JP5821672B2 - Acrylic acid production method - Google Patents

Description

  The present invention relates to a method for producing acrylic acid, and in particular, in the production of acrylic acid by separating and purifying acrylic acid from an acrylic acid-containing gas produced by gas phase oxidation of propylene or the like, in the acrylic acid distillation purification process, The present invention relates to a method for producing acrylic acid for preventing acid polymerization.

As a method for producing acrylic acid, for example, a method through the following steps (1) to (5) is known.
(1) Oxidation reaction step (2) in which propylene, which is a hydrocarbon having 3 carbon atoms (C3), or propane and molecular oxygen is subjected to a gas phase oxidation reaction in the presence of a catalyst to generate a reaction gas containing acrylic acid. ) Collection step for obtaining an acrylic acid aqueous solution by bringing the obtained acrylic acid-containing gas into contact with water to absorb acrylic acid (3) Water in the obtained acrylic acid aqueous solution is azeotropically distilled using a solvent. Dehydration-distillation step to remove (4) Light-boiling separation step to remove crude boiling acid in acrylic acid obtained by dehydration to obtain crude acrylic acid (5) Distilling crude acrylic acid to obtain product acrylic acid Purification step In some cases, instead of the above (3) dehydration distillation step, acrylic acid in the acrylic acid aqueous solution is extracted into a solvent in a solvent extraction step, and the extract is purified by distillation.

As the above-mentioned collection step, conventionally, the acrylic acid-containing reaction product gas is cooled by watering in a quenching tower, then introduced into an indirect heat exchanger and cooled to obtain an aqueous acrylic acid solution, and the waste gas is further absorbed into an absorption tower. A method of feeding and collecting uncollected residual acrylic acid in water is known (Patent Document 1).
In addition, as another general method, an acrylic acid-containing reaction product gas is introduced into the bottom of the collection tower, and water for absorption is supplied from the top of the tower. There is a method in which the liquid extracted from the middle stage is cooled by a heat exchanger and then circulated through an absorption tower (Non-Patent Document 1).

Such a collection step of acrylic acid is devised so that the concentration of the resulting acrylic acid aqueous solution is higher in order to reduce the load required for purification of acrylic acid in the subsequent step.
For example, a method using a gauze-type ordered packing or the like having an extremely high separation performance as an interpolator in an absorption tower (Patent Document 2), a method for reducing the moisture concentration in a raw material gas used for a gas phase oxidation reaction (Patent Document 3), a method of extracting crude acrylic acid from the middle stage of an absorption tower and circulating and concentrating a heavy liquid from a downstream process to the tower bottom (Patent Document 4), partially absorbing the tower bottom liquid of the absorption tower A method of concentrating acrylic acid by volatilizing automatically and circulating volatile gas to the middle stage of the absorption tower (Patent Document 5) has been proposed.

  Acrylic acid is a compound that is very easy to polymerize. In particular, polymerization of acrylic acid is promoted under conditions of a predetermined temperature or higher in which water coexists. When acrylic acid is polymerized in the acrylic acid production process, the apparatus and piping equipment are blocked by the solid matter produced by the polymerization, and if it is remarkable, the operation cannot be continued. In addition, even if the operation is not stopped due to the blockage of the equipment and piping facilities, there are a number of things such as the frequency of strainer cleaning during normal operation and the amount of required polymerization inhibitor, and the increase in internal cleaning load during regular maintenance. A problem occurs.

  For this reason, in the acrylic acid production process, it has become an important issue to prevent the polymerization of acrylic acid. Conventionally, in the collection process of obtaining an aqueous solution of acrylic acid, absorption is performed to prevent the polymerization of acrylic acid. A polymerization inhibitor is added to the water, and if necessary, measures such as lowering the operating temperature, shortening the residence time, eliminating the residence part in the device, and adopting an insert in the device that is less likely to cause solids to adhere, etc. Has also been taken.

In the acrylic acid aqueous solution obtained in the collection process, relatively high boiling by-products such as aromatic compounds and tar-like substances are dissolved, causing numerous troubles and products in the subsequent acrylic acid purification process. It is known that it becomes a factor of a purity fall (patent document 6).
In addition, the effects on aldehydes such as acrolein have been studied, and the concentration of residual acrolein in the reaction product gas containing acrylic acid is reduced, or the aqueous solution of acrylic acid obtained in the collection process is led to a diffusion tower to reduce the acrolein concentration. A method is also shown (Patent Document 7).

JP 50-95217 A Japanese Patent Laid-Open No. 2001-19655 JP 2004-359611 A JP 2007-217401 A JP 2009-263348 A JP-A-61-218556 JP 2000-290221 A

Encyclopedia of chemical processing and design Vol-1

  Although various problems described above have greatly improved the blockage problem caused by the polymerization of acrylic acid in the collection process for obtaining an aqueous acrylic acid solution, the purification process after the collection process still involves acrylic acid polymerization. The current situation has many problems. Except for some specific compounds, these problems have been studied as problems in the purification process itself, and appropriate countermeasures have been found, but they are still not sufficient and the effects on the collection process are suspected. However, the causal relationship has not been elucidated.

  This invention is made | formed in view of the said conventional actual condition, and makes it a subject to provide the manufacturing method of acrylic acid which prevents the superposition | polymerization of acrylic acid in the process of separating and refining acrylic acid from acrylic acid aqueous solution.

  The present inventor has studied to solve the above problems, and even if the composition of the acrylic acid aqueous solution finally obtained through the step of collecting acrylic acid is substantially equivalent, due to the difference in the collection method. Then, it was found that there was a difference in the occurrence of acrylic acid polymerization in the subsequent acrylic acid separation and purification step. And further investigation, when the acrylic acid in the acrylic acid-containing reaction product gas is collected as two kinds of acrylic acid aqueous solution at a specific ratio and sent to the separation and purification step of acrylic acid, It has been found that polymerization of acrylic acid in the process can be prevented.

  The present invention has been achieved on the basis of such findings, and the gist thereof is as follows.

[1] An oxidation reaction step of obtaining a reaction product gas containing acrylic acid by subjecting a hydrocarbon having 3 carbon atoms to gas phase catalytic oxidation, and introducing the reaction product gas containing acrylic acid into a quenching tower to produce a reaction containing acrylic acid A quenching process for condensing a part of acrylic acid in the gas, and an absorption process for obtaining an acrylic acid aqueous solution by introducing the acrylic acid-containing gas discharged from the quenching process into an absorption tower to which absorption water is supplied from the top of the tower A method for producing acrylic acid, wherein the condensate from the quenching step and the acrylic acid aqueous solution from the absorption step are fed to an acrylic acid separation and purification step to separate the acrylic acid, the quenching step In the method, the acrylic acid-containing reaction product gas is condensed with 25 to 65% of the acrylic acid, and the aqueous solution of acrylic acid from the absorption step is rapidly quenched without heating or cooling in the absorption step. A method for producing acrylic acid, which is fed to the acrylic acid separation and purification step without passing through the step.

[2] Oite to [1], the production method of acrylic acid, wherein the formaldehyde concentration of the condensate obtained in said rapid cooling step is 0.3 wt% or less.

  According to the present invention, acrylic acid is collected from an acrylic acid-containing reaction product gas obtained by a catalytic gas phase oxidation reaction, and an acrylic acid aqueous solution is distilled and purified to produce a product acrylic acid. In the collection step, a part of acrylic acid in the reaction product gas containing acrylic acid is liquefied (condensed) in the rapid cooling step, and the remaining part is absorbed in water in the absorption step to form an aqueous acrylic acid solution. Polymerization of acrylic acid in the acrylic acid separation and purification step can be effectively prevented by feeding it to the next separation and purification step without circulation to the step. For this reason, the blockage of equipment and piping facilities is prevented, and the strainer cleaning frequency during normal operation, the amount of polymerization inhibitor required, and the internal cleaning load during regular maintenance are reduced, ensuring stable and efficient performance over the long term. A typical acrylic acid can be produced.

It is a systematic diagram which shows roughly an example of the manufacturing equipment of acrylic acid for enforcing the method of this invention.

  Embodiments of the method for producing acrylic acid of the present invention will be described in detail below.

  The method for producing acrylic acid according to the present invention comprises an oxidation reaction step of obtaining a reaction product gas containing acrylic acid by subjecting a hydrocarbon having 3 carbon atoms to a gas phase catalytic oxidation reaction, and introducing the reaction product gas containing acrylic acid into a quenching tower Then, a quenching step for condensing a part of acrylic acid in the acrylic acid-containing reaction product gas, and an acrylic acid-containing gas discharged from the quenching step are introduced into an absorption tower to which absorbed water is supplied from the top of the tower. An acrylic acid aqueous solution having an absorption step of obtaining an acrylic acid aqueous solution, and supplying the condensed liquid from the quenching step and the acrylic acid aqueous solution from the absorption step to the next acrylic acid separation and purification step to separate the acrylic acid. It is a manufacturing method, Comprising: The acrylic acid aqueous solution from the said absorption process is supplied to the said acrylic-acid separation refinement | purification process, without passing through the said rapid cooling process.

  In the present invention, as described above, a part of acrylic acid in the acrylic acid-containing reaction product gas is condensed and liquefied in the quenching tower, and the acrylic acid in the exhaust gas of the quenching tower is absorbed in water by the absorption tower and acrylic acid is obtained. Prevent the polymerization of acrylic acid in the next acrylic acid separation and purification step by supplying it to the next step together with the acrylic acid-containing liquid from the quenching tower without circulating this acrylic acid aqueous solution to the quenching tower. The details of the mechanism of action that can be performed are not clear, but one reason is presumed as follows.

  The acrylic acid-containing reaction product gas contains a substance having a higher boiling point than acrylic acid (heavy) and a substance having a lower boiling point than acrylic acid (light). When such an acrylic acid-containing reaction product gas is quenched and a part of acrylic acid is liquefied (condensed), heavy components in the acrylic acid-containing reaction product gas are condensed together with the acrylic acid. The most abundant heavy component is maleic acid, and in addition there are various by-products such as phthalic acid, benzoic acid and trimellitic acid. In addition, the presence of oxidation catalyst powder, carbides and the like has been confirmed in an amount that is difficult to quantify. On the other hand, in an absorption tower in which acrylic acid in the exhaust gas of the quenching tower is absorbed by water, light components are absorbed by water together with acrylic acid. One of these light forms is formaldehyde. Formaldehyde is a substance with a very low boiling point (boiling point -21 ° C), but forms a wide variety of hydrates in water, and its behavior during distillation and condensation is similar to that of water (boiling point 100 ° C). . For this reason, when the acrylic acid aqueous solution of the absorption tower containing such formaldehyde is circulated to the quenching tower for condensing acrylic acid and heavy components, the high-temperature reaction gas, the heavy components and the light components are contained in the quenching tower. A state is formed in which the liquid containing the liquid comes into contact. This promotes the polymerization of acrylic acid or participates in the formation of substances that promote the polymerization of acrylic acid.

  In the present invention, the acrylic acid aqueous solution from the absorption tower containing light components such as formaldehyde is not circulated to the quenching tower to prevent any undesired reaction in the quenching tower, and polymerization of acrylic acid in the distillation purification process. Suppress.

  In the following, referring to FIG. 1 which is a system diagram schematically showing an example of a collection step in an acrylic acid production facility for carrying out the method of the present invention, the present invention will be described. As a representative example, production of acrylic acid using propylene as a raw material will be described as an example. However, the present invention is not limited to the production of acrylic acid using propylene as a raw material, but can be applied to the overall production of acrylic acid using a hydrocarbon having 3 carbon atoms as a raw material.

[Oxidation reaction process]
In the oxidation reaction step, air, steam and / or nitrogen as a diluent, and propylene as a reaction raw material are supplied to a first oxidation reactor (previous reactor) to convert propylene into acrolein. The reaction product gas of the oxidation reactor is supplied to the second oxidation reactor (the latter reactor) to convert acrolein into acrylic acid. The concentration of propylene in the reaction raw material gas supplied to the preceding reactor is usually 6 to 10% by volume, and the oxygen / propylene ratio is usually 1.5 to 2.5. The pre-reactor is filled with a solid oxidation catalyst composed of molybdenum (Mo) -bismuth (Bi) -based composite metal oxide, and the temperature is controlled to 300 to 350 ° C. by circulation of a heat medium. The structure of the former reactor is generally a multi-tube heat exchanger type or a plate heat exchanger type. The latter reactor is filled with a solid oxidation catalyst composed of a molybdenum (Mo) -vanadium (V) -based composite metal oxide, and the temperature is controlled to 250 to 300 ° C. by circulation of a heat medium. Air or the like may be added to the latter reactor. The structure of the latter reactor is the same as that of the former reactor. In addition, the reaction pressure of a front | former stage reactor and a back | latter stage reactor is 0.02-0.2 MPa-G (megapascal gauge) normally.

[Rapid cooling process]
The reaction product gas containing acrylic acid obtained in the oxidation reaction step is usually a high-temperature gas of about 250 to 300 ° C. and is cooled to about 140 to 200 ° C. by an indirect heat exchanger provided on the reactor outlet side. Then, it introduce | transduces into the quenching tower 1 through the piping 11 of FIG. 1, and a part of acrylic acid in gas is condensed and liquefied.
Quenching method in the quenching tower 1, as shown, a portion of the condensate in the bottom of the quenching tower 1 is extracted through a pipe 12 having a pump P _1, in the heat exchanger H ₁ to about 40 to 70 ° C. A direct quenching method is preferred in which after cooling it is circulated to the top of the quenching tower 1. As shown in FIG. 1, the circulating cooling liquid is not limited to a form in which the circulating cooling liquid is sprayed from one place in the quenching tower 1, and may be sprayed in a plurality of places in the height direction of the quenching tower 1.

  In the quenching tower 1, a part of water vapor and most of the maleic acid which is a reaction by-product can be condensed together with acrylic acid to obtain an acrylic acid aqueous solution having high acidity.

  In order to shorten the residence time as much as possible, the quenching tower 1 is preferably not provided with shelves or packing, and a form in which the circulating cooling liquid is sprayed with a shower nozzle is preferable. However, when drift occurs in the gas rising in the tower As a result, the efficiency of heat exchange between the circulating cooling liquid and the reaction gas is lowered, that is, a sufficient amount of condensate cannot be obtained. This tendency becomes stronger as the tower becomes larger. Therefore, in order to adjust the flow of the gas that rises in the tower, rectifying plates, baffle plates, shelves, etc. are added as necessary, but even if shelves are provided, the number of stages should be 2 or 3 or less. Is preferred. If the surface of the inserted plates is wet with the circulating cooling liquid, the part helps increase the efficiency of heat exchange. By subdividing the circulating coolant with a nozzle, heat exchange with the reaction product gas can be accelerated. However, if the sprayed coolant becomes mist, minute droplets of the coolant will rise with the reaction product gas rising in the quenching tower. Therefore, atomization should be avoided or lower than the quenching tower 1. It is preferable that only the provided nozzles are atomized. The condensate condensed in the quenching tower 1 (acrylic acid aqueous solution) is a small amount compared to the acrylic acid aqueous solution handled in the conventional absorption tower. Therefore, even in normal equipment design, the liquid holding amount of the quenching tower 1 is Less. The quenching tower 1 is preferably adapted to reduce the amount of liquid retained by reducing the diameter of the bottom of the tower or by forming an inverted cone.

  Since the operation temperature of the quenching tower 1 is relatively high at 75 to 90 ° C., it is preferable to supply a polymerization inhibitor. For this reason, in FIG. 1, the polymerization inhibitor is added to the circulating coolant pipe 12 from the pipe 13. Moreover, in order to suppress the increase of the acrylic acid dimer by Michael addition, it is preferable to refrain from supplying water as much as possible, and it is preferable to use acrylic acid as a solvent for the solution of the polymerization inhibitor. However, since the amount of the polymerization inhibitor solution to be supplied is usually a little less than 1% by weight compared to the condensate, the polymerization inhibitor can be dissolved and supplied in water or condensate. When acrylic acid is used as the solvent, a water-insoluble polymerization inhibitor such as phenothiazine can be used. Such a water-insoluble polymerization inhibitor has an advantage that the polymerization prevention effect can be maintained until a further downstream purification step.

  Since the reaction product gas supplied to the quenching tower 1 also contains solids and fine particles carried from the oxidation reaction system, a solids removal device such as a filter is installed in the condensate circulation pipe 12. It is desirable to do. The mesh size of the filter may be appropriately adjusted to the recommended value of the device manufacturer according to the specifications of the shower nozzle. In this case, if an insoluble polymer is generated in the quenching tower 1, a coarser filter is installed in front of the filter to more reliably avoid operation stoppage due to clogging of the shower nozzle. Can do.

In the quenching tower 1, the amount of heat to be cooled is such that one or more of the amount and temperature of the liquid to be condensed, the gas temperature at the top of the quenching tower 1, and the temperature at the top of the absorption tower 2 described later are within a certain range. It is desirable to control. As changing the cooling to heat, like the process side fluid outlet temperature of the heat exchanger H ₁ becomes constant, while changing the amount of refrigerant supplied to the heat exchanger H _1, is circulated and supplied to the heat exchanger H ₁ By changing the amount of refrigerant supplied to the heat exchanger H ₁ while keeping the flow rate of the process fluid circulated and supplied to the heat exchanger H ₁ constant. There is a method of changing the process side fluid outlet temperature of the exchanger H ₁ . For example, when the tower bottom liquid is extracted from the bottom of the quenching tower 1 through the pipe 19 at a constant speed, the amount of liquid to be condensed is adjusted by adjusting the amount of heat to be cooled so that the liquid level height at the bottom of the quenching tower is constant. Is kept constant.

The tower bottom liquid of the quenching tower 1 is usually an acrylic acid aqueous solution having the following composition, and the remainder of the circulating cooling liquid to be circulated through the pipe 12 passes through the pipe 19 having the pump P ₂ , and the subsequent acrylic acid separation and purification step. 3 is sent.

<Tower liquid composition>
Acrylic acid: 65-80% by weight
Maleic acid: 0.5 to 3% by weight
Acetic acid: 1.5 to 3% by weight
Formaldehyde: 0.05-0.3% by weight
Water: 15-35% by weight

  On the other hand, the top gas of the quenching tower 1 is fed to the absorption tower 2 through the pipe 14.

  In the present invention, the amount of acrylic acid condensed in the quenching tower 1 (hereinafter referred to as “acrylic acid condensation ratio”) is preferably 25 to 65% of acrylic acid in the acrylic acid-containing reaction product gas. When the acrylic acid condensation rate is lower than the lower limit, stable operation of the quenching tower 1 is difficult. On the other hand, when the acrylic acid condensation rate is higher than the upper limit, a large amount of water vapor is condensed together with acrylic acid. It is impossible to sufficiently obtain the effect of preventing polymerization of acrylic acid in the step 3 for separating and purifying acrylic acid.

  In view of the stable operation of the quenching tower 1 and the effect of preventing polymerization of acrylic acid in the acrylic acid separation and purification step 3, the condensation ratio of acrylic acid in the quenching tower is preferably 25 to 65%, particularly preferably 25 to 50%. The formaldehyde concentration of the condensate obtained in the column 1 is preferably 0.3% by weight or less.

[Absorption process]
The exhaust gas obtained from the top of the quenching tower 1 contains uncondensed acrylic acid and light components in the reaction product gas, and is sent from the pipe 14 to the lower part of the absorption tower 2. It is desirable that the absorption tower 2 is substantially composed only of a tower body and does not have a heat exchanger for heating or cooling, or a circulation line thereof. Since the absorption tower 2 has a simple structure in which water or an aqueous solution for absorbing acrylic acid is supplied from the top of the tower, and the acrylic acid is absorbed and then taken out from the bottom of the tower, the residence time in the tower can be shortened. it can. In order to absorb acrylic acid efficiently, a corresponding number of theoretical plates is required. Since the increase in the number of theoretical plates is accompanied by an increase in the equipment cost, the number of required theoretical plates in consideration of economics varies depending on the situation, but is usually at least 10 theoretical plates, preferably about 20 theoretical plates. Although there are a shelf and a packing as the insertion in the tower, the absorption tower 2 is preferably a packed tower in order to shorten the residence time. The temperature in the absorption tower 2 is usually relatively low, about 55 ° C. to 75 ° C., the residence time is short, and there is almost no maleic acid. Therefore, the amount of acrylic acid dimer produced by Michael addition is higher than that of the quenching tower 1. It is so small that it can be ignored.

  In the absorption tower 2, although the risk of polymerization blockage is low, in order to realize a more stable operation, it is desirable to supply a small amount of polymerization inhibitor from the top of the tower. As the solvent for dissolving the polymerization inhibitor, water or an aqueous solution used for absorption is optimal. In FIG. 1, a water-soluble polymerization inhibitor is added to the absorption water introduction pipe 15 from the pipe 16. Examples of the water-soluble polymerization inhibitor used here include phenol compounds, manganese and copper acetate compounds, and alkyl pyridyl oxide compounds.

  The absorption tower 2 has substantially no change other than the flow rate of the absorption water and the polymerization inhibitor solution supplied from the top of the tower, and there is no operation condition that needs to be changed or adjusted as long as the absorption tower 2 is operated under a constant condition. However, in order to confirm that the operation is stable, it is preferable to monitor the flow rate of the liquid extracted from the column bottom, the pressure at the column top / column bottom, and the temperature in the column.

In the absorption tower 2, the resulting acrylic acid aqueous solution is usually about 55 to 75 ° C. having the following composition, and after being cooled to about 20 to 40 ° C. by the heat exchanger H ₂ , the absorption tower from the pipe 18 having a pump P ₃ through the second lower liquid retaining portion 2A is fed to the acrylic acid separation purification step 3. However, when an aqueous solution containing impurities other than water is used as the absorbing solvent, the impurity concentration of the aqueous acrylic acid solution obtained accordingly increases.

<Acrylic acid aqueous solution composition>
Acrylic acid: 50-65% by weight
Maleic acid: 0.2% by weight or less Acetic acid: 2-3% by weight
Formaldehyde: 1-3% by weight
Water: 35-60% by weight

  The exhaust gas discharged from the top of the absorption tower 2 via the pipe 17 usually contains water, oxygen (2 to 6% by volume), carbon dioxide, and organic substances such as acetic acid, formaldehyde, and acrylic acid. If necessary, an oxygen source such as air is added, and after being treated by a normal catalytic combustion method, it is discharged out of the system.

[Transmission of condensate and acrylic acid aqueous solution]
In the present invention, the condensate from the bottom of the quenching tower 1 and the acrylic acid aqueous solution from the absorption tower 2 may be mixed and supplied to the extraction tower or distillation tower which is the next acrylic acid separation and purification step 3. However, since it is desirable to change a supply location according to the difference in composition, it is desirable to feed each to the acrylic acid separation and purification step 3 without mixing. Specifically, in the azeotropic dehydration distillation tower, the condensate from the quenching tower having a higher acrylic acid concentration is supplied below the distillation tower than the acrylic acid aqueous solution from the absorption tower 2, and in the extraction tower, On the other hand, it is desirable to supply more upward.

  In any case, in the present invention, the acrylic acid aqueous solution from the absorption tower 2 is fed to the acrylic acid separation and purification step 3 without being circulated to the quenching tower 1. Also, the condensate from the quenching tower 1 is naturally fed to the acrylic acid separation and purification step 3 without passing through the absorption tower 2.

[Acrylic acid separation and purification process]
In this invention, there is no restriction | limiting in particular about the acrylic acid separation refinement | purification process in which the condensate from the quenching tower 1 and the acrylic acid aqueous solution from the absorption tower 2 are introduce | transduced, Acrylic acid is purified by distillation through the extraction tower using a solvent. It may be supplied to a distillation column, or may be supplied to a distillation column through which an acrylic acid is further purified by distillation through an azeotropic distillation column using a solvent. Further, the acrylic acid distillation purification step may be a multistage distillation system in which treatment is sequentially performed in a light boiling separation distillation column, a heavy boiling separation distillation column, and a purification distillation column.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example of oxidation reaction]
<Oxidation reaction example 1>
As a reaction raw material gas, a mixed gas composed of 9% by volume of propylene, air and water vapor is supplied to a single-tube first stage reactor having an inner diameter of 25 mm and a length of 3 m filled with a Mo—Bi-based solid oxidation catalyst. In which propylene is oxidized to acrolein, and then the gas is supplied to a single-tube post-stage reactor having an inner diameter of 25 mm and a length of 2.5 m, which is filled with a Mo-V solid oxidation catalyst, and from the reactor, A reaction product gas 1 containing 65.4% by volume of nitrogen and oxygen, 23.8% by volume of water vapor, and 8.1% by volume of acrylic acid and having 650 g / h equivalent as acrylic acid was obtained.

<Oxidation reaction example 2>
A gas phase catalytic oxidation reaction was carried out in the same manner as in Oxidation Reaction Example 1 except that a mixed gas consisting of 9% by volume of propylene, air, water vapor and nitrogen was used as the reaction raw material gas, and nitrogen and oxygen 69.8 volumes. %, Water vapor 19.3% by volume, acrylic acid 8.0% by volume, and a reaction product gas 2 having an acrylic acid equivalent of 640 g / h was obtained.

<Oxidation reaction example 3>
Nitrogen and oxygen 62.6% by volume, water vapor 28.6 in the same manner as in the oxidation reaction example 1 except that a mixed gas composed of 7.5% by volume propylene, air, water vapor and nitrogen was used as the reaction raw material gas. A reaction product gas 3 containing vol% and acrylic acid 6.8 vol% and having an acrylic acid equivalent to 500 g / h was obtained.

[Device configuration and operating conditions]
The structures and operating conditions of the quenching tower and the absorption tower used in the following examples, reference examples and comparative examples are as follows.

<Quenching tower>
The quenching tower is a vertical cylindrical shape having an inner diameter of 100 mm and a height of 400 mm. Within the tower, four plates are erected at intervals of 20 mm from the bottom of the tower to the middle position in the height direction of the tower. Yes. The plate is intended to arrange the flow of the reaction gas in the tower and to exchange heat between the circulating coolant and the reaction gas on the plate surface. The reaction product gas is supplied to the lower part of the side of the quenching tower by a double pipe maintained at 140 ° C. or higher by steam. Most of the condensate in the tower extracted from the bottom of the quenching tower by piping is cooled to 40 ° C. with a double-pipe heat exchanger by a feed pump, and then circulated to the quenching tower as a circulating cooling liquid, with the remainder Is branched off at the piping tip at the bottom of the tower and extracted from the system by a liquid feed pump.
Acrylic acid having 1.5% by weight of phenothiazine as a polymerization inhibitor is added to the circulating coolant pipe at a rate of 5 mL / h. The piping of the circulating cooling liquid is divided into two parts, and the circulating cooling liquid is supplied to the center position and the upper part of the side surface of the quenching tower in the height direction. A shower nozzle is installed at each end of the supply pipe.
The tower top of the quenching tower and the lower part of the side face of the absorption tower described later are connected by a pipe for introducing uncondensed gas.

<Absorption tower>
The absorption tower is a packed tower having an inner diameter of 50 mm, a height of 900 mm, and a coil pack of 5 mm as an insert. The residual gas discharged from the top of the absorption tower is sent to an exhaust gas combustion apparatus through a cleaning device using caustic soda. Absorption water is supplied from the upper side of the absorption tower while adjusting the flow rate according to the operating conditions. Further, an aqueous solution containing 5% by weight of hydroquinone as a polymerization inhibitor is added to the absorbed water at a rate of 5 mL / h. A piping and a switching valve are provided so that the aqueous acrylic acid solution extracted from the bottom of the absorption tower can be extracted out of the system as it is or can be circulated to the quenching tower.

[Comparative Example 1]
<Collection of acrylic acid>
The reaction product gas 1 was led to the quenching tower, and all the bottom liquid of the absorption tower was circulated to the quenching tower. Absorption water to the absorption tower was supplied at a rate of 400 g / h. The amount of circulating coolant supplied to the heat exchanger of the quenching tower was adjusted so that the acrylic acid concentration of the condensate in the quenching tower was about 60% by weight. The bottom liquid obtained in the quenching tower is acrylic containing 60.9% by weight of acrylic acid, 34.6% by weight of water, 2.6% by weight of acetic acid, 0.9% by weight of formaldehyde and 0.5% by weight of maleic acid. It was an acid aqueous solution.

<Concentration adjustment, filtration, dehydration distillation>
A small amount of distilled water was added to the resulting aqueous acrylic acid solution to adjust the acrylic acid concentration to 60% by weight, and suction filtration was performed with a filter having a mesh size of 1 μm. 200 g of that was added to a round bottom flask together with 20 g of toluene, A 600 mm high column filled with a 3 mm coil pack was placed in the flask. The column top pressure was reduced to 10 kPa, and toluene containing 50 wt ppm of phenothiazine was supplied from the column top at a rate of 300 ml / h for dehydration distillation. During the distillation operation, air was continuously blown into the liquid in the flask at a rate of 5 ml / min.
The oil bath temperature for heating was fixed at 98 ° C., and dehydration distillation was continued for about 80 minutes until the liquid temperature in the flask reached 85 ° C. as an indicator that water and toluene in the flask were substantially lost. did.

<Suction filtration>
When the obtained crude acrylic acid was cooled to 20 ° C. and subjected to suction filtration at a reduced pressure of −50 kPa with a filter having a mesh size of 1 μm, clogging was observed. The recovery rate calculated by the ratio of the amount of filtrate to the amount of crude acrylic acid subjected to suction filtration was 40%.

[Example 1]
In Comparative Example 1, the bottom liquid of the absorption tower was taken out without being circulated to the quenching tower.
The condensed liquid obtained from the quenching tower contained 78% by weight of acrylic acid, 17.3% by weight of water, 2.4% by weight of acetic acid, 1.9% by weight of maleic acid, and 0.1% by weight of formaldehyde. The acid was 30% in the reaction product gas 1 (acrylic acid condensation ratio = 30%).
In addition, by adjusting the amount of water absorbed in the absorption tower to 450 g / h, the composition of the mixed liquid in which the condensate in the quenching tower and the bottom liquid in the absorption tower were mixed was 61.3% by weight of acrylic acid, water The content was 34.3% by weight, acetic acid 2.5% by weight, formaldehyde 1.0% by weight, and maleic acid 0.5% by weight.
When this mixture was subjected to concentration adjustment, filtration, dehydration distillation, and suction filtration in the same manner as in Comparative Example 1, clogging and the like were not confirmed, and the entire amount could be suction filtered at a reduced pressure of −30 kPa. (Recovery rate 100%).

[Example 2]
In Example 1, acrylic acid was collected from the reaction product gas 1 in the same manner except that maleic acid was added at a rate of 3 g / h in the absorption water supplied to the absorption tower.
The composition of the mixed liquid obtained by mixing the condensate of the quenching tower and the bottom liquid of the absorption tower is 60.3% by weight of acrylic acid, 35.2% by weight of water, 2.6% by weight of acetic acid, 1.0% by weight of formaldehyde, Maleic acid was 0.8% by weight.
When this mixed solution was filtered, dehydrated and distilled and then suction filtered in the same manner as in Comparative Example 1, no obvious clogging or the like was confirmed, and the entire amount was suction filtered at a reduced pressure of −30 kPa ( Recovery rate 100%).

[Reference Example 1]
In Example 1, acrylic acid was collected from the reaction product gas 1 in the same manner except that formaldehyde was added at a rate of 10 g / h to the circulating coolant of the quenching tower.
The condensate obtained from the quenching tower contains 76.3% by weight of acrylic acid, 19.0% by weight of water, 2.3% by weight of acetic acid, 1.9% by weight of maleic acid, and 0.4% by weight of formaldehyde. Acrylic acid was 30% in the reaction product gas 1 (condensation ratio of acrylic acid = 30%).
The composition of the mixed liquid obtained by mixing the condensate of the quenching tower and the bottom liquid of the absorption tower was 60.3% by weight of acrylic acid, 34.7% by weight of water, 2.5% by weight of acetic acid, and 1.8% by weight of formaldehyde. % And maleic acid 0.5% by weight.
When this mixed liquid was filtered, dehydrated and distilled and then suction filtered in the same manner as in Comparative Example 1, clogging was observed, and the liquid volume was 70% of the total at a reduced pressure of −50 kPa (recovery rate 70). %).
In Reference Example 1, it is estimated that clogging occurred due to the addition of formaldehyde to the circulating coolant in the quenching tower.

[Example 3]
In Example 1, by increasing the amount of cooling water supplied to the heat exchanger of the quenching tower, 67% by weight of acrylic acid, 29.1% by weight of water, and 2.4% by weight of acetic acid are used as the bottom liquid of the quenching tower. A condensate of 1.0% by weight maleic acid and 0.3% by weight formaldehyde was obtained. The condensed acrylic acid was 55% in the reaction product gas (acrylic acid condensation ratio = 55%).
In addition, by adjusting the supply amount of absorbed water in the absorption tower to 300 g / h, 60.0% by weight of acrylic acid and 35. A liquid mixture having a composition of 3% by weight, acetic acid 2.4% by weight, formaldehyde 1.1% by weight and maleic acid 0.5% by weight was obtained.
When this mixture was subjected to concentration adjustment, filtration, dehydration distillation, and suction filtration in the same manner as in Comparative Example 1, a decrease in filtration rate due to clogging was confirmed, but the entire amount was sucked at a reduced pressure of less than -50 kPa. It could be filtered (100% recovery).

[Comparative Example 2]
In Example 3, by further increasing the amount of cooling water supplied to the heat exchanger of the quenching tower, 62.5% by weight of acrylic acid, 33.5% by weight of water, acetic acid, 2. A condensate of 4% by weight, 0.7% by weight maleic acid and 0.4% by weight formaldehyde was obtained. The condensed acrylic acid was 70% in the reaction product gas (acrylic acid condensation ratio = 70%).
Further, in the absorption tower, by adjusting the supply amount of absorbed water to 200 g / h, 62.0% by weight of acrylic acid and water 33 are obtained as a mixed liquid in which the condensate of the quenching tower and the bottom liquid of the absorption tower are mixed. A mixed solution having a composition of 1% by weight, 2.5% by weight of acetic acid, 1.1% by weight of formaldehyde and 0.5% by weight of maleic acid was obtained.
When this mixture was subjected to concentration adjustment, filtration, dehydration distillation, and suction filtration in the same manner as in Comparative Example 1, the filtrate that could be filtered at a reduced pressure of -50 kPa was 20% of the total (recovery rate 20%). ). The suction pressure was further reduced to -80 kPa, but the filtrate amount was 25% of the total (recovery rate 25%).
Further, the same operation as described above was performed except that the amount of the polymerization inhibitor supplied to the quenching tower and the absorption tower was doubled, but the amount of the filtrate that could be finally suction filtered was 20% of the whole. (Recovery rate 20%).

[Comparative Example 3]
In Example 1, by reducing the amount of cooling water supplied to the heat exchanger of the quenching tower, the bottom liquid of the quenching tower was 80.1% by weight of acrylic acid, 14.5% by weight of water, 2.2% of acetic acid. A condensate of 5% by weight, 2.7% by weight maleic acid and 0.05% by weight formaldehyde was obtained. The condensed acrylic acid was 20% in the reaction product gas (acrylic acid condensation ratio 20%).
In addition, by adjusting the amount of absorption water supplied to the absorption tower to 480 g / h, a mixed liquid of the condensate of the quenching tower and the bottom liquid of the absorption tower was mixed with 60.7% by weight of acrylic acid, 34. A liquid mixture having a composition of 4 wt%, acetic acid 2.4 wt%, formaldehyde 0.8 wt%, and maleic acid 0.5 wt% was obtained.
However, generation of insoluble polymer was confirmed in the quenching tower, and the mixed solution was not capable of suction filtration after concentration adjustment.
Further, the same operation as described above was performed except that the amount of the polymerization inhibitor supplied to the quenching tower and the absorption tower was doubled, but the suction filtration treatment was impossible.

[Comparative Example 4]
The reaction product gas 2 was introduced to the quenching tower, and the bottom liquid of the absorption tower was circulated to the quenching tower. Absorbed water to the absorption tower was supplied at a rate of 370 g / h. The amount of cooling water supplied to the heat exchanger of the quenching tower was adjusted so that the acrylic acid concentration in the condensate of the quenching tower was about 60% by weight. The bottom liquid obtained in the quenching tower contains 61.1% by weight of acrylic acid, 34.4% by weight of water, 2.7% by weight of acetic acid, 0.9% by weight of formaldehyde, and 0.5% by weight of maleic acid. It was.
When this tower bottom liquid was subjected to concentration adjustment, filtration, dehydration distillation, and suction filtration in the same manner as in Comparative Example 1, clogging was observed, and the filtrate amount was 20% of the total (recovery rate 20%). ).

[Example 4]
In Comparative Example 4, the bottom liquid of the absorption tower was taken out without being circulated to the quenching tower. The condensate obtained from the quenching tower contains 78.9% by weight of acrylic acid, 16.2% by weight of water, 2.4% by weight of acetic acid, 1.9% by weight of maleic acid, and 0.1% by weight of formaldehyde. Acrylic acid was 30% in the reaction product gas 2 (acrylic acid condensation ratio = 30%).
Moreover, by adjusting the supply amount of absorbed water in the absorption tower to 410 g / h, as a mixed liquid in which the condensate of the quenching tower and the bottom liquid of the absorption tower are mixed, 60.2% by weight of acrylic acid, 35. A mixed solution having a composition of 3 wt%, acetic acid 2.6 wt%, formaldehyde 0.9 wt%, and maleic acid 0.5 wt% was obtained.
The mixture was filtered, dehydrated and distilled in the same manner as in Comparative Example 1, and then suction filtration was performed. A slight decrease in filtration rate due to clogging was confirmed, but the entire amount was suction filtered at a reduced pressure of -30 kPa. (Recovery rate 100%).

[Comparative Example 5]
The reaction product gas 3 was introduced to the quenching tower, and the bottom liquid of the absorption tower was circulated to the quenching tower. Absorption water to the absorption tower was supplied at a rate of 360 g / h. The amount of cooling water supplied to the heat exchanger of the quenching tower was adjusted so that the acrylic acid concentration in the condensate of the quenching tower was about 60% by weight. The bottom liquid obtained in the quenching tower contains 60.4% by weight of acrylic acid, 35.1% by weight of water, 2.6% by weight of acetic acid, 1.0% by weight of formaldehyde and 0.5% by weight of maleic acid. It was.
When this column bottom liquid was filtered, dehydrated and distilled and then suction filtered in the same manner as in Comparative Example 1, clogging was observed, and the filtrate amount at a suction pressure of −80 kP was 20% of the total (recovery). Rate 20%).

[Example 5]
In Comparative Example 5, the liquid at the bottom of the absorption tower was taken out without circulating to the quenching tower. The condensate obtained from the quenching tower contains 65.7% by weight acrylic acid, 30.5% by weight water, 2.1% by weight acetic acid, 1.2% by weight maleic acid and 0.2% by weight formaldehyde. Acrylic acid was 40% in the reaction product gas 3 (condensation ratio of acrylic acid = 40%).
Moreover, by adjusting the supply amount of absorbed water in the absorption tower to 330 g / h, a mixed liquid of the condensate in the quenching tower and the bottom liquid in the absorption tower is mixed with 61.2% by weight of acrylic acid and 34. A liquid mixture having a composition of 8 wt%, acetic acid 2.6 wt%, formaldehyde 0.9 wt%, and maleic acid 0.5 wt% was obtained.
When this mixture was subjected to concentration adjustment, filtration, dehydration distillation, and suction filtration in the same manner as in Comparative Example 1, clogging and the like were not confirmed, and the entire amount could be suction filtered at a reduced pressure of −30 kPa. (Recovery rate 100%).

1 quenching tower 2 absorption tower 3 acrylic acid separation and purification process P ₁ , P ₂ , P ₃ pump H ₁ , H ₂ heat exchanger

Claims (2)

An oxidation reaction step of obtaining a reaction product gas containing acrylic acid by subjecting a hydrocarbon having 3 carbon atoms to a gas phase catalytic oxidation reaction;
A quenching step of introducing the acrylic acid-containing reaction product gas into a quenching tower and condensing a part of the acrylic acid in the acrylic acid-containing reaction product gas;
An absorption step of introducing an acrylic acid-containing gas discharged from the quenching step into an absorption tower to which absorption water is supplied from the top of the tower to obtain an aqueous acrylic acid solution,
A method for producing acrylic acid, wherein the condensate from the quenching step and the acrylic acid aqueous solution from the absorption step are fed to an acrylic acid separation and purification step to separate the acrylic acid,
In the quenching step, 25 to 65% of acrylic acid in the acrylic acid-containing reaction product gas is condensed,
Without heating or cooling in the absorption step,
A method for producing acrylic acid, wherein the aqueous acrylic acid solution from the absorption step is fed to the acrylic acid separation and purification step without going through the quenching step. Oite to claim 1, method for producing acrylic acid, wherein the formaldehyde concentration of the condensate obtained in said rapid cooling step is 0.3 wt% or less.

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