JPH01165543A - Production of acrylic acid - Google Patents

Abstract

PURPOSE:To prevent the blockage trouble of a latter-stage catalyst layer with a by-product of former-stage reaction in the production of acrylic acid from propylene using a two-stage vapor-phase catalytic oxidation process comprising the former stage reaction and the latter stage reaction, by inserting a rod or plate insert into a gas-inlet of the latter-stage reaction tube. CONSTITUTION:Propylene is oxidized mainly to acrolein by a vapor-phase catalytic oxidation in a first reactor filled with an oxide catalyst containing Bi, Mo and Fe and the reaction product gas is directly supplied to a heat- exchange tubular reactor which is separated from the first reactor, directly connected with the reactor through a pipe and filled with an oxide catalyst containing Mo and V to effect the vapor-phase catalytic oxidation of acrolein acrylic acid. In the above two-stage oxidation process for the production of acrylic acid, a rod or plate insert is inserted in a space of a gas-inlet part of the catalyst tube of the second reactor to an extent to get a free volume ratio in the pipe of 40-99%. The blockage of the latter-stage catalyst layer with the by-product existing in the former-stage reaction product gas can be prevented by this process to enable smooth and stable production of the objective compound on an industrial scale.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing acrylic acid from propylene by a catalytic gas phase oxidation reaction.

To be more specific, the present invention consists of a so-called front and rear linkage reaction consisting of a first stage reaction in which propylene is catalytically oxidized in a gas phase to mainly produce acrolein, and a second stage reaction in which this acrolein is converted into acrylic acid. The present invention provides a method for smoothly and industrially stably producing acrylic acid from propylene by preventing catalyst layer clogging troubles due to occlusive substances contained in the gas produced by the first stage reaction.

<Prior art> When producing acrylic acid from propylene by a catalytic vapor phase oxidation method, propylene is first oxidized to acrolein in a catalytic vapor phase.
The catalyst used in this process is referred to as the "first-stage catalyst"), and then this acrolein is oxidized in a catalytic gas phase to convert it into acrylic acid (hereinafter, this reaction is referred to as the "second-stage reaction", and the catalyst used in this is the second-stage reaction). catalyst J), a so-called two-stage oxidation reaction is generally employed.

The catalyst used in the first stage catalyst is generally a multi-element catalytic oxide containing molybdenum, bismuth and iron, but when propylene is catalytically oxidized using these catalysts, the main product acrolein is In addition to this, compounds with relatively high boiling points such as maleic acid and terephthalic acid are produced as by-products.
At the same time, polymers and tar-like substances are included in the generated gas. If the reaction gas containing these substances is directly subjected to the subsequent reaction, these substances will cause blockages in the pipes and in the latter catalyst packed bed, increasing pressure loss, decreasing catalyst activity, and causing damage to acrylic acid. This may cause a decrease in selectivity. Such troubles often occur when the propylene supply m is increased in order to increase the productivity of acrylic acid, that is, when l1affi is increased or the propylene concentration is increased.

Therefore, a commonly adopted method to prevent this problem is to periodically stop the reaction and fill the gas inlet side of the latter stage catalyst with an inert gas in order to prevent blockage in the catalyst layer and decrease in catalyst activity. The process of optimizing the oxidation reaction can be carried out by extracting a substance such as a ceramic pole and replacing it, or by separating acrolein from the gas produced by the membrane reaction and then supplying this separated acrolein to the subsequent reaction. A method has been proposed in which the reaction is carried out by diluting the concentration of the raw material gas more than necessary to lower the amount of by-products. However, all of these methods are complicated and expensive as industrial methods, and are not satisfactory. In addition, in order to suppress excessive oxidation by reducing the oxygen content of the reaction gas composition in both the first and second reactions, it is common to recycle the waste gas from the reaction gas as an inert gas.
In addition, a method has been proposed in which the shape of the catalyst used in the post-stage reaction is specified and the porosity between the catalysts is increased to suppress clogging of solids from the pre-stage reactor (Japanese Unexamined Patent Publication No. 61-221149). . Measures to prevent blockage problems on the gas inlet side of the second stage reactor are becoming an increasingly important issue now that the development of advanced stage catalysts is progressing, and it is becoming possible to lower the reaction humidity and increase the load. It is becoming.

Problems to be Solved by the Present Invention> The present invention uses a rod-shaped or provides a method in which the reaction can be carried out smoothly and stably on an industrial scale by inserting a plate-shaped insert to prevent clogging of the latter stage catalyst layer due to by-products contained in the first stage reaction product gas. It is something to do.

<Means> That is, the present invention is specified as follows.

In a first reactor filled with a catalytic oxide containing bismuth, molybdenum, and iron, propylene is catalytically oxidized in a gas phase to mainly produce acrolein, and the resulting reaction product gas is directly transferred from the first reactor. separated,
When the acrolein is catalytically oxidized in gas phase to produce acrylic acid by supplying it to a heat conversion type multi-tubular second reactor filled with a catalytic infusion containing molybdenum and vanadium, which is directly connected with piping, A two-stage oxidation method characterized in that a rod-shaped or plate-shaped insert is inserted into the gas inlet space of a catalyst-filled tube in two reactors, and the porosity in the tube is made to be 40 to 99%. Method for producing acrylic acid.

Here, the porosity is defined as below.

Spatial volume - insert volume The present invention will be further explained in detail below.

When producing the corresponding acrylic acid from propylene by catalytic gas phase oxidation reaction, a so-called two-stage oxidation method is often employed. In this two-stage oxidation method, acrolein is separated from the mixed gas mainly containing acrolein generated in the moe stage catalyst layer, and is supplied to the latter stage catalyst bed to convert it into acrylic acid by ζ catalytic oxidation method. There is a method of converting it into acrylic acid by a catalytic gas phase method by directly supplying it to a later stage catalyst layer, but these methods also involve recycling the combustion gas of the reaction exhaust gas after recovering the active ingredient, or converting unreacted acrolein into acrylic acid. There is a method of recycling by mixing it with propylene. By the way, when a multicomponent catalyst containing bismuth, molybdenum, and iron is used as the first-stage catalyst, the production of high-boiling compounds such as maleic acid and terephthalic acid, polymers, or tar-like substances is unavoidable. Furthermore, polymers, tar-like substances, or fume-like solids are generated from reaction products thermally in the piping or by collision with the walls of the piping. Therefore, when producing acrylic acid by the process described above, such polymers and by-products circulate within the equipment in the form of gases, solid particles, or fumes.
It cannot be avoided that it is introduced into the reactor, and there are many chances that it will be entrained in multiple layers, especially in the later stage reactor. Under such circumstances, the lower the temperature of the mixed gas introduced into the post-stage reactor, the more likely by-products such as high-boiling compounds will become solid, and they will stick or adhere to the post-catalyst inlet side, leading to blockage. easy.

Furthermore, as the temperature of propylene rises, the amount of by-products such as high-boiling compounds and tar-like substances in the reaction product gas increases, which also tends to cause clogging problems. In addition to the methods described above, methods to avoid such clogging troubles include increasing the gas temperature before entering the downstream reactor, or providing a preheating layer in the downstream reactor up to the catalyst inlet. However, each of these countermeasures has its own problems when used as a normal method. Even if the temperature of the gas supplied to the latter catalyst layer is increased, it is necessary to suppress the autooxidation of acrolein generated in the former catalyst layer, and furthermore, due to restrictions such as having to avoid the explosive range, There is a limit.If a gas preheating layer is provided in a hollow cylinder before entering the catalyst layer, the layer length of the hollow cylinder needs to be increased to some extent, and the reactor needs to be made larger accordingly.Also,
Even when an inert carrier is placed in the preheating layer portion, there is a risk of clogging in this portion. As a result of studying methods for solving the blockage problem under these circumstances, the inventors of the present invention obtained the following knowledge. In other words, acrylic acid is produced by catalytic gas phase oxidation reaction of propylene! When building a
When a two-stage oxidation method is adopted, the produced gas in the first reactor is usually sufficiently cooled to prevent auto-oxidation and to avoid the combustion range, but as mentioned above, the gas temperature is If it is cooled too much, the by-product will become solid or fume-like, and if left as it is, it will cause a blockage on the inlet side of the catalyst layer of the latter stage reactor. In order to avoid this, it is possible to raise the gas temperature as quickly as possible while increasing the linear velocity to facilitate overreaction of the side reaction products from the first stage reaction on the second stage catalyst. As a result of conducting inspections from the viewpoint that the blockage in the latter catalyst layer could be avoided, it was found that filling the inert carrier or preheating the latter catalyst layer could not cause any blockage problems. Surprisingly, simply inserting a rod-shaped or plate-shaped insert made of metal or ceramic into the space on the inlet side of the second-stage catalyst produces a preheating effect on the second-stage reaction gas, and prevents blockage. The present inventors have discovered that the reaction can be avoided and the reaction can continue stably for a long period of time, and that autooxidation of acrolein can be suppressed in the process of an eddy electric upper field, leading to the completion of the present invention.

In this case, if the insert is rod-shaped, it may be linear, zigzag, or twisted. The rod-shaped insert may be cylindrical or cylindrical. Moreover, in the case of a plate shape, it may be a tanzak shape, a zigzag shape, or a twisted shape.

It may be plate-shaped, a complete plate, or made of wire mesh. The maximum porosity in the space varies depending on the shape of the insert, and for rod-shaped inserts, the porosity is preferably 40% or more and 99.0% or less.
In the case of a plate-shaped insert, it is preferably 50% or more and 99.0% or less. By adopting this range, clogging by solid matter in the insert layer is prevented, a preheating effect is achieved, and the reaction in the subsequent catalyst layer can be carried out smoothly. The material of these inserts is preferably a metal with high thermal conductivity, such as iron, nickel, aluminum, or alloys, particularly stainless steel, but metals whose surface has been chemically treated to make them rustproof may also be used. Further, as a material made of ceramic, for example, zirconia or alumina may be used in the form of a sheet.

Before clarifying the effects of the present invention through examples, an experiment was conducted as a preliminary experiment to examine the effect of preheating gas by the insert defined in the present invention. A steel pipe with an inner diameter of 30M and a wall thickness of 2# was used, and molten salt was used as the heat source. Air preheated to 255° C. was used as the gas supplied thereto. The air flow rate here was 1.9 m3 per hour under standard conditions. When the temperature of the molten salt is 290℃, the length of the hollow cylinder is approximately 800"-900m to preheat the air temperature to 280℃, but it is made of stainless steel with a width of 18 mm and the length is zigzag at a 90 degree angle. Insert a plate bent into a shape (porosity 98%)
It was found that an insertion length of 300a+ was sufficient to raise the temperature to 280°C.

The advantages of the method according to the present invention are that there is no need to forcibly raise the temperature of the gas introduced into the post-stage reactor, so there is no risk of autooxidation or explosion, and that a catalyst that is highly active even at low temperatures can be used as the post-stage catalyst. , there is no need to forcibly lengthen the hollow cylinder to create a gas preheating layer, there is no need to extract the inert carrier due to blockage at the inlet of the latter catalyst layer, and even when propylene is used at a high concentration. It has been found that not only can blockage caused by high-boiling compounds etc. be avoided, but also that there is no decrease in yield, making it possible to continuously operate the production of acrylic M under industrially advantageous conditions.

The reaction conditions for carrying out the present invention are as follows: propylene is 1 to 15% by volume, molecular oxygen is 1 to 20% by volume,
The raw material gas containing 1 to 30% by volume of water vapor and other inert gases such as nitrogen and carbon dioxide is heated to the reaction temperature (reactor heat medium temperature)
200~450℃, space velocity 300~10,000hr
-1(STP)T' is mainly supplied to a bismuth-molybdenum-iron-containing multicomponent catalyst for conversion into acroleine. Secondary air or water vapor is added to the pre-stage outlet gas as necessary, and the temperature of this mixed gas is preferably maintained at 150°C or higher so that it does not cause blockage in the piping and does not fall within the autooxidation or explosion range. It is kept at a low temperature and supplied to the downstream catalyst.

Next, the content of the present invention will be made clearer by showing an example of a shell.

Example 1 Ammonium molybdate 10.
3 K'J, ammonium paratungstate 3,2
Ky was added and stirred vigorously. (This is called liquid A).

Separately, add 6.8 Ky of cobalt nitrate to 2J2 of water, 2.4 Kg of ferric nitrate to 21 of water, and 2.9K of bismuth nitrate.
y is concentrated nitrate M0.6j! Each of these three types of nitrate solutions was dissolved in water 31 which had been made acidic by adding these three types of nitrate solutions, and a liquid mixture of these three types of nitrate solutions was added dropwise to the above liquid A. Next, silica sol 2,4 K'J containing 20% by weight in terms of silicon dioxide and a solution prepared by dissolving 20.20% potassium hydroxide in 1.51% water were added, and the resulting suspension was heated and evaporated. The catalyst was then molded and calcined at 450° C. for 6 hours under air circulation to prepare a catalyst. The composition of this catalyst with elements other than oxygen is CoaFe1Bi1W2Mo1oSi1. , +5Ko
, it was os.

Preparation of second-stage catalyst While heating and stirring water 601, 1.3 Ky of ammonium paratungstate, 1.1 kg of ammonium metavanadate, 4.3 g of ammonium molybdate, and 150 Q of ammonium dichromate were respectively mixed and dissolved, and separately dissolved in nitric acid. An aqueous solution was prepared by dissolving copper 1.1/Cy in 0.721 water, and both were mixed. The thus obtained mixed solution was placed in a stainless steel evaporator equipped with a steam heater, and the carrier base material was made of α-alumina and the surface area was 1 m.
2/g or less, porosity 42%, pore size of 75 to 250 microns, and the volume occupied by pores is 92% of the total pore volume. Add 12 pieces of granular carrier with a diameter of 3 to 5 mm, and evaporate with stirring. After drying and adhering to the carrier, it was heated at 400℃ for 5 minutes.
A catalyst was prepared by calcination for a period of time. The composition of elements other than oxygen excluding the carrier of this catalyst is Mo 12V4.6 in atomic ratio.
It was Cu2.2CrO,6W2.4.

Reaction method The above-mentioned pre-catalyst 12.25 J was prepared with an inner diameter of 25#, a length of 3,
A multitubular reactor consisting of 10 OOO mm steel reactors, whose shell side was capable of heat exchange by circulating molten salt, was evenly filled and heated to 330°C.

Separately, the latter stage catalyst 21.8j! Inner diameter 25#, length 7,
A multitubular reactor consisting of 10 OOOInM steel reaction tubes, whose shell side was capable of heat exchange by circulating molten salt, was evenly filled and heated to 255°C.

two reactors are connected by a conduit equipped with a nozzle for the addition of molecular oxygen-containing gas and water vapor and equipped with a heat exchanger,
The reaction product gas discharged from the reactor containing the front stage catalyst was introduced into the reactor containing the rear stage catalyst. At this time, the gas wetness was maintained at 220° C. until it entered the second stage reaction tube in the second stage reactor. Furthermore, the upper part of the catalyst layer of the latter reaction tube (reaction gas inlet side)
For this purpose, a 300-sided metal plate made by bending a 5US304 plate with a wall thickness of 0.4 rm and a width of 17# in a zigzag shape at an angle of about 90 degrees with a pitch of 35 m was inserted 20 mm from the inlet of the reaction tube.
It was inserted from 0 m so as to rest on the upper end of the latter stage catalyst. At this time, the porosity of the metal plate insertion portion was 98%.

A mixed gas consisting of propylene 9 volume ω%, air 76 volume D%, and water 15 volume % is fed into the reactor containing the front stage catalyst 19,6
0ONJl/hrr is introduced, and 2.70ONJ! is introduced from the molecular oxygen-containing gas introduction nozzle of the conduit connecting the Sarani front reactor and the second reactor! /hr of air and 2.940 NJ/hr of steam from a steam introduction nozzle were added to carry out the reactions in the first and second stages. At this time, the pressure difference at the rear reactor outlet was 270 rMHg. Further repeat this reaction in 4. It continued for 00 hours. During this time, it was necessary to raise the molten salt temperatures in the front and rear reactors by 10°C and 5°C, respectively.

At the start of the reaction and 4. The reaction results after OO hours are shown in Table 1.

Here, the propylene conversion rate is calculated from the amount of propylene consumed at the inlet of the first reactor and the outlet of the second reactor, and the single flow acrylic acid yield is calculated from the amount of acrylic acid produced at the outlet of the second reactor and the amount of propylene consumed at the outlet of the second reactor. Shows the ratio of propylene fed to the reactor.

Comparative Example 1 The latter catalyst was packed in the same manner as in Example 1, without putting an insert into the latter catalyst inlet side of the latter reactor, so that the upper surface of the catalyst was located 500 Ivn from the reactor inlet side. Other than that, the reaction was carried out according to the method of Example 1.

The performance at the start of this reaction is shown in Table 1. Although this reaction was continued for a long period of time, the pressure between the inlet and outlet of the latter reactor rose to 390 mH (J) in about OOO hours.
1).

When the reaction was stopped and the second stage reactor was inspected, it was found that the second stage catalyst inlet side catalyst layer was clogged with polymers and the like. Further, in order to avoid this blockage, the length of the hollow cylinder on the inlet side of the latter catalyst layer was set to 1.500 m.

The results were reported at the start of the reaction and in 4. Table 1 shows the results after the reaction continued for OOO hours. The reaction method was otherwise the same as Example 1.
(Comparative Example 1-2゜) In this case, the reason why the yield was low as is clear from the batter is that the length of the hollow cylinder became long and autoxidation occurred (-carbon oxide and acetic acid (increases), and 4. After OOO time, the pressure loss also increased slightly.

Example 2 An insert having a structure in which a metal plate of the same material and dimensions as used in Example 1 was wound in a spiral shape was used. The total length of this insert was 300M (porosity 97.5%). The reaction method was in accordance with Example 1. The reaction results are shown in Table 1.

Example 3 Instead of the insert used in Example 1, an insert 30 was prepared by bending a cylindrical metal bar made of stainless steel 304 and having an outer diameter of 5M into a zigzag shape at an angle pitch of approximately 35 mm at approximately 90 degrees.
0# length was used. The porosity at this time was approximately 96%. The reaction method was in accordance with Example 1. The results are shown in Table 1. - Comparative Example 2 In Example 3, the outer diameter of the cylindrical rod was made thinner, and the porosity of the inserted portion within the reaction tube was made 99.3%. Rod insertion and reaction were conducted according to Example 3 (Comparative Example 2-1). The reaction results are shown in Table 1. The preheating effect was insufficient and the pressure loss increased with the reaction.

On the other hand, in Example 3, the outer diameter of the cylindrical rod was increased so that the porosity was 36%. The rod insertion and reaction method were in accordance with Example 3 (Comparative Example 2-2). The results are shown in Table 1. As a result, the pressure loss increased even at the start of the reaction due to the insertion of a thick rod, but the pressure loss further increased as the reaction continued. When the reaction was stopped and the latter reactor was inspected, it was found that solid matter had precipitated between the insert and the inner wall of the reaction tube, causing a blockage.

Comparative Example 3 Instead of the insert in Example 1, a stainless steel Raschig ring with a wall thickness of 0.4 mm and a diameter of 10 mφ x 10 sL was filled into the reactor of the latter stage reactor. The filling method was such that the cavity on the inlet side of the reactor was 200 mm, the layer height of the Raschig ring insert was 300 M, and the latter stage catalyst was packed below that. Raschig ring full 1a1
The porosity of M was 91%. The reaction method was in accordance with Example 1. The results are shown in Table 1.

As the reaction progressed, the pressure loss at the inlet and outlet of the second stage reactor increased.

3. When the reaction was stopped after 00 hours and the latter stage reactor was inspected, it was found that solid substances such as polymers were precipitated in a blocked state with a Raschig ring filling of 11 iW. It was found that although the porosity was large, the state of occlusion was greatly influenced by the shape of the filling.

Example 4 Alumina sheet with wall thickness of 0.4# and width of 17mm.

A 300 m long plate was inserted according to the method of Example 1.

At this time, the porosity at the alumina sheet insertion part was 98.3%.
Met. The reaction method and catalyst loading method were the same as in Example 1, and the results shown in Table 1 were obtained.

Claims (1)

[Claims] (1) In a first reactor filled with a catalyst oxide containing bismuth, molybdenum, and iron, propylene is catalytically oxidized in a gas phase to mainly produce acrolein, and the resulting reaction product gas is directly transferred to the first reactor. The second reactor is separated from the reactor and directly connected to the heat exchange type multi-tubular reactor filled with a catalyst oxide containing molybdenum and vanadium, where the acrolein is catalytically oxidized in vapor phase and converted into acrylic. When producing acid, a rod-shaped or plate-shaped insert is inserted into the gas inlet space of the second reactor catalyst-filled tube, and the porosity in the tube is made to be 40 to 99% by the insert. A method for producing acrylic acid using a two-stage oxidation method.