KR830000024B1 - How to recover acrylic acid - Google Patents

Abstract

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Description

How to recover acrylic acid

1 is a flow sheet showing one example of a process for recovering acrylic acid of the present invention.

2 is a flow sheet showing another example of the present invention.

The present invention relates to a method for recovering isacrylic acid, and in particular, to recover acrylic acid advantageously from dimers or trimers of acrylic acid produced in the production process of acrylic acid, and at the same time to recover hydroquinone used as a polymerization inhibitor in the process. In more detail, in the production of acrylic acid by the catalytic gas phase oxidation of propylene or acrolein, the acrylic acid oligomer produced in the production apparatus and concentrated in the bottom liquid of the acrylic acid rectification column, which is a final process, is heated and decomposed. The present invention relates to a method for recovering hydroquinone, which is preferably recovered as acrylic acid and used as a polymerization inhibitor in the same process and is concentrated in the bottom liquid of the acrylic acid rectification column.

The process of producing acrylic acid by catalytically oxidizing propylene or acrolein with molecular oxygen-containing gas is mainly an oxidation process, a process of absorbing an oxidation reaction product into water and collecting it into an aqueous solution, and the acrylic acid in the aqueous solution such as ethyl acetate and ethyl acrylate. It consists of a process of extracting and removing water with an extraction solvent, a solvent separation process, by-product acetic acid separation process, and acrylic acid purification process.

It is well known that acrylic acid is extremely rich in polymerizability and even in the various processes described above, the polymer is formed in the apparatus, particularly in each heavy oil column, which often hinders operation of the apparatus and at the same time causes a decrease in the yield of acrylic acid as a product. For this reason, the method of attaching a polymerization inhibitor to these various processes, especially an absorption tower, a distillation column, etc. is widely employ | adopted conventionally as a countermeasure against polymerization of acrylic acid. As a typical polymerization inhibitor, hydroquinone is well known, and it is common to use another effective polymerization inhibitor, for example, at least one of molecular oxygen, phenols, amines, quinones, inorganic and oils and fats and the like. . In addition to the polymerization, as described above, acrylic acid also easily oligomerizes such as dimerization and trimerization. Such oligomerization is mainly considered to be a sequential reaction, and dimers are mainly produced in the above several processes.

Furthermore, the production of acrylic acid dimers by dimerization of acrylic acid is remarkably influenced by temperature and residence time, and it is impossible to completely suppress the addition of the polymerization inhibitor. That is, the production of acrylic acid dimer is determined according to the temperature and the residence time thereof. Therefore, production of dimers of 1 to 5% by weight of acrylic acid cannot be avoided even when the heating temperature is lowered or the residence time is shortened in a normal acrylic acid purification step, in particular a distillation step. The acrylic acid dimer thus produced and the polymerization inhibitor to be added are sequentially concentrated in each step, and each of the acrylic acid dimers is concentrated to 10 to 50 times higher than the original concentration at the bottom of the rectifying column of the final step.

Discarding the bottom liquid containing acrylic acid dimer and polymerization inhibitor at such a high concentration as it is extremely disadvantageous economically, there have been some proposals for its use, in particular, a method of decomposing and recovering acrylic acid dimer into acrylic acid. For example, Japanese Patent Application No. 45-19281 discloses a secondary amine, a tertiary amine, a tertiary phosphine, and the like, by heating the residual liquid in the presence of a catalyst to decompose the polymerized product into an acrylic acid monomer and recovering it. Here's how. Further, No. 3,086,064 describes a method for recovering acrylic acid by introducing an acrylic acid dimer-containing vapor obtained by evaporating the distillation residual liquid into a thin film evaporator into a tube of heated stainless steel and decomposing it therein. However, even if these methods are carried out on a laboratory scale, the recovery rate of acrylic acid is up to 60 to 80 weights, and a large amount of high-viscosity residues are generated. Thus, the recovery rate is lowered and the acid recovery rate is not satisfactory.

In addition, Japanese Patent Laid-Open No. 51-61,208 proposes a method of reusing the polymerization inhibitor in the effluent obtained by evaporating 60 to 80% of the tower bottom liquid of the rectifier tower in a process, but recovering the polymerization inhibitor. It cannot be said that it is getting enough effect. This is because, in the residue discharged from the evaporator, hydroquinone, a considerable amount of polymerization inhibitors, dimers and trimmers of acrylic acid, etc. remain, which must eventually be discarded.

Therefore, the objective of this invention is providing the method of collect | recovering acrylic acid from the oligomer of acrylic acid produced | generated in the manufacturing process of acrylic acid.

Another object of the present invention is to provide a method for recovering acrylic acid from the acrylic acid dimer concentrated in the column bottom liquid of the acrylic acid rectification column and at the same time recovering the hydroquinone.

These objectives are acrylic acids obtained by catalytic gas phase oxidation of an olefinic compound having the general formula CH ₂ = CHX, wherein X is at least one group selected from the group consisting of CH ₃ and CHO. In the method for producing acrylic acid, the acrylic acid is collected as an aqueous solution by contacting the containing reaction product gas with water, and the acrylic acid is separated and purified from the aqueous solution. 1 to 25%, acrylic dimer 9 to 49% by weight (but the sum of acrylic acid and acrylic acid dimer is 10 to 50% by weight) and other 90 to 50% by extraction with water to acrylic acid, acrylic dimer and hydroquinone It is achieved by a method for recovering acrylic acid, characterized in that the extraction and separation.

The method of the present invention can be applied to a conventional acrylic acid production method. This acrylic acid production method is characterized in that an olefinic compound having a general formula CH ₂ = CHX such as propylene and acrolein, wherein X is at least one member selected from the group consisting of CH ₃ and CHO, may be prepared by molecular oxygen such as air. The acrylic acid-containing reaction product gas obtained by the catalytic gas phase oxidation with the containing gas is brought into contact with water in the presence of hydroquinone as a polymerization inhibitor to collect acrylic acid as an aqueous solution and to separate acrylic acid from the aqueous solution. The acrylic acid separation process is mainly a process of extracting and removing water from the aqueous solution for extraction purposes such as ethyl acetate and ethyl acrylate, solvent separation, and by-product separation and acetic acid rectification of acetic acid. In the acrylic acid collection step, depending on the acrylic acid collection conditions, it may be omitted, resulting in an acrylic acid rectification step (the distillation method using the required number of distillation columns, azeotropic distillation method, etc.).

Acrylic acid dimer is already generated in the process of capturing the acrylic acid produced by the oxidation reaction as an aqueous solution. In the subsequent extraction operation, acrylic acid dimer is extracted together with acrylic acid, and is increased with each distillation operation, and is supplied to the rectification column of the final process. It accumulates at the bottom. Thus, the rectifier column bottom liquid of acrylic acid contains acrylic acid, acrylic acid dimers, polymerization inhibitors, and other high boiling points. The composition of the bottom liquid may vary greatly depending on the operating conditions of each process, but 20 to 65% by weight of acrylic acid, 30 to 60% of acrylic acid dimer, 5 to 15% by weight of a polymerization inhibitor such as hydroquinone and 20% of other high boilers It exists in the range of% or less.

According to the method of the present invention, first, the column bottom liquid is evaporated, and the acrylic acid dimer in the column bottom liquid is decomposed to acrylic acid and evaporated together with the acrylic acid contained in the column bottom liquid to recover as an outflow product, and even a part of the acrylic acid dimer is allowed to flow out. To operate it. Surprisingly, it has also been possible to simultaneously recover hydroquinone, in which a dimer acts as an entrainer and is concentrated in a large amount as a polymerization inhibitor. Subsequently, the residue obtained in the evaporation process is extracted with water, and the composition of the acrylic acid, acrylic acid dimer and the feed supplied to the extraction process is 1 to 25% by weight of acrylic acid and 9 to 49% by weight of acrylic acid dimer (except acrylic acid and acrylic acid). The sum of the dimers is 10 to 50% by weight) and 90 to 50% by weight of high boiling point or other such as hydroquinone, and the acrylic acid is suspended if the high boiling point is suspended in water without separation as oil layer. Separation and recovery of the acrylic acid dimer and hydroquinone becomes difficult. Therefore, when the evaporation residue is supplied to the water extraction step as it is, it is necessary to operate the evaporation residue so as to have the above composition. In addition, when the evaporation residue is to be treated again as described below, it is necessary to operate the feed to the water extraction process after the treatment so as to have the composition.

In the evaporation process, acrylic acid, acrylic acid dimer and hydroquinone recovered as the effluent can be circulated to the process of separating acrylic acid from the aqueous solution, and hydroquinone is reused as a polymerization inhibitor and acrylic acid contributes to the improvement of recovered alcohol. . The separation process to be circulated includes a solvent extraction step, a solvent separation step, an acetic acid separation step, an acrylic acid purification step, and the like, of which acetic acid separation is most preferred.

The evaporation residue may be decomposed as necessary and then circulated to the evaporation process. Such circulation causes high boiling point substances to accumulate in the system, so that some of the decomposed products are extracted and transferred to the water extraction step. In addition, the acrylic acid, acrylic acid dimer, and hydroquinone recovered by evaporation of a part of the decomposition product may be circulated in the acrylic separation step, for example, the acrylic acid purification step, in the same manner as in the evaporation step.

Further, the evaporation residue is decomposed as necessary and then circulated to the evaporation step, and part of it is sent to the water extraction step.

As described above, the acrylic acid dimer generated in the system is separated into acrylic acid in the evaporation process and the decomposition process, is evaporated and recovered together with the acrylic acid dimer and hydroquinone, and recycled into the purification system as the acrylic acid dimer solution of acrylic acid and hydroquinone. Furthermore, unrecovered acrylic acid, acrylic acid dimer and hydroquinone are recovered as extracts in the water extraction process and recycled to the various processes as aqueous solutions, such as acrylic acid collection process or solvent extraction process, preferably collection process. Therefore, 80 to 98% of the acrylic acid dimer generated by the method of the present invention can be recovered as acrylic acid, and can be recovered and reused up to 70 to 95% of hydroquinone as a polymerization inhibitor, which is an expensive polymerization inhibitor with a large increase in the purification yield of acrylic acid. The cost of hydroquinone can be greatly reduced.

This invention will be described in more detail with reference to the accompanying drawings.

In the apparatus shown in FIG. 1, propylene or acrolein supplied from the line 1 or a mixture thereof is connected to the reactor 3 in a molecular oxygen-containing gas such as air supplied from the line 2. Oxidation and the oxidation reaction product gas containing acrylic acid are sent to the absorption tower 5 in line 4 and recovered as an aqueous solution by countercurrent contact with water in the presence of hydroquinone as the polymerization inhibitor.

The aqueous solution containing acrylic acid thus obtained is transferred to the extraction column 7 by line 6, extracted with an organic solvent such as ethyl acetate, ethyl acrylate, water is discharged from line 8 and the extract is line 9 ) Is transferred to the solvent separation tower (10). The solvent separated in separation column 10 is circulated from line 11 to extraction column 7. Acrylic acid and the like are transferred to the acetic acid separation tower 13 by line 12, acetic acid, which is an oxidative byproduct, is separated in line 14, and crude acrylic acid is transferred to the acrylic acid rectifying tower 16 in line 15. . Acrylic acid flows out from the top of the rectification column 16 and is stored in the storage tank 18 via the condenser 17. A part of it is returned to the rectification tower by reflux, and the remainder is taken out as a product. At the bottom of the rectifying column 16, acrylic acid including acrylic acid dimer, concentrated acrylic acid dimer, hydroquinone, and other high-boiling substances such as a polymerization compound and a casting compound is accumulated at the bottom of the column 16. This column bottom liquid is supplied to the acrylic acid dimer decomposition evaporation apparatus 21 via the line 20 by the pump 19, and the evaporation liquid is liquefied in the condenser 22, stored in the storage tank 23, and the pump 24 ) Is circulated through the line 25 to an acrylic acid separation process, for example, an acetic acid separation tower 13, and recovered as acrylic acid, dimer and hydroquinone. This may also be circulated to the solvent extraction column 7, the solvent separation column 10, or the acrylic acid rectification column.

On the other hand, the bottom extraction liquid is stored in the decomposition storage tank 27 via the line 26, and part of it is recycled to the decomposition evaporation apparatus 21 via the pump 28 and the line 29 to be decomposed in the decomposition storage tank 27. Acrylic acid is recovered by evaporation. The other part is transferred to the extraction tower 31 via the line 30. These decomposition evaporation apparatuses 21 may be of any type, but it is advantageous to use a thin film evaporator. The thin film evaporator has a jacket and is capable of heating the heat transfer surface by steam or the like. The thin film evaporator has a reduced pressure to separate the diacrylic acid from acrylic dimer, hydroquinone, a polymerization inhibitor, and other high boiling points such as polymers. Must be able to withstand driving Operation conditions, such as heating temperature and pressure of the said decomposition evaporation apparatus 21, are in the range of in-phase heating temperature 120-220 degreeC, and operation pressure 20-500 mmHg. When the polymerization pants such as amine compounds, organic and inorganic copper compounds are used in combination with hydroquinone in the separation and purification process of acrylic acid, the compound acts as a decomposition catalyst of acrylic acid dimer to acrylic acid, thereby advantageously separating acrylic acid dimer. The heating temperature can be reduced to 120 to 180 ° C.

The composition of the rectifier column bottom liquid supplied to the decomposition evaporator 21 in the line 220 may vary greatly according to the operating conditions of various processes as described above, but usually 20 to 65% by weight of acrylic acid and dimer 30 To 60% by weight, 5 to 15% by weight of the polymerization inhibitor hydroquinone, and other high-boiling substances mainly composed of higher polymers of acrylic acid. 40 to 80% by weight of such a feed solution is decomposed and evaporated to condensate in the condenser 22 and then flowed out into the reservoir 23. 40 to 80% by weight of such a feed solution is decomposed and evaporated to condensate in the condenser 22 and then flowed out into the reservoir 23. The outflow composition is 20 to 99% by weight acrylic acid, 1 to 60% by weight acrylic acid dimer, 0.1 to 10% by weight polymerization inhibitor, and the composition of the liquid entering the decomposition storage tank 27 via line 26 is 0.5% acrylic acid. To 25% by weight, 9.5 to 65% by weight of acrylic acid dimer, 5 to 30% by weight of hydroquinone, and 80 to 40% by weight of other high boilers such as polymers. In the decomposition storage tank 27, in order to decompose the acrylic acid dimer, the structure is 120 to 220 ° C, preferably 150 to 200 ° C, preferably 150 to 200 ° C. It is sufficient to be 1 to 8 hours and preferably 3 to 8 hours for the liquid flow time.

The decomposition reaction of acrylic acid dimer as acrylic acid is assumed to have an equilibrium relationship. Actually, other high-boiling substances include trimers and tetramers of acrylic acid and their equilibrium relationship in their multicomponent systems, and their speed and equilibrium concentrations are not well known. It was found that acrylic acid dimers were decomposed by causing dimerization without causing them to decompose acrylic acid dimers (and trimers, tetramers) above 120 ° C. For this reason, the heating temperature of the said decomposition evaporation apparatus 21 and the decomposition storage tank 27 needs to be 120 degreeC or more.

The decomposition evaporation apparatus 21 manipulates temperature and pressure in the operating range so that acrylic acid and some dimers are evaporated but other high-boiling substances such as high polymers of acrylic acid dimers or the like are not evaporated. Therefore, in the apparatus 21, the outflow of the acrylic acid dimer acts as an entrainer of hydroquinone, so that the hydroquinone can be recovered as the acrylic acid dimer solution.

In the decomposition evaporation apparatus 21, since acrylic acid flows out of the system immediately after the decomposition reaction, the equilibrium is shifted to the acrylic acid side, and the decomposition reaction proceeds well, and the residence time may be as small as about 10 minutes. However, since acrylic acid decomposed in the decomposition storage tank 27 does not flow out of the system, a residence time of 1 to 8 hours is required as described above. Although the required residence time varies depending on the heating temperature and the liquid composition, a residence time of 3 to 8 hours is required under the temperature and composition conditions in the decomposition storage tank 27. A residence time of more than 10 hours is economically wasteful as there is no decomposing advantage in terms of equilibrium relationship.

When a part of the effluent is supplied from the decomposition storage tank 27 to the extraction tower 31, the decomposition of the acrylic acid dimer is insufficient in the decomposition evaporation apparatus 21 and the decomposition storage tank 27 or the outflow of acrylic acid or the dimer is decomposed. When the total amount of acrylic acid and acrylic acid dimer in the extraction liquid composition of 27) exceeds 50% by weight in total, the forming property of forming a uniform phase with water in the extraction column remains and cannot be extracted. Also, if the acrylic acid dimer is excessively advanced to recover acrylic acid and acrylic acid dimer out of the system, and the total sum of acrylic acid and acrylic acid dimer of this liquid composition is less than 10% by weight, the extraction liquid becomes a solid at room temperature, and thus extraction is impossible. In order to supply the effluent from the decomposition storage tank 27 to the extraction tower 31, the operating conditions are selected in consideration of the supply liquid composition of the decomposition evaporation apparatus 31, and the acrylic acid and the extraction liquid composition of the decomposition storage tank 27 are selected. The sum of acrylic acid dimers should be adjusted to 50 wt% or less, usually 20 to 45 wt%. The acrylic acid, dimer and hydroquinone solutions are circulated through the solvent separation and acetic acid separation processes, and the effluent of the decomposition evaporation apparatus 21 is recovered and reused as a polymerization inhibitor.

Extraction liquid from the decomposition evaporation device 21 of the decomposition storage tank 27 is passed above the extraction column 31 via the pump 28 and the line 30, while water is transferred from the bottom of the column via the line 32. Supplying and extracting countercurrently, the extract is recovered as an aqueous solution of acrylic acid, acrylic acid dimer and hydroquinone via line 33, and the acrylic acid is collected as it is as an aqueous solution [absorption tower 5] and its extraction process. It is circulated and recovered as a polymerization inhibitor in a solvent separation step via light oil. In addition, the addition liquid of other high boilers, such as a polymer, is taken out out of the system via the line 34, and is processed as waste oil. Extraction column 31 may be any type, but it is advantageous to employ a rotary type because the viscosity of the balance is high and the adhesion is large.

As extraction conditions, the temperature is 5 to 90 ° C., preferably 20 to 60 ° C., and the extraction ratio is the bottom extraction liquid: water = 1: 1 to 10 (1 / ｗ), preferably 1: 3 to 6 The recovery rates of acrylic acid dimer and hydroquinone in the extraction column are 70 to 95% by weight and 50 to 90% by weight. Even if the water ratio is increased to 1: 6 or more, an increase in the recovery rate of acrylic acid dimers or hydridequinones cannot be expected. Rather, it is economically disadvantageous as a result of the recovery in a dilute aqueous solution of acrylic acid dimers or hydroquinones. In addition, when the main ratio is less than 1: 3, water is reduced, leading to a rapid decrease in the recovery rate of acrylic acid dimer, and also a reduction in the recovery rate in relation to hydroquinone. And, if it does not reach 1: 1, a uniform phase is formed and extraction is impossible.

2 shows another embodiment of the present invention, in which the effluent of the first cracked evaporation device 21 is transferred to a cracking reservoir 27 via a line 26, some of which are pump 28 and a line. (29) is recycled to the cracking evaporator (21) and the other part is transferred to the second cracking evaporator (36) via line (35). The evaporated liquid is liquefied in the condenser 37, stored in the reservoir 38, and then recycled to the acrylic acid dimer solution of acrylic acid and hydroquinone by the pump 39 and the line 40 in the above various processes. On the other hand, the bottom leachate is stored in the decomposition reservoir 42 via line 41, part of which is recycled to the device 36 via pump 43 and line 44, and part of line 30 is different. It is transferred to the extraction tower 31 through. The cracked evaporator 36 may be of any type, but usually the same as the first cracked evaporator 21 is used. The operating conditions are also the same as those of the first decomposition evaporator 21. The same reference numerals as those in FIG. 1 in FIG. 2 denote the same apparatus except for the above points.

As described above, addition of an inhibitor such as hydroquinone is indispensable in the separation and purification process of acrylic acid, and it is impossible to completely suppress the production of acrylic acid dimer, but according to the present invention, acrylic acid dimer decomposition evaporation apparatuses 21 and 36 ), 70 to 95% of the added hydroquinone is recovered by the decomposition storage tanks 27 and 42 and the extraction column, and 80 to 98% by weight of the resulting acrylic acid dimer can be decomposed and recovered as acrylic acid.

At the same time, the acrylic acid in the column bottom liquid can also be recovered by 90% by weight or more, thereby greatly increasing the purification yield.

In addition, in the method of the present invention, it is possible to recover substantially as an acrylic acid dimer solution of hydroquinone instead of an aqueous solution containing acrylic acid dimer and hydroquinone without employing an extraction column. However, in this case, the fall of the recovery rate of acrylic acid dimer and hydroquinone cannot be avoided.

Specifically, by increasing the heating temperature in the decomposition evaporation process or by lowering the operating pressure, acrylic acid and acrylic acid dimers are decomposed and evaporated as much as possible without evaporating polymers and other high-boiling substances, and at this time, hydroquinone is also recovered. .

Therefore, it is inevitable that the total amount of acrylic acid dimer in the bottom extraction liquid composition of the apparatus 21 or 36 must be 10% by weight or less naturally, and an appropriate disposal treatment must be performed as waste oil without performing an extraction operation.

For example, the recovery effect will be described.

Example 1

Capacity of 1m in acrylic acid production equipment using 25,000 tons of hydroquinone per year as a polymerization inhibitor by contact gas phase oxidation method using propylene as a raw material³of Linkage area 300m with digester²The thin film evaporator of the acrylic acid dimer decomposition evaporator was installed, and a rotating disc extraction tower having a tower diameter of 400 mm ψ 20 stages was further installed.

The decomposition evaporator was heated with steam at 180 ° C., and the pressure in the system was reduced to 50 mmHg. In addition, the decomposition storage tank was heated to 180 ° C. Under the above operating conditions, the rectified column bottom liquid of the acrylic acid production apparatus was supplied to the decomposition evaporation apparatus, and the evaporation amount was 76.0 wt%. The decomposition rate of acrylic acid dimer to acrylic acid and the recovery rate of hydroquinone in the cracking evaporator and cracking magnetic field bath were 48.9 (97.8% vs. generated dimer) and 36.9)% by weight, respectively.

Subsequently, the device extraction liquid after decomposition and evaporation is supplied to the extraction column to the upper part of the extraction column, and 5 times (공급 / ｗ) of water from the lower part is supplied at room temperature to extract the acrylic acid dimer and hydroquinone in a countercurrent manner. It was recovered and recovered from the top of the extraction column as an aqueous solution containing 5 and 2% by weight of quinone as acrylic acid dimer and hydride, respectively. The recovery rates were 90% acrylic acid dimer and 80% hydroquinone. About 50% of the balance was extracted from the bottom of the extraction tower with respect to the feed liquid and treated as waste oil. The previous yields of acrylic acid dimer and hydroquinone were 94.9% by weight and 87.4% by weight, respectively. The acrylic acid and hydroquinone acrylic acid dimer solution recovered from the decomposition evaporation device is a solvent separation step and an acetic acid separation step of the acrylic acid production device, and the acrylic acid dimer and hydroquinone aqueous solution recovered from the extraction tower are acrylic acid collection step or acrylic acid. It was circulated and used as a polymerization inhibitor in the solvent process through the extraction process of. After more than 6 months of the acrylic acid production apparatus, it was possible to operate smoothly without abnormalities such as concentration and adhesion of high-boiling substances such as polymers in the various processes. In addition, compared with the process which does not employ | adopt the process by this invention, the cost of hydroquinone was 1/5, and the purification yield of acrylic acid increased by about 3%.

Example 2

The same apparatus as in Example 1 was carried out under the same conditions, except that only extraction conditions (rejection ratio) were extracted with twice the amount of water with respect to the feed liquid, that is, the recovery rates of acrylic acid dimer and hydroquinone in the extraction column were 60.1 wt% and 70.3. % By weight.

Example 3

The same apparatus as in Example 1 was carried out under the same conditions, and when the hydroquinone and the copper compound (0.1 wt% as copper in the dimer decomposition evaporator feed-in) were used as the polymerization inhibitor, the decomposition temperature was 160 ° C due to the catalytic effect of the copper compound. The decomposition and recovery effect of acrylic acid dimer equivalent to Example 1 was obtained in the above.

Example 4

Under the same conditions as in Example 1, only the operating conditions of the acrylic acid dimer decomposition evaporation apparatus were operated at a heating temperature of 180 ° C. and a pressure of 20 mmHg, that is, 85% of the feed liquid was leaked. The composition of the feed liquid, the effluent liquid, the bottom extraction liquid, and the decomposition tank outlet liquid at this time was as Table 2. The decomposition recovery rate of the acrylic acid dimer as the decomposition evaporation device was 36.6% (relative to 97% generated in the system), and the recovery rate of hydroquinone was 49.2%. The total recovery of acrylic acid dimer and hydroquinone was 84.1 wt% and 92.4 wt%, respectively.

Comparative Example 1

The same device as in Example 1 was fed directly to the extraction column of the rectifier tower bottom liquid of the acrylic acid production apparatus without passing through the decomposition evaporation apparatus under the same conditions. Quinones cannot be recovered.

Comparative Example 2

The extraction was carried out under the same conditions as in Example 1, but only the extraction conditions (rejection ratio) were extracted with 0.6 times (ｗ / ｗ) of water with respect to the feed solution. And hydroquinone could not be recovered.

Example 5

As shown in FIG. 2, two acrylic acid dimer decomposition evaporation apparatuses of the same type as those used in Example 2 and a rotating disc type extraction column of 20 stages with a tower inner diameter of 400 mm were used as the apparatus.

All of these decomposition evaporation apparatuses were heated with water vapor at 180 ° C, and the system pressure was reduced to 300 mmHg in the first stage and to 80 mmHg in the second stage. Each digester was heated to 180 ° C. When the rectifier column bottom liquid of the acrylic acid production apparatus as shown in Example 1 was supplied to the decomposition evaporation apparatus under these operating conditions, the evaporation amount of the device in the first stage was 55.6% by weight, and the evaporation amount of the device in the second stage. Was 63.0 wt%. The compositions of the feed liquid, the effluent liquid, the bottom extraction liquid and the decomposition tank outlet liquid of the first and second decomposition evaporation apparatuses were as shown in Table 3. The decomposition rate of acrylic acid dimer as acrylic acid dimers and each of the two decomposition tanks in the decomposition evaporation apparatus and the hydrolysis tank was 49.2% by weight (96% by weight of dimer) and 58.3% by weight, respectively.

After the decomposition and evaporation, the extraction liquid of the decomposition tank of the second stage is then supplied to the upper part of the extraction column, while at the bottom of the extraction column, 5 times (w / w) of water is supplied to the feed liquid at room temperature, and condensed acrylic acid dimer and Hydroquinone was extracted and recovered from the top of the extraction column as an aqueous solution containing 5% by weight and 2% by weight of acrylic dimer and hydroquinone, respectively. The recovery rates were 75% by weight of acrylic acid dimer and 80% by weight of hydroquinone. About 50% of the extraction residue was extracted from the bottom of the extraction tower with respect to the feed liquid and treated as waste oil. The total recoveries of acrylic acid dimer and hydroquinone were 87.3 wt% and 91.7 wt%, respectively. The acrylic acid dimer solution of the acrylic acid solution and hydroquinone recovered from the decomposition evaporation device is a solvent separation step and an acetic acid separation step of the acrylic acid production device, and the acrylic acid dimer and hydroquinone aqueous solution recovered from the extraction tower are the acrylic acid collection step or the acrylic acid solution. It was circulated and used as a polymerization inhibitor through an extraction step and a solvent separation step.

[Comparative Example]

Under the same conditions as in Example 5, only the operating conditions of the acrylic acid dimer decomposition evaporation apparatus of the second stage were operated at a heating temperature of 180 ° C. and a pressure of 10 mmHg, that is, 85% of the feed liquid was leaked. The composition of the feed liquid, the effluent liquid, the bottom extraction liquid, and the decomposition tank outlet liquid at this time was as Table 4.

The outlet liquid of the second decomposition tank was solidified at room temperature, and acrylic acid dimer and hydroquinone extraction could not be recovered. The decomposition rate of the acrylic acid dimer in these decomposition evaporation apparatus was 54.1, and the recovery rate of hydroquinone was 70.8%.

Claims (1)

Acrylic acid-containing reaction product gas obtained by contact gas phase oxidation of an olefinic compound having the general formula CH ₂ = CHX (wherein X is at least one group selected from the group consisting of CH ₃ and CHO) by molecular oxygen-containing gas. In which acrylic acid is collected as an aqueous solution, and acrylic acid is separated and purified from the aqueous solution. %, Acrylic acid dimer 9 to 49% by weight (however, the sum of acrylic acid and acrylic acid dimer is 10 to 50% by weight) and other 90 to 50% by weight extraction to extract acrylic acid, acrylic acid dimer and hydroquinone A method for recovering acrylic acid, characterized in that.

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