JP6907516B2 - (Meta) Acrylic acid manufacturing method - Google Patents

Description

The present invention relates to a method for producing (meth) acrylic acid, which comprises extracting (meth) acrylic acid with an organic solvent. In particular, in the production process of (meth) acrylic acid, the heat load in the distillation process is reduced to perform an energy-advantageous operation, the occurrence of oil-water suspension state in the extraction process is prevented, and water separation in the extraction process is performed. It relates to a method for producing high quality (meth) acrylic acid in a stable manner while maintaining good quality.

(Meta) acrylic acid [acrylic acid and / or methacrylate] is propylene or propane which is a hydrocarbon having 3 (C3) carbon atoms or isobutylene or butanol which is a hydrocarbon having 4 carbon atoms (C4) and tertiary butanol. Is obtained as an oxidation reaction gas by vapor-phase catalytic oxidation using two types of solid catalysts together with air, which is an oxygen source, and steam and nitrogen. After cooling, the obtained oxidation reaction gas is separated as a (meth) acrylic acid aqueous solution by gas-liquid contact with absorbed water containing a polymerization inhibitor in an absorption tower, and the unabsorbed gas is introduced into the waste gas treatment step. It is detoxified and then discarded, but part of it is recycled in the oxidation reaction process.

The (meth) acrylic acid aqueous solution obtained from the absorption tower is usually purified by extraction or azeotropic distillation to produce (meth) acrylic acid (Non-Patent Document 1). In the extraction method, an aqueous solution of (meth) acrylic acid is extracted in an extraction tower using an extraction solvent selected from ketones, alcohols, ethers, esters or hydrocarbons, and extracted with (meth) acrylic acid. It becomes an extract that is a mixed solution with a solvent. This extract is further introduced into the (meth) acrylic acid purification system and refined by distillation, crystallization, etc. to obtain the (meth) acrylic acid of the product.

In the manufacturing process of (meth) acrylic acid, stains such as polymers accumulate in the equipment and piping, so it is necessary to periodically open-clean the equipment. At that time, the accumulated liquid in each device is discharged once and held in a storage tank such as a tank. In addition, an operation trouble occurs, and a discharge liquid is generated when the process is partially or wholly stopped. These effluents contain a large amount of valuable resources such as acrylic acid, and it is not preferable to dispose of them in terms of basic unit. Therefore, it is necessary to re-deliver these discharged liquids into the process after the cleaning is completed and the operation of the process is restarted. In addition, these discharged liquids may contain a large amount of water, and ideally they are sent to an extraction step, which is a step of removing water from acrylic acid. However, at the same time, these effluents also contain components that have an adverse effect on oil-water separation, although the exact origin has not been clarified. Therefore, when these discharged liquids are sent to the extraction step, depending on the content of the oil-water separation deterioration component and the operating conditions, a suspension state of oil-water may occur, resulting in poor separation, which may cause an operation trouble. Therefore, in the prior art, these effluents have been sent to the distillation process (for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2003-292470 Japanese Unexamined Patent Publication No. 2013-151455

Eizo Omori, "Acrylic Acid and Its Polymer [I]", 3rd Edition, Shokodo Co., Ltd., April 28, 1978, p10 to 13 (1.4 Purification method of acrylic acid)

As described above, the effluent discharged from the (meth) acrylic acid production process also contains components with large latent heat of vaporization such as water, and when the operation is carried out by the above method, the distillation column is multi-staged. It was energetically disadvantageous because it was necessary to take measures such as increasing the heat load during operation. In addition, the reboiler and extraction pipe of the distillation column are contaminated due to the influence of components such as (meth) acrylic acid oligomers / polymers, maleic acid derivatives, and phenolic resins contained in the waste liquid, increasing the frequency of open cleaning of equipment. There were also concerns.
The present invention reduces the heat load in the distillation step in the (meth) acrylic acid production process to perform an energetically advantageous operation, prevents the occurrence of an oil-water suspension state in the extraction step, and prevents water in the extraction step. An object of the present invention is to provide a method for stably producing high-quality (meth) acrylic acid while maintaining good separation.

As a result of diligent studies to solve the above problems, the present inventors reduced the heat load in the distillation process by sending the effluent discharged from the (meth) acrylic acid production process to the extraction process. It was found that the operation is energetically advantageous and the pollution derived from the effluent can be reduced. However, as described above, the effluent discharged from the (meth) acrylic acid production process may contain a large amount of components that adversely affect oil-water separation, and these components are sent to the extraction process. This may worsen the oil-water separation in the extraction process. If the oil-water separation deteriorates in the extraction process, water may be distributed downstream in a state of being contained in the extraction solvent, which may cause an increase in the purification load and deterioration of product quality in the downstream. In order to prevent them, it is conceivable to maintain the liquid load below a certain level to ensure oil-water separation, but for that purpose, it is necessary to set a limit on the processing capacity during operation, and in some cases production. It causes a decrease in ability.

As a result of further studies to solve this problem, the present inventors have carried out the following operations to prevent deterioration of oil-water separation in the extraction process and to stably perform high-quality (meth) acrylic acid. Found that it can be manufactured.
(A) A liquid containing the discharge liquid discharged from the (meth) acrylic acid production process is held as a recovery liquid, and the held recovery liquid is sent to the extraction step.
(B) The recovered liquid is sent to the same place where the (meth) acrylic acid aqueous solution is supplied in the extraction step.
(C) The concentration of the Michael adduct in the mixed composition of the (meth) acrylic acid aqueous solution and the recovery liquid is 0.05 to 0.7% by weight.
(D) After distilling the recovered liquid, the distillate is sent to the extraction step.
(E) After separating the recovered liquid into oil and water, the oil phase is sent to the extraction step.
(F) The extraction temperature in the extraction step is adjusted to 30 to 90 ° C.

The prior art does not have the above problems. That is, the present invention has found and solved a novel problem that has not been recognized at all in the past. Those skilled in the art who are not aware of the above problems usually do not reduce the cost merit of adding new steps such as retention of recovered liquid, distillation, oil-water separation, or equipment for performing these to the manufacturing process. In addition, in continuous production, in the extraction process, it is basic to set a constant amount of charge and charge ratio, but the extraction step is to extract the liquid obtained by operations such as holding the recovered liquid, distilling, and separating oil and water. It is not usually carried out to send the liquid to the liquid because it includes the possibility of causing fluctuations in the charging amount and the charging ratio. That is, in the production of (meth) acrylic acid, it is not usually carried out to send the discharged liquid to the extraction step after taking a lot of time and effort.

The present invention is as follows.
<1>
An oxidation reaction step of obtaining a reaction gas containing (meth) acrylic acid by vapor-phase catalytic oxidation, an absorption step of bringing the reaction gas into gas-liquid contact with water to obtain a (meth) acrylic acid aqueous solution, and the (meth) acrylic. A (meth) acrylic acid comprising an extraction step of contacting an aqueous acid solution with an extraction solvent to extract crude (meth) acrylic acid and a distillation step of distilling (meth) acrylic acid from the crude (meth) acrylic acid. In the manufacturing method
(Meta) acrylic, in which a liquid containing the drained liquid discharged from at least one step of the step is used as a recovery liquid, the recovered liquid is held for 1 to 60 days, and the held recovered liquid is sent to the extraction step. Method of producing acid.
<2>
An oxidation reaction step of obtaining a reaction gas containing (meth) acrylic acid by vapor-phase catalytic oxidation, an absorption step of bringing the reaction gas into gas-liquid contact with water to obtain a (meth) acrylic acid aqueous solution, and the (meth) acrylic. A (meth) acrylic acid comprising an extraction step of contacting an aqueous acid solution with an extraction solvent to extract crude (meth) acrylic acid and a distillation step of distilling (meth) acrylic acid from the crude (meth) acrylic acid. In the manufacturing method
A liquid containing the discharge liquid discharged from at least one step of each step is used as a recovery liquid, the recovery liquid is separated into oil and water, and the oil phase separated by the oil and water is sent to the extraction step. Production method.
<3>
An oxidation reaction step of obtaining a reaction gas containing (meth) acrylic acid by vapor-phase catalytic oxidation, an absorption step of bringing the reaction gas into gas-liquid contact with water to obtain a (meth) acrylic acid aqueous solution, and the (meth) acrylic. A (meth) acrylic acid comprising an extraction step of contacting an aqueous acid solution with an extraction solvent to extract crude (meth) acrylic acid and a distillation step of distilling (meth) acrylic acid from the crude (meth) acrylic acid. In the manufacturing method
A method for producing (meth) acrylic acid, which comprises using a liquid containing the discharge liquid discharged from at least one step of each step as a recovery liquid, distilling the recovery liquid, and sending the distilled distillate to the extraction step. .. <4>
The method for producing (meth) acrylic acid according to any one of <1> to <3>, wherein in at least one step of each step, the reaction product in the step and the discharged liquid in the step are discharged at the same time. ..
<5>
The method for producing (meth) acrylic acid according to any one of <1> to <4>, wherein the recovered liquid contains water.
<6>
The (meth) acrylic acid according to any one of <1> to <5>, wherein the recovery liquid to be sent to the extraction step is supplied to the same place where the (meth) acrylic acid aqueous solution is supplied in the extraction step. Manufacturing method.
<7>
The (meth) according to any one of <1> to <6>, wherein the concentration of the Michael adduct in the mixed composition of the recovered liquid and the (meth) acrylic acid aqueous solution is 0.05 to 0.7% by weight. ) Acrylic acid manufacturing method.
<8>
The method for producing (meth) acrylic acid according to any one of <1> to <7>, wherein the extraction temperature in the extraction step is 30 to 90 ° C.
<9>
The (meth) acrylic acid according to any one of <1> to <8>, wherein the extraction solvent is a solvent containing a water-insoluble aromatic compound having a boiling point lower than the boiling point of (meth) acrylic acid as a main component. Manufacturing method.
<10>
The method for producing (meth) acrylic acid according to <9>, wherein the water-insoluble aromatic compound is at least one compound selected from the group consisting of benzene, toluene and xylene.

According to the present invention, it is possible to reduce the heat load of the distillation step in the production process of (meth) acrylic acid, perform an energy-advantageous operation, and reduce the contamination derived from the effluent. Furthermore, it is possible to prevent deterioration of oil-water separation in the extraction step, maintain a high level of water and other impurity removal performance, and stably produce high-quality (meth) acrylic acid.

It is the schematic which shows an example of the (meth) acrylic acid production facility of this invention.

Hereinafter, embodiments of the method for producing (meth) acrylic acid of the present invention will be described in detail.
The method for producing (meth) acrylic acid of the present invention is an oxidation reaction step of obtaining a reaction gas containing (meth) acrylic acid by vapor phase catalytic oxidation, and (meth) acrylic by bringing the reaction gas into gas-liquid contact with water. An absorption step of making an acid aqueous solution, an extraction step of bringing the (meth) acrylic acid aqueous solution into contact with an extraction solvent to extract crude (meth) acrylic acid, and a (meth) acrylic acid from the crude (meth) acrylic acid. In a method for producing (meth) acrylic acid including a distillation step of distilling, a liquid containing a liquid discharged from at least one step of the step is held as a recovery liquid, and the held recovery liquid is sent to the extraction step. It is essential to make a liquid ((a) below), and preferably, the operation is performed so as to satisfy the following conditions ((b) to (f) below).
(A) A liquid containing the discharge liquid discharged from the (meth) acrylic acid production process is held as a recovery liquid, and the held recovery liquid is sent to the extraction step.
(B) The recovered liquid is sent to the same place where the (meth) acrylic acid aqueous solution is supplied in the extraction step.
(C) The concentration of the Michael adduct in the mixed composition of the (meth) acrylic acid aqueous solution and the recovery liquid is 0.05 to 0.7% by weight.
(D) After distilling the recovered liquid, the distillate is sent to the extraction step.
(E) After separating the recovered liquid into oil and water, the oil phase is sent to the extraction step.
(F) The extraction temperature in the extraction step is adjusted to 30 to 90 ° C.

As described in (a), the present invention is characterized in that a liquid containing the discharge liquid discharged from the (meth) acrylic acid production process is held as a recovery liquid in, for example, a storage tank. The recovered liquid may be recovered during the production of (meth) acrylic acid or may be recovered when the production is stopped. Further, the supply of the reactant and the discharge of the discharged liquid in each step may be performed at the same time. By holding the recovered liquid, the discharged liquids having various compositions are mixed to homogenize the components, and the concentration of the components that worsen the oil-water separation is diluted. In addition, the effect of facilitating the removal of deteriorating components can be obtained by sedimenting the solid matter and separating the oil and water. The effluent discharged from the (meth) acrylic acid production process in the present invention may be any effluent discharged from the process during unsteady operation such as periodic repair / cleaning or plant trouble, and specifically, absorption. It refers to the liquid discharged from the tower, extraction tower, evaporation can, distillation column, etc. Further, the holding in the present invention refers to an operation of putting a liquid in a storage tank such as a buffer tank, an off-spec tank, or a run-down tank, and the holding period is 1 to 60 days, preferably 2 to 40 days. It is preferably 2 to 10 days. In this specification, one day is 24 hours. If this period is too short, the effects of diluting the concentration of components that worsen oil-water separation and the effect of solid matter sedimentation / oil-water separation cannot be obtained sufficiently, and if it is too long, new impurities such as Michael adducts and polymers will be added. Due to the formation, the oil-water separability is adversely deteriorated.
If the liquid discharged from the (meth) acrylic acid production process is promptly supplied to the extraction process without performing the holding operation, the oil-water separation is deteriorated, and the water is contained in the extraction solvent and is downstream. It may be distributed to the downstream and cause an increase in the purification load in the downstream and deterioration of the product quality.

As described above, the effluent discharged from the (meth) acrylic acid production process contains components that worsen oil-water separation, but the content of the oil-water separation-deteriorating substance depends on the timing of discharge of the effluent. fluctuate. Maintaining the concentration within an appropriate range while monitoring the concentration of these components is considered to be the most efficient operation method, but it is considered that there are multiple components that worsen oil-water separation, and it is accurate. It was difficult to monitor because it was not clear.

In response to this problem, in the present invention, as a result of further studies, it has been found that the Michael adduct can be used as an index substance for oil-water separation, and it is possible to prevent deterioration of oil-water separation by controlling the concentration within a certain range. Reached to be. As described in (c), as a method for controlling the oil-water separability, the concentration of the Michael adduct in the mixed composition of the (meth) acrylic acid aqueous solution and the recovery liquid is 0.05 to 0.7% by weight. It is preferable to manage it. The concentration of the Michael adduct is more preferably 0.05 to 0.6% by weight, still more preferably 0.1 to 0.5% by weight. If the concentration of the Michael adduct is too low, the conditions of the oxidation reaction step and the absorption step will be restricted, and if it is too high, the oil-water separation in the extraction step will be deteriorated. The mixed composition described here refers to the composition of the mixed liquid when the recovered liquid is mixed with the (meth) acrylic acid aqueous solution in the pipe, and the recovered liquid is used in a pipe different from the (meth) acrylic acid aqueous solution. When supplying to the extraction step, it refers to the assumed composition when mixed, which is calculated from each composition and flow rate ratio. The concentration of the Michael adduct can be measured by a known method. For example, it can be measured by gas chromatography.

As a method for maintaining the above concentration range, it is conceivable to adjust the flow rate of the recovered liquid or to separately supply high-purity acrylic acid to adjust the concentration of the Michael adduct. In that case, Will have a limit on the amount of processing. Therefore, as described in (d), it is preferable to perform a distillation operation before sending the recovered liquid to the extraction step. By performing a distillation operation and sending the distillate to the extraction step, it is possible to prevent deterioration of oil-water separation in the extraction step. Here, the distillate refers to a condensate of components obtained from the top of the column when the distillation operation is performed using the distillation column. It is thought that there are multiple components that worsen oil-water separation in the extraction process, and although it has not been clarified clearly, it is a Michael adduct of (meth) acrylic acid, a polymer of (meth) acrylic acid, and other high boiling point compounds. And solid substances are considered to be contained, and it is presumed that the removal of these components by distillation contributes to the prevention of deterioration of oil-water separation.

Further, by performing the oil-water separation operation of the recovered liquid as in (e), deterioration of oil-water separation in the extraction step can be prevented. Although the reason has not been clarified, some of the components that worsen oil-water separation include components that are soluble in water, so by sending the oil phase to the extraction process after oil-water separation. , It is considered that deterioration of oil-water separation in the extraction process can be prevented.

The recovered liquid is preferably sent to the extraction step during the production of (meth) acrylic acid after passing through one or more selected from the group consisting of retention, distillation, and oil-water separation, and the extraction step during continuous production. It is more preferable that the liquid is sent to. As described in (b), the place where the recovered liquid is sent is preferably the same place as the place where the (meth) acrylic acid aqueous solution is supplied in the extraction step. As a method, a method of mixing the recovered liquid in a pipe through which the (meth) acrylic acid aqueous solution flows, or a method of supplying the recovered liquid to a place where the (meth) acrylic acid aqueous solution is supplied by another pipe can be considered. As an example of the latter, when an extraction tower is used as the extraction step and the (meth) acrylic acid aqueous solution is supplied to the tower top, a method of supplying the recovered liquid to the tower top by another pipe can be considered. If the recovered liquid is supplied to the same place as the extraction solvent without carrying out this method, the extraction efficiency of (meth) acrylic acid will be lowered.

Further, since the mutual solubility of oil and water increases as the temperature at the time of oil / water separation increases, the temperature at the time of extraction is generally low at about 20 to 30 ° C. (for example, Patent Document 2), but at low temperatures Since the separation rate of oil and water is slow, it should not be too low from the viewpoint of preventing oil and water suspension. As described in (f), the optimum temperature at which the mutual solubility of oil and water and the oil-water separation rate are best balanced and the formation of new components that deteriorate the oil-water separation can be suppressed is preferably 30 to 90 ° C. , More preferably 40 to 80 ° C, still more preferably 40 to 60 ° C. As a method of adjusting the temperature, it is most efficient to adjust the temperature of the (meth) acrylic acid aqueous solution supplied to the extraction step, the above-mentioned recovered solution, or a mixed solution thereof within an appropriate range.

Hereinafter, with reference to FIG. 1, which schematically shows an example of a (meth) acrylic acid production facility, the production of acrylic acid using propylene as a raw material is illustrated as a typical example of the production of (meth) acrylic acid. The present invention will be described. However, the present invention is not limited to the production of acrylic acid using propylene as a raw material, and can be applied to the general production of acrylic acid or methacrylic acid using a hydrocarbon having 3 carbon atoms or a hydrocarbon having 4 carbon atoms as a raw material.

1) Oxidation reaction step Air (11), water vapor and / or nitrogen as a diluent (12), and propylene (10) as a reaction raw material are mixed and supplied to an oxidation reactor (pre-reactor) (1). Will be done. The first stage reactor (1) is filled with a solid catalyst made of a molybdenum (Mo) -bismuth (Bi) -based composite metal oxide, and the temperature is controlled by circulation of a heat medium. The structure of the first stage reactor (1) is generally a multi-tube heat exchanger type or a plate heat exchanger type. The reaction-producing gas in which propylene is converted to acrolein in the first-stage reactor (1) is then supplied to the oxidation reactor (second-stage reactor) (2). Air (11) or the like may be added to the subsequent reactor (2). The latter-stage reactor (2) is filled with a molybdenum (Mo) -vanadium (V) -based composite metal oxide catalyst, and the temperature is controlled by circulation of a heat medium. The structure of the latter-stage reactor (2) is the same as that of the first-stage reactor (1). Acrolein is converted to acrylic acid in the subsequent reactor (2) to obtain an oxidation reaction gas (13).

2) Absorption step The oxidation reaction gas (13) is cooled to 150 to 200 ° C. in the heat exchanger (9-1) and then introduced into the absorption tower (3) to prepare an aqueous acrylic acid solution, and the heat exchanger (9) is used. The temperature is controlled by -3). Specifically, the oxidation reaction gas cooled by the heat exchanger (9-1) is introduced into the absorption tower (3) and contains a polymerization inhibitor (15) supplied from the top of the absorption tower (3). The absorbed water (17) and the oxidation reaction gas come into gas-liquid contact, and acrylic acid and the like in the oxidation reaction gas are absorbed to form an acrylic acid aqueous solution (14). As the absorption tower (3), a stage tower or a packed tower having 10 to 20 theoretical stages is usually used. The top temperature of the absorption tower (3) is usually 30 to 70 ° C., the bottom temperature is usually 35 to 85 ° C., and the temperature is controlled by using a heat exchanger (9-3).

The main component of the waste gas from the top of the absorption tower (3) is nitrogen, which contains water and unreacted oxygen and propylene, and carbon dioxide (CO ₂ ), acetic acid, formaldehyde, etc., which are by-products of the oxidation reaction. Further contains a small amount of acrylic acid that was not absorbed. A part of the waste gas may be recycled to the oxidation reaction step as it is, but usually after being detoxified in the waste gas treatment step (4), it is recycled to the oxidation reactor (1) or (2) (23). ), And the rest is discarded as waste gas (22).

The acrylic acid concentration of the acrylic acid aqueous solution (14) in the bottom liquid is about 30 to 70% by weight, and is added to by-products such as formaldehyde, acetic acid, maleic acid and phthalic acid and the top of the absorption tower (3). Includes polymerization inhibitors and the like.

Various substances have been proposed as substances used as polymerization inhibitors in the process of producing acrylic acid. For example, in addition to phenolic compounds such as hydroquinone and hydroquinone monomethyl ether, there are phenothiazine compounds, copper salt compounds, manganese salt compounds, amine compounds, nitroso compounds and N-oxyl compounds.

For each compound, for example, examples of the phenothiazine compound include phenothiazine and bis- (α-methylbenzyl) phenothiazine.
The copper salt compound is not particularly limited and may be either an inorganic salt or an organic salt, and many compounds can be used. For example, there are copper dialkyldithiocarbamate, copper acetate, copper acrylate, copper naphthenate, copper sulfate, copper paratoluate, copper nitrate and copper carbonate, but since the liquid in the absorption tower (3) is an aqueous solution, Water-soluble compounds are preferable, and for example, copper acetate, copper acrylate, copper carbonate, copper sulfate and copper paratolunate are preferable.
As the manganese salt compound, manganese acetate, manganese formic acid, manganese acrylate, manganese naphthenate, manganese sulfate and manganese carbonate are suitable.
Examples of the nitroso compound and the amine compound include p-nitrosophenol, N-nitrosophenylhydroxylamine and its ammonium salt, and N-nitrosodiphenylamine and its ammonium salt.
Examples of the N-oxyl compound include tertiary butyl nitrooxide, 2,2,6,6-tetramethylpiperidine-1-oxyl, 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl, 4 , 4', 4 "-tris (2,2,6,6-tetramethylpiperidinooxyl) phosphite and the like.

3) Waste gas treatment process The waste gas discharged from the top of the absorption tower (3) is usually water, oxygen (O ₂ ), carbon dioxide (CO ₂ ), and organic substances such as acetic acid, formaldehyde, and acrylic acid. include. The detoxification treatment of the waste gas is usually carried out by a catalytic combustion method. As the catalyst, a honeycomb-shaped catalyst or the like is used.

4) Extraction step The acrylic acid aqueous solution (14) from the bottom of the absorption tower (3) is heat-exchanged by the heat exchanger (9-2), and the temperature is adjusted to about 20 to 90 ° C. to extract the extraction tower (5). ), And is subjected to liquid contact treatment with the extraction solvent (16) to be separated into an acrylic acid extract (18) and extraction residual water (19).

If the extraction temperature in the extraction tower (5) is too high, the mutual solubility of water and the extraction solvent increases, but if it is too low, it takes time to separate oil and water, so it is preferably about 30 to 90 ° C.

As the extraction solvent (16), the water-insoluble solvent described below is preferably used. By extracting with a water-insoluble solvent, the water concentration in the extract (18) after extraction becomes low, so that clogging due to the polymerization of acrylic acid in the subsequent acrylic acid purification step (7) should be prevented. At the same time, the heat load in the purification step (7) can be reduced. Further, by using a water-insoluble solvent, the concentration of other impurities such as acetic acid and maleic acid in the extract (18) after extraction can be lowered, and the concentration of these impurities can be reduced from each device. It is also preferable to use a water-insoluble solvent for treating the effluent in the extraction step.

Examples of the water-insoluble solvent used for extracting acrylic acid include a water-insoluble aromatic compound solvent, and the main component is a solvent having a boiling point lower than the boiling point of acrylic acid due to the separation efficiency of the solvent during purification of acrylic acid. Is preferable. The main component is 50% by weight or more, preferably 60% by weight or more, and more preferably 80% by weight or more of the water-insoluble aromatic compound having a boiling point lower than the boiling point of acrylic acid in the extraction solvent. ..
A typical type of water-insoluble aromatic compound solvent is a water-insoluble aromatic hydrocarbon solvent, and the water-insoluble aromatic hydrocarbon solvent is an extractor / water ratio of acrylic acid and acetic acid in an extraction operation. It has the advantage that the ratio of the distribution coefficient of is large and the selectivity of acrylic acid is high. The water-insoluble aromatic hydrocarbon solvent is selected to have a water solubility of 1.5% by weight or less at 20 ° C., but the water solubility is more preferably 0.5% by weight or less, and 0. It is more preferably 1% by weight or less, and most preferably 0.06% by weight or less. Examples of the water-insoluble aromatic hydrocarbon solvent include benzene, toluene, xylene, ethylbenzene, mesitylene and the like, and among them, benzene, toluene and xylene are preferable in terms of high extraction efficiency and low solubility in water. Is. The water-insoluble aromatic hydrocarbon solvent may be used alone or as a mixed solvent of two or more kinds.
It can also be used as a mixed solvent with another water-insoluble solvent, but in this case, it is preferable that 70% by weight or more of the mixed solvent is a water-insoluble aromatic hydrocarbon solvent. As the water-insoluble aromatic hydrocarbon solvent, toluene is most preferable in terms of high extraction efficiency and low water solubility.

The weight ratio (S / F ratio) of the extraction solvent (16) to the acrylic acid aqueous solution (14) is usually in the range of 1 to 5. If the S / F ratio is lower than 1, the acrylic acid concentration in the extract (18) increases, but the acrylic acid extraction rate decreases and the water concentration in the extract (18) also increases, which is not preferable. When the S / F ratio exceeds 5, the extraction rate is high, but the acrylic acid concentration in the extract (18) decreases, and the separation equipment and energy in the subsequent purification step (7) become large, which is not preferable. In order to reduce the water concentration in the extract (18) as much as possible, the S / F ratio is preferably 1 to 3.5.

The number of theoretical plates of the extraction tower (5) is usually 4 or more, preferably 6 or more, and most preferably 7 or more. The larger the number of theoretical plates, the better the extraction rate of acrylic acid. The upper limit of the number of theoretical plates of the extraction tower (5) is not particularly limited, but is usually 20 or less. The extraction rate of acrylic acid is usually 95% or more, preferably 98% or more, and most preferably 99% or more.

As the extraction tower (5), a shelf-stage extraction tower, a rotary disk extraction tower (RDC tower), or a reciprocating plate type extraction tower (for example, a curl column or the like) is used. From the viewpoint of the number of theoretical plates and the amount of processing liquid, a reciprocating plate type extraction tower is preferable.

The acrylic acid concentration of the extract (18) obtained in the extraction tower (5) is usually 10 to 40% by weight, and the extract (18) contains a small amount of acetic acid and water. On the other hand, the extracted residual water (19) contains acetic acid, by-products of an oxidation reaction such as formaldehyde and maleic acid, and a polymerization inhibitor and the like. The composition of the extract (18) and the extracted residual water (19) is determined by the liquid equilibrium composition, the S / F ratio, the number of theoretical plates of the extraction tower (5), and the like.

5) Acrylic acid purification step This step includes a distillation step of distilling and separating acrylic acid from crude acrylic acid. In the extract (18) obtained from the top of the extraction tower (5), impurities such as acetic acid and the extraction solvent are separated from the extraction solvent by a purification means such as distillation separation in the acrylic acid purification step (7), and the acrylic acid (20) Is manufactured. The distillation-separated extraction solvent (16) is recycled to the extraction tower (5). The acrylic acid concentration in the extraction solvent (16) has an important effect on the acrylic acid extraction rate of the extraction tower (5). The lower the concentration of acrylic acid in the extraction solvent (16), the higher the extraction rate. Therefore, the concentration is preferably 1% by weight or less, more preferably 0.5% by weight or less. In order to reduce the concentration of acrylic acid in the extraction solvent (16) to 0.4% by weight or less, the number of stages of the distillation column must be increased and the amount of reflux must be increased for the distillation separation of the solvent and acrylic acid. Since a large amount of energy is required, these conditions are controlled to appropriate conditions in relation to the extraction rate of acrylic acid and the distillation load.

6) Extraction residual water treatment step The extraction residual water (19) from the extraction tower (5) needs to be discharged as waste liquid and treated. Combustion treatment and activated sludge treatment are generally used as waste liquid treatment methods, but the combustion treatment of a large amount of extracted residual water requires a large amount of energy and is active because formaldehyde is contained in the extracted residual water (19). Sludge treatment is also difficult. Therefore, it is preferable that the extracted residual water (19) is recycled to the absorption tower (3) and reused as the absorbed water, but the extracted residual water (19) is contained in the extraction solvent in the extraction tower (5). Since by-products (for example, maleic acid, phthalic acid, etc.) from the oxidation reaction step remaining without being extracted into the solvent are concentrated, the absorption tower (3) after preventing the accumulation of these by-products in the system. ), It is necessary to separate the by-product from the extracted residual water (19) and discharge the separated by-product as a waste liquid to the outside of the system. When treating the extracted residual water (19), a part of the extracted residual water (19) is recycled (24) as it is to the absorption tower (3) as absorbed water, and only the remaining portion is heat-concentrated to separate the waste liquid. As a result, it is possible to reduce the size of the equipment for the heat concentration treatment and optimize the energy.

The equipment used for heating and concentrating the extracted residual water (19) is generally an evaporation can (6) as shown in FIG. The evaporation can (6) has an evaporation tank, a reboiler for heat distillation, and a condenser for condensing evaporated steam. The tank may have a mist separator that prevents droplets from entering, or may have a distillation unit such as a shelf in the upper part of the tank. However, the heating and concentrating equipment is not limited to the evaporation can, for example, a multi-effect can, a stirring tank having a jacket for heating or a heat exchanger, a membrane separation equipment, a diffuser tower, a thin film evaporator or a centrifugal thin film evaporation. A vessel (for example, a controller) or the like can also be adopted.

7) Emission liquid recovery process from each device The above-mentioned contents are incorporated for the preferable conditions for holding the recovered liquid, distillation, oil-water separation, sending the recovered liquid, etc. described in this column.
The manufacturing method of the present invention includes the case of unsteady operation such as during troubles and periodic inspections, and during these unsteady times, the discharge liquid from each device is once stored in a storage tank such as a buffer tank or an off-spec tank (8). Hold on. By retaining, effluents having various compositions are mixed to homogenize the components and dilute the concentration of the components that worsen oil-water separation. In addition, the effect of facilitating the removal of deteriorating components can be obtained by sedimenting the solid matter and separating the oil and water. It is preferable that these discharged liquids are supplied as the recovered liquid (25) to the same place where the acrylic acid aqueous solution (14) is supplied in the extraction step. As this method, a method of mixing the recovered liquid in the pipe through which the acrylic acid aqueous solution (14) flows, or a method of supplying the recovered liquid to a place where the acrylic acid aqueous solution is supplied by another pipe can be considered. As an example of the latter, when the extraction tower (5) is used as the extraction step and the acrylic acid aqueous solution is supplied to the tower top, a method of supplying the recovered liquid to the tower top by another pipe can be considered. If the recovered liquid is supplied to the same place as the extraction solvent (16) without carrying out this method, the extraction efficiency of acrylic acid may be lowered.
The recovered liquid may be sent to the extraction step as it is, but in order to prevent the occurrence of an oil-water suspension state in the extraction step, the recovered liquid is distilled in a distillation facility, and the distilled liquid after distillation is used in the extraction step. It is preferable to send the liquid. As the distillation equipment, an evaporation can can be used. The evaporation can has an evaporation tank, a reboiler for heat distillation, and a condenser for condensing evaporated steam. The tank may have a mist separator that prevents droplets from entering, or may have a distillation unit such as a shelf in the upper part of the tank. However, the distillation equipment is not limited to the evaporator, and for example, a multi-effect can, a stirring tank having a jacket for heating or a heat exchanger, a dissipation tower, a thin film evaporator, or the like can be adopted.
Steam or a heat medium is used as a heat source for heating such as an evaporation can. Alternatively, a high temperature process fluid or the like can be used.
Further, for the purpose of preventing the occurrence of an oil-water suspension state in the extraction step, an oil-water separation operation of the recovered liquid may be performed and only the oil phase may be sent. The extraction temperature in the extraction step is preferably 30 to 90 ° C. It is more preferably 40 to 80 ° C, still more preferably 40 to 60 ° C. As a method of adjusting the temperature, it is most efficient to adjust the temperature of the acrylic acid aqueous solution, the above-mentioned recovered solution, or a mixed solution thereof supplied to the extraction step within an appropriate range. The appropriate range is 20 to 90 ° C, more preferably 30 to 90 ° C, still more preferably 30 to 7.
It is 0 ° C.

Further, when the operation of the extraction step including the supply of the recovered liquid is carried out, it is preferable to manage the Michael adduct as an index substance. The concentration of the Michael adduct in the mixed composition of the acrylic acid aqueous solution and the recovery liquid is preferably 0.05 to 0.7% by weight, more preferably 0.05 to 0.6% by weight, still more preferably. 0.1 to 0.5% by weight. If the concentration of the Michael adduct is too low, the conditions of the oxidation reaction step and the absorption step are restricted, and if it is too high, the oil-water separation in the extraction step may be deteriorated. As a method for maintaining the above concentration range, it is effective to carry out the above-mentioned distillation of the recovered liquid and the oil-water separation operation, but in addition to this, it is possible to adjust the flow rate of the recovered liquid and to obtain high purity. It is conceivable to supply acrylic acid separately to adjust the concentration of Michael adduct.

8) Waste liquid treatment step The waste liquid (21) discharged from the evaporation can (6) contains high boiling point components, formaldehyde, and high boiling point components generated in the oxidation reaction step and remaining in the extraction residual water (19) in the extraction tower (5). Contains polymerization inhibitors and the like. The waste liquid (21) is treated by incineration or the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.
In addition, Example 6 shall be read as Comparative Example 3.

[Analysis of sampling liquid]
The identification of the substance contained in the sampling solution and the quantification of the substance were analyzed by gas chromatography. For gas chromatography, GC-14A manufactured by Shimadzu Corporation was used. A capillary column (HP-FFAP) manufactured by Agilent was used as the separation column, and FID and TCD were used as the detectors.

(Reference example 1)
Acrylic acid was produced by the following steps using the acrylic acid production equipment shown in FIG. Specifically, an oxidation reaction step of obtaining an oxidation reaction gas by a vapor phase contact oxidation reaction of propylene, an absorption step of bringing the oxidation reaction gas and absorbed water containing a polymerization inhibitor into gas-liquid contact to obtain an acrylic acid aqueous solution. Acrylic acid was produced through an extraction step in which an aqueous acrylic acid solution was used as an extraction solvent and toluene was used to prepare an extract, and an acrylic acid purification step in which the extract was distilled and purified to obtain acrylic acid.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.0% by weight, acrylic acid dimer: 0.31% by weight, acrylic acid trimmer: 0.0013% by weight, water: 38.3% by weight, acetic acid: obtained in the absorption step. (2.6% by weight, maleic acid: 0.44% by weight) 33 ml was put into a colorimetric tube. Next, 67 ml of toluene used in the extraction step was put into the same color tube. This colorimetric tube was set in a rotator (Tietech RT50) and rotated and mixed at 30 rpm for 1 minute in a room temperature environment of 21 ° C. After that, when the oil and water were allowed to stand and the separation status of oil and water was visually confirmed, they were rapidly separated into an oil phase containing acrylic acid, toluene and the like and an aqueous phase containing water, acetic acid, maleic acid and the like within 50 seconds.

(Example 1)
In Example 1, toluene was used as a mixed solution obtained by mixing the acrylic acid aqueous solution obtained in the absorption step and the recovery liquid holding the discharged liquid discharged from the acrylic acid production process in the extraction step in Reference Example 1. This is a change to the extraction process that uses the extract as an extract.
The following extraction test was carried out in order to carry out a simple observation of the absorption process.
Acrylic acid aqueous solution (acrylic acid: 57.0% by weight, acrylic acid dimer: 0.31% by weight, acrylic acid trimmer: 0.0013% by weight, water: 38.3% by weight) obtained in the absorption step of Reference Example 1. , Acetic acid: 2.6% by weight, maleic acid: 0.44% by weight) and the recovered liquid (acrylic acid 63.3% by weight) after holding the waste liquid discharged from the acrylic acid production process in a storage tank for 4 days. Acrylic acid dimer 2.1% by weight, acrylic acid trimmer 0.022% by weight, water 11.4% by weight, acetic acid 0.030% by weight) were mixed at a weight ratio of 10: 1, and 33 ml of a mixed solution was put into a colorimetric tube. did. Next, 67 ml of toluene used in the extraction step of Reference Example 1 was put into the same color tube. When the oil-water separation status was confirmed by performing the mixing operation in the same manner as in Reference Example 1, the oil phase containing acrylic acid, toluene, etc. and the aqueous phase containing water, acetic acid, maleic acid, etc. were quickly separated within 50 seconds. did.

(Comparative Example 1)
In Comparative Example 1, toluene was used as a mixed solution obtained by mixing the acrylic acid aqueous solution obtained in the absorption step and the discharge liquid (not retained) discharged from the acrylic acid production process in the extraction step in Reference Example 1. This is a change to the extraction process that uses the extract as an extract.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.0% by weight, acrylic acid dimer: 0.31% by weight, acrylic acid trimmer: 0.0013% by weight, water: 38.3% by weight) obtained in the absorption step of Reference Example 1. , Acetic acid: 2.6% by weight, maleic acid: 0.44% by weight) and the effluent (not retained) discharged from the acrylic acid production process (acrylic acid 73.3% by weight, acrylic acid dimer 5.9). 33 ml of a mixed solution prepared by mixing (% by weight, 0.052% by weight of acrylic acid trimmer, 20.4% by weight of water, 0.16% by weight of acetic acid) at a weight ratio of 10: 1 was put into a colorimetric tube. Next, 67 ml of toluene used in the extraction step of Reference Example 1 was put into the same color tube. When the mixing operation was performed in the same manner as in Reference Example 1 and the separation status of the oil and water was confirmed, the suspended phase of the oil and water was maintained even after 90 seconds, and the oil and water phases did not separate.

(Example 2)
In Example 2, the extraction step in Reference Example 1 was a distillate obtained by simple distillation of the acrylic acid aqueous solution obtained in the absorption step and the recovery liquid holding the discharge liquid discharged from the acrylic acid production process. The mixture is changed to an extraction step in which toluene is used as an extract.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.0% by weight, acrylic acid dimer: 0.31% by weight, acrylic acid trimmer: 0.0013% by weight, water: 38.3% by weight) obtained in the absorption step of Reference Example 1. , Acetic acid: 2.6% by weight, maleic acid: 0.44% by weight) were sampled. 100 g of the recovered liquid obtained by holding the discharged liquid discharged from the acrylic acid production process in a storage tank for 2 days was put into a 200 cc flask, and the distillate obtained by simple distillation at 80 ° C. and 10 kPa was sampled. Next, 33 ml of a mixed solution obtained by mixing the acrylic acid aqueous solution and the distillate at a weight ratio of 10: 1 was put into a colorimetric tube. Further, 67 ml of toluene used in the extraction step of Reference Example 1 was put into the same color tube. When the oil-water separation status was confirmed by performing the mixing operation in the same manner as in Reference Example 1, the oil phase containing acrylic acid, toluene, etc. and the aqueous phase containing water, acetic acid, maleic acid, etc. were quickly separated within 50 seconds. did.

(Example 3)
In Example 3, in the extraction step in Reference Example 1, the acrylic acid aqueous solution obtained in the absorption step and the oil phase obtained by oil-water separation of the recovery liquid holding the discharge liquid discharged from the acrylic acid production process were obtained. This is a modification of the extraction step in which the mixed solution is used as an extract using toluene.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.0% by weight, acrylic acid dimer: 0.31% by weight, acrylic acid trimmer: 0.0013% by weight, water: 38.3% by weight) obtained in the absorption step of Reference Example 1. , Acetic acid: 2.6% by weight, maleic acid: 0.44% by weight) were sampled. The collected liquid discharged from the acrylic acid production process was held in a storage tank for 2 days, and the recovered liquid was collected in a colorimetric tube, toluene was added at a weight ratio of 1: 1 and this colorimetric tube was set in a rotator (Titec RT50). In a room temperature environment of 21 ° C., the mixture was rotated and mixed at 30 rpm for 1 minute. After that, it was allowed to stand to separate the oil and water, and the oil phase was sampled. Next, 33 ml of a mixed solution obtained by mixing the acrylic acid aqueous solution and the oil phase at a weight ratio of 10: 1 was put into a colorimetric tube. Further, 67 ml of toluene used in the extraction step of Reference Example 1 was put into the same color tube. When the oil-water separation status was confirmed by performing the mixing operation in the same manner as in Reference Example 1, the oil phase containing acrylic acid, toluene, etc. and the aqueous phase containing water, acetic acid, maleic acid, etc. were quickly separated within 50 seconds. did.

(Reference example 2)
Acrylic acid was produced by the following steps using the acrylic acid production equipment shown in FIG. Specifically, an oxidation reaction step of obtaining an oxidation reaction gas by a vapor phase contact oxidation reaction of propylene, an absorption step of bringing the oxidation reaction gas and absorbed water containing a polymerization inhibitor into gas-liquid contact to obtain an acrylic acid aqueous solution. Acrylic acid was produced through an extraction step in which an aqueous acrylic acid solution was used as an extraction solvent and toluene was used to prepare an extract, and an acrylic acid purification step in which the extract was distilled and purified to obtain acrylic acid.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.5% by weight, acrylic acid dimer: 0.25% by weight, acrylic acid trimmer: 0.0014% by weight, water: 37.7% by weight, acetic acid: obtained in the absorption step. (2.6% by weight, maleic acid: 0.46% by weight) 33 ml was put into a colorimetric tube. Then, the toluene used in the extraction step was put into a 67 ml same-color tube. This colorimetric tube was set in a rotator (Tietech RT50) and rotated and mixed at 50 rpm for 1 minute in a room temperature environment of 21 ° C. After that, when it was allowed to stand, it was rapidly separated into an oil phase containing acrylic acid, toluene and the like and an aqueous phase containing water, acetic acid, maleic acid and the like within 40 seconds.

(Comparative Example 2)
In Comparative Example 2, toluene was used as a mixed solution obtained by mixing the acrylic acid aqueous solution obtained in the absorption step and the discharge liquid (not retained) discharged from the acrylic acid production process in the extraction step in Reference Example 2. This is a change to the extraction process that uses the extract as an extract.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.5% by weight, acrylic acid dimer: 0.25% by weight, acrylic acid trimmer: 0.0014% by weight, water: 37.7% by weight) obtained in the absorption step of Reference Example 2. , Acetic acid: 2.6% by weight, maleic acid: 0.46% by weight) and the effluent (not retained) discharged from the acrylic acid production process (acrylic acid 73.3% by weight, acrylic acid dimer 5.9). 33 ml of a mixed solution prepared by mixing (% by weight, 0.052% by weight of acrylic acid trimmer, 20.4% by weight of water, 0.16% by weight of acetic acid) at a weight ratio of 10: 1 was put into a colorimetric tube. Next, 67 ml of toluene used in the extraction step of Reference Example 2 was put into the same color tube. When the mixing operation was performed in the same manner as in Reference Example 2 and the separation status of the oil and water was confirmed, the suspended phase of the oil and water was maintained even after 90 seconds had passed, and the oil phase and the aqueous phase did not separate.

(Example 4)
In Example 4, the extraction step in Reference Example 2 was a distillate obtained by simple distillation of the acrylic acid aqueous solution obtained in the absorption step and the recovery liquid holding the discharge liquid discharged from the acrylic acid production process. The mixture is changed to an extraction step in which toluene is used as an extract.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.5% by weight, acrylic acid dimer: 0.25% by weight, acrylic acid trimmer: 0.0014% by weight, water: 37.7% by weight) obtained in the absorption step of Reference Example 2. , Acetic acid: 2.6% by weight, maleic acid: 0.46% by weight) were sampled. 100 g of the recovered liquid used in Comparative Example 2 in which the discharged liquid discharged from the acrylic acid production process was held in a storage tank for 2 days was put into a 200 cc flask, and the distillate simply distilled at 80 ° C. and 10 kPa was sampled. .. Next, 33 ml of a mixed solution obtained by mixing the acrylic acid aqueous solution and the distillate at a weight ratio of 10: 1 was put into a colorimetric tube. Further, 67 ml of toluene used in the extraction step of Reference Example 2 was put into the same color tube. When the oil-water separation status was confirmed by performing the mixing operation in the same manner as in Reference Example 2, the oil phase containing acrylic acid, toluene, etc. and the aqueous phase containing water, acetic acid, maleic acid, etc. were quickly separated within 40 seconds. did.

(Example 5)
In Example 5, in the extraction step in Reference Example 2, the acrylic acid aqueous solution obtained in the absorption step and the oil phase obtained by oil-water separation of the recovery liquid holding the discharge liquid discharged from the acrylic acid production process were obtained. This is a modification of the extraction step in which the mixed solution is used as an extract using toluene.
The following extraction test was conducted to perform a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.5% by weight, acrylic acid dimer: 0.25% by weight, acrylic acid trimmer: 0.0014% by weight, water: 37.7% by weight) obtained in the absorption step of Reference Example 2. , Acetic acid: 2.6% by weight, maleic acid: 0.46% by weight) were sampled. The collected liquid discharged from the acrylic acid production process was held in a storage tank for 2 days, and the recovered liquid was collected in a colorimetric tube, toluene was added at a weight ratio of 1: 1 and this colorimetric tube was set in a rotator (Titec RT50). In a room temperature environment of 21 ° C., the mixture was rotated and mixed at 30 rpm for 1 minute. After that, it was allowed to stand to separate the oil and water, and the oil phase was sampled. Next, 33 ml of a mixed solution obtained by mixing the acrylic acid aqueous solution and the oil phase at a weight ratio of 10: 1 was put into a colorimetric tube. Further, 67 ml of toluene used in the extraction step of Reference Example 2 was put into the same color tube. When the oil-water separation status was confirmed by performing the mixing operation in the same manner as in Reference Example 2, the oil phase containing acrylic acid, toluene, etc. and the aqueous phase containing water, acetic acid, maleic acid, etc. were quickly separated within 40 seconds. did.

(Reference example 3)
Acrylic acid was produced by the following steps using the acrylic acid production equipment shown in FIG. Specifically, an oxidation reaction step of obtaining an oxidation reaction gas by a vapor phase contact oxidation reaction of propylene, an absorption step of bringing the oxidation reaction gas and absorbed water containing a polymerization inhibitor into gas-liquid contact to obtain an acrylic acid aqueous solution. Acrylic acid was produced through an extraction step in which an aqueous acrylic acid solution was used as an extraction solvent and toluene was used to prepare an extract, and an acrylic acid purification step in which the extract was distilled and purified to obtain acrylic acid.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.5% by weight, acrylic acid dimer: 0.25% by weight, acrylic acid trimmer: 0.0014% by weight, water: 37.7% by weight, acetic acid: obtained in the absorption step. (2.6% by weight, maleic acid: 0.46% by weight) 33 ml was put into a colorimetric tube. Then, the toluene used in the extraction step was put into a 67 ml same-color tube. This colorimetric tube was immersed in a warm water bath at 42 ° C. for 10 minutes, set in a rotator (Tietech RT50), and rotated and mixed at 50 rpm for 1 minute. After that, when it was allowed to stand, it was rapidly separated into an oil phase containing acrylic acid, toluene and the like and an aqueous phase containing water, acetic acid, maleic acid and the like within 50 seconds.

(Example 6)
In Example 6, toluene was used as a mixed solution obtained by mixing the acrylate aqueous solution obtained in the absorption step and the recovery solution holding the effluent discharged from the acrylate production process in the extraction step in Reference Example 2. The extraction process was changed to an extract at a temperature of 42 ° C.
The following extraction test was carried out in order to carry out a simple observation of the extraction process.
Acrylic acid aqueous solution (acrylic acid: 57.5% by weight, acrylic acid dimer: 0.25% by weight, acrylic acid trimmer: 0.0014% by weight, water: 37.7% by weight) obtained in the absorption step of Reference Example 3. , Acetic acid: 2.6% by weight, maleic acid: 0.46% by weight) were sampled. Discharge liquid discharged from the acrylic acid production process (acrylic acid 73.3% by weight, acrylic acid dimer 5.9% by weight, acrylic acid trimmer 0.052% by weight, water 20.4% by weight, acetic acid 0.16% by weight) ) Was measured and found to be 20 ° C. The recovered liquid in which the discharged liquid was held in a storage tank for 2 days was sampled. Next, 33 ml of a mixed solution obtained by mixing the acrylic acid aqueous solution and the recovered solution at a weight ratio of 100: 6 was put into a colorimetric tube. Further, 67 ml of toluene used in the extraction step of Reference Example 3 was put into the same color tube. Similar to Reference Example 3, after immersing this colorimetric tube in a warm water bath at 42 ° C. for 10 minutes, a mixing operation was performed to check the separation status of oil and water. As a result, an oil phase containing acrylic acid, toluene, etc., water, acetic acid, etc. were confirmed. It was rapidly separated from the aqueous phase containing maleic acid and the like within 50 seconds.

As can be seen from the results of Comparative Example 1, deterioration of oil-water separability was confirmed when the effluent discharged from the acrylic acid production process was added. Further, the concentration of the Michael adduct including the acrylic acid dimer and the acrylic acid trimmer at that time exceeded 0.7% by weight. On the other hand, when the holding, distillation, and oil-water separation operations were carried out in Examples 1, 2 and 3, the oil-water separability did not deteriorate, and the concentration of the Michael adduct at that time was 0.7% by weight or less. As can be seen by comparing the results of Comparative Example 2 with the results of Examples 4 and 5, the above tendency is the same even if the rotation speed is increased and the mixing strength is changed.
On the other hand, as shown in the results of Reference Example 3 and Example 6, when the extraction temperature was 42 ° C., the concentration of the Michael adduct was 0.7 by adding the effluent discharged from the acrylic acid production process. The oil-water separability did not deteriorate even if it exceeded the weight%.

1, Oxidation reactor 3 Absorption tower 4 Waste gas treatment process 5 Extraction tower 6 Evaporative can 7 Acrylic acid refining process 8 Storage tank 9-1, 9-2, 9-3 Heat exchanger 10 Propene 11 Air 12 Diluter (steam) Or nitrogen)
13 Oxidation reaction gas 14 Acrylic acid aqueous solution 15 Antipolymerization solvent 16 Extraction solvent 17 Absorbent water 18 Extract 19 Extraction residual water 20 Acrylic acid 21 Waste liquid 22 Waste gas 23 Recycled gas 24 Extraction residual water recycling 25 Discharge from acrylic acid production process Recovery liquid

Claims (7)

An oxidation reaction step of obtaining a reaction gas containing (meth) acrylic acid by vapor-phase catalytic oxidation, an absorption step of bringing the reaction gas into gas-liquid contact with water to obtain a (meth) acrylic acid aqueous solution, and the (meth) acrylic. A (meth) acrylic acid containing an extraction step of bringing a crude (meth) acrylic acid into contact with an aqueous acid solution and an extraction solvent, and a distillation step of distilling the (meth) acrylic acid from the crude (meth) acrylic acid. In the manufacturing method
A liquid containing the drained liquid discharged from at least one step of the step is used as a recovery liquid, the recovered liquid is held for 2 to 10 days, and the held recovered liquid is sent to the extraction step.
The concentration of the Michael adduct in the mixed composition of the recovered liquid and the (meth) acrylic acid aqueous solution is 0.05 to 0.5% by weight.
Method for producing (meth) acrylic acid. The method for producing (meth) acrylic acid according to claim 1, wherein in at least one step of each step, the reaction product in the step and the discharged liquid in the step are discharged at the same time. The method for producing (meth) acrylic acid according to claim 1 or 2 , wherein the recovered liquid contains water. The (meth) acrylic acid according to any one of claims 1 to 3 , wherein the recovery liquid to be sent to the extraction step is supplied to the same place where the (meth) acrylic acid aqueous solution is supplied in the extraction step. Manufacturing method. The method for producing (meth) acrylic acid according to any one of claims 1 to 4 , wherein the extraction temperature in the extraction step is 30 to 90 ° C. The (meth) acrylic acid according to any one of claims 1 to 5 , wherein the extraction solvent is a solvent containing a water-insoluble aromatic compound having a boiling point lower than the boiling point of (meth) acrylic acid as a main component. Manufacturing method. The method for producing (meth) acrylic acid according to claim 6 , wherein the water-insoluble aromatic compound is at least one compound selected from the group consisting of benzene, toluene and xylene.

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