JP5171031B2 - Reactor for catalytic gas phase oxidation and method for producing acrylic acid using the same - Google Patents

Description

  The present invention relates to a fixed-bed multitubular heat exchange reactor for performing catalytic gas phase oxidation, and more particularly, to efficiently produce acrylic acid by catalytic vapor phase oxidation of propylene using one reactor. The present invention relates to a fixed-bed multitubular heat exchange reactor used.

  The production of acrylic acid by two-stage catalytic gas phase oxidation of propylene is widely performed industrially. This method consists of a pre-stage reaction in which propylene is contacted by vapor phase oxidation with acrolein and a post-stage reaction in which acrolein is contacted with acrylic acid by vapor phase oxidation.

  In carrying out such a reaction, conventionally, two methods, roughly divided into a method using two reactors and a method using one reactor, have been proposed.

  As a method using two reactors, for example, in Patent Document 1 and Patent Document 2, two reactors, a first-stage reactor filled with a first-stage catalyst suitable for a first-stage reaction and a second-stage reactor filled with a second-stage catalyst suitable for a second-stage reaction, are disclosed. Using a reactor, a reaction gas mainly containing acrolein from the former reactor and an inert gas such as recycle gas, oxygen, nitrogen or water vapor are introduced into the latter reactor to further oxidize the acrolein to obtain acrylic acid. A method of manufacturing is disclosed.

  On the other hand, as a method for producing acrylic acid from propylene in one reactor, for example, in Patent Document 3, Patent Document 4 or Patent Document 5, the shell side is divided into two reaction zones by a partition plate, and each reaction is performed. The heat medium can be circulated independently on the shell side of the belt, the reaction tube of one reaction zone is filled with a pre-stage catalyst suitable for the pre-stage reaction, and the post-stage suitable for the post-stage reaction is filled in the other reaction zone. A process for producing acrylic acid from propylene using a single reactor packed with catalyst is disclosed.

  Patent Document 6 discloses a technique for increasing the efficiency of removing generated heat due to an oxidation reaction by a heat medium by attaching a baffle plate or the like in order to regulate the flow of the heat medium in each shell. .

  Patent Document 7 discloses a technique for fixing a partition plate installed in a shell to a shell inner wall through a cylindrical mounting plate, which may be welding.

JP-A-53-15314 JP-A-55-102536 JP 54-19479 A JP 54-21966 A Japanese Patent Laid-Open No. 11-130722 Japanese Patent Laid-Open No. 2001-137689 Japanese Patent Publication No. 7-73684

  However, when the two reactors described above are used, the equipment such as the reactor and piping is expensive, the installation floor area is large, and the apparatus is large. Furthermore, since the gas residence time in the piping until the gas mainly containing acrolein from the former reactor is introduced into the latter reactor is relatively long, acrolein is likely to be auto-oxidized, and the carbides associated therewith are likely to accumulate. There is a problem. Further, the catalyst is contaminated by the carbides and the like, and as a result, performance degradation and phenomena such as blocking of a reaction agent and pressure loss are likely to occur in a relatively short period.

  In addition, when one reactor described above is used, it is necessary to previously include an oxygen amount sufficient to be consumed in both the first-stage reaction and the second-stage reaction in the source gas of the first-stage reaction. It is not possible to optimize the gas composition at each. Therefore, even if it is attempted to increase the raw material propylene concentration in order to improve productivity, it is necessary to include the amount of oxygen necessary for the second-stage reaction in the first-stage reaction raw material gas gas. The effect on the catalyst performance increases. In addition, there is a problem that there is a limit to increasing the concentration of propylene from the relationship of the explosion range.

  Thus, an object of the present invention is to solve the problems of the prior art as described above, and in the production of acrylic acid from propylene, a new reactor that can change the gas composition in the subsequent reaction using one reactor. Is to provide.

  When producing acrylic acid by a catalytic oxidation reaction of propylene, the present inventors have two heat exchange type multi-tubular reaction zones in one reactor and an external space between the two reaction zones. The present inventors have found that the above problems can be achieved by using a reactor in which a space having a mechanism for introducing a gaseous substance from is installed, and the present invention has been completed.

  Here, the partitioned heat exchange type multi-tubular reaction zone has a plurality of reaction tubes in a shell partitioned by two upper and lower tube plates. While supplying and carrying out catalytic vapor phase oxidation, a heat medium is circulated on the shell side to remove reaction heat.

  That is, the present invention is a fixed-bed multitubular reactor used for catalytic gas phase oxidation and the like, and a reactor having the following configuration and a method for producing acrylic acid using such a reactor. is there.

  (1) One reactor is provided with a space section having two partitioned reaction zones and a mechanism for introducing a gaseous substance from the outside between the two reaction zones.

  (2) Further, a mechanism for mixing the first reaction zone outlet gas and the external additional gas is installed in the space.

  (3) The space is filled with a substance that is substantially inert to the reaction gas.

  (4) Furthermore, a gas temperature adjusting unit for adjusting the reaction gas temperature is installed at the inlet of the second reaction zone.

  (5) A method for producing acrylic acid by catalytic gas phase oxidation of propylene using any of the reactors described above.

  In the present invention, by adopting the above configuration, the problems of the conventional reactor can be solved, and when producing acrylic acid from propylene, it is possible to use one reactor and change the gas composition in the subsequent reaction. And a new reactor suitable for increasing the concentration of propylene could be provided.

  Further, by using the reactor, it is difficult to deposit carbides even during a long-term operation, and as a result, a more efficient method for producing acrylic acid could be provided.

  FIG. 3 shows one embodiment of the reactor of the present invention. The production of acrylic acid by catalytic gas phase oxidation of propylene using the reactor of FIG. 3 will be described below.

  In FIG. 3, the reaction raw material gas is supplied from above the reactor, but the flow direction of the reaction raw material gas is not particularly limited and can be appropriately selected according to the situation.

  When raw material gas is supplied from above the reactor, the reactor is filled with a catalyst suitable for converting propylene into acrolein (hereinafter sometimes abbreviated as “pre-stage catalyst”) in the reaction tube in order from the top. The first reaction zone, a space provided with a mechanism for introducing a gaseous substance from the outside of the reactor, and a catalyst suitable for converting acrolein into acrylic acid in the reaction tube (hereinafter abbreviated as “second-stage catalyst”) A reactor equipped with a second reaction zone filled with (is) is used.

  The raw material gas containing propylene and molecular oxygen is supplied from the upper part of the reactor to the first reaction zone, where it is converted into acrolein and the reaction gas exiting from the first reaction zone flows into the space. Here, it is mixed with an additional gas (for example, recycle gas or air) separately supplied from the outside and flows into the second reaction zone where it is converted into acrylic acid and flows out of the reactor.

  Here, as the pre-stage catalyst, an oxidation catalyst generally used for producing acrolein by gas-phase oxidation of a raw material gas containing propylene can be used. Similarly, the latter catalyst is not particularly limited, and is an oxidation generally used for producing acrylic acid by gas phase oxidation of a reaction gas mainly containing acrolein obtained by the former catalyst by the two-stage catalytic gas phase oxidation method. A catalyst can be used.

Specifically, as the pre-stage catalyst, for example, the following general formula (I):
Mo _a Bi _b Fe _c X1 _d X2 _e X3 _f X4 _g O _x (I)
(Where Mo is molybdenum, Bi is bismuth, Fe is iron, X1 is at least one element selected from cobalt and nickel, X2 is at least one element selected from alkali metals, alkaline earth metals and thallium, X3 is at least one element selected from tungsten, silicon, aluminum, zirconium and titanium, X4 is at least one element selected from phosphorus, tellurium, antimony, tin, cerium, lead, niobium, manganese, arsenic and zinc, O represents oxygen, and a, b, c, d, e, f, g and x represent atomic ratios of Mo, Bi, Fe, X1, X2, X3, X4 and O, respectively, when a = 12. , B = 0.1 to 10, c = 0.1 to 20, d = 2 to 20, e = 0.001 to 10, f = 0 to 30, g = 0 to 4, and x is each The oxide catalyst is a numerical value determined by the oxidation state of the element.

Moreover, as a back | latter stage catalyst, the following general formula (II):
_{Mo h V i W j Y1 k} Y2 l Y3 m Y4 n O y (II)
(Where Mo is molybdenum, V is vanadium, W is tungsten, Y1 is at least one element selected from antimony, bismuth, chromium, niobium, phosphorus, lead, zinc and tin, and Y2 is selected from copper and iron. At least one element, Y3 is at least one element selected from alkali metals, alkaline earth metals and thallium; Y4 is at least one element selected from silicon, aluminum, titanium, zirconium, yttrium, rhodium and cerium; O represents oxygen, and h, i, j, k, l, m, n, and y represent the atomic ratios of Mo, V, W, Y1, Y2, Y3, Y4, and O, respectively, when h = 12. I = 2 to 14, j = 0 to 12, k = 0 to 5, l = 0.01 to 6, m = 0 to 5, n = 0 to 10, and y depends on the oxidation state of each element. And an oxidation catalyst represented by the formula (1).

  There is no restriction | limiting in particular also about the shape, A thing of well-known shapes, such as spherical shape, cylinder shape, and ring shape, is used.

  The catalyst charged in the first reaction zone and the second reaction zone need not be a single catalyst. For example, in the first reaction zone, a plurality of types of pre-stage catalysts having different activities are used and activated. The catalyst may be filled in a different order, or a part of the catalyst may be diluted with an inert carrier. The same applies to the second reaction zone.

  A suitable temperature in the first reaction zone is usually from 300 to 380 ° C, and a suitable temperature in the second reaction zone is usually from 250 to 350 ° C. The difference between the inlet temperature and the outlet temperature of the heat medium in the first reaction zone and the second reaction zone is 10 ° C. or less, preferably 5 ° C. or less. In the present invention, the temperature in the first reaction zone and the temperature in the second reaction zone substantially correspond to the heat medium inlet temperature in each reaction zone, and the heat medium inlet temperature is within the above range. It is determined according to the set temperature of each of the first reaction zone and the second reaction zone set in (1).

  In this way, in order to control the temperature of each reaction zone, the heat medium whose temperature is controlled by the heat medium circulation device attached to the outside of the reactor may be separately circulated to the shell of each reaction zone. The direction of circulation is not particularly limited. For example, as the circulation direction of each heat medium, in FIG. 3, both the first reaction zone and the second reaction zone are circulated from below to above, but in the opposite direction, or in the first reaction zone, from above to below, In the second reaction zone, it can be appropriately selected such that the circulation direction is from below to above or vice versa.

  At this time, in order to regulate the flow of the heat medium in each shell, for example, a baffle plate or the like as described in JP-A-2001-137789 is attached, thereby removing the heat generated by the oxidation reaction by the heat medium. Is preferable.

  Furthermore, a partition plate can be installed in the shell of each reaction zone, each reaction zone itself can be divided into two or more, a heat medium can be circulated separately, and the temperature can be controlled separately. In that case, the partition plate may be directly fixed to the reaction tube by welding or the like, but in order to prevent thermal distortion in the partition plate or the reaction tube, the heat medium can be circulated substantially independently. In the range, an appropriate gap may be provided between the partition plate and the reaction tube.

  Specifically, the interval between the partition plate and the reaction tube is preferably about 0.2 to 5 mm. The partition plate may be directly fixed to the inner wall of the reactor by welding or the like, but may be fixed to the inner wall via a cylindrical mounting plate as described in Japanese Patent Publication No. 7-73684.

  The gaseous substance added from the outside of the reactor to the space between the first reaction zone and the second reaction zone is not particularly limited as long as it can be adjusted to a desired gas composition in the second reaction zone. , Air, oxygen, nitrogen, steam, waste gas (recycle gas), and a mixed gas thereof.

According to the present invention, if a mechanism for efficiently mixing the first reaction zone outlet gas and the additional gaseous substance is installed in the space, the capacity of the space can be further reduced and the reactor can be downsized. This is preferable because it is possible. Although it does not specifically limit as a mixing mechanism, For example, the following mechanism etc. are mentioned.
(A) A method in which a large number of outlets for additional gaseous substances are provided to increase the contact area and mix (FIG. 5B).
(A) A method in which an additional gaseous substance is introduced into the reactor in an oblique direction and mixed by a vortex flow (FIG. 5C). For example, the additional gaseous substance may be introduced in a horizontal oblique direction with respect to the reactor.
(C) A method of mixing by attaching a constriction to the space between the first reaction zone and the second reaction zone, adding a gaseous substance there, and attaching a dispersion plate provided thereunder (FIG. 6) .

  In the present invention, the space can be filled with a substance that is substantially inert to the reaction gas.

  There are no particular restrictions on the substance that is substantially inert to the reaction gas to be filled, and examples include α-alumina, alundum, mullite, carborundum, stainless steel, silicon carbide, steatite, ceramics, porcelain, iron, and various ceramics. Can be mentioned. The shape is not particularly limited as long as there is no significant increase in pressure loss due to the inert substance itself. In addition to granular shapes such as Raschig rings, spheres, cylinders, rings, etc., lumps, rods, plates, gold A net-like shape can also be mentioned.

  The first reaction zone outlet gas has a relatively high temperature, and acrolein contained as a main component tends to cause a post-reaction such as auto-oxidation. Filling the space with such an inert substance shortens the gas residence time in the space, which is effective in preventing acrolein autooxidation. Preferably, the filling amount of the inert substance is set so that the gas residence time in the space is within 6 seconds.

  By filling with such an inert substance, molybdenum components scattered from the catalyst layer filled in the first reaction zone, high-boiling substances such as terephthalic acid which is a by-product in the first reaction, and acrolein Contamination of the catalyst charged in the second reaction zone due to carbides accompanying auto-oxidation, as well as performance degradation, and blockage of the space and increase in pressure loss can be further reduced.

  In the present invention, in order to cool or heat the mixed gas of the first reaction zone outlet gas and the additional gaseous substance to a temperature range suitable for the reaction in the second reaction zone, the space portion and the second reaction zone are used. It is preferable to provide a gas temperature adjusting unit between the two.

  By this gas temperature control unit, the first reaction zone outlet gas can be sufficiently cooled in a short time, and post-reactions such as acrolein auto-oxidation can be suppressed.

  On the other hand, if the inlet gas to the second reaction zone is excessively cooled due to the addition of gas from the outside, sufficient catalytic activity cannot be obtained in the second reaction zone. This gas temperature control unit can be heated to the temperature necessary for the second reaction sufficiently in a short time.

  The structure of the gas temperature control unit is not particularly limited, and examples thereof include a structure in which a fin tube meanders in the space, or a plurality of tubes through which a reaction gas flows and a shell through which a heat medium flows. In this case, the reaction gas flow pipe is not filled with anything and may be empty, but in order to facilitate heat exchange between the heat medium and the reaction gas, the reaction gas flow pipe is reacted. Is preferably filled with a substantially inert substance.

  There is no restriction | limiting in particular as an inert substance with which it fills, (alpha)-alumina, alundum, mullite, carborundum, stainless steel, silicon carbide, a steatite, earthenware, porcelain, iron, various ceramics, etc. are mentioned. The shape is not particularly limited as long as there is no significant increase in pressure loss due to the inert substance itself. In addition to granular shapes such as Raschig rings, spheres, cylinders, rings, etc., lumps, rods, plates, gold A net-like shape can also be mentioned.

  The temperature control in the gas temperature control unit can be performed by circulating the heat medium independently of each reaction zone, or by circulating the heat medium in the first reaction zone or the second reaction zone.

  When the reaction is performed, when the gas is used as a preheating layer for cooling the outlet gas of the first reaction zone and / or controlling the temperature of the reaction gas in the second reaction zone, It is possible to control the temperature of the gas temperature adjusting unit by circulating the medium or circulating the heating medium before entering the second reaction zone or the heating medium that has come out of the second reaction zone to the gas temperature adjusting unit.

  On the other hand, by reducing the residence time of gas in the space according to the present invention and adjusting the gas concentration by introducing additional gas, in the production of acrylic acid by propylene oxidation over a long period under high load conditions, acrolein The generation of carbides by high-boiling substances such as auto-oxidation and terephthalic acid can be greatly improved. However, in the production over a long period of time, if the first reaction zone outlet gas is cooled to fill the catalyst at the second reaction zone inlet, or the space or gas temperature control portion with an inert substance, the gas is charged. On the other hand, not a few carbides are generated on the inert material, which can cause clogging and increased pressure loss.

  For the carbide generated on the catalyst and inert substance at the inlet of the second reaction zone, the catalyst and inert substance at the inlet of the second reaction zone are preferably added periodically, preferably at a frequency of once / year. It can be replaced or burned off by aeration with an oxygen-containing gas flowing at high temperatures.

  In carrying out such aeration, the second stage reaction zone is usually 350 ° C. or less, preferably 330 ° C. or less, more preferably because the latter catalyst causes deterioration of the catalyst performance by contacting the oxygen-containing gas at a high temperature. Is preferably maintained at 320 ° C. or lower, and only the first reaction zone and / or the gas temperature controller is set at a high temperature of 320 ° C. or higher. In carrying out the operation, the heat medium is circulated independently in the gas temperature control unit as described above, or the heat medium before entering the first reaction zone or the heat medium that has exited from the first reaction zone is circulated at a relatively high temperature. You can also.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. Hereinafter, for convenience, “parts by mass” may be simply referred to as “parts”.
<Example 1>
[Preparation of catalyst 1]
While heating and stirring 1000 parts of distilled water, 385.2 parts of ammonium molybdate and 39.3 parts of ammonium paratungstate were dissolved (solution A). Separately, 264.6 parts of cobalt nitrate was dissolved in 140 parts of distilled water (Liquid B), and 80.8 parts of ferric nitrate was dissolved in 80 parts of distilled water (Liquid C), and further 100 parts of distilled water. 105.8 parts of bismuth nitrate was dissolved in a solution made acidic by adding 20 parts by volume of nitric acid (60%) to the solution (D solution). The three types of nitrate solutions (B, C, and D solutions) were added dropwise to the A solution. Subsequently, a solution prepared by dissolving 0.469 parts of potassium hydroxide in 30 parts of distilled water was added. The suspension thus obtained was heated, stirred and evaporated, and then molded into an outer diameter of 8 mm, an inner diameter of 3 mm, and a length of 7 mm, and calcined at 460 ° C. for 8 hours under air flow to prepare a catalyst. The metal composition excluding oxygen of this catalyst was as follows in terms of atomic ratio.
Mo ₁₂ Bi _1.2 Fe _1.1 Co _5.0 K _0.05 W _0.8
[Preparation of pre-stage catalyst 2]
The catalyst was prepared in the same manner as the pre-catalyst 1 except that the outer diameter was 6 mm, the inner diameter was 2 mm, and the length was 6 mm.
[Preparation of latter catalyst 1]
While heating and stirring 2000 parts of distilled water, 365.4 parts of ammonium paramolybdate, 100.9 parts of ammonium metavanadate and 55.9 parts of ammonium paratungstate were dissolved therein. Separately, 83.3 parts of copper nitrate was dissolved in 400 parts of distilled water while heating and stirring. After mixing the obtained two liquids, put them in a magnetic evaporator on a hot water bath, add 1000 parts by volume of a spherical carrier made of α-alumina with an average particle diameter of 8 mm, and evaporate to dryness while stirring. Then, the catalyst was prepared by calcining at 400 ° C. for 6 hours in an air atmosphere. The metal composition excluding oxygen of this catalyst was as follows in terms of atomic ratio.
Mo ₁₂ V ₅ W _1.2 Cu ₂
[Preparation of latter stage catalyst 2]
It was prepared in the same manner as the latter catalyst 1 except that a spherical carrier having an average particle diameter of 5 mm was used.
[Reactor and oxidation reaction]
In order from the top, the first reaction zone (24 SUS reaction tubes with a length of 3000 mm and an inner diameter of 25 mm), the space (1500 mm above the second reaction zone upper tube plate with a length of 1500 mm), perpendicular to the reactor A reactor having a 400 mm inner diameter provided with a second reaction zone (24 SUS reaction tubes having a length of 3000 mm and an inner diameter of 25 mm) was used. (See FIG. 3 and FIG. 5 (a))
The first reaction zone is filled with the front catalyst 1 from the gas inlet side to a length of 800 mm and the front catalyst 2 to a length of 2200 mm, and the second reaction zone is filled with the rear catalyst 1 from the gas inlet side to a length of 700 mm, The latter stage catalyst 2 was filled to a length of 2300 mm.

The heat medium was allowed to flow from below to above in the first reaction zone, the gas temperature control unit, and the second reaction zone. A raw material gas having the following composition was introduced from above the reactor to carry out an oxidation reaction under the following conditions.
<Raw gas composition>
12% by volume of propylene, 15% by volume of oxygen, 9% by volume of water vapor, and 64% by volume of inert gas such as nitrogen.
<Air volume>
A gas having the above composition was supplied at 47.7 m ³ / Hr.
<Additional gas>
Air is supplied to the space at 13.6 m ³ / Hr.
<Catalyst layer temperature>
First reaction zone temperature (heat medium inlet temperature in the first reaction zone): 320 ° C.
Second reaction zone temperature (heat medium inlet temperature in the second reaction zone): 265 ° C
<Performance evaluation>
Table 1 shows the propylene conversion rate and acrylic acid yield after 48 hours and 4000 hours after the start of the reaction, and the pressure loss increase from the initial stage after 4000 hours.

Further, when the state after 4000 hours was confirmed, precipitation of carbide was observed from the entrance of the catalyst in the second reaction zone to 30 mm.
<Aeration>
A mixed gas of 12 volume% oxygen, 50 volume% water vapor and 38 volume% inert gas such as nitrogen was supplied at 21.2 m ³ / Hr. Flowed for 24 hours at a first reaction zone temperature of 350 ° C and a second reaction zone temperature of 320 ° C.
When aeration was carried out under the above conditions, the removal of carbide was confirmed without a rapid increase in the catalyst layer temperature, and the pressure loss also returned at the start of the reaction. Table 1 shows the performance evaluation after the treatment.
<Example 2>
The reaction was carried out under the same conditions as in Example 1 except that the additional gas introduction tube was tangential to the reactor. The results are shown in Table 1. (See FIG. 3 and FIG. 5 (c))
When the state after 4000 hours was confirmed, precipitation of carbide was observed from the inlet of the catalyst in the second reaction zone to 10 mm. Thereafter, aeration was carried out under the same conditions as in Example 1. As a result, the removal of carbide was confirmed without a rapid increase in the catalyst layer temperature, and the pressure loss also returned at the start of the reaction. Table 1 shows the performance evaluation after the treatment.
<Example 3>
[Reactor and oxidation reaction]
In order from the top, the first reaction zone (24 SUS reaction tubes with a length of 3000 mm and an inner diameter of 25 mm), a space (a length of 1500 mm, 1300 mm above the gas temperature control unit, a gas introduction tube tangential to the reactor A reactor having a 400 mm inner diameter and equipped with a gas temperature control unit (24 tubes having a length of 500 mm and an inner diameter of 25 mm) and a second reaction zone (24 reaction tubes made of SUS having a length of 3000 mm and an inner diameter of 25 mm). .

  The first reaction zone is filled with the front catalyst 1 from the gas inlet side to a length of 700 mm and the front catalyst 2 to a length of 2300 mm. The second reaction zone is filled with the rear catalyst 1 from the gas inlet side to a length of 800 mm, The latter stage catalyst 2 was filled to a length of 2200 mm.

  The gas temperature control unit was filled with an SUS Raschig ring having an outer diameter of 6 mm and a length of 7 mm as an inert substance so as to have a length of 500 mm. The heat medium was allowed to flow from the bottom to the top in both the first reaction zone and the second reaction zone. The heat medium inlet temperature of the gas temperature control unit was 260 ° C. The reaction conditions were the same as in Example 1. The results are shown in Table 1.

When the state after 4000 hours was confirmed, precipitation of carbide was observed on the inert substance filled in the gas temperature control part, but no carbide was observed in the catalyst layer. Thereafter, aeration was performed under the same conditions as in Example 1 except that the temperature of the heat medium in the gas temperature control unit was changed to 340 ° C. As a result, the removal of carbide was confirmed without a rapid increase in the catalyst layer temperature, and the pressure loss was also reduced. It was back at the start of the reaction. Table 1 shows the performance evaluation after the treatment.
<Example 4>
The reaction was performed under the same conditions as in Example 3 except that the space part was filled with ceramic balls having a diameter of 40 mm as an inert substance so that the gas residence time in the space part was 6 seconds. The results are shown in Table 1. (Refer to FIG. 4 and FIG. 5C)

When the state after 4000 hours was confirmed, a slight amount of carbide was observed on the surface of the inert substance filled in the space, but no carbide was observed in the inert substance and catalyst layer filled in the gas temperature control part. Thereafter, aeration was carried out under the same conditions as in Example 1. As a result, the removal of carbide was confirmed without a rapid increase in the catalyst layer temperature, and the pressure loss also returned at the start of the reaction. Table 1 shows the performance evaluation after the treatment.
<Comparative Example 1>
The reaction was carried out using the same catalyst as in Example 1 using two conventional reactors.
[Reactor and oxidation reaction]
First reactor (24 SUS reaction tubes with a length of 3000 mm and an inner diameter of 25 mm), gas temperature control unit (24 tubes with a length of 500 mm and an inner diameter of 25 mm) at the outlet of the first reactor, and a second reactor (long A reactor having an inner diameter of 400 mm provided with 24 SUS reaction tubes having a thickness of 3000 mm and an inner diameter of 25 mm was used. Each reactor was connected with a SUS pipe having an inner diameter of 200 mm and a length of 6000 mm. Further, an additional gas pipe was connected to the first reactor outlet. (See Figure 1)
The first reactor is filled with the front catalyst 1 from the gas inlet side to a length of 800 mm and the front catalyst 2 to a length of 2200 mm, and the second reactor is filled with the rear catalyst 1 from the gas inlet side to a length of 700 mm, The latter stage catalyst 2 was filled to a length of 2300 mm.

The gas temperature control unit at the outlet of the first reactor was filled with a SUS Raschig ring having an outer diameter of 6 mm and a length of 7 mm to a length of 500 mm. The heat medium was allowed to flow from below to above in both the first reaction zone and the second reaction zone. A raw material gas having the following composition was introduced from above the reactor to carry out an oxidation reaction under the following conditions.
<Raw gas composition>
12% by volume of propylene, 15% by volume of oxygen, 9% by volume of water vapor, and 64% by volume of inert gas such as nitrogen.
<Air volume>
A gas having the above composition was supplied at 47.7 m ³ / Hr.
<Additional gas>
Air is supplied at 13.6 m ³ / Hr.
<Catalyst layer temperature>
First reactor temperature (heat medium inlet temperature in the first reaction zone): 320 ° C.
Gas temperature control part temperature (heat medium inlet temperature of gas temperature control part): 260 ° C
Second reactor temperature (heat medium inlet temperature in second reaction zone): 265 ° C.
The results are shown in Table 1.

Further, when the state after 4000 hours was confirmed, precipitation of carbide was observed on the connecting pipe of the reactor and the inert material, and further, carbide was recognized from the inlet of the catalyst in the second reaction zone to 200 mm.
<Aeration>
A mixed gas of 12 volume% oxygen, 50 volume% water vapor and 38 volume% inert gas such as nitrogen was supplied at 21.2 m ³ / Hr. When aeration was carried out under conditions of a first reaction zone temperature of 350 ° C. and a second reaction zone temperature of 320 ° C., a sudden increase (runaway) of the catalyst layer temperature was observed, which was interrupted. Thereafter, when the reaction was resumed, the catalyst was deactivated and the reaction could not be continued.

The schematic diagram of the reactor in the case of using two conventional reactors. Schematic diagram of a reactor when using one conventional reactor FIG. 2 is a schematic diagram of a reactor used in the present invention, in which a reaction source gas is supplied from above the reactor, and a contact gas having a space portion having a mechanism for introducing a gaseous substance from the outside between the two reaction zones. It is a schematic diagram of the reactor for phase oxidation. FIG. 2 is a schematic diagram of a reactor used in the present invention, which has a gas temperature control section, and a catalytic gas phase oxidation reaction in the form of a first reaction zone outlet gas in the space section of the reactor filled with an inert substance in the space section. It is a schematic diagram of a vessel. It is a cross-sectional schematic diagram of the introduction part of the additional gaseous substance of the reactor used by this invention. (A) The cross-sectional schematic diagram of the introduction part of a normal additional gaseous substance. (B) The cross-sectional schematic diagram of the introduction part of the additional gaseous substance in which the injection mechanism of many additional gaseous substances was provided and the mechanism which mixes by raising a contact area was installed. (C) The cross-sectional schematic diagram of the introduction part of the additional gaseous substance in which the mechanism which introduces an additional gaseous substance in a slanting direction with respect to a reactor, and was mixed by a vortex flow was installed. In the schematic diagram of the reactor used in the present invention, as a mechanism for efficiently mixing the first reaction zone outlet gas and the additional gaseous substance in the space of the reactor, the first reaction zone and the second reaction zone. A schematic diagram of a catalytic gas phase oxidation reactor in a form in which a mechanism for mixing by adding a gaseous substance there and attaching a dispersion plate provided therebelow is provided in the space between is there.

Explanation of symbols

1 reaction tube 2 upper tube plate 3 middle tube plate 4 lower tube plate 5 heat medium dispersion plate (baffle plate)
6 Inert substance filled in space 7 Inert substance filled in gas temperature control part 8 Gas outlet

Claims (3)

A fixed-bed multitubular reactor used in a catalytic gas-phase oxidation reaction for producing acrylic acid by catalytic gas-phase oxidation of propylene, wherein two reaction zones (first reaction zone) are contained in one reactor. , The second reaction zone), and a space portion having a mechanism for introducing a gaseous substance from the outside is installed between the two reaction zones, and the first reaction zone outlet gas and the additional gaseous state are installed in the space portion. A reactor for catalytic gas phase oxidation , in which a mechanism for mixing a substance is installed and a substance that is substantially inert to a reaction gas is filled . The reactor for catalytic gas phase oxidation according to claim 1, further comprising a gas temperature adjusting unit between the second reaction zone and the space. A method for producing acrylic acid by catalytic vapor phase oxidation of propylene, wherein the reactor for catalytic vapor phase oxidation according to claim 1 or 2 is used.

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