JP2007039354A - Method for producing acrylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing acrylic acid, by which an existing acrylic acid-producing installation using propylene as a raw material can be diverted into an acrylic acid-producing installation using propane as a raw material by a simple method, and the acrylic acid can be produced in high efficiency. <P>SOLUTION: This method for producing the acrylic acid is characterized by comprising a process for subjecting propane to a gaseous phase catalytic oxidation reaction using the first fixed bed reactor to produce a mixture gas containing acrylic acid, a process for subjecting propane to a gaseous phase catalytic oxidation reaction using the second fixed bed reactor connected to the first fixed bed reactor in parallel to produce a mixture gas containing acrylic acid, and a process for recovering the acrylic acid from the obtained acrylic acid-containing mixture gases, wherein the particle sizes of the first and second composite metal oxide catalysts are adjusted so that a gas pressure loss between the first reactor entrance and exit of the first multi-tubular type fixed bed reactor is substantially identical to a gas pressure loss between the second reactor entrance and exit of the second multitubular type fixed bed reactor. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing acrylic acid by subjecting propane to a gas phase catalytic oxidation reaction using a fixed bed reactor having a composite metal oxide catalyst.

  Acrylic acid is industrially used as a raw material for fibers, synthetic resins, synthetic rubbers and the like. As an industrial production method of acrylic acid, a process for producing acrolein by using propylene as a raw material and contacting it with a composite metal oxide catalyst in the presence of oxygen (first process), acrolein obtained in the first process In general, a two-stage reaction that undergoes a step (second step) of contacting a mixed metal oxide catalyst with oxygen in the presence of oxygen (Patent Document 1). On the other hand, this propylene is usually expensive because it is obtained by thermally decomposing raw material naphtha together with steam, and attempts have been made to produce acrylic acid using inexpensive propane as an alternative raw material.

The production method of acrylic acid using propane as a raw material mainly improves the composition of the composite metal oxide catalyst, improves the conversion rate of propane and improves the selectivity of acrylic acid, and improves the production process itself. It is mainly approached from two aspects. In the former, for example, a Mo-V-Te catalyst (Patent Document 2), a Mo-V-Sb catalyst (Patent Document 3), a Mo-V-Sb-Nb catalyst (Patent Document 4), and the like are known. . However, the propane conversion rate of these catalysts is still low industrially and is not satisfactory. In order to improve this point, it is conceivable to carry out the reaction at a high temperature, but a side reaction occurs, and not only the product other than the target product, particularly carbon monoxide and carbon dioxide, increases, but also the acrylic acid selectivity decreases. This also leads to a reduction in catalyst life. For this reason, methods have been proposed in which the propane conversion rate is kept low and the propane concentration to be supplied is increased, but a step of recovering unreacted propane is required. On the other hand, the improvement of the production process itself occurs due to the performance of the catalyst. For example, as a method for improving the recovery process of propane, a process of recovering propane by selectively adsorbing it to an aqueous solution containing an alkaline substance. (Patent Document 5) has been proposed. Although this method is advantageous for effective utilization of unreacted propane, it cannot be said that the production efficiency of acrylic acid is necessarily good, and there remains an industrial problem. Patent Document 6 describes that when propane is converted to propylene in the presence of an appropriate oxidative dehydrogenation catalyst and propylene and unreacted propane are supplied to the propylene oxidation step, the conversion efficiency of acrolein from propylene is improved. In this method, the residual gas from which acrylic acid has been recovered in the final step is recycled to the propane oxidative dehydrogenation step to effectively use the raw material gas. However, this method requires a step of oxidative dehydrogenation of propane, and is not necessarily an economical method.
In this way, no special equipment is required and an efficient method for producing acrylic acid is desired.

JP 2002-161066 A JP-A-6-279351 Japanese Patent Laid-Open No. 9-316023 JP-A-11-285636 JP 2004-51589 A Special Table 2000-502719

The reaction method of converting raw material propane to acrylic acid using a two-stage reaction process in parallel using propylene as a raw material and using a two-stage reaction process in parallel is economical because it uses existing equipment. Moreover, it is considered that the low conversion rate of the propane oxidation catalyst can be supplemented and the production efficiency can be increased. However, existing acrylic acid production facilities are designed to optimize the catalyst composition and reactors, maximizing the conversion rate of raw materials and the selectivity of target products, and taking into account runaway reactions due to catalyst life and abnormal heat storage. Has been. In particular, not only the catalyst composition is different between the first step and the second step, but also the diameter of the reaction tube may be different. When diverting equipment having different pipe diameters in the first step and the second step to the propane oxidation reaction, it is most efficient to bring the reaction conditions close to the same in the first step and the second step. it is conceivable that. That is, the raw material gas introduction pipe of the first step is extended to the gas introduction pipe of the second step, the raw material gas can be supplied simultaneously in both steps, and the reaction gas outlet port of the first step is provided separately, or the second step If the first and second processes are used in parallel by connecting to the reaction gas outlet of the process and the conditions such as pressure and temperature are the same in both processes, the catalyst life in both processes and the supply gas before and after both processes The need to finely control the composition is reduced.
An object of the present invention is to provide a method capable of diverting an existing acrylic acid production facility using propylene as a raw material to an acrylic acid production facility using propane as a raw material, and producing acrylic acid with high efficiency by a simple method. And

The present inventors have completed the present invention as a result of intensive studies to solve the above problems.
That is, the present invention provides (1) at least the following steps (a) to (c):
Step (a): Propane is subjected to a gas phase catalytic oxidation reaction using a first multitubular fixed bed reactor having a plurality of first reaction tubes filled with a first composite metal oxide catalyst, Step (b) of generating a mixed gas containing: a plurality of second reaction tubes filled with propane and a second mixed metal oxide catalyst and connected in parallel with the first multitubular fixed bed reactor Step (c): a gas phase catalytic oxidation reaction using a second multi-tubular fixed bed reactor having a gas to produce a mixed gas containing acrylic acid: obtained in steps (a) and / or (b) A process for recovering acrylic acid from a mixed gas containing acrylic acid, and the gas pressure loss between the first reaction tube inlet and the outlet of the first multitubular fixed bed reactor is the second multitubular fixed bed reactor. So that the gas pressure loss between the second reaction tube inlet and outlet is substantially the same. Process for producing acrylic acid, characterized by adjusting the particle diameter of the secondary of the composite metal oxide catalyst,
(2) The method for producing acrylic acid according to the above (1), wherein the first and second composite metal oxide catalysts are supported catalysts in which a catalytically active component is supported on an inert support,
(3) The particle diameters of the first and second composite metal oxide catalysts are adjusted by using inert carriers having different particle diameters with the same loading amount of the catalytically active component. A method for producing acrylic acid,
(4) The residual gas from which acrylic acid has been recovered in step (c) is mixed with the raw material gas in the first and / or second multitubular fixed bed reactor and used in the above (1) to (3) A method for producing acrylic acid according to any one of the above is provided.

  According to the present invention, it is possible to divert to an acrylic acid production facility that uses propane, which is cheaper than propylene, as a raw material without greatly changing the existing acrylic acid production facility. Can be manufactured. Therefore, the present invention is extremely useful industrially.

The conceptual diagram of an example of the manufacturing process in this invention is shown in FIG. The production method of the present invention comprises at least two propane oxidation steps (steps (a) and (b)) and a step of recovering acrylic acid from the product gas obtained in step (a) and / or step (b) ( Step (c)). In step (a) and step (b), the product gas (acrylic acid-containing mixed gas) contains acrylic acid, a small amount of acrolein, unreacted propane and by-products (mainly carbon monoxide and carbon dioxide). As will be described later, acrylic acid may be recovered from the acrylic acid mixed gas (step (c)) and then supplied to step (a) and / or step (b). Further, the second fixed bed reactor in the present invention has a common raw material gas supply port as shown in FIG. 1, for example, with the first fixed bed reactor, and this form is “parallel”.
Hereinafter, the first embodiment of the present invention will be described.
The first fixed bed reactor in the present invention is a known apparatus for converting a mixed gas of propylene as a raw material into acrolein by a gas phase catalytic oxidation reaction, and the second fixed bed reactor is the above-mentioned first fixed bed reactor. The apparatus which converts the product gas from one fixed bed reactor into acrylic acid by vapor-phase catalytic oxidation reaction can be diverted, respectively. Even if the mixed metal oxide catalysts in the first and second fixed bed reactors have different catalytic active component compositions, they can produce the same effect as in the present invention, but the production of the catalyst itself. In view of efficiency, it is preferable to use those having substantially the same catalytic active component composition in both reactors. Here, the substantially same catalytically active component composition means that the effective metal composition (metal type and composition ratio) in the composite metal oxide is substantially the same.

  As a catalyst active component composition, the catalyst described in patent documents 2-4 and the Mo-V-Ti- (Sb / Te) type | system | group catalyst described in Unexamined-Japanese-Patent No. 2002-361085 can be used. The shape of the catalyst is not particularly limited and may be any of a spherical shape, a cylindrical shape, a ring shape, etc., but the catalyst can be filled into the reaction tube with good reproducibility, and the gas pressure loss between the reaction tube inlet and outlet is substantially the same. In order to achieve this, the preferred shape is a sphere. A known method can be applied to obtain a spherical composite metal oxide catalyst. The catalyst may be a molded catalyst in which the catalytically active component is formed into a spherical shape with an appropriate molding device, or a supported catalyst in which the catalytically active component is supported on an inert carrier such as silica or alumina. The latter is preferred because it is too high and can lead to a runaway reaction. In obtaining a molded catalyst, it is preferable to mix water, ethanol, polyvinyl alcohol, silica sol and other binders, diatomaceous earth, inorganic fibers and the like in order to increase the mechanical strength of the catalyst.

  In the present invention, a mixed metal oxide catalyst having the same or different particle diameter is used in the first fixed bed reactor and the second fixed bed reactor according to the diameter of each reaction tube. In the case of a molded catalyst, the particle size of the composite metal oxide catalyst can be adjusted by adjusting the amount of the mixture and the driving conditions of the molding machine. It can be adjusted by changing the loading amount of the component, or by changing the particle size of the inert carrier while keeping the loading amount constant. The particle size of the composite metal oxide catalyst used in the present invention is selected according to the inner diameter of the reaction tube, but is usually 3 to 100 mm, preferably about 3.5 to 8 mm.

The particle diameters of the first mixed metal oxide catalyst charged in the first fixed bed reactor and the second mixed metal oxide catalyst charged in the second fixed bed reactor are determined at the inlet of each reaction tube in both reactors. And the gas pressure loss between the outlet and the outlet are adjusted to be substantially the same. When compared with the same tube diameter and the same filling volume, the gas pressure loss increases as the particle diameter of the composite metal oxide catalyst decreases.
By adjusting the pressure loss in the first and second steps to be substantially the same, it is possible to supply gas to both steps equally, and complicated operations such as delicate control of reaction conditions and adjustment of the supply gas composition are possible. It becomes unnecessary and can be controlled most efficiently. In addition, the gas pressure loss between each reaction tube inlet and outlet is substantially the same. When the gas pressure loss in each reaction tube is measured independently, the pressure loss difference between them is about 10% or less. Point to. If the gas pressure loss between the reaction tube inlet and outlet of both reactors cannot be adjusted to be substantially the same, the catalyst performance cannot be exhibited sufficiently.

The first fixed bed reactor in the first embodiment of the present invention has a propane supply port, a first reaction tube connected to the propane supply port, and a product gas outlet port connected to the first reaction tube. It is an apparatus that performs a reaction by heating with a heat medium. The reaction conditions in the first fixed bed reactor vary depending on the length of the first reaction tube, the packing length of the catalyst, etc., and cannot be generally stated, but usually propane: oxygen: steam: dilution gas (nitrogen, inert Gas etc.) = 1: 0.1 to 10: 0 to 70: 0 to 20 (volume ratio) is supplied at a space velocity (SV), usually at a rate of 100 to 10,000 hr ⁻¹ . The reaction temperature is usually 250 to 500 ° C. as the temperature of the heat medium.
Propane that has undergone gas phase catalytic oxidation in the first fixed bed reactor is converted into acrylic acid, and is derived from the product gas outlet of the first fixed bed reactor (step (a)). The second fixed bed reactor has the same structure as the first fixed bed reactor, and the supplied propane is subjected to gas phase catalytic oxidation to convert it into acrylic acid (step (b)). The reaction temperature in the second fixed bed reactor is preferably in the same range as the first fixed bed reactor. If the reaction temperatures in both reactors differ significantly, the overall reaction control becomes complicated and acrylic acid production efficiency Not only being different, but also affecting the life of the catalyst in each reactor, leading to a difference in catalyst replacement timing between the first and second reactors.
The product gas derived from the product gas outlets of the first and second fixed bed reactors is collected by a cooling and / or absorption tower and extracted and separated to recover the target acrylic acid. (Step (c)).

  In the embodiment of the present invention, propane conversion and acrylic acid selectivity are increased / decreased depending on the catalyst performance and the required acrylic acid production amount, but when there is a large amount of unreacted propane, the second embodiment is performed as described below. It may be applied.

  In the second embodiment of the present invention, the residual gas after finally recovering acrylic acid in the first embodiment is heated to heat the first fixed bed reactor and / or the second fixed bed. Recirculate to reactor. The main purpose of the recycle is to oxidize unreacted propane as described above, but also to effectively utilize the residual gas in which oxygen is consumed by the oxidation reaction as an inert gas. Therefore, the recirculation of the residual gas in the second embodiment of the present invention is performed so that the composition of the mixed gas supplied to the first fixed bed reactor and / or the second fixed bed reactor falls within the above range. Propane, oxygen, water vapor, inert gas, and the like are mixed with the residual gas as appropriate, adjusted and supplied.

Next, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited to a following example, unless the main point is exceeded.
Moreover, the propane conversion rate and acrylic acid selectivity in the following examples are respectively defined as follows.
Propane conversion (mol%) = 100 × (number of moles of propane supplied−number of moles of unreacted propane) / (number of moles of propane supplied)
Acrylic acid selectivity (mol%) = 100 × (number of moles of produced acrylic acid) / (number of moles of supplied propane−number of moles of unreacted propane)

Example 1
After adding 1 kg of ammonium molybdate, 200 g of ammonium metavanadate, and 300 g of telluric acid to 12 liters of water at 80 ° C., the solution is cooled to 50 ° C. or lower to obtain Solution A.
Add 640 g of niobium hydrogen oxalate hydrate to 4 liters of water, stop heating at 50 ° C. and add to solution A. The obtained solution was evaporated to dryness and then calcined in air at 300 ° C. for 2 hours, and then calcined in nitrogen at 600 ° C. for 2 hours to obtain a catalyst powder. The amount of the calcined powder was adjusted so as to account for 50% by weight with respect to the molded catalyst, and supported on an inert carrier using a tumbling granulator. The average particle size of the catalyst was 3.5 mm. Next, the same calcined powder was used and supported on an inert carrier having a different particle size so that the supported amount was 50% by weight to obtain a catalyst having an average particle size of 4.7 mm. The reaction was carried out using a fixed bed flow reactor in which two stainless steel reaction tubes with different inner diameters of 22.6 mm and 25.4 mm were connected in parallel and each of which was able to circulate reaction gas. . Note that the pressure can be controlled and measured independently for each reaction gas supply side and the outlet side for each reaction tube. A catalyst having an average particle diameter of 4.6 mm was packed in a reaction tube having an inner diameter of 22.6 mm, and a catalyst having an average particle diameter of 3.5 mm was packed in a reaction tube having an inner diameter of 25.4 mm so as to have a packing length of 3.5 m. A raw material mixed gas composed of propane, air and water vapor was circulated at a molar ratio of propane / air / water vapor = 1/15/14 and a space velocity of 1000 hr ^−1, and the pressure loss was measured separately for each reaction tube. It was 7.1 kPa. The reaction temperature was set to 370 ° C. in the reaction tubes, and the reaction test was performed by simultaneously passing gas through both reaction tubes. The reaction product was analyzed by gas chromatography. As a result of the reaction, the propane conversion was 53% and the acrylic acid selectivity was 57%.

Comparative Example 1
Using only the catalyst having an average particle diameter of 3.5 mm prepared in Example 1, both the reaction tubes having the different inner diameters as in Example 1 were packed so as to have a filling length of 3.5 m. Otherwise, the pressure loss was measured separately under the same conditions. As a result, the reaction tube inner diameter was 8.5 kPa when the reaction tube inner diameter was 22.6 mm, but 7.0 kPa when the reaction tube inner diameter was 25.4 mm. When the reaction was carried out at a reaction temperature of 370 ° C. in the same manner as in Example 1, the propane conversion decreased to 44% and the acrylic acid selectivity became 59%.

Two propane oxidation steps (steps (a) and (b)) are connected in parallel to recover acrylic acid from the product gas obtained in steps (a) and (b) (step (c)) and acrylic It is the conceptual diagram which showed the process example which supplies the gas after acid collection | recovery to process (a) and (b).

Claims (4)

At least the following steps (a) to (c)
Step (a): Propane is subjected to a gas phase catalytic oxidation reaction using a first multitubular fixed bed reactor having a plurality of first reaction tubes filled with a first composite metal oxide catalyst, Step (b) of generating a mixed gas containing: a plurality of second reaction tubes filled with propane and a second mixed metal oxide catalyst and connected in parallel with the first multitubular fixed bed reactor Step (c): a gas phase catalytic oxidation reaction using a second multi-tubular fixed bed reactor having a gas to produce a mixed gas containing acrylic acid: obtained in steps (a) and / or (b) A step of recovering acrylic acid from the mixed gas containing acrylic acid, and the gas pressure loss between the inlet and outlet of the first reaction tube of the first multi-tube fixed bed reactor is reduced to the second multi-tube fixed bed. So that the gas pressure loss between the inlet and outlet of the second reactor tube of the reactor is substantially the same. And method for producing acrylic acid, characterized by adjusting the particle diameter of the second composite metal oxide catalyst. The method for producing acrylic acid according to claim 1, wherein the first and second composite metal oxide catalysts are supported catalysts in which a catalytically active component is supported on an inert support. The particle size of the first and second mixed metal oxide catalysts is adjusted by using inert carriers having different particle sizes, with the same amount of the catalytically active component supported. Production method. The residual gas which collect | recovered acrylic acid at the process (c) is mixed with the raw material gas in a 1st and / or 2nd multitubular fixed bed reactor, and is used for any one of Claim 1 to 3 A method for producing acrylic acid.

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