately after receiving the aqueous mixture in a direct-flow or counter-current spray dryer (the temperature at the outlet of the dryer is usually from 100 to 150 ° C), and a particularly thoroughly mixed dry mixture is obtained, first of all, if to the dryer, the aqueous mixture is an aqueous solution or an aqueous suspension.

As the starting compounds for the preparation of a mixture of metal oxides (II) (sources of elementary constituents), the above compounds intended for the preparation of mixtures of oxides (I) are suitable.

Use a mixture of metal oxides (II) and obtain the corresponding molded products can be similar to the above-described mixtures of metal oxides (I). Mixtures of metal oxides (II) can be molded, for example, by coating on a substrate, as described below for mixtures of metal oxides (III), extrusion and / or tabletting in a finely divided state, to which finely dispersed preliminary mixtures of oxides (II) can also be subjected )

Mixtures of metal oxides (II) can also be used like mixtures of oxides (I) in a state diluted with finely dispersed materials.

Catalysts based on mixtures of metal oxides (II) can be shaped into spherical particles, solid cylinders or rings (hollow cylinders), the longitudinal size of which, as a rule, is from 1 to 10 mm. The length of the cylinders is preferably from 2 to 10 mm, the outer diameter from 4 to 10 mm. The wall thickness of the rings is usually from 1 to 4 mm. Suitable ring-shaped catalyst particles may also have the following geometric parameters: a length of 3 to 6 mm, an outer diameter of 4 to 8 mm, and a wall thickness of 1 to 2 mm. Along with this, the possibility of using annular particles having parameters of 7 mm × 3 mm × 4 mm or 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) is not ruled out.

The intensities of the diffraction reflections in the corresponding X-ray diffraction pattern are described in German patent applications DE-A 19835247, DE-A 10051419 and DE-A 10046672.

That is, if А ¹ means the peak of diffraction reflex 1, В ¹ means the nearest minimum, which appears to the left of peak А ¹ on the line of the X-ray diffraction pattern, when viewed along the intensity axis perpendicular to the axis 2θ (shoulders of diffraction reflections are not taken into account), В ² means the nearest the minimum that appears to the right of peak A ¹ , and C ¹ means the point at which a line drawn from peak A ¹ perpendicular to the axis 2θ intersects the line connecting points B ¹ and B ² , then the intensity of diffraction reflex 1 is determined by the length of the line segment A ¹ connecting peak A ¹ with point C ¹ . The minimum in this case means the point at which the gradient of the slope of the tangent to the curve in the region of the base of the diffraction reflex 1 changes the value from negative to positive, or the point at which the gradient of the gradient passes through zero, and the coordinates of the 2θ axis and the intensity axis are used to determine the gradient .

The half-width in this case is the length of the line segment formed between the intersection points of H ¹ and H ² , if in the middle of the segment A ¹ C ¹ draw a line parallel to the 2θ axis, and H ¹ and H ^{2 are} respectively considered the first intersection points of this parallel line with the specified above the line of x-ray diffraction patterns to the left and to the right of peak A ¹ .

An example of determining the half-width and intensity is presented in FIG. 6 of German patent application DE-A 10046672.

Along with the diffraction reflections h, i and k on the X-ray diffraction pattern of the preferred catalytically active mixtures of metal oxides (II), as a rule, additional reflections can be detected whose peaks correspond to the following diffraction angles (2θ):

9.0 ± 0.4 ° (l),

6.7 ± 0.4 ° (o) and

7.9 ± 0.4 ° (p).

Preferably, if an additional diffraction reflex is present on the X-ray diffraction pattern of the catalytically active oxide mixtures of the general formula (I), the apex of which corresponds to the diffraction angle (2θ): 45.2 ± 0.4 ° (q).

Reflections of 29.2 ± 0.4 ° (m) and 35.4 ± 0.4 ° (n) can also often be found on the X-ray diffraction pattern of mixtures of metal oxides (II).

The X-ray diffraction pattern of some mixtures of metal oxides (II) may lack a diffraction reflection, the peak of which corresponds to an angle of 2θ = 50.0 ± 0.3 °, which indicates the absence of a k phase in such mixtures.

Nevertheless, mixtures of metal oxides (II) can also contain the k phase, and other reflections, as a rule, also appear on the X-ray diffraction pattern, the peaks of which correspond to diffraction angles (2θ):

36.2 ± 0.4 ° and

50.0 ± 0.4 °.

If we take the intensity of the diffraction reflex h for 100, it is preferable that the following diffraction reflections i, I, m, n, o, p, q according to the corresponding scale have the following intensity values:

i: from 5 to 95, often from 5 to 80, in particular from 10 to 60;

l: 1 to 30;

m: from 1 to 40;

n: from 1 to 40;

about: from 1 to 30;

p: from 1 to 30 and

q: 5 to 60.

If the above additional reflexes are present on the X-ray diffraction pattern, their half-width, as a rule, is less than or equal to 1 °.

All the above data refer to X-ray diffraction patterns obtained using Cu-Ka X-ray diffraction (Siemens Theta-Theta D-2000 diffractometer, tube voltage 40 kV, tube current 40 mA, aperture diaphragm V20 (interchangeable), aperture diaphragm V20 ( interchangeable), diaphragm of a secondary monochromator (0.1 mm), diaphragm of a detector (0.6 mm), measurement interval (2θ) 0.02 °, measurement time (per step) 2.4 sec, scintillation counter as a detector )

The specific surface of a mixture of metal (II) oxides is often from 1 to 30 m ² / g (BET method, nitrogen atmosphere).

Catalyst (III) is also suitable for the oxidation of propane, which is a catalytically active mixture of metal oxides of the above formula (I) deposited on the surface of a substrate.

It is preferable to use mixtures of oxides of the general formula (I), where M ¹ is tellurium (Te). As M ² , niobium (Nb), tantalum (Ta), tungsten (W) and / or titanium (Ti) are preferred. It is preferable to use as M ² niobium (Nb).

Preferred are the following ranges of stoichiometric coefficients for a mixture of oxides of the general formula (I) in the composition of catalyst (III): “b” from 0.1 to 0.6, “c” from 0.01 to 1, or from 0.05 to 0, 4 and “d” from 0.01 to 1 or from 0.1 to 0.6. Especially preferred are mixtures of oxides whose stoichiometric coefficients “b”, “c” and “d” are simultaneously within the above preferred ranges.

Other suitable stoichiometric compositions of mixtures of oxides of the general formula (I) are given in the above documents, in particular in European patent applications EP-A-0608838, EP-A-0962253, international patent application WO 00/29106 and Japanese patent application JP -A 11/169716.

It is also particularly preferred to prepare catalyst (III) by depositing the above-described mixtures of metal oxides (II) as mixtures of oxides having the formula (I) on an appropriate carrier.

Carriers are preferably chemically inert materials, that is, they mainly do not participate in the catalytic gas-phase oxidation of propane to acrylic acid. As the carrier material, for example, alumina, silica, silicates, in particular clay, kaolin, steatite, pumice, aluminosilicate and magnesium silicate, silicon carbide, zinc dioxide, thorium dioxide can be used.

The surface of the carrier particles may be smooth or rough. Carriers having a rough surface are preferred, since the roughness provides an increase in the adhesion of the active oxide mixture deposited thereon.

The surface roughness R _{z of the} carrier is often in the range from 2 to 200 μm, in particular in the range from 20 to 100 μm (determination of roughness according to DIN 4768, sheet 1, using a Hommel tester to measure surface parameters according to DIN-ISO, manufactured by Hommelwerke , Germany).

In addition, the carrier may have a porous or monolithic structure. It is advisable to use a monolithic carrier with a ratio of the total pore volume to the volume of the carrier less than or equal to 1 vol.%.

The thickness of the shell formed on the surface of the carrier by an active mixture of metal oxides is preferably from 10 to 1000 microns. It can also be from 50 to 700, 100 to 600, 300 to 500, or 150 to 400 microns. A shell thickness of 10 to 500, 100 to 500, or 150 to 300 microns is also possible.

In principle, the carrier particles can have any geometric parameters, and the longitudinal size, as a rule, is from 1 to 10 mm. Carriers in the form of spherical or cylindrical particles, in particular in the form of hollow cylinders (rings), are preferred. The preferred diameter of the spherical particles of the carrier is from 1.5 to 4 mm. If the carrier particles have a cylindrical shape, their length is preferably from 2 to 10 mm, the outer diameter is preferably from 4 to 10 mm. The wall thickness of the annular particles of the carrier is usually from 1 to 4 mm Suitable annular particles may have a length of 3 to 6 mm, an outer diameter of 4 to 8 mm, and a wall thickness of 1 to 2 mm. A carrier in the form of particles with geometric parameters of 7 mm × 3 mm × 4 mm or 5 mm × 3 mm × 2 mm (outer diameter × length × inner diameter) may also be used.

The simplest way to obtain catalysts (III) is to prepare active mixtures of oxides of the general formula (I), transfer them to a finely dispersed state and apply the carrier particles to the surface by means of a liquid binder. For this, the surface of the particles is moistened with a liquid binder, on the wetted surface, a layer of a finely dispersed active mixture of oxides of the general formula (I) is fixed in a non-contact manner, after which the coated carrier particles are dried. Repeatedly repeating the described process, it is possible to apply more and more layers, obtaining a carrier with an increased coating thickness.

The dispersion of the catalytically active mixture of oxides of the general formula (I) applied to the surface of the carrier particles is selected depending on the desired coating thickness. For shells with a thickness of 100 to 500 μm, suitable, for example, are powdered active mixtures of at least 50% of the total amount of particles passing through a sieve with a hole size of 1 to 20 μm, and the content of particles with a longitudinal size exceeding 50 μm, is less than 10%. The dispersion of particles of powder mixtures of oxides, determined by the size of the longitudinal size, is usually described by a Gaussian distribution, which is due to the method of their preparation.

The above-described method for coating a carrier on a technical scale is recommended to be carried out using, for example, the technological principle set forth in German patent application DE-A 2909671. This means that the media to be coated are loaded into a container that rotates preferably in an inclined position, for example, into a rotary disk tank or a panning drum, and the angle of inclination (the angle between the central axis of the rotating container and the horizontal plane) is usually from 0 to 90 °, most often from 30 to 90 °. A carrier in a rotating reservoir in the form of particles having, for example, a spherical or cylindrical shape, passes under two metering devices located at a certain distance from each other. It is advisable that by means of the first of the dispensers, which is a nozzle (for example, a spray nozzle driven by compressed air), a liquid binder is sprayed onto the surface of the carrier particles rolling on rotating plates, while controlling the degree of moisture.

The second metering device is located outside the spray cone of the liquid binder and serves to supply a finely dispersed active mixture of oxides, for example, by means of a swinging trough or screw. Particles of a carrier, for example, spherical or cylindrical, moistened with a controlled amount of a liquid binder, absorb a dosed active powder mixture, which is compacted on the outer surface of the particles, forming a shell firmly attached to it.

If necessary, carrier particles with the coating layer created by the method described above with continued rotation of the tank again pass under the spray nozzle, where they are subjected to controlled wetting so that during the further movement it is possible to apply an additional layer of a finely dispersed active oxide mixture, and this process can be repeated repeatedly ( intermediate drying of the carrier, as a rule, is not required). A fine mixture of oxides and a liquid binder in this case, as a rule, serves continuously and synchronously.

Excess liquid binder can be removed at the end of the coating, for example by purging the carrier with hot gases, in particular hot nitrogen or air. It should be noted that the described coating method provides excellent mutual adhesion of successively applied layers and excellent adhesion of the base layer to the surface of the carrier.

An important feature of the coating method described above is that the surface of the carrier particles is moistened in a controlled manner. That is, the surface of the carrier particles is recommended to be moistened so that the liquid binder is adsorbed on it without the formation of a liquid phase, which would be noticeable by visual observation. Too much wetting of the surface of the carrier leads to the unification of particles of a finely dispersed catalytically active mixture of oxides into agglomerates instead of their uniform distribution over the surface of the particles. For more information on this, see German patent application DE-A 2909671.

The removal of the liquid binder mentioned above can be carried out in a controlled manner, for example, by evaporation and / or sublimation. In the simplest case, the binder can be removed by purging the carrier with gas heated to an appropriate temperature, often between 50 and 300 ° C, in particular 150 ° C. Due to the effect of hot gases, a preliminary drying of the carrier can also be carried out. The final drying of the carrier can be carried out in any type of drying ovens, for example, in tape dryers, while the temperature acting on the carrier should not exceed the temperature at which calcination (heat treatment) is carried out to obtain an active mixture of oxides. Drying can also be done using only a drying oven.

The type of binder used for coating does not depend on the type and geometric parameters of the carrier particles. As a binder, you can use water, monovalent alcohols, in particular ethanol, methanol, propanol and butanol, polyvalent alcohols, in particular ethylene glycol, 1,4-butanediol, 1,6-hexanediol or glycerol, mono-or polyvalent carboxylic acids, in particular propionic, oxalic, malonic, glutaric or maleic acid, amino alcohols, in particular ethanolamine or diethanolamine, as well as mono- or polyvalent organic amides, in particular formamide. Preferred binders are also solutions consisting of water (20 to 90 wt.%) And an organic compound dissolved in it (10 to 80 wt.%), The boiling or sublimation of which at normal pressure (1 atm) exceeds 100 ° C, preferably 150 ° C. The organic compound is preferably selected from the above list of possible organic binders. The preferred content of the organic compounds in these aqueous solutions of the binder is from 10 to 50 wt.%, Particularly preferably from 20 to 30 wt.%. Monosaccharides and oligosaccharides, in particular glucose, fructose, sucrose or lactose, as well as polyethylene oxides and polyacrylates, are also suitable as organic components.

Catalytically active mixtures of oxides of the general formula (I) can be prepared by known methods described in the cited documents according to the prior art. This means that they can be obtained, for example, by both hydrothermal and conventional methods.

In the latter case, catalytically active mixtures of oxides of the general formula (I) are prepared by preparing from the corresponding sources of elementary components a possibly more thoroughly mixed, preferably finely divided, dry mixture and subjecting it to heat treatment at a temperature of 350 to 700 ° C, 400 to 650 ° C, or from 400 to 600 ° C. Heat treatment and thorough mixing of the starting compounds can be carried out similarly to the method described above for producing a mixture of metal oxides (II).

In the framework of the above-described method for producing catalytically active mixtures of metal oxides of the general formula (I), the starting compounds that are used to obtain the above-described mixture of metal oxides (I) are suitable as sources of elementary components.

Particularly preferred catalysts are coated carriers consisting of a mixture of metal oxides (II) as a catalytically active mixture of oxides of the general formula (I).

Active catalyst mixtures of oxides of the general formula (I) described in international patent application WO 00/29106 and having a predominantly amorphous structure, which is found in the X-ray diffraction pattern in the form of very wide diffraction reflections with peaks in the region of diffraction angles, are also suitable for preparing coated catalysts. 2θ) 22 ° and 27 °.

Also suitable are active mixtures of oxides of the general formula (I) described in European patent applications EP-A-0529853 and EP-A-0608838, in which X-ray diffraction patterns show very narrow diffraction reflections with peaks in the region of diffraction angles (2θ) 22, 1 ± 0.3 °, 28.2 ± 0.3 °, 36.2 ± 0.3 °, 45.2 ± 0.3 ° and 50.0 ± 0.3 °.

Coated catalysts in the form of coated carriers can be obtained not only by applying finely dispersed active mixtures of oxides of the general formula (I) onto the wetted surface of the carrier particles, but also by applying finely dispersed oxide pre-mixtures on a surface prepared in a similar way using similar methods using similar binders , and calcining the carrier coated thereon after preliminary drying. Fine pre-mixture of oxides can be obtained, for example, as follows. First, from the sources of elementary components of an active mixture of oxides of the general formula (I) of the desired composition, a finely mixed, finely divided dry mixture is obtained (for example, by spray drying an aqueous suspension or solution of sources of elementary components), and then this mixture is subjected to heat treatment for several hours ( if necessary, after tableting, carried out with the addition of fine graphite in an amount of from 0.5 to 2 wt.%) at a temperature of from 150 to 350 ° C, preferably from 2 50 to 350 ° C, in an oxidizing oxygen-containing atmosphere (for example, an atmosphere of air) and, if necessary, grinding. After applying a preliminary mixture to the carrier particles, they are preferably calcined in an inert gas atmosphere (any other atmosphere can be used) at a temperature of from 360 to 700 ° C, from 400 to 650 ° C or from 400 to 600 ° C.

The above-described mixtures of metal oxides (II) or catalysts (III) in combination with a mixture of metal oxides (II) can also be used as a catalytically active mixture for the oxidation of propene, which can be carried out in the presence of propane, which acts as a gaseous diluent, although some can oxidize to acrylic acid.

Oxidation of propane can be carried out by any methods known to those skilled in the art without any restrictions, for example, by the method described in European patent application EP-A-0608838 or international patent application WO 00/29106. This means that gas B supplied to stage (c) for catalytic oxidation carried out at a temperature of, for example, from 200 to 550 ° C, from 230 to 480 ° C or from 300 to 440 ° C, can have, for example, the following composition:

propane: from 1 to 15, preferably from 1 to 7 vol.%, air: from 44 to 99 vol.% and water vapor: from 0 to 55 vol.%.

Other possible compositions of the gas mixture B supplied to stage (c) are, in particular, the following:

propane: from 70 to 95 vol.%, molecular oxygen: from 5 to 30 vol.% and water vapor: from 0 to 25 vol.%.

For the oxidation of propane, plate reactors-heat exchangers described in German patent application DE-A 199 52964 are also suitable. According to another embodiment of the invention, propane is oxidized by the methods described in German patent applications DE-A 19837517, DE-A 19837518, DE-A 19837519 and DE-A 19837520.

The composition of the reaction mixture resulting from the oxidation of propene and / or propane in step (c) according to the method according to the invention, along with the predominantly desired products contained in it, that is, acrolein and / or acrylic acid, typically includes unconverted molecular oxygen, propane and propene, molecular nitrogen, water vapor and carbon dioxide, formed as by-products and / or used as gaseous diluents, as well as small amounts of low molecular weight aldehydes, hydrocarbon in and other inert diluents gazooobraznyh.

Target products (acrolein and / or acrylic acid) can be isolated from a mixture of oxidation products by known methods, for example by azeotropic distillation, fractional distillation, carried out in the presence of a solvent or without it, or crystallization.

For example, suitable methods of isolation are partial condensation of acrylic acid, its absorption with water or a high boiling hydrophobic organic solvent, or the absorption of acrolein with water or aqueous solutions of low molecular weight carboxylic acids, followed by treatment of the absorbate. An alternative way to isolate the desired products from the reaction mixture is fractionated condensation (see, for example, European patent application EP-A-0117146, German patent applications DE-A 4308087, DE-A 4335172, DE-A 4436243, DE-A 19924532 and DE-A 19924533.

According to a particularly preferred embodiment of the method according to the invention, the propane and / or propene that is not converted in step (c) are separated from the gas mixture remaining after isolation of the target product by implementing steps (a) and (b), and they are returned to step (c) again.

The gas mixture A used in step (a) of the method according to the invention may have a composition similar to that of the gas mixture resulting from the catalytic dehydrogenation of propane to propene. Moreover, the propane dehydrogenation can be oxidative, that is, carried out with the addition of oxygen, or without the addition of oxygen, in particular, mainly without the addition of oxygen. When it comes to dehydrogenation with the addition of oxygen, the following two options are possible. In the first embodiment, all of the generated hydrogen is oxidized through the use of excess oxygen, as a result of which hydrogen is completely absent in gaseous dehydrogenation products, but they contain excess oxygen (oxidative dehydrogenation). In the second embodiment, oxygen is supplied only in the amount necessary to compensate for the thermal effect of the reaction; therefore, oxygen is completely absent in the gaseous reaction products, however, they contain hydrogen (autothermal process). Propane dehydrogenation can be carried out by catalytic or non-catalytic (homogeneous) method.

The propane dehydrogenation can be carried out, for example, as described in German patent application DE-A 3313573 and European patent application EP-A-0117146.

In principle, oxidative dehydrogenation can be carried out in the form of a homogeneous and / or heterogeneous oxydehydrogenation of propane to propene using molecular oxygen.

If this first step of the reaction consists in homogeneous oxidative dehydrogenation, in principle it can be implemented as described in US patent US-A-3798 283, Chinese patent application CN-A-1105352, Applied Catalysis, 70 (2), 1991, S.175-187, Catalysis Today 13, 1992, S.673-678, and German patent application DE-A-19622331, whereby air can also be used as an oxygen source.

A suitable temperature range for homogeneous oxidative dehydrogenation is from 300 to 700 ° C, preferably from 400 to 600 ° C, particularly preferably from 400 to 500 ° C. The operating pressure may be from 0.5 to 100 bar, in particular from 1 to 10 bar. The residence time is usually from 0.1 or 0.5 to 20 seconds, preferably from 0.1 or 0.5 to 5 seconds. As the reactor, you can use, for example, a tube furnace or a shell and tube reactor, for example a countercurrent tube furnace with flue gas as a heat carrier or a shell and tube reactor with a salt melt as a heat carrier. The propane: oxygen ratio in the gas mixture leaving the reactor is preferably from 0.5: 1 to 40: 1, in particular from 1: 1 to 6: 1, more preferably from 2: 1 to 5: 1. The gas mixture may also contain other, mainly inert components, in particular water, carbon dioxide, carbon monoxide, nitrogen, noble gases and / or propene, and we can also talk about the components returned to stage (a), which generally indicate like recycle gas.

If propane dehydrogenation is carried out in the form of a heterogeneous catalytic oxidative dehydrogenation, then in principle it can be implemented as described, for example, in US patent US-A 4788371, Chinese patent application CN-A 1073893, Catalysis Letters 23 (1994), 103- 106, W.Zhang, Gaodeng Xuexiao Huaxue Xuebao, 14 (1993) 566, Z. Huang, Shiyou Huagong, 21 (1992), 592, international patent application WO 97/36849, German patent application DE-A 19753817, patents US-A 3862256 and US-A 3887631, German patent application DE-A 19530454, US-A-4341664, J. of Catalysis 167, 560-569 (1997), J. of Catalysis 167, 550-559 ( 1997), Topics in Catalysis 3 (1996), 265-275, US Pat. No. 5,086,032, Catalysi s Letters 10 (1991), 181-192, Ind. Eng. Chem. Res. 1996, 35, 14-18, US Pat. No. 4,255,284, Applied Catalysis A .: General, 100 (1993), 111-130, J. of Catalysis 148, 56-67 (1994), V. Cortes Corberan und S .Vic.Bellon (Ed.), New Developments in Selective Oxidation II, 1994, Elsevier Science BV, S.305-313, 3 ^rd World Congress on Oxidation Catalysis, RK Grasselli, ST Oyama, AMGaffney and JELyons (Ed.), 1997, Elsevier Science BV, S.375 ff. Air can be used as an oxygen source, but a source containing at least 90 mol% of oxygen, more preferably 95 mol% of oxygen (relative to a source containing 100 mol% of oxygen) is preferred.

For heterogeneous catalytic oxidative dehydrogenation without any special restrictions, any catalysts known to those skilled in the art of chemical technology capable of catalyzing the oxidation of propane to propene are suitable. In particular, any of the oxidation dehydrogenation catalysts described in the above documents may be used. Preferred are, for example, mixtures of molybdenum, vanadium and niobium oxides or vanadyl pyrophosphate used in conjunction with the promoter. A particularly suitable catalyst is, for example, a mixture of metal oxides containing, as main components, molybdenum (Mo), vanadium (V), tellurium (Te), oxygen (O) and X, wherein X represents at least one element, selected from the group consisting of niobium, tantalum, tungsten, titanium, aluminum, zirconium, chromium, manganese, iron, ruthenium, cobalt, rhodium, nickel, palladium, platinum, antimony, bismuth, boron, indium and cerium. In addition, mixtures of several metal oxides or catalysts A described in German patent application DE-A-1975381717 are particularly suitable oxidative dehydrogenation catalysts, wherein metal oxide mixtures or catalysts A indicated in this application as preferred have a particularly favorable catalytic effect . This means that as active mixtures, in particular, mixtures of several metal oxides (IV) of the general formula IV are used.

in which M ¹ is cobalt (Co), nickel (Ni), magnesium (Mg), zinc (Zn), manganese (Mn) and / or copper (Cu),

M ² is tungsten (W), vanadium (V), tellurium (Te), niobium (Nb), phosphorus (P), chromium (Cr), iron (Fe), antimony (Sb), cesium (Cs), tin ( Sn) and / or lanthanum (La),

and equal to 0.5-1.5,

b is 0-0.5,

x is a number determined by the valency and repeatability of elements other than oxygen in formula (IV).

Suitable active mixtures (IV) can, in principle, be obtained in the following simple way. From suitable sources of elementary constituents, a possibly more thoroughly mixed, preferably finely divided, dry mixture of the required stoichiometric composition is obtained and calcined at a temperature of 450 to 1000 ° C. As sources of elementary constituents of active mixtures of metal (IV) oxides, oxides and / or compounds are used which, by heating, carried out, at least in the presence of oxygen, can be converted to oxides. We are primarily talking about halides, nitrates, formates, oxalates, citrates, carbonates, complex amino salts, ammonium salts and / or hydroxides. Thorough mixing of the starting compounds to obtain mixtures of metal oxides (IV) can be carried out by the dry method, for example, using the corresponding fine powders, or by the wet method, for example, in the presence of water as a solvent. Mixtures of metal oxides (IV) can be used in powder form or in the form of shaped particles having certain geometric parameters, and molding can be performed before or after calcination. Complete catalysts can be used, or a powdered active or pre-mixed oxide can be shaped into a specific form by coating them on a preformed inert carrier. The support materials may be conventional porous or monolithic aluminas, silicon dioxide, thorium dioxide, zinc dioxide, silicon carbide or silicates, and the carrier particles may have a regular or irregular shape.

The temperature of the heterogeneous catalytic oxidative dehydrogenation of propane preferably lies in the range from 200 to 600 ° C, in particular in the range from 250 to 500 ° C, more preferably in the range from 350 to 440 ° C. The operating pressure is preferably from 0.5 to 10 bar, in particular from 1 to 10 bar, more preferably from 1 to 5 bar. Particularly preferred is a working pressure of more than 1 bar, for example from 1.5 to 10 bar. Heterogeneous oxidative dehydrogenation of propane is carried out using, as a rule, a stationary catalyst bed, which, according to a suitable embodiment of the method, is loaded into the tubes of a shell-and-tube reactor described, for example, in European patent applications EP-A-0700893 and EP-A-0700714, as well as in the literature cited in these applications. A suitable average residence time of the reaction mixture in the catalyst bed is from 0.5 to 20 seconds. The ratio of propane to oxygen varies depending on the desired degree of conversion of propane and the selectivity of the catalyst, moreover, a suitable ratio is from 0.5: 1 to 40: 1, in particular from 1: 1 to 6: 1, more preferably from 2: 1 to 5 :one. The selectivity of the propene yield with an increase in the degree of conversion of propane, as a rule, decreases, and therefore the propane dehydrogenation is preferably carried out in such a way as to provide high selectivity of the propene yield at relatively low degrees of propane conversion. A particularly preferred degree of conversion of propane corresponds to a range of from 5 to 40%, more preferably from 10 to 30%, while the degree of conversion means that part of the propane of its total input quantity that undergoes the conversion. A particularly preferred selectivity is in the range from 50 to 98%, more preferably from 80 to 98%, the term "selectivity" means the percentage of the number of moles of obtained propene to the number of moles of converted propane.

In 100 wt.% The initial mixture used for the oxidative dehydrogenation of propane, preferably contains from 5 to 95 wt.% Propane. The initial mixture along with propane and oxygen may contain other, in particular, inert components, for example water, carbon dioxide, carbon monoxide, nitrogen, inert gases and / or propene. Heterogeneous oxidative dehydrogenation can also be carried out in the presence of diluents, for example water vapor.

Both homogeneous and heterogeneous catalytic oxidative dehydrogenation can be carried out in any sequence known to those skilled in the art. For example, dehydrogenation can occur in one, two or more stages, between which oxygen is supplied. In addition, it is possible to combine homogeneous and heterogeneous catalytic oxidative dehydrogenation.

Possible components of the reaction mixture resulting from the oxidative dehydrogenation of propane are, for example, the following compounds: propene, propane, carbon dioxide, carbon monoxide, water, nitrogen, oxygen, ethane, ethene, methane, acrolein, acrylic acid, ethylene oxide, butane, acetic acid, formaldehyde, formic acid, propylene oxide and butene. A 100 wt.% Mixture of products resulting from the oxidative dehydrogenation of propane preferably contains 5 to 10 wt.% Propene, 1 to 2 wt.% Carbon monoxide, 1 to 3 wt.%, Carbon dioxide, 4 to 10 wt.% water, from 0 to 1 wt.% nitrogen, from 0.1 to 0.5 wt.% acrolein, from 0 to 1 wt.% acrylic acid, from 0.05 to 0.2 wt.% acetic acid , from 0.01 to 0.05 wt.% formaldehyde, from 1 to 5 wt.% oxygen, from 0.1 to 1.0 wt.% of the other components of the above, in particular residual propane.

In the General case, the gas mixture And can also be obtained by heterogeneous catalytic dehydrogenation of propane, mainly carried out in the presence of excess oxygen, as described in German patent application DE-A 3313573 or described below.

Since dehydrogenation is accompanied by an increase in volume, the degree of conversion of propane can be increased by lowering its partial pressure. The simplest way to achieve this goal can be, for example, the implementation of dehydrogenation of propane under reduced pressure and / or the introduction of predominantly inert gaseous diluents, for example water vapor, which behaves like an inert gas in conventional dehydrogenation. An additional advantage of diluting propane with water vapor is, as a rule, the reduction of coking of the dehydrogenation catalyst, since water vapor reacts with the coke formed on the principle of coal gasification. In addition, water vapor can serve as a gaseous diluent for the mixture fed to subsequent oxidation (step (c)). Along with this, water vapor can be partially or completely separated from the gas mixture supplied to stage (c), for example, by condensation, which makes it possible to increase the content of nitrogen in this mixture used as a gaseous diluent. Other suitable propane dehydrogenation gaseous diluents are, for example, carbon monoxide, carbon dioxide, nitrogen and noble gases, in particular xenon, neon and argon. These gaseous diluents can be used both individually and in a mixture with each other. In a preferred embodiment, they are generally suitable for diluting the gas mixture supplied to step (c). In general, it is preferable to use an inert gaseous diluent to carry out the corresponding reactions (the permissible chemical change in the diluent does not exceed 5 mol%, preferably it is not more than 3 mol%, and more preferably not more than 1 mol%). For dehydrogenation of propane, in principle, any dehydrogenation catalysts according to the prior art, which can be roughly divided into the following two groups, are suitable. The first group consists of catalysts having an oxide nature, for example, chromium oxide and / or alumina. The second group consists of catalysts, which are at least one, usually noble metal (for example, platinum) deposited on a support, usually an oxide.

Among other things, dehydrogenation catalysts recommended in international patent application WO 99/46039, US patent US-A 4788371, European patent application EP-A-0705136, international patent WO 99/29420, US patents US-A 4220091, can be used. US-A 5430220 and US-A 5877369, European patent application EP-A-0 117146, German patent applications DE-A 19937196, DE-A 19937105 and DE-A 19937107. In particular, the catalysts obtained according to the examples can be used 1, 2, 3 and 4, presented in German patent application DE-A 19937107.

We are talking about dehydrogenation catalysts containing from 10 to 99.9 wt.% Zinc dioxide, from 0 to 60 wt.% Alumina, silicon dioxide and / or titanium dioxide and from 0.1 to 10 wt.%, at least one element from the first and second main groups, one element from the third subgroup, one element from the eighth subgroup of the periodic system of elements, lanthanum and / or tin, provided that the corresponding amount is 100 wt.%.

For propane dehydrogenation, in principle, any types of reactors corresponding to the prior art and process embodiments are suitable. Descriptions of such options are provided, for example, in all documents relating to dehydrogenation catalysts according to the prior art.

A sufficiently detailed description of a suitable dehydrogenation method according to the invention is also provided in the Catalytical Studies Division, Oxidative Dehydrogenation and Alternative Dehydrogenation Processes, Study Number 4192 OD, 1993, 430 Ferguson Drive, Mountain View, California, 94043-5272, USA.

A characteristic feature of partial heterogeneous catalytic dehydrogenation of propane is endothermicity. This means that the heat (thermal energy) necessary to establish the required reaction temperature must be supplied to the reaction gas before and during catalytic dehydrogenation.

Along with this, a characteristic feature of heterogeneous catalytic dehydrogenation of propane, requiring the use of high temperatures, is the formation of small amounts of heavy boiling high molecular weight organic compounds, up to carbon, which form deposits on the surface of the catalyst, which leads to its deactivation. To minimize this undesirable side effect, propane supplied to the surface of the dehydrogenation catalyst carried out at elevated temperature can be diluted with water vapor. Under these conditions, partial or complete elimination of carbon deposits occurs according to the principle underlying coal gasification.

Another possibility of removing deposits formed by hydrocarbon compounds is that an oxygen-containing gas is periodically passed through a dehydrogenation catalyst at an elevated temperature, whereby a certain portion of the carbon deposits burns out.

The formation of carbon deposits can also be reduced by introducing molecular hydrogen into the composition of the catalytic dehydrogenation of propane before passing the propane through a dehydrogenation catalyst heated to a high temperature.

In addition, it is possible to add a mixture of water vapor and molecular hydrogen to the catalytic dehydrogenation propane. The addition of molecular hydrogen also helps to suppress the undesired formation of catalytic dehydrogenation by-products of propane such as allen and acetylene.

A suitable reactor for propane dehydrogenation is a shell-and-tube reactor with a fixed catalyst bed loaded in a single tube or tube bundle. The reaction tubes are heated by burning combustible gas, for example, hydrocarbon, in particular methane, in the surrounding volume. In this direct method, it is preferable to heat only the first 20-30% of the fixed catalyst bed placed in the contact tubes. The necessary reaction temperature in the rest of the tubes should be maintained through the use of radiant heat released during the combustion of combustible gas. Thanks to this heating method, practically isothermal dehydrogenation conditions can be provided. A suitable diameter of the reaction tubes is from 10 to 15 cm. A typical shell-and-tube dehydrogenation reactor contains from 300 to 1000 reaction tubes. The temperature inside the tubes is from 300 to 700 ° C, preferably from 400 to 700 ° C.

It is preferable to heat the reaction gas supplied to the tubular reactor to the reaction temperature. The temperature of the mixture of products leaving the reactor is often 50-100 ° C below the reaction temperature. To implement the above method of oxidative dehydrogenation, it is advisable to use catalysts based on chromium oxide and / or alumina. Often, pure propane free of gaseous diluents is used predominantly as the reaction reaction gas. The dehydrogenation catalyst in most cases also does not contain diluents.

For large-scale production, it would be advisable to use three shell-and-tube reactors, two of which would be operated in a dehydrogenation mode, and a third reactor in a catalyst regeneration mode.

For carrying out the propane dehydrogenation described above, for example, the BASF-Linde method known from the literature is used.

Along with it, they use the so-called active steam reforming (STAR) process, developed by Phillips Petroleum Co. (see, for example, US patents US-A 4902849, US-A 4996387 and US-A 5389342). As a dehydrogenation catalyst in this case, it is preferable to use platinum containing promoters on zinc (magnesium) spinel as a carrier (see, for example, US Pat. No. 5,073,662). Unlike the BASF-Linde process, the propane dehydrogenated according to the STAR process is diluted with water vapor. A typical molar ratio of water vapor: propane is from 4: 1 to 6: 1. The working pressure is most often in the range from 3 to 8 atm; it is advisable to maintain the reaction temperature in the range from 480 to 620 ° C. A typical load of the total reaction mixture on the catalyst is from 0.5 to 10 hours. ^-1 .

Propane dehydrogenation can also be carried out in a moving bed reactor. The catalyst can be placed, for example, in a reactor with a radial gas flow, in which the catalyst is slowly lowered from top to bottom, while the mixture of reaction gases moves in the radial direction. A similar principle is used, for example, for dehydrogenation by the so-called UOP-Oleflex method. Since the reactors used to implement this method operate in a quasi-adiabatic mode, it is advisable to operate several series-connected reactors (in the typical case, their number reaches four). Due to this, it is possible to avoid too large a temperature difference between the mixture of reaction gases at the inlet and outlet of the reactor (in the adiabatic dehydrogenation mode, the initial mixture of reaction gases acts as a coolant, and the reaction temperature depends on its ability to retain heat) and to achieve the necessary degrees of conversion.

The catalyst bed leaving the reactor is sent for regeneration and subsequent reuse. For the implementation of this method, you can use, for example, a dehydrogenation catalyst with a spherical particle shape, mainly consisting of platinum, deposited on the surface of round particles of aluminum oxide used as a carrier. According to the UOP method, hydrogen is added to the propane supplied for dehydrogenation to prevent premature aging of the catalyst. Typically, the operating pressure is from 2 to 5 bar. The ratio of hydrogen: propane, it is advisable to maintain in the range from 0.1: 1 to 1: 1. The reaction temperature is preferably from 550 to 650 ° C, the contact time of the catalyst with the reaction gas mixture is from 2 to 6 hours ^-1 .

In dehydrogenation methods involving the use of a stationary catalyst layer, the catalyst particles can have either a spherical or a cylindrical shape (hollow or solid cylinders).

According to another embodiment described in Proceedings De Witt, Petrochem. Review, Houston, Texas, 1992 a, N1, heterogeneous catalytic dehydrogenation of propane can be carried out in a fluidized bed without diluting propane.

In this case, it is advisable to use two fluidized beds, in one of which the catalyst is usually subjected to regeneration. As the active mixture, chromium oxide is used on an alumina support. Typically, the operating pressure is from 1 to 1.5 atm, and the dehydrogenation temperature, as a rule, is in the range from 550 to 600 ° C. The heat necessary for the dehydrogenation to enter the reaction system due to the preliminary heating of the catalyst to the reaction temperature. Working pressure is from 1 to 2 atm, a typical reaction temperature is from 550 to 600 ° C. The dehydrogenation process described is known in the literature as the Snamprogetti-Yarsintez process.

An alternative to those described above is the ABB Lummus Crest method for heterogeneous catalytic catalytic dehydrogenation of propane carried out with almost complete exclusion of oxygen (see Proceedings De Witt, Petrochem. Review, Houston, Texas, 1992, P1).

A common feature of the hitherto known methods of heterogeneous catalytic dehydrogenation of propane, carried out with the almost complete exclusion of oxygen, is that the degree of conversion of propane in a single pass through the reactor exceeds 30 mol.%, As a rule, less than or equal to 60 mol.%. Advantages can be achieved by limiting the degree of conversion to an interval of greater than or equal to 5 mol%, but less than or equal to 30 mol%, or less than or equal to 25 mol%. This means that propane dehydrogenation can be implemented to the extent of its conversion in a single pass, comprising from 10 to 20 mol.%. This leads, in particular, to the fact that, in the subsequent step (c), unconverted propane is diluted with molecular oxygen, thereby reducing the yield of by-products such as propionic aldehyde and / or propionic acid.

For the implementation of the above propane conversion degrees, dehydrogenation at an operating pressure of 0.3 to 3 atm is preferred. Along with this, dilution of the propane dehydrogenated with steam plays a favorable role. Due to the high heat capacity of water, on the one hand, it is possible to partially compensate for the endothermic effect of dehydrogenation, and, on the other hand, dilution with water vapor reduces the partial pressure of the dehydrogenation product, which favorably affects the equilibrium position. In addition, as reported above, the use of water vapor has a beneficial effect on the durability of the catalyst. If necessary, molecular hydrogen can be added to the initial mixture as an additional component, and its molar ratio to propane is usually less than or equal to 5: 1. Given the relatively low degree of conversion of propane, the molar ratio of water vapor: propane can be from greater than or equal to 0: 1 to 30: 1, it is advisable from 0.1: 1 to 2: 1, preferably from 0.5: 1 to 1: 1 . A favorable feature of the method for the dehydrogenation of propane with a low degree of its conversion is also that when a reaction gas is passed through the reactor once, a relatively small amount of heat is consumed and a relatively low reaction temperature is sufficient to achieve conversion.

It may be appropriate to carry out the dehydrogenation of propane to a relatively low degree of its conversion under (quasi) adiabatic conditions. This means that the initial gaseous reaction mixture is heated, as a rule, to a temperature of from 500 to 700 ° C (for example, by direct fire heating of the walls of the reactor) or from 550 to 650 ° C. In a typical situation, a single adiabatic transmission of the feed gas through the catalyst bed is sufficient to achieve the desired degree of conversion, while the temperature of the reaction mixture decreases by 30-200 ° C (depending on the degree of conversion). The implementation of dehydrogenation in adiabatic mode also contributes to the use of water as a coolant. The reduced reaction temperature allows to extend the life of the catalyst bed used for dehydrogenation.

Dehydrogenation of propane at a relatively low degree of its conversion, regardless of the mode (adiabatic or isothermal), in principle, can be realized in a reactor with either a fixed or a moving or fluidized catalyst bed.

It is noteworthy that to carry out dehydrogenation, in particular in adiabatic mode, it is sufficient to use a shaft furnace as a reactor with a fixed catalyst bed, and the reaction mixture is passed in axial and / or radial directions.

In the simplest case, we are talking about a separate, closed reaction volume, for example, a tank whose internal diameter is from 0.1 to 10 m, possibly also from 0.5 to 5 m, and the fixed catalyst bed is placed on a supporting device, for example, grate the lattice, and the hot propane-containing reaction gas is passed axially through the reaction volume filled with the catalyst provided with thermal insulation, so that the reactor can be operated in adiabatic mode. The catalyst may take the form of spheres, rings or rods. Since we are talking about using an extremely economical reaction device, the catalyst particles can have any geometric parameters that can provide a low pressure loss of the reaction gas. First of all, catalysts with geometric parameters are used that make it possible to create a large hollow space or structure, for example, similar to a cellular one. To realize a radial flow of propane-containing reaction gas, the reactor can, for example, consist of two cylindrical, coaxial relative to each other, placed in the shell of the grate, and the catalyst is loaded into the annular gap between them. To carry out dehydrogenation in adiabatic mode, the metal shell should be provided with thermal insulation.

As catalysts for the dehydrogenation of propane to a relatively limited depth of its conversion, achieved by a single pass through the reactor, in particular, the catalysts described in German patent application DE-A 19937107, especially those described in German patent application DE-A 19937107, are suitable , first of all, given in the corresponding examples.

After prolonged use, these catalysts can be regenerated in a simple way, according to which in the first stage, carried out at a temperature of from 300 to 600 ° C, in particular from 400 to 500 ° C, air diluted with nitrogen is passed through the catalyst bed. The load of the regenerating gas mixture on the catalyst can be, for example, from 50 to 10,000 h ^-1 , and the oxygen content is from 0.5 to 20 vol.%.

The next stage of regeneration is carried out under similar conditions, but air is used as the regenerating gas. From a technological point of view, it is advisable to purge the catalyst with an inert gas, such as nitrogen, before regeneration.

In conclusion, it is generally recommended that the final regeneration of the catalyst be carried out by passing pure molecular hydrogen or molecular hydrogen diluted with an inert gas (the hydrogen content must be greater than or equal to 1 vol.%), While the remaining regeneration conditions remain unchanged.

Dehydrogenation of propane to a relatively small conversion depth (less than or equal to 30 mol.%) In all cases can be carried out subject to the same catalyst loads (regarding both the total reaction gas and the propane contained in it), as well as in variants with a high degree of transformations (more than 30 mol.%). The load of the reaction gas on the catalyst can be, for example, from 100 to 10,000 h ^-1 , in particular from 100 to 3,000 h ^-1 , that is, often from 100 to 2,000 h ^-1 .

Particularly attractive is the implementation of the method of dehydrogenation of propane to a relatively small depth of conversion in a chordal reactor.

In a chordal reactor, several layers of dehydrogenation catalyst are preferably arranged in series, preferably in the radial or axial direction, the number of which can be from 1 to 20, preferably from 2 to 8, and also from 3 to 6. From a technological point of view, it is advisable to use fixed layers in chord reactors catalyst.

In the simplest case, the fixed catalyst layers are located axially in the shaft furnace or in the annular gaps between the cylindrical grate grates coaxially inserted into each other. It is also possible that the catalyst is placed in segments of annular gaps located at different levels, and the gas supplied in the radial direction flows from one segment to another, located lower or higher than the first.

It is advisable to preheat the mixture of reaction gases in a chord reactor, for which, on the way from one catalyst bed to the next, this mixture is passed, for example, through a finned heat exchanger heated by hot gases or through a pipe heated by hot combustible gases.

If the chordal reactor is operated in adiabatic mode, for the desired degree of propane conversion (less than or equal to 30 vol.%), Carried out, in particular, using the catalysts described in German patent application DE-A 19937107, in particular, in embodiments, presented in the corresponding examples, it is enough to introduce into the chord reactor a mixture of reaction gases preheated to 450-550 ° C and maintain this temperature inside it. Thus, propane dehydrogenation can be carried out at extremely low temperatures, which ensures a particularly long service life of the fixed catalyst beds between two successive regeneration cycles.

More effective is the direct intermediate heating of the reaction gases (autothermal heating method). According to this method, a small amount of molecular oxygen is added to the mixture of reaction gases leaving the first catalyst bed and / or passing between subsequent layers. Depending on the characteristics of the catalyst used for dehydrogenation, this leads to limited combustion of the reaction gases contained in the mixture, as well as, if necessary, deposits of coal or carbon-like compounds and / or hydrogen formed on the catalyst surface during the dehydrogenation of propane and / or introduced into the composition of the mixture of reaction gases. From a technological point of view, it may be appropriate to introduce additional catalyst layers into the chordal reactor, which contribute to the specific (selective) combustion of hydrogen (and / or hydrocarbons). Such additional catalysts are reported, for example, in US patents US-A 4788371, US-A 4886928, US-A 5430209, US-A 5530171, US-A 5527979 and US-A 5563314. For example, the layers formed by them can alternate in chord reactor with dehydrogenation catalyst beds. The heat generated through the use of the quasi-autothermal method allows heterogeneous catalytic dehydrogenation of propane in almost isothermal mode. Moreover, with an increase in the residence time of the reaction gas in the catalyst bed, it becomes possible to dehydrogenate propane at a decreasing or predominantly constant temperature, which allows for a particularly long period of operation of the catalyst between two successive regeneration cycles.

The aforementioned oxygen replenishment should be carried out, as a rule, so that the oxygen content in the mixture of reaction gases is from 0.5 to 10 vol.% With respect to the propane and propene contained in this mixture. The oxygen source can be either pure molecular oxygen or oxygen diluted with inert gases, for example carbon monoxide, carbon dioxide, nitrogen, noble gases, and in particular air. The gases generated during combustion, as a rule, play the role of additional diluents, due to which they contribute to the occurrence of heterogeneous catalytic dehydrogenation of propane.

A more complete approximation to the isothermal regime during heterogeneous catalytic dehydrogenation of propane can be achieved by placing in a chord reactor, namely in the free space between the catalyst layers, closed, if necessary, previously evacuated, and, possibly, unevacuated internal elements, for example, in the form of pipes . Such elements can also be placed directly in the catalyst bed. They contain suitably selected solid or liquid substances that evaporate or melt at a certain temperature, which consumes the corresponding thermal energy, and where the temperature is below the point of evaporation or melting, condensation of these substances is accompanied by heat.

Another possibility of heating the reaction gas mixture is to burn a certain part of the propane and / or hydrogen contained therein by adding the necessary amount of molecular oxygen (for example, by simply passing and / or passing the reaction gases through specific combustion catalysts) and using the result of burning thermal energy to heat the gas to the desired temperature. Products arising from combustion, in particular carbon dioxide, water, as well as nitrogen, if necessary, supplied together with molecular oxygen used for combustion, play the role of preferably inert gaseous diluents.

According to the invention, propane not converted in step (c) (if necessary, together with propene) after isolation of the desired products (acrolein and / or acrylic acid) can be subjected to dehydrogenation, carried out as described above, and the resulting mixture of gaseous products is processed at stage (a).

In the general case, propane that is not converted during dehydrogenation plays the role of a gaseous diluent in stage (c).

In addition, if, in particular, propane is dehydrogenated, it is possible to add pure propane and / or propene to the gas B fed to step (c).

If stage (c) is the conversion of propene to acrylic acid, the corresponding gas, along with the components not converted during the oxidation process, namely propane, nitrogen, and residual oxygen, also contains side components capable of oxidizing, for example, carbon monoxide, formic acid, formaldehyde, acetic acid, as well as small amounts of acrylic acid. According to a particularly preferred embodiment of the invention, these by-products can be subjected to catalytic oxidation by residual oxygen and, if necessary, additional molecular oxygen before dehydrogenation of propane to heat the gas supplied to the dehydrogenation. The oxidation of by-products can be carried out in the presence of an afterburning catalyst, in particular palladium supported on an alumina support, for example, an RO-20/13 or RO-20/25 (BASF) catalyst.

Preferred embodiments of the invention are presented in figures 1-7, which in more detail explain the invention, without limiting its scope.

Figure 1-5 schematically depicts the preferred methods, and for simplicity not shown all inlet and outlet flows. Figure 1 shows the following stages of the process: 1 - absorption and desorption, 2 - oxidation of propene to acrolein and / or acrylic acid, and 3 - allocation. In step 1, from a mixture containing propane, propene, hydrogen, carbon monoxide and carbon dioxide, as well as possibly nitrogen and other hydrocarbons, propane and propene are isolated by absorption with a suitable absorbent, which are then stripped by stripping with air. By carrying out this step, hydrogen, carbon oxides, other hydrocarbons and nitrogen are removed. Then the gas stream containing propene and, if necessary, propane, is sent to oxidation stage 2, where propene is oxidized to acrolein and / or acrylic acid. The product obtained in stage 2 is sent for processing to stage 3, where acrolein or acrylic acid is isolated from it as the target products. Unconverted propene, as well as propane, carbon oxides and, if necessary, residual nitrogen and oxygen are sent to the absorption and desorption stage 1.

The numbers given in the remaining drawings mean the same as in figure 1.

In contrast to figure 1, figure 2 shows the stage of dehydrogenation of propane 4, which can be carried out with or without oxygen supply. The gas mixture obtained by the dehydrogenation of propane and containing along with propane and propene hydrogen, carbon oxides and possible residual amounts of nitrogen and hydrocarbons is sent to the absorption / desorption stage 1.

In contrast to FIG. 1, in FIG. 3, instead of the propene oxidation step 2, step 22 is presented, in which the propane is oxidized to acrolein and / or acrylic acid.

According to Fig. 4, the products isolated in stage 3 are sent to the propane 4 dehydrogenation stage, which is carried out with or without oxygen supply, and the gas mixture formed at this stage is fed to the absorption / desorption stage 1.

Figure 5 shows another preferred embodiment of the invention, according to which, after the stage of absorption and desorption 1 carry out the dehydrogenation of propane 5 with the supply of oxygen.

6 and 7 show other preferred methods. The method depicted in FIG. 6 corresponds to the flow chart shown in FIG. 4. As can be seen from the diagram in Fig. 6, three reactors are used to carry out propane dehydrogenation (stage 4), in the first of which carbon monoxide (CO-NV) is burned before propane dehydrogenation, and in the next two reactors before propane dehydrogenation (PDH) post-burn hydrogen (H ₂ -NV). Due to the afterburning of these products, the thermal energy necessary for dehydrogenation of propane is obtained. The number of reactors designed for dehydrogenation of propane is not limited to three. Propane is fed to the dehydrogenation stage 4 via a pipeline (30), and air can flow through a pipeline (6). The gas mixture resulting from the propane dehydrogenation is fed through a heat exchanger W and compressor V to an absorption column K1 and a desorption column K2. The adsorbent after desorption in the column K2 is returned to the absorption column K1. Gas not absorbed by the absorbent is removed from the process in the form of gas (33), if necessary, previously passed through the afterburner E. The gas stream containing the separated propane and / or propene enters oxidation stage 2, which includes four reactors. The number of reactors intended for oxidation, however, is not limited to four. After that, at stage 3, acrolein and / or acrylic acid are isolated as the target products and they are removed through a pipeline (31). Non-converted propane and / or propene in the form of recycle gas is returned via pipeline (32) to the dehydrogenation stage 4 together with other gaseous components not selected by absorption.

As shown in Fig. 7, the recycle gas (1) leaving the recovery stage 3 at a temperature of from 10 to 90 ° C and a pressure of from 0.8 to 5 bar, which can be subjected to additional compression, for example, by means of a compressor VO to pressure from 2 to 10 bar, heated to a temperature of from 100 to 650 ° C, passing through a heat exchanger W1, into which countercurrent reaction gas (2), obtained by dehydrogenation of propane (PDH) in stage 4, is supplied. Here and in the further description given on Fig. 7 diagrams of pressure value are indicated in absolute units.

Compression of gas mixtures can be carried out by any suitable compressor known to those skilled in the art, the design of which will be described in more detail below.

The recycle gas stream (1) contains from 40 to 80 vol.% Nitrogen, from 1 to 5 vol.% Carbon dioxide, from 0.1 to 2 vol.% Carbon monoxide, from 2 to 5 vol.% Oxygen, from 0, 5 to 25 vol.% Moisture, other oxidation by-products, from 5 to 40 vol.% Unconverted propane and from 0.1 to 3 vol.% Unconverted propene. Before or after heating, this gas stream is mixed with fresh propane (3) and preferably water and steam (4) before being directed to the propane dehydrogenation step 4. Any available gases or liquids containing propane are suitable as a source of fresh propane. The preferred source of fresh propane is, however, technical propane (the main product content of more than 90%, in particular more than 95%, particularly preferably more than 98% at the limited content of C ₄ ⁺⁾ or pure propane (the main product content greater than 99%). The molar ratio of water or water vapor to propane in the gas stream is from 0.05: 1 to 5: 1, preferably from 0.1: 1 to 2: 1. A favorable role can be played by the additional introduction of hydrogen (5), air (6) or an oxygen-containing gas into the composition of this gas stream, as well as other components that are converted during the dehydrogenation of propane with an exothermic effect, for example, carbon monoxide or its mixtures with hydrogen, in particular synthesis gas. No claims are made regarding the purity of these gases. The exothermic oxidation of combustible components in the process of propane dehydrogenation compensates for the endothermic effect accompanying dehydrogenation, so it may be necessary to supply only a limited amount of thermal energy from the outside, and in the most optimal situation it may not be necessary at all.

The propane dehydrogenation pressure is from 0.3 to 10 bar, preferably from 1 to 5 bar, temperature from 350 to 700 ° C, preferably from 400 to 600 ° C. For propane dehydrogenation, reactors of any design type known to those skilled in the art can be used, for example, apparatuses with axial direction of gas flow, in particular chord reactors, as well as apparatuses with several catalyst layers arranged in the form of hollow cylinders and radial direction of gas flow, or several separate apparatuses, for example in the form of columns, cakes (Tortenform) or spheres. The number of reactors used for dehydrogenation of propane is not limited to three. Several separate devices are used because it provides the simplicity of the intermediate supply of additional gases. In addition, this allows during the process to carry out the processing of the catalyst in a particular reactor, for example, its regeneration, regardless of what happens in other reactors. For this, for example, the reactor with the catalyst to be regenerated is isolated from the main gas stream by means of corresponding shutoff bodies, for example, dampers, valves or valves located on pipelines connecting separate reactors, the gases necessary for its regeneration, for example nitrogen, depleted in nitrogen, are passed through the catalyst bed oxygen air or enriched air or oxygen gases and remove deposits formed on the surface of the catalyst. The remaining reactors, the total number of which can be from 1 to 20, preferably from 2 to 5, continue to supply the main gas stream, receiving as the target product propene.

In reactors intended for dehydrogenation of propane, the catalyst layers can be laid on gratings, granular masses from an inert material, or other support devices known to those skilled in the art. The catalyst particles can be of any shape without any restrictions, including, for example, crushed particles, spheres, short rods, rings, cylinders, as well as structured packing or monoliths. Preferred are geometric parameters, which correspond to a minimum pressure loss.

Devices known to those skilled in the art can be used to evenly distribute the gas supplied to the catalyst, for example, mesh plates, ring or tube gas distributors, as well as random fillings or structured nozzles, such as static mixers.

In reactors designed for dehydrogenation of propane, several layers of catalyst can be placed, each of which performs a specific function. If several such layers are used, then one or more layers consisting of catalysts are preferably placed in front of the dehydrogenation catalyst layer, under the influence of which the oxidation of substances other than propane or propene, for example hydrogen (H ₂ -NV catalyst), carbon monoxide (catalyst CO-NV) and / or another oxidizable component. However, if these functions are performed by the propane dehydrogenation catalyst itself or the loss of propane as a result of its oxidation is economically viable, the use of additional catalysts should be abandoned, if possible.

The specific productivity of propane dehydrogenation catalysts can be from 100 to 20,000 normal liters (nl) of propane per liter of catalyst per hour. Preferably, this indicator is in the range from 500 to 10,000, more preferably from 1,000 to 10,000. The specific productivity of the catalysts, mainly oxidizing, for example, carbon monoxide or hydrogen, while slightly oxidizing propane or propene, is usually in the range from 5,000 to 30,000 nl per liter of catalyst in hour.

The degree of conversion of propane during dehydrogenation is from 10 to 60%, preferably from 20 to 50%, in particular from 88 to 96%. The complete conversion of gaseous carbon monoxide, hydrogen or other combustible gases introduced into the reactor is preferred. The degree of conversion of hydrogen generated in the process of propane dehydrogenation, depending on the degree of conversion of propane itself, is from 1 to 99%, most often from 10 to 80%, in particular from 30 to 70%.

The reaction gas (2) resulting from the propane dehydrogenation contains from 20 to 60 vol.% Nitrogen, from 1 to 5 vol.% Carbon dioxide, from 0.5 to 45 vol.% Water, from 5 to 45 vol.% propane, from 1 to 20 vol.% propene from 1 to 20 vol.% hydrogen, as well as other by-products, for example ethane, ethene, methane and C ₄ ⁺ .

The reaction gas (2) formed during the dehydrogenation of propane has a temperature of from 400 to 650 ° C, more preferably from 450 to 600 ° C, and a pressure of from 0.3 to 10 bar, more preferably from 1 to 5 bar. Gas (2) due to heat exchange in a counterflow heat exchanger W1 with recirculation gas (1) is cooled to a temperature of at least 5 ° C, better at least 50 ° C and preferably at least 100 ° C higher than the temperature of the recirculation gas (1) at the inlet to the heat exchanger. Then, the gas stream (3), depending on the temperature at the outlet of the countercurrent heat exchanger W1, is subjected to additional cooling of 10-60 ° C, carried out in one or several stages. When using several stages, depending on the temperature level, cooling in the heat exchanger W2 can occur by generating steam or supplying cooling air, and cooling in the heat exchanger W3 can be achieved by supplying cooling air, water or brine. Moreover, depending on the pressure, temperature and moisture content of the gas streams (3) - (5), moisture condensation occurs, which is separated from the gas stream (5) in the separator A1. The separator may be of any design known to those skilled in the art and suitable for gas separation.

Then, the cooled and, if necessary, partially dehydrated gas stream (6) is subjected to compression, the compression ratio being in the range limited by the gas pressure at the outlet of the separator A1, on the one hand, and 50 bars, on the other. Compression can be carried out by means of a single-stage or multi-stage compressor with or without intermediate cooling. Compressor V1 can have any design known to those skilled in the art. For example, piston, rotary, screw, diaphragm, vane, turbine and centrifugal compressors, as well as rotary and centrifugal blowers, can be used, with turbine and centrifugal compressors being preferred. The criteria for choosing the type of compressor are the degree of compression and the amount of gas to be compressed. In multi-stage compression with intermediate cooling, condensation occurs of moisture and, if necessary, other condensable components that can be extracted from the gas stream, as described above, after intermediate cooling or during its implementation, before directing the gas stream to the next compression stage . Compressed to the required final pressure, the gas stream (7) can be subjected to single or multi-stage cooling, as described above, moreover, moisture and, if necessary, other condensable components can be separated from the gas flows (7) - (9).

As the drive of the compressor V1, electric motors can be used, as well as steam or gas turbine units. The choice of drive type depends on the production infrastructure, but most often steam turbines are used as the drive, which are characterized by the highest cost-effectiveness.

If it is necessary to increase the ratio of water to the propane supplied for dehydrogenation, the combination of condensed streams, for example, stream (11) (after increasing the pressure) and stream (12), is returned to the propane dehydrogenation stage, and the residue is blocked and, if necessary, burned. The condensate stream (13) is evaporated or subjected to any other treatment, for example, purification, before recirculation or sludging.

The gas stream (10) is sent to the absorption column K1, where the absorbent in contact absorbs C ₃ hydrocarbons (propane and / or propene) and, if necessary, other components. As the absorbent material, any substances known to those skilled in the art are used, the above absorbents being preferred. Preferred is multi-stage countercurrent contacting of the gas stream (10) with the absorbent. The absorption temperature may be from 10 to 150 ° C, preferably from 20 to 80 ° C, preferably from 30 to 60 ° C, and the pressure from 1 to 50 bar, preferably from 3 to 30 bar, preferably from 5 to 20 bar.

Suitable constructions of the K1 absorber known to those skilled in the art are suitable, for example, those described in Thermische Trennver-fahren, Klaus Sattel, VCH, 1988, (ISBN 3-527-28636-5). Preferred are columns with internal elements also known to those skilled in the art, for example, absorbers with mesh plates, double-flow plates, cap, tunnel, trellised or valve plates, absorbers with random filling, for example, Raschig rings, Pale rings, Intalox seats, Burley saddles, Super or Torus saddles, inner bodies or rings made of metal fabric, and absorbers with a structured nozzle (for example, Sulzer-Kerapak, Sulzer-Packung BX or CY, or, for example, nozzles from Montz and other manufacturers). Especially suitable is the Ralu-Pak 250 nozzle. YC from Raschig. At the same time, the built-in elements that allow the absorber to be operated with an increased liquid flow rate (high irrigation density), for example, unstructured filling or structured nozzles, are preferred. In a preferred embodiment, the irrigation density should be more than 50 m ³ , more preferably more than 80 m ^{3 of} liquid per square meter of free surface per hour. Built-in elements can be made of metal and ceramic, as well as polymers or combinations of several materials. The basic principle when choosing a material suitable for use as a backfill or nozzle is good wetting with an absorbent.

The ratio between the flows of absorbent (24) and gas (10) supplied to the absorber is established based on the relevant requirements of thermodynamics. It depends on the number of stages of selection, temperature, pressure, absorption capacity of the absorbent and the desired degree of separation of the absorbed product. The specified ratio is usually from 1: 1 to 50: 1, in particular from 1: 1 to 30: 1, preferably from 1: 1 to 20: 1 (kg / kg) with the number of theoretical stages from 1 to 40, in particular from 2 to 30, preferably 5 to 20. The theoretical number of steps can be calculated using specialized literature, for example, Thermische Trennverfahren, Klaus Sattel, VCH, 1988 (ISBN 3-527-28636-5).

In order to reduce the loss of absorbent, if necessary, the gas stream (14) freed from propane and / or propene can be directed to the hardening stage. The corresponding principle is explained in more detail in the following description of the desorption step.

After possible quenching, the gas stream (14) can be decompressed, which can be accomplished by single or multi-stage throttling without energy recovery or by single or multi-stage regeneration of mechanical energy in a T1 gas turbine. In the latter case, the gas stream (14) sometimes needs to be heated before being fed into the turbine. The heating can be carried out directly by catalyzed or non-catalyzed oxidation of the combustible and oxidizable components contained in this gas stream or introduced externally, or by indirectly supplying heat by means of steam or external fire heating. The mechanical energy resulting from decompression can be used to drive the drive of one of the compressors, preferably compressor V1, as an additional or main source of energy and / or to generate electric current.

Depending on the degree of purity, the decompression stream obtained from decompression (15) can be directed to catalyzed or non-catalyzed combustion or discharged into the atmosphere.

The absorbent stream (16), mainly consisting of propane (from 2 to 30 vol.%) And / or propene (from 2 to 30 vol.%) And, if necessary, containing other components (for example, carbon dioxide, C ₂ ^- , C ₄ ⁺ , water), if necessary, subjected to decompression, and then sent to the desorption column K2. Decompression of the absorbent can be carried out without regeneration of mechanical energy by single or multi-stage throttling, as well as with the regeneration of mechanical energy, for example, in a turbine or in a centrifugal pump rotating in the opposite direction. It may be necessary to heat the absorbent (16) before desorption, which is preferably effected by heat exchange in a counterflow heat exchanger W6 with a stream (17). The need for additional heating of the stream (16) emerging from this heat exchanger is not ruled out.

The desorption of propane and / or propene in the K2 stripper can be realized by distillation (single simple evaporation) or by evaporation, and desorption is promoted by pressure reduction to 0.1-10 bar, in particular to 1-5 bar, preferably to 1.5-3 bar.

When it comes to desorption by distillation, it can be carried out by any method known to those skilled in the art. A particularly simple form of desorption is a single-stage simple (instantaneous) evaporation of the absorbent in an apparatus designed for this purpose. Before this operation, it is advisable to heat the stream (16) to a temperature of from 20 to 300 ° C, in particular from 40 to 200 ° C, preferably from 50 to 150 ° C. The appropriate apparatus should be designed to provide the proper thermodynamic conditions for the separation of propane or propene from the absorbent and the proper hydrodynamic conditions for the separation of gas from the liquid. In particular, the apparatus may take the form of a cylinder or a sphere, as well as another structural form known to specialists. If it has a cylindrical shape, it can be placed both vertically and horizontally. The supply line, as a rule, is located between the fittings designed to drain, respectively, gas and liquid. In the simplest case, the device does not have any additional built-in elements. In order to create optimal thermodynamic conditions for desorption, integrated elements commonly used in the distillation, absorption and stripping techniques, in particular the elements described above in the description of absorption, can be mounted inside the apparatus. To ensure optimal hydrodynamic conditions for the separation of gas from the liquid inside the apparatus, appropriate built-in elements known to those skilled in the art can be integrated, for example wire fabric, direction-changing partitions, or similar elements. In addition, devices that provide heat supply, such as heated coils or screens, can be included in the apparatus.

If in this case air or a similar stripping medium is available, for example water vapor, nitrogen, fresh propane or another gas necessary for use in the technological process, it is advisable to use them to support the process of instant evaporation of the absorbent.

In this case, a special form of the process is the multi-stage evaporation of volatile components (propane and / or propene) by means of an initial gas stream (25) intended for oxidation (in this case, as with single-stage evaporation, all additionally stripped from the stream (10) absorbed components, as well as other substances that could be formed due to their volatility). In the simplest case, the source gas stream (25) is the air necessary for the oxidation of propane to acrolein or acrylic acid. In this case, the compression of air or the initial gas stream can be carried out both before desorption and after it. The source gas stream (25) along with air may also contain recirculation gas from the stage of acrylic acid production, as well as water vapor, fresh propane or other inert gas components. Especially favorable for the desorption process is a countercurrent or a cross current of the feed gas stream (25) with respect to the liquid absorbent. In the case of a counterflow, the stripper can be made similar to the absorption column described above.

It is advisable to use the cross current if the boundary of the explosion region is crossed during the desorption process. This situation arises if, from the point of view of a tendency to ignite, the source gas stream (25) is a “lean” gas mixture, and the gas stream (18) leaving the stripper containing propane and / or propene is a “greasy” gas mixture . A gas mixture is called “lean” if it contains too few flammable substances to have the ability to ignite, and “greasy” if it contains too many flammable substances to have such ability.

When using cross current, the total gas stream is not supplied to the cube of the desorption column, but is introduced as separate streams into several points located along it so that no flammable gas mixture is present in any part of the stripper. In this case, the stripper can be located both in the vertical and in the horizontal plane.

Another way to solve the problem of explosion hazard during the desorption of flammable components of oxygen-containing gas streams is to mix the initial gas stream before entering the desorption column with a substance (for example, propane, propene, methane, ethane, butane, water and so on) due to the presence of which the gas mixture supplied to the stripper becomes “greasy”. It is also possible to separate the feed gas stream and introduce into the cube of the desorption column feed gas not containing propane or propene in order to ensure the lowest possible content of propane and / or propene in the absorbent stream (17), and the feed gas, the “fat content” of which is increased, for example due to the addition of propane and / or propene, feed to that part of the stripping column where a combustible gas mixture may form.

The flow of absorbent (17) with a low content of propane and / or propene after possible passing through counterflow heat exchanger W6 and increasing the pressure carried out by pump P1 can be subjected to additional single or multi-stage cooling (for example, in heat exchanger W7) and through a pipeline (24 ) again sent to the absorber K1.

In the general case, multi-stage desorption can be carried out at any pressure and temperature. Preferred, however, are lower pressures and higher temperatures than absorption. In this case, the pressure is from 1 to 5 bar, in particular from 2 to 3 bar, temperature from 20 to 200 ° C, in particular from 30 to 100 ° C, particularly preferably from 35 to 70 ° C.

The ratio of the absorbent stream (17) to the source gas stream (25) must meet the requirements of thermodynamics, and it depends on the number of stages of separation, temperature, pressure, the ability of the absorbent to desorb absorbed substances and the required degree of separation. Usually it is from 1: 1 to 50: 1, in particular from 5: 1 to 40: 1, preferably from 10: 1 to 30: 1 (kg / kg) with a theoretical number of stages of separation from 1 to 20, in particular from 2 to 15, preferably from 3 to 10.

In the general case, the initial gas stream containing propane and / or propene without additional processing can be directed to oxidation stage 2. However, it may be advisable to direct it to an additional technological stage before oxidation, for example, in order to reduce losses of the stripped absorbent. The absorbent can be separated from the gas stream supplied for oxidation by any methods known to those skilled in the art, one of which is abrupt cooling (quenching) of the gas stream by water. Water flushing (quenching) can be performed in the upper part of the desorption column above the liquid trapping plate or in a separate apparatus. To enhance the separation effect inside the quenching device, built-in elements similar to those commonly used in distillation, absorption and desorption and described above in the description of absorption can be mounted. The same applies to a separate quenching apparatus.

The mixture of water and absorbent resulting from the separation of the absorbent from the propane and / or propene gas stream by washing with water (19) can be phase separated in device D1, and the gas stream freed from water (18) after possible heating is sent to the stage oxidation of propane (2).

Phase separation can be implemented in any form known to those skilled in the art, for example, by liquid extraction. In the simplest case, the organic absorbent is separated from the water used for quenching in horizontally or vertically mounted devices of elongated shape, equipped with built-in elements or without them. The ratio of the diameter of such devices to the length can be from 1: 1 to 1: 100, in particular from 1: 1 to 1:10, preferably from 1: 1 to 1: 3. The device may be completely filled with liquid or may contain a gas cushion. For better separation of the organic phase, it can be equipped with a dome from which absorbent can be drained. Better phase separation can be facilitated by the use of built-in elements known to those skilled in the art, such as wire fabrics, Wickelkerzen candles, or baffles that change direction. Rotating devices, such as centrifuges, can also be used to separate phases.

The absorbent (20) resulting from the phase separation can be returned to the stripper. Quenching water before returning to the quenching apparatus, if necessary, can be cooled or heated in the heat exchanger W9. Large quantities of quenching water are more preferably pumped with a suitable pump P2. The irrigation density in the quenching apparatus exceeds 30 m ³ , in particular 50 m ³ , preferably 80 m ³ , but is less than 1000 m ³ , in particular less than 500 m ³ , preferably less than 300 m ^{3 of} water per square meter of free cross-sectional area of the quenching apparatus in hour.

Losses of water during quenching can be compensated by the supply of aqueous condensate (21) or acid-containing water (22) generated during the acrylic acid production step. To avoid overflow, part of the reverse quenching water is sluice in the form of a cleaning stream (23) and sent to the incinerator or eliminated in another way (for example, sent to the wastewater treatment plant).

If the gas stream (18) supplied to oxidation stage 2 has a temperature below 90 ° C, in particular below 70 ° C, and a pressure of 1 to 3 bar, then it is advisable to add water, which is carried out by mixing it with water vapor or saturation water in a saturator known to specialists of the structural type.

The gas stream (18) contains from 30 to 70 vol.% Nitrogen, from 5 to 20 vol.% Oxygen, from 2 to 15 vol.% Propene, from 2 to 40 vol.% Propane, from 0.5 to 25 vol. % water and other components, in particular carbon dioxide, methane, ethane, ethene, C ₄ ⁺ . It can be directed to oxidation stage 2, carried out as described above, or by methods known from the patent literature. The oxidation of propene or acrolein can be carried out in reactors according to the prior art with a salt bath, for example, the production of a shipyard Deggendorfer or in reactors of another type. Between the first (production of acrolein) and the second (production of acrylic acid) oxidation steps, additional feeding of the reaction gas with air or steam can be carried out. The increased content of C ₃ hydrocarbons in the gas stream supplied to oxidation stage 2 (18) in any case contributes to the removal of the reaction heat from the reaction volume. Suitable is the supply of propene in an amount of from 50 to 350, in particular from 90 to 300, preferably from 100 to 250, nl per liter of catalyst per hour.

The separation of acrylic acid in stage 3 from the reaction gas (26) coming from oxidation stage 2 can be carried out as described above, for example, using high boiling solvents, in particular a mixture of diphyl and dimethyl phthalate, as well as by water absorption or fractional condensation.

Acrylic acid can be purified from impurities by steam and distillation, azeotropic distillation or crystallization.

The method, carried out in accordance with the flowchart shown in Fig. 7, is suitable both for re-equipment of any existing plants intended for the production of acrolein and / or acrylic acid, and for combination with new plants for the synthesis of acrylic acid.

It was unexpectedly discovered that, as a rule, the expected presence of absorbent residues in the composition of gas B does not lead to any negative effect on the oxidation process and the properties of the catalyst used for its implementation. There were also no problems due, if necessary, to occur at the stage of oxidation of propane and / or propene to the formation of any oxidation products of the absorbent. If, nevertheless, there were any problems associated with the presence of absorbent residues, which, as a rule, can be avoided when using high-boiling hydrocarbons, in particular paraffins, as absorbents, such problems can be solved by using water quenching or adsorption.

Thus, it was unexpectedly found that absorption can be used in the method according to the invention. In contrast to the adsorption used in accordance with Japanese patent application JP-A-1036311, the absorption of propane and / or propene according to the present invention allows much easier and more economical control.

In addition, an advantage of the present invention is that plants where propene is used as the starting material for the production of acrolein and / or acrylic acid can be conveniently converted to use cheaper propane as the starting material.

The invention explains the example below regarding a preferred embodiment of the method according to the invention.

Example

Acrylic acid is obtained by the method schematically depicted in FIG. 7, therefore, the same numerals are used below as in FIG. 7.

2090 nl / h of recirculation gas (1) after process stage 3, with a temperature of 30 ° C and a pressure of 1.2 bar, is fed to a VO compressor, where it is compressed to 2.0 bar, and then to a counterflow heat exchanger W1, in which it is heated to a temperature of 450 ° C due to heat exchange with the reaction gas (2) coming from the propane dehydrogenation stage. In this case, and with the following description of the example, the absolute value of pressure in bars is indicated.

Recirculation gas (1) contains 60.3 vol.% Nitrogen, 1.2 vol.% Carbon dioxide, 0.5 vol.% Carbon monoxide, 3.4 vol.% Oxygen, 1.9 vol.% Water, 32, 2 vol.% Propane and 0.4 vol.% Propene, as well as by-products of oxidation. Before entering the heat exchanger, the recirculation gas is mixed with fresh propane (3) supplied in an amount of 170 nl / h and water vapor (4). 1: 0.5 is used as fresh propane technical propane to the major product over 98% and the C ₄ ⁺ equal to 100 million ^-1 molar ratio of steam to propane fed to the dehydrogenation in the gas stream..

The gas mixture is introduced into the first of four reactors with an internal diameter of 50 mm. The design of the reactors allows the possibility of their operation in autothermal mode. Each reactor contains a catalyst bed 110 mm high. The catalyst is a short rods with a diameter of 3 mm and a height of 5 mm.

The propane conversion in the four reactors is 20% with a propene selectivity of 92%.

The gas leaving the dehydrogenation reactors (2) contains 44.9 vol.% Nitrogen, 2.7 vol.% Carbon dioxide, 16.9 vol.% Water, 24.0 vol.% Propane, 5.8 vol.% Propene, 5.5 vol.% Hydrogen, as well as a small amount of by-products, in particular ethane, ethene, methane and C ₄ +.

The reaction gas (2) after dehydrogenation with a temperature of 520 ° C and a pressure of 1.5 bar is cooled to 30 ° C. Gas cooling is accompanied by condensation of about 350 g / h of water (11).

The cooled gas stream (6) is subjected to single-stage compression by a piston compressor to 7.5 bar, and then again cooled to 30 ° C. The water condensate formed during cooling (12) is combined with the condensate (11), partially evaporated and mixed with the recirculation stream (1 ) The other part of the condensate (21) is sent to the quenching device, and the remainder is subjected to lockout.

2340 nl / h of gas flow (10) is fed into the cube of the absorption column K1 (metal casing, internal diameter 80 mm, length 3 m). The internal volume of the absorber is 60% filled with Montz packing elements (Montz-Pak, type B1).

The gas stream (10) contains 53.9 vol.% Nitrogen, 3.3 vol.% Carbon dioxide, 0.4 vol.% Water, 28.8 vol.% Propane, 7.0 vol.% Propene, 6, 6 vol.% hydrogen and small amounts of other by-products, in particular ethane, ethene, methane and C ₄ ⁺ .

35 kg / h of tetradecane (24) having a temperature of 30 ° C and containing a small amount of C ₃ hydrocarbons are fed to the upper part of the absorption column K1 from the stripper K2.

Abgaz (14) containing 1150 million ^-1 vol. propane and 750 million ^-1 vol. propene, passed through a pressure-supporting valve to reduce temperature and pressure to the corresponding atmospheric values, and then burned.

The flow of absorbent (16) from the bottom of the K1 column is passed through a pressure-supporting valve, reducing the pressure to 2.4 bar, and fed to the top of the desorption column K2.

The dimensions of the K2 desorption column and the type of nozzle filling it are similar to the K1 absorption column.

1310 nl / hr of compressed air up to 2.45 bar with a temperature of 30 ° C is fed into the cube of the desorption column. The column is thermostated at a temperature of 40 ° C.

Abgas leaving the desorption column (2190 nl / hr) and containing 30.7 vol.% Propane, 7.4 vol.% Propene, 12.3 vol.% Oxygen, 46.4 vol.% Nitrogen, 1.5 vol. % water, 1.6% vol. carbon dioxide and a small amount of tetradecane, sent to the quenching apparatus located in the upper part of the desorption column K2.

The absorbent from the bottom of the K2 desorption column is pumped by pump P1 to the heat exchanger W7 and then to the upper part of the absorption column K1.

The quenching apparatus is a metal column with an internal diameter of 80 mm, similar to an absorption column K1 containing built-in elements. Water quenching is carried out at a temperature of 30 ° C, the flow rate of irrigating water is 120 l / h. The two-phase liquid mixture taken from the cube of the quenching apparatus is sent to a phase separation device D1, which is a horizontal reservoir with a diameter of 200 mm and a length of 500 mm, the first third of the internal volume of which (in the direction of flow movement) is filled with a specially arranged thin wire cloth . The aqueous phase separated in device D1 is pumped to the upper part of the quenching apparatus, and the isolated tetradecane (its average amount is about 1 g / h) is sent to the corresponding collection. The loss of water during quenching is compensated for by adding water condensate (21).

The gas from the quenching apparatus is heated to a temperature of 200 ° C and sent to a two-stage oxidation.

The oxidation is carried out in modeling tubes 4 m long with an inner diameter of 26 mm. 2.7 m of the first modeling tube is filled with the catalyst described in European patent application EP-A-0575879, and 3.0 m of the second modeling tube is filled with the catalyst described in European patent application EP-A-0017000. Between the first and second stages of oxidation serves additional air in the amount of 315 nl / hour.

The selection of acrylic acid from the reaction gas (26) resulting from oxidation, and its purification from impurities is carried out in accordance with European patent application EP-A-0982289.

According to this method, an average of 440 g / h of crude acrylic acid (27) is obtained with a main product content of more than 99.5%.

Claims (16)

1. The method of producing acrolein and / or acrylic acid from propane and / or propene, comprising the following stages: a) the allocation of propane and / or propene from the propane and / or propene-containing gas mixture A by absorbing them with an absorbent, b) recovering propane and / or propene from the absorbent to produce propane and / or propene-containing gas B and c) using the gas B obtained in step (b) to oxidize propane and / or propene to acrolein and / or acrylic acid, moreover, between stages (b) and (c) do not carry out heterogeneous catalytic dehydrogenation of propane without oxygen. 2. The method according to claim 1, characterized in that at the stage (a) serves a gas mixture And containing along with propane and / or propene, at least one additional component selected from hydrogen, nitrogen or carbon oxides. 3. The method according to p. 1 or 2, characterized in that at the stage (a) at least one alkane with 8-20 carbon atoms or an alkene with 8-20 carbon atoms is used as absorbent. 4. The method according to one of paragraphs. 1-3, characterized in that the separation of propane and / or propene from the absorbent in stage (b) is carried out by steaming, flash evaporation and / or distillation. 5. The method according to one of the preceding paragraphs, characterized in that at the stage (C) carry out the oxidation of propene to acrolein and / or acrylic acid. 6. The method according to one of paragraphs. 1-4, characterized in that in stage (C) carry out the oxidation of propane to acrolein and / or acrylic acid. 7. The method according to claim 6, characterized in that as a catalyst for the oxidation of propane in stage (C) using a mixture of metal oxides of the formula (I)

in which M ¹ is tellurium (Te) and / or antimony (Sb); M ² is at least one element from the group consisting of niobium (Nb), tantalum (Ta), tungsten (W), titanium (Ti), aluminum (Al), zirconium (Zr), chromium (Cr), manganese (Mn), gallium (Ga), iron (Fe), ruthenium (Ru), cobalt (Co), rhenium (Rh), nickel (Ni), palladium (Pd), platinum (Pt), lanthanum (La), bismuth (Bi), boron (B), cesium (Cs), tin (Sn), zinc (Zn), silicon (Si) and indium (In); b is from 0.01 to 1; c is equal to greater than 0 to 1; d is from greater than 0 to 1; n is a number determined by the valency and repeatability of the elements that are different from oxygen in the formula (I). 8. The method according to one of the preceding paragraphs, characterized in that the non-converted after stage (c) propane and / or propene is isolated in stages (a) and (b) and returned to stage (c). 9. The method according to one of the preceding paragraphs, characterized in that the composition used in stage (a) of the gas mixture A is similar to the composition of the gas mixture, which is obtained by homogeneous and / or heterogeneous catalytic dehydrogenation of propane and / or propene. 10. The method according to claim 9, characterized in that the propane dehydrogenation is carried out with the addition of oxygen. 11. The method according to one of the preceding paragraphs, characterized in that the propane that is not converted after carrying out step (c) and, if necessary, propene is sent to the propane dehydrogenation step and the resulting product mixture is again processed in step (a). 12. The method according to one of the preceding paragraphs, characterized in that stage (c) is carried out immediately after stage (b). 13. The method according to one of paragraphs. 1-11, characterized in that after stage (b) and before stage (c), water quenching is performed to isolate the absorbent. Priority on points and signs: 06/20/2000 - p. 7, except for the sign “M ² is at least one element from the group including gallium (Ga), lanthanum (La), tin (Sn), zinc (Zn), silicon (Si) and indium (In) "; 07/07/2000 - the sign "M ² is at least one element from the group comprising gallium (Ga)"; 04/17/2001 - the sign "M ² is at least one element from the group comprising lanthanum (La), tin (Sn), zinc (Zn), silicon (Si) and indium (In)".

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