MXPA98008885A

MXPA98008885A - A method for the production of acid acril

Info

Publication number: MXPA98008885A
Application number: MXPA/A/1998/008885A
Authority: MX
Inventors: Kawajiri Tatsuya; Tanimoto Michio; Uekawa Kazuyuki
Original assignee: Nippon Shokubai Co Ltd
Priority date: 1997-10-27
Filing date: 1998-10-26
Publication date: 2000-07-01

Abstract

The present invention relates to a high efficiency efficiency acrylic propylene acrylic acid method by catalytic oxidation of two phases using only shell type heat exchanger reactor and fixed bed or bed tube. The method comprises dividing the envelope space of said reactor into an upper space and the lower space with a partition plate, allowing a heating medium to circulate in each of the spaces, substantially independent of each other, and carrying out oxidation in vapor phase under specific conditions. Such specific conditions include providing a first phase catalyst layer to the lower portion of each of the reaction tubes, a second phase catalyst layer to the upper portion thereof and a layer of inert substance therebetween, and making the ratio of holes of the inert substance to 40-99.

Description

A METHOD FOR THE PRODUCTION OF ACRYLIC ACID.

Field of Invention This invention relates to a method for the production of acrylic acid. More specifically, the invention relates to a method for producing acrylic acid from propylene at high efficiency, using only one reactor of shell heat exchanger type and fixed bed or bed tube.

Background of the Invention The production of acrylic acid by means of catalytic gas oxidation of two phases of propylene has been widely practiced industrially. This method employs a first phase reactor loaded with a first phase catalyst suitable for gaseous oxidation of propylene to acrolein and a second phase reactor loaded with a second stage catalyst suitable for gaseous oxidation of acrolein to acrylic acid, said method comprises introducing the reaction gas REF, 28583 containing the acrolein mainly and leaving the first phase reactor in the second phase reactor, and further oxidizing said acrolein in the second phase reactor to produce acrylic acid. Large numbers of catalysts hitherto have been proposed as suitable for said first phase catalysts and second phase catalysts.

Whereas, if it should possibly be possible to practice the same two-phase catalytic oxidation method using only one reactor to produce propylene acrylic acid at high efficiency, instead of using the two reactors as above, numbers of reactors can be markedly reduced. incidental instruments and devices that lead to appreciable reduction in production costs and economic benefits. Such two-phase catalytic oxidation methods for producing propylene acrylic acid using only one reactor have also been proposed.

For example, Patent Publication Japanese No. 21966/1979 A, in particular, Example 5 thereof, discloses a method for producing propylene acrylic acid by a method of oxidation of the two-phase catalyst which uses only one reactor of the heat exchanger type of enclosure and tube in which each reaction tube is charged with a first phase catalyst and a second phase catalyst. In said method, each reaction tube in the reactor is first charged with a second phase catalyst which forms a second phase catalyst layer, then with aluminum oxide to cool the reaction gas which forms an oxide layer. aluminum in front of said second phase catalyst layer, and finally with a first phase catalyst to form the first phase catalyst layer in the aluminum oxide layer. The catalytic oxidation of two phases is directed by introducing a starting gas containing propylene in the reaction thus loaded in tubes, from the dome to the bottom.

Japanese Patent Publication No. 73674/1995 Bl discloses the use of a multi-tube reactor whose enclosure space is supplied with a partition plate in a method for producing propylene acrylic acid, but said publication does not teach any extensive particular.

According to our studies, it was found that there still remained a problem that had to be solved before industrially manufacturing acrylic acid from propylene following the method described in previous Patent Publication No. 21966/1979 A. The problem is caused by the loading of two types of oxidation catalysts that have different activity mechanisms in one and the same reactor. More specifically, the reaction tubes are inclined to be plugged with a component of the catalyst that sublimes towards the downstream direction, which originates from the first phase catalyst located upstream of the reaction gas and is entrained by the gas stream. of reaction (for example, when a molybdenum-containing oxidation catalyst is used as the first-stage catalyst, the molybdenum component was sublimed from the catalyst), and such high-boiling, side-producing substances produced terephthalic acid and the like. The clogging increases the pressure drop.

Thus, the present invention aims to solve the problems in conventional methods such as the above, and provides a method for producing propylene acrylic acid at high efficiency, through a two-phase reaction of catalytic oxidation using only one reactor.

Description of the invention.

The applicant has discovered that the above objective can be achieved by a method of the production of propylene acrylic acid by the method of oxidation of the two-phase catalyst using a reactor of shell heat exchanger and fixed bed type , comprising an envelope and a large number of reaction tubes provided vertically within the envelope, said envelope having a space divided into two parts of upper and lower spaces with a partition plate or plate, each of said two spaces being designed to allow the circulation of a heating medium independently of each other, and each of the reaction tubes being provided with a first phase catalyst layer and a second phase catalyst layer; said method characterized in that a layer of an inert substance is provided between the first phase catalyst layer and the second phase catalyst layer in each reaction tube, said layer of the inert substance having a gap ratio within a range specific and also finding the conditions that have a sufficient length to cool the gas of the reaction of the first phase catalyst layer at a convenient temperature for its introduction into the second catalyst layer and which is located in such a position that the catalyst The upper end of the first phase catalyst layer and the catalyst at the lower end of a second phase catalyst layer is not thermally affected by the partition plate.

Thus, according to the present invention, there is provided an acrylic acid production method, which uses a shell heat exchanger and fixed bed tube type reactor, comprising a shell and a large number of reaction tubes provided vertically within the shell. the envelope, said envelope having a space divided in two with a partition plate to provide an upper space and a lower space, each of said two spaces that are designed to allow the circulation of a heating medium substantially independently of one another and in each of the reaction tubes forming a first phase catalyst layer of a suitable catalyst to produce acrolein mainly through the oxidation of propylene and a second phase catalyst layer of a suitable catalyst to produce acrylic acid through the oxidation of acrolein; and comprising oxidizing propylene to the vapor phase with the catalyst of the first phase to form acrolein mainly, and subsequently oxidizing the acrolein to the vapor phase with the catalyst of the second phase to produce acrylic acid; the method characterized in that this vapor phase oxidation is conducted under the following conditions: in the lower part of each reaction tube, that is, the part of each reaction tube located within the lowest space in the shell, the first phase catalyst layer loaded with the catalyst of the first phase is provided , to the top of each reaction tube, that is, the part of each reaction tube located within the upper space in the shell, the second phase catalyst layer loaded with the catalyst of the second phase is provided, and a layer of the inert substance charged with an inert substance is provided between the first phase catalyst layer and the second phase catalyst layer; the gap ratio of said layer of the inert substance is between 40 and 99.5%; the layer of said inert substance has a sufficient length to cool the reaction gas of the first phase catalyst layer to a suitable temperature for its introduction into the second phase catalyst layer., and is located at such a position that the catalyst at the upper end of the first phase catalyst layer and the catalyst at the lower end of the second phase catalyst layer, are substantially free from the thermal influence of the partition plate, and a gaseous starting material containing propylene is introduced from the lower parts of the reaction tubes and the gas reaction passes through the reaction tubes as updrafts.

Next, the present invention is specifically explained, referring to the attached drawings.

Figure 1 schematically shows, as an example, an interchange type heat exchanger intern reactor and fixed bed tube, which is disclosed in the aforementioned Japanese Patent Publication No. 21966/1979 A, in which only one tube of reaction between many reaction tubes is indicated to present the remainder for convenience. As can be seen from Figure 1, the space of the envelope in the reactor is divided into the upper space and the lower space with a partition plate 11; in the upper part of each reaction tube 12 (that is, the part of each reaction tube placed within the upper space of the shell) a catalyst layer of the first phase 13 is provided; in the lower part of each reaction tube 12 (that is, the part of each reaction tube placed in the lower space of the shell) a catalyst layer of the second phase 14 is provided; and between said layer 13 of the catalyst of the first phase and the catalyst layer of the second phase 14, a layer of aluminum oxide (Alundum) is provided. Starting gas 16 is introduced from the upper part of the reactor and the gaseous reaction 17 is discharged from the bottom of the reactor.

Figure 2 schematically shows an example of an enclosed heat exchanger casing and fixed bed tube type reactor that is useful for the present invention, in which only one reaction tube between the many reaction tubes is shown to represent the rest of the tubes conveniently. As can be seen in Figure 2, the space of said envelope in the reactor of shell heat exchanger type and fixed bed tube, is divided in the upper space and the lower space with a partition plate 21, and a heating medium 28 can circulate through the upper space and the lower space sub tancely independently of one another. In each of the reaction tubes 22 a catalyst layer of the first phase 23 filled with catalyst of the first phase is provided, in said catalyst layer 23 of the first phase, an inert substance of layer 25 was filled with a substance provided inert, and additionally in this layer 25 inert substance, a second catalyst of the layer phase 24 was filled with a second catalyst of the phase provided. Since said first stage catalyst layer 23, the inert substance layer 25, likewise the inert substance layer 25 and the catalyst layer of the second phase 24, is normally in direct contact, if necessary such a member as a piece of wire can be put between these layers. Starting gas 26 is introduced from the bottom part of the reactor, and gaseous reaction 27 is discharged from the reactor dome.

Said construction of an envelope-type heat exchanger reactor and fixed bed tube is known per se (see Japanese Patent Publication No. 21966/79 A). In the present invention, the partition plate 21 can be arranged directly in those reaction tubes 22 by welding or the like. Whereas, in order to prevent the thermal distortion from occurring in the partition plate 21 or the reaction tubes 22, preferably a suitable gap is provided between the plate 21 and the tubes 22, within a range allowing the substantially independent circulation of a medium heat in the upper space and the lower space. Specifically, it is advisable to provide a gap of approximately 0.2 to 5 mm between the plate 21 and the tubes 22. Again, while the partition plate 21 can be arranged directly on the inner wall of the reactor by welding or by similar means, this can be arranged at the inner wall through a cylindrical installation plate (see Japanese Patent Publication No. 73674/1995 Bl).

In the shell type heat exchanger reactor and fixed bed tube, a heating element can be circulated through the two spaces substantially independently of one another, which allows easier control of the temperatures of the catalyst layers in the reaction tubes, corresponding to the respective spaces (ie, the temperature of the first phase catalyst layer 23 which is charged to the parts of the reaction tubes located within the lower space and that of the second phase catalyst layer 24 which is charged to the parts of the located reaction tubes within the upper space) within each of the temperature range suitable for the catalyst to exhibit the respective oxidation function, independently of one another.

The catalyst useful in the first phase according to the invention is not subject to any specific limitation, but any conventional oxidation catalyst used for the vapor phase oxidation of start-up gases containing propylene to produce acrolein can be used mainly. However, the second phase catalysts are not subject to any specific limitation, but any conventional oxidation catalyst used for the vapor phase oxidation of the gaseous reaction containing acrolein mainly to produce acrylic acid is used. Specific examples of those catalysts are as follows.

As the first phase catalyst, for example, those expressed by the formula: Moa Bi Fec Ad Be Cf Dg Ox (where Mo symbolizes molybdenum, Bi symbolizes bismuth, Fe symbolizes iron, A is at least one element selected from the group consisting of cobalt and nickel, B symbolizes at least one element selected from the group which consists of alkali metal, alkaline earth metal and thallium, C symbolizes at least one element selected from the group consisting of tungsten, silicon, aluminum, zirconium and titanium, D symbolizes at least one element selected from the group consisting of phosphorus, Tellurium, antimony, tin, cerium, lead, niobium, manganese, arsenic and zinc, and 0 symbolize oxygen, and, b, c, d, e, f, g and x, express the atomic proportions of Mo, Bi, Fe, A , B, C, D, and 0, respectively in which, when it is 12, b is 0.1-10, c is 0.1-20, d is 2.20, e is 0.001-10, f is 0-30, g is 0- 4, and x is a numerical value determined by the oxidized state of each of the elements) can be named.

As the second phase catalysts, for example, those expressed by the formula, Mo, Vb, Wc, Ad, Be, Cf, Dg, Ox (where Mo symbolizes molybdenum, V symbolizes vanadium, W symbolizes tungsten, A symbolizes at least one element selected from the group consisting of antimony, bismuth, chromium, niobium , phosphorus, lead, zinc and tin, B symbolizes at least one element selected from the group consisting of copper and iron, C symbolizes at least one element selected from the group consisting of alkali metal, alkaline metal and thallium, D symbolizes at least one element selected from the group consisting of silicon, aluminum, titanium, zirconium, yttrium, rhodium and cerium, and O symbolizes oxygen, and a, b, c, d, e, f, g and x express the proportions Atoms of Mo, V, W, A, B, C, D and 0, respectively, in which, when a is 1'2, b is 2-14, c is 0-12, d is 0-5, e is 0.0-6, f is 0-5, g is 0-10 and x is a numerical value determined by the oxidized phase of each of the elements) can be named.

In addition, this first phase catalyst and second phase catalyst constitute the first phase catalyst layer and the second phase catalyst layer and is not necessarily each a catalyst alone. For example, the plural first stage catalyst of different activity levels can be charged by the order of its level activity to form a first phase catalyst layer; or, a part of the catalyst can be diluted with an inert carrier or the like, to vary the level activity along the length of the direction of the catalyst layer (direction of gas flow). It is also applicable to the second phase catalyst.

The preferred temperature of the first phase catalyst layer 23 typically ranges from 300-380 ° C, and that the second phase catalyst layer 24 is typically from 250-350 ° C. The temperature difference between the first phase catalyst layer and the second phase catalyst layer 23 and 24 can be 10-110 ° C, preferably 30-80 ° C. It should be noted that the temperature of the first phase catalyst layer 23 and that of the second phase catalyst layer 24 according to the invention substantially corresponds to those of the heating medium 28 to the entrances in the spaces of the envelope (i.e. lower and upper space corresponding to the respective layers.

Therefore, the temperatures of the entrance of the heating medium 28 in the two enclosing spaces are determined in correspondence to the respective temperatures of the first phase catalyst layer and the second phase catalyst layer 23 and 24, what is set for be within the specific ranges above.

As an inert substance for forming the inert substance of layer 25 can be provided between the first phase catalyst layer 23 and the second phase catalyst layer 24, any of those having a hollow ratio within the specific range in this invention, As an inert substance for the reaction of acrolein containing gas from the first phase catalyst layer, and is capable of cooling said reaction gas to a temperature level convenient for the reaction to the second phase catalyst layer, it can be used .

The shape of such an inert substance is not critical, so long when it can be filled or it can be accommodated in the reaction tubes. For example, it can be granular, such as a Raschig ring, spherical, cylindrical, ring-forming, or it can be in the shapes of masses, rods, plates or wire. Of those, Raschig rings can be used conveniently. When granular or solid inert substances are used, their sizes are not necessarily uniform. Preferably, however, those in which the individual particles have a maximum diameter less than the internal diameter of the reaction tube and more than 1/10 of said internal diameter is used. When an inert substance formed from a rod is used, two or more such particles can be tied up for use. The rolling substances may be suitably curved or projected for use.

A layer of the inert substance according to the invention therefore includes, in addition to such layers formed by charged granular or solid inert substances, those formed by filling or touching the forming rod or laminate of the inert substances in the reaction tubes. For example, in addition, by touching or bending the inert substance in the form of a sheet, it will be necessary to provide a means by expediently holding the second phase catalyst layer immediately afterwards, like a wire mesh. The material of the inert substance is not critical again, typical examples include a-alumina, aluminum oxide, murita, carborundum, stainless steel, silicon carbide, steatite, earthenware, porcelain, iron and various ceramics.

Although it is not always necessary for an inert substance to constitute the layer of the inert substance, for example, a granular inert substance, it is uniformly loaded on top of the entire layer of the inert substance, a substantially uniform charge on top of the entire inert substance is preferred. by the effective cooling of the reaction gas. This statement also applies to the inert substance that has forms other than granules.

One of the actions and functions of the inert substance layer is to turn off the acroleí containing the reaction gas of the first phase catalyst layer to drop the temperature of the reaction gas at a suitable range for the reaction of the oxidation in the second phase catalyst layer. For this purpose, the layer of the inert substance needs to have a sufficient length to exhibit said action and function. In addition, when the first phase catalysts and the second phase catalysts are in direct contact with the partition plate through the reaction tube walls, their performance deteriorates under the influence of the directed heat of the plate. The situation of the layer of the inert substance, therefore, must be determined in such a way as to prevent such deterioration of the action.

Accordingly, accordingly, according to the invention, the layer of the inert substance must have a sufficient length to cool the first phase catalyst layer reaction gas to a suitable temperature level for its introduction into the second catalyst layer. phase, and such a position must be substantially arranged to prevent the thermal influence of the partition plate from affecting the catalyst at the upper end of the first phase catalyst layer (ie, the catalyst adjacent to the lower end of the substance layer). inert) and the catalyst at the lower end of the second phase catalyst layer (ie, the catalyst adjacent to the upper end of the layer of the inert substance).

More specifically, it is preferred that the length of the partition plate to the lower end of the layer of the inert substance be at least 30 mm, and that the length of the layer of the inert substance be sufficient to cool the gas of the reaction that enters the second phase catalyst layer of the layer of the inert substance (that is, the reaction gas at the entrance of the second phase catalyst layer) at a temperature no higher than the temperature of the entry of the heating medium into the upper space by more than 15 ° C.

Normally the distance between the partition plate and the upper end of the layer of the inert substance ranges from 200-700 mm, preferably from 250-600 mm, and that between the partition plate and the lower end of the layer. the inert substance have ranges ranging from 30-300 mm, preferably 50-200 mm.

Other actions and functions of the inert substance layer are to prevent an increase in pressure drop during the gas passage of the reaction of the first phase reaction zone, which is caused by clogging of the reaction tubes with impurities that they are contained in the reaction gas, for example, the molybdenum component sublimed from the first phase catalyst and the high boiling substances produced as the terephthalic acid; and also to prevent these impurities from entering directly into the second phase catalyst layer to deteriorate the last caking action. These actions and functions are reinforced when the gap ratio of the inert substance decreases. Whereas, the excessively low gap ratio increases pressure loss and is indelible.

According to the present invention, the void ratio of the layer of the inert substance is set to be 40-99.5%, preferably 45-99%. The term, "the gap ratio" as used here is defined by the formula below.

Ratio of voids (volume of true volume layer inert substance) inert) X100 volume of inert substance layer In addition, the term, "true volume", as used herein means, taking a ring for example, the solid volume not included in the central space thereof.

When the gap ratio is less than 40%, the pressure loss increases. Whereas, when it is higher than 99.5%, the function of both to entrap the impurities and to cool the reaction gas are reduced to produce undesirable results.

According to the present invention, the gaseous starting material containing propylene is introduced from a lower part of each reaction tube and the reaction gas is allowed to pass as an upward current. With what is made possible, as compared to the known methods of introducing propylene containing a starting gas over the reaction tubes and the reaction gas is passed as a downward current, to reduce the contamination of the second catalyst. phase with, for example, component of sublimating molybdenum of the first stage catalyst and high boiling substances such as terephthalic acid, and the resulting deterioration in performance of the second phase catalyst and increase in pressure loss caused by the blockage of the tubes the reaction can be decreased.

According to the present invention, the heating medium is preferably allowed to have upward flow from a lower part, or in the lower space exclusively from the two spaces of the enclosure or in both of the upper and lower spaces. To provide a heating medium as an updraft, the entrance of the heating medium is provided to a lower part of said space or spaces, and the outlet, to an upper part of the space or spaces, and the heating medium is circulated with a heating device. the circulation of heating element installed outside the reactor. The heating medium is allowed to flow at least in the space of the lower envelope according to the present invention., because when the heating medium is allowed a downward flow in the space of the lower envelope, a space without the heating medium is formed in the area to an upper part of the lower space near the reaction tubes, causing a drop in temperature to an inner area of the corresponding reaction tubes, which produces in excess occurrence substantially cooled in part to give rise to such problems as clogging of the reaction tubes and subsequent increase in pressure drop.

The number of entries for the calorific medium is not critical, since it can be one or more than one, and can be determined optionally for individual occasions. Similarly, the input position (s) can be adequately determined, so long as it avoids the formation of spaces without heating means and the upward flow of the heating medium or a downflow can take hold of that.

Said "the temperature of the entrance of a heating medium" according to the invention means, with respect to the space of the lower enclosure, the temperature of the passage of the heating element through the entrance located to the lower end of the space because the flow of the heating element is limited. medium calorific to the upward direction. With respect to the headspace, it means the temperature of the passage of the heating element through the inlet located to the lower end of said space when the heating element forms an upward flow, and the inlet located to the upper end when the heating element forms a downward flow .

As mentioned above, according to the present invention, the propylene containing a start gas is introduced from the lower ends of the reaction tubes into each of the first phase catalyst layers to direct the vapor phase oxidation of propylene , and consecutively the reaction of the acrolein-containing gas is mainly introduced into the second phase catalyst layers in the reaction tubes to direct the vapor phase oxidation of acrolein, in that the object that the acrylic acid is produced. On that occasion, the starting gas composition and the reaction conditions in the first phase catalyst layer and second phase catalyst layer are not subject to critical limitations, but a composition and the reaction conditions conventionally employed for this type of reactions can be adopted.

According to the present invention, an acrylic acid can be produced at a high propylene efficiency by the two-phase catalyst oxidation method, using only one reactor. Accordingly, it was compared to conventional methods of conducting oxidation of two-phase catalyst using two reactors, means such as pipe conduction and heat exchangers are unnecessarily put to industrial advantage.

Again according to the present invention, problems such as clogging the central parts of the reaction tubes and the subsequent increase in pressure loss can be solved by the provision of a previously described layer of an inert substance. In addition, because the reaction gas of the first phase catalyst layer that is inclined to induce post-reaction as an acrolein autoxidation can be sufficiently cooled within a short time under a suitable temperature range for the reaction in the catalyst layer of the catalyst. second phase, post-reaction can be effectively prevented in the present invention. According to the invention, a fall in performance due to excessive oxidation of acrolein can thus be prevented, allowing acrylic acid to produce the high yield of the object. Still further, the invention prevents a clandestine reaction taking place under severe excessive oxidation thus, and safe operation is ensured.

According to the invention, in addition, a starting gas containing propylene is introduced from the lower parts of the reaction tubes and the reaction gas is passed as a stream, whereby the contamination of the second phase catalyst with molybdenum component which is sublimated from the first phase catalyst layer or with such high boiling product as terephthalic acid and can be prevented. Consequently, deterioration in the performance of the second phase catalyst due to contamination, clogging the reaction tubes and increase in pressure loss can also be reduced.

Again according to the invention, a heating medium is allowed upward flow in the space of the lower enclosure or, in both the spaces of the lower and upper enclosure, the formation of spaces without the heating means can be prevented, which enables the control of substantially uniform temperature over the entire length of the first phase catalyst layer or, that of the first phase catalyst layer and second phase catalyst layer. Thus, such a problem as a drop in acrylic acid yield due to the occurrence of areas of the supernatant in the reaction tubes can be solved.

Then the invention will be explained more concretely, referring to the working examples.

E j empl o 1 [First stage catalyst] In 150 ml of water under heating and stirring, 106.2 g of ammonium molybdate and 32.4 g of para-tungsten ammonium were dissolved. Separately, 70.0 g of cobalt nitrate was dissolved in 20 ml of distilled water, 24.3 g of ferric nitrate, in 20 ml of distilled water, 29.2 g of bismuth nitrate, in 30 ml of distilled water. which had been made acid by the addition of 6 ml of concentrated nitric acid. These three types of nitrate solutions were mixed and added dropwise to the first ammonium salt solution. Consecutively, a solution formed by dissolving 24.4 g of silica containing 20% by weight of silicon dioxide and 0.202 g of potassium hydroxide in 15 ml of distilled water was added. The suspension thus obtained was heated under stirring to evaporate water and the residue was formed and calcined at 450 ° C for six hours while the air passed through the system to prepare a catalyst. The metallic composition of this catalyst was as follows, as expressed by atomic proportions: Co4 Fe? Bii W2 Moio Si? .35 K0.o6 * [Second phase catalyst] In 2500 ml of heated and stirred water, 350 g of ammonium paramolybdate, 106.3 g of ammonium metavanadate and 44.6 g of ammonium paratungs were dissolved. Separately, 87.8 g of copper nitrate was dissolved in 750 ml of heated and stirred water, and in said solution 5.9 g of cuprous oxide was added. Thus two liquids were formed, mixed and placed in a porcelain vaporizer in a hot water bath. In the additional 1000 ml vaporizer of the 3-5 mm diameter spherical carrier made of α-alumina was added, and was vaporized until dried under stirring, followed by 6 hours of calcination at 400 ° C. Thus a catalyst was obtained in the carrier support. The metallic composition of this catalyst was as follows, as expressed by the atomic ratio: MO12 V5.5 Wi Cu2, [Reaction A reactor formed of stainless steel reaction tubes of 6,000 mm in total length and 25 mm in internal diameter, and a shell covering the reaction tubes was used. A 50 mm thick partition plate was provided at a position of 3000 mm from the bottom of the enclosure to divide the enclosure space in the upper space and in the lower space and a heating medium was flowed upwards in both the upper space and the lower space.

Each reaction tube is charged with, from bottom to top, a first phase catalyst, an inert substance and a second phase catalyst in the declared order, at the respective lengths of 2,800 mm, 700 mm and 2,500 mm. The inert substance was a Raschig stainless steel ring of about 8 mm in outside diameter, and the void ratio of the inert substance layer was 98.5%.

A starting gas composed of 6% by volume of propylene, 60% by volume of air and 34% by volume of steam was introduced from the lower ends of the reaction tubes and subjected to the oxidation reactions under the following conditions (flow rate and temperatures of the catalyst layer). < Flow rate > The space velocity (SV) through the first phase catalyst layer was set to be 1500 hr "1. < Catalyst layer temperature > The temperature of the first phase catalyst layer (the inlet temperature of the heating medium in the lower space): 325 ° C.

The temperature of the second phase catalyst layer (the heat input temperature in the upper space): 260 ° C.

The propylene conversions and the acrylic acid yields in the reaction of the initial phase and after 1,000 hours of reaction are shown in Table 1, together with the temperatures of the reaction gas at the entrance of the second catalyst layer. phase.

The reaction was continuously stabilized for 4,000 hours without any problem. The pressure drop in the reaction tubes was 6,000 mm (water column) in the initial phase which was 6,200 mm after 4,000 hours of operation, the increase was only 200 mm.

E jmplo 2 Example 1 was repeated only that the Raschig stainless steel ring of 6 mm in outside diameter was used as the inert substance and the void ratio of the layer of the inert substance became 85%.

The propylene conversions and the acrylic acid yields in the initial reaction phase and after 1,000 hours the reaction is shown in Table 1, with the reaction gas temperatures at the entry into the second phase catalyst layer.

The reaction was continuously stabilized for 4,000 hours without any problem. The pressure drop in the reaction tubes was 6.050 mm (water column) in the initial phase, which was 6.300 mm after 4,000 reaction hours, the increase was only 250 mm. 3 Example 1 was repeated only that porcelain beads of 8 mm in outside diameter were used as the inert substance and the ratio of empty spaces of the inert substance was made from Four. Five% .

The propylene conversions and the acrylic acid yields in the initial reaction phase and after 1,000 hours of reaction are shown in Table 1, with the reaction gas temperatures at the entry into the second phase catalyst layer.

The reaction was continuously stabilized for 4,000 hours without any problem. The loss of pressure in the reaction tubes was 6,100 mm (water column) in the initial phase which was 6,700 mm after 4,000 reaction hours.

Example 4 Example 1 was repeated only that the length of the layer of the inert substance was reduced to 450 mm.

The reaction was continuously stabilized for 4,000 hours Example 5 Example 1 was repeated only that the length of the layer of the inert substance was reduced to 500 mm.

The reaction stabilized continually for 4,000 hours Example 1 Comparative Example 1 was repeated only that the 4 mm outer diameter porcelain beads were used as the inert substance and the void ratio of the inert substance layer became 35%. However, the pressure drop in the 6200 mm reaction tubes (water column) to the initial reaction phase rose to 8,000 mm after 4000 reaction hours, and the continuation of the reaction over a prolonged period was It made it difficult. After completion of the reaction, inside the reaction tubes was examined and the accumulation of crystalline catalyst component and deposit of the solid in the layer of the inert substance was recognized, which was the cause for the increase in the fall of Pressure.

Example 2 Comparative The reaction under the identical conditions with those of Example 1 was attempted, only that the lengths of the first phase catalyst layer, the inert substance and the second phase catalyst layer were changed to 3,000 mm, 200 mm and 2,800 mm, respectively. The reaction, however, was inoperable due to the abnormal temperature rise in the second phase catalyst layer that occurred immediately after the initiation of the reaction.

Example 3 Comparative The reaction of Example 1 was repeated only that the flow direction of the heat medium in the upper space and the lower space was made downward. However, the pressure drop in the reaction tubes of 6,000 mm (water column) in the initial reaction phase was ?? go to 7,800 mm after 4,000 reaction hours.

TABLE 1 It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.

Having described the invention as above, the content of the following is claimed as property.

Claims

1. An acrylic acid production method, which uses a shell inter-heat exchanger type reactor and fixed bed or bed tube comprising a shell and a large number of reaction tubes provided vertically within the shell, the shell has a space divided in two with a partition plate to provide a top space and a bottom space, each of the two spaces are designed to allow the circulation of a heating means substantially independently of each other and in each of the tubes of the reaction forming a first phase catalyst layer of a catalyst suitable for producing acrolein mainly through the oxidation of propylene and a second phase catalyst layer of a catalyst suitable for producing acrylic acid through the oxidation of acrolein; which comprises oxidizing propylene in the vapor phase with the first phase catalyst to form acrolein mainly, and successively oxidizing the acrolein in the vapor phase with the second phase catalyst to produce acrylic acid; the method characterized in that this vapor phase oxidation is carried out under the following conditions: in the lower part of each reaction tube, that is, the part of each reaction tube located within the lowest space in the shell, is provided the first stage catalyst layer loaded with the first phase catalyst, in the upper part of each reaction tube, that is, the part of each reaction tube located within the upper space in the shell, provides the second phase catalyst layer loaded with the second phase catalyst, and a layer of the Inert substance charged with an inert substance is provided between the first phase catalyst layer and the second phase catalyst layer; the gap ratio of the inert substance layer is between 40 and 99.5%; the layer of the inert substance has a sufficient length to cool the reaction gas of the first phase catalyst layer at a convenient temperature for its introduction into the second phase catalyst layer, and is located at such a position that the catalyst in the upper end of the first phase catalyst layer and the catalyst at the lower end of the second phase catalyst layer are substantially free from the thermal influence of the partition plate, and a gaseous starting material containing propylene is introduced. from, the lower parts of the reaction tubes and the reaction gas passes through the reaction tubes as updrafts.

2. The method according to claim 1, characterized in that the heating means is left in ascending flow in at least the lower space of two spaces.

3. The method according to claim 1 or 2, characterized in that the length of the partition plate at the lower end of the layer of the inert substance is at least 30 mm, and the length of the layer of the inert substance is sufficient to cool the reaction gas entering the second phase catalyst layer through the layer of the inert substance at a temperature above the temperature of the entrance of the heating medium into the upper space by more than 15 ° C.