JP4358877B2 - Acrylic acid recovery method - Google Patents

Description

  The present invention relates to a method for recovering acrylic acid, and more specifically, contacting acrylic acid-containing gas obtained by catalytic gas phase oxidation of acrylic acid containing acrylic acid dimer and maleic acid, particularly propylene and / or acrolein, with water. Acrylic acid is collected as an acrylic acid aqueous solution, and crude acrylic acid obtained by distillation of this acrylic acid aqueous solution in the presence of an azeotropic solvent is further purified by a high boiling point impurity separation tower to produce high purity acrylic acid. The present invention relates to a method for efficiently and stably recovering acrylic acid from crude acrylic acid containing acrylic acid dimer and maleic acid obtained as a can of the high boiling point impurity separation tower in the process.

  Conventionally, in producing high-purity acrylic acid by catalytic vapor phase oxidation of propylene and / or acrolein, acrylic acid-containing gas from the oxidation step is brought into contact with water to collect acrylic acid as an aqueous acrylic acid solution. Acrylic acid is extracted from this aqueous acrylic acid solution using a suitable extraction solvent, and then acrylic acid and the solvent are separated. The crude acrylic acid obtained in this solvent separation step contains acrylic acid dimer and maleic acid. In other words, the high-boiling impurities such as the above are contained, and further purification steps are provided to purify and to separate and remove the high-boiling impurities.

  However, since the high-boiling impurities obtained in this way contain acrylic acid dimer in addition to acrylic acid, it is economical to immediately discard this as waste oil. It is disadvantageous.

In view of this, Patent Documents 1 to 4 and the like have proposed methods for increasing the recovery rate of acrylic acid by thermally decomposing and recovering acrylic acid dimer in the high-boiling impurities as acrylic acid.
However, in recent years, instead of the above-described solvent extraction method in which acrylic acid is recovered from an aqueous acrylic acid solution using an extraction solvent, distillation is performed using an azeotropic solvent that forms an azeotrope with water, and azeotropic separation is performed. An azeotropic separation method in which an azeotropic mixture of water and a solvent is distilled from the top of the tower and acrylic acid is recovered from the bottom of the tower is the mainstream.

  In this case, usually, an oxidation step in which propylene and / or acrolein is contacted by gas phase oxidation to produce acrylic acid, a collecting step in which acrylic acid-containing gas is brought into contact with water and acrylic acid is collected as an aqueous acrylic acid solution, The aqueous solution of acrylic acid is distilled in the presence of an azeotropic solvent in an azeotropic separation tower to remove crude acrylic acid from the bottom of the tower, followed by a purification process for purifying the crude acrylic acid. Manufactures acrylic acid. The purification step is usually performed using a high boiling point impurity separation column for removing high boiling point impurities in the crude acrylic acid, and an acetic acid separation column for removing acetic acid provided as necessary.

Japanese Examined Patent Publication No. 45-19281 JP-A-51-91208 Japanese Patent Publication No. 61-35977 Japanese Examined Patent Publication No. 61-36501

  Even in the process of producing acrylic acid using the above azeotropic separation method, the high-boiling impurities separated and removed in the purification step include acrylic acid dimer and maleic acid in addition to acrylic acid. Yes.

  Therefore, it is desirable to recover acrylic acid from the high-boiling impurities in the process of producing high-purity acrylic acid using the azeotropic separation method. For this recovery operation, high-purity acrylic acid is used according to the solvent extraction method described above. It is conceivable to apply the method described in the above-mentioned patent publication proposed for the process for producing an acid.

  However, for example, an acrylic acid dimer (dimer) decomposition / evaporation apparatus (first step) described in Patent Document 4 is used, where acrylic acid dimer is decomposed, acrylic acid obtained by this decomposition, and the initial When the acrylic acid contained in the product is distilled at the same time, it has been found that impurities are mixed into the product acrylic acid and the purity is lowered.

  The present inventors have determined that the cause of the above problem is due to maleic acid contained in high boiling point impurities. This maleic acid is substantially separated and removed in the solvent extraction step in the process using the solvent extraction method and does not remain in the crude acrylic acid, but in the process using the azeotropic separation method, It remains in the crude acrylic acid and is mixed in the high boiling point impurities obtained by refining the crude acrylic acid at a ratio of several percent.

  Since maleic acid is distilled together with acrylic acid from the above-mentioned acrylic acid dimer (dimer) decomposition distillation apparatus, in order to recover acrylic acid from this distillate, the previous step, for example, as a purification step It is thought that maleic acid accompanies this when it is circulated to the high-boiling impurity separation tower, and condenses at the bottom of the high-boiling impurity separation tower and eventually mixes with the product acrylic acid to lower its purity. It has been.

  Further, in the step of recovering acrylic acid from the crude acrylic acid containing acrylic acid dimer and maleic acid, maleic acid is transferred to fumaric acid and deposited in the recovery step, thereby hindering stable operation.

  Thus, the present invention solves the above-mentioned problems, and in a process for producing crude acrylic acid containing acrylic acid dimer and maleic acid, particularly acrylic acid using an azeotropic separation method, The present invention provides a method for efficiently and stably recovering acrylic acid from crude acrylic acid containing acrylic acid dimer and maleic acid obtained as a liquid.

  The present inventors can achieve the above object by providing an acrylic acid recovery device and an acrylic acid dimer decomposition device instead of the acrylic acid dimer (dimer) decomposition distillation device (first step). I found.

  That is, the high-boiling impurities are introduced into an acrylic acid recovery tower where maleic acid is separated and extracted from the bottom of the tower, and acrylic acid with a significantly reduced maleic acid content is recovered from the top of the tower, while containing maleic acid. The bottom of the column is introduced into a thermal decomposition tank, where the acrylic acid dimer is thermally decomposed, and then a part of the decomposition product is circulated to the acrylic acid recovery column to reduce the purity of the product acrylic acid. The inventors have found that acrylic acid can be efficiently recovered from high-boiling impurities, and have completed the present invention based on this finding.

That is, the present invention, in recovering acrylic acid from crude acrylic acid containing acrylic acid dimer and maleic acid,
(1) The crude acrylic acid is introduced into a distillation column having a theoretical plate number of 1 to 5 equipped with a thin film evaporator, and the concentration of maleic acid in the acrylic acid distillate from the top of the distillation column is 0. Distilled under conditions of ˜3 wt% (excluding 3 wt%), and recovered by distilling acrylic acid from the top of the column,
(2) The can A from the thin film evaporator is introduced into the pyrolysis tank, where the acrylic acid dimer in the can A is decomposed at a temperature in the range of 120 to 220 ° C., and (3) the above A method for recovering acrylic acid, characterized in that at least a part of the can liquid B from the pyrolysis tank is circulated to the thin film evaporator of the distillation column.

In addition, the present invention also includes contacting acrylic acid-containing gas obtained by catalytic gas phase oxidation of propylene and / or acrolein with water, collecting acrylic acid as an aqueous acrylic acid solution, and azeotropically separating the aqueous acrylic acid solution. In the process of distillation in the presence of an azeotropic solvent that forms an azeotrope with water in the tower, and then purifying the crude acrylic acid obtained from the bottom of the azeotropic separation tower in a high boiling impurity separation tower, In recovering acrylic acid from crude acrylic acid containing acrylic acid dimer and maleic acid from the bottom of the high boiling point impurity separation tower,
(1) The crude acrylic acid containing the acrylic acid dimer and maleic acid is introduced into a distillation column having a theoretical plate number of 1 to 5 provided with a thin film evaporator, where 10 to 100 mmHg and a column bottom temperature of 60 to Distilled under the condition of 120 ° C., distilled and recovered acrylic acid from the top of the column and recycled to the previous step,
(2) The can A from the thin film evaporator is introduced into the pyrolysis tank, where the acrylic acid dimer in the can A is decomposed at a temperature in the range of 120 to 220 ° C., and (3) the above Acrylic, characterized in that can liquid B from the pyrolysis tank is circulated in the thin film evaporator of the distillation tower at a ratio of 1 to 20 times that of crude acrylic acid containing acrylic acid dimer and maleic acid. This is an acid recovery method.

  According to the present invention, the acrylic acid dimer can be efficiently decomposed, and the acrylic acid recovery rate can be increased.

  According to the present invention, since the maleic acid content in the acrylic acid recovered from the top of the acrylic acid recovery tower is remarkably reduced, even if this is recycled to the purification process, the accumulation in the purification process etc. There is little, and it does not mix with product acrylic acid, and the purity is not reduced.

  Therefore, according to the present invention, acrylic acid can be efficiently recovered from the acrylic acid dimer and high-purity acrylic acid can be produced.

  According to the present invention, it is possible to prevent the formation of precipitates due to maleic acid, and thus it is possible to stably recover acrylic acid. Also, safe driving over a long period of time is possible.

  The crude acrylic acid containing acrylic acid dimer and maleic acid of the present invention contains at least 20% by mass of acrylic acid dimer and acrylic acid, respectively, and 3 to 10% by mass of maleic acid, In addition, a high boiling point substance such as acrylic acid trimer may be included. The method of the present invention is particularly preferably used for recovering crude acrylic acid from acrylic acid containing 5 to 10% by mass of maleic acid in addition to acrylic acid dimer.

  A typical example is that an acrylic acid-containing gas obtained by catalytic vapor phase oxidation of propylene and / or acrolein is brought into contact with water, and acrylic acid is collected as an aqueous acrylic acid solution. The aqueous acrylic acid solution is used as an azeotropic solvent. It is a can obtained by purifying crude acrylic acid obtained by distillation in the presence of a high-boiling-point impurity separation column after purification in another distillation column if necessary. Although the specific composition of this can liquid varies depending on the operating conditions of each process, it cannot be specified unconditionally. For example, acrylic acid 20 to 65% by mass, acrylic acid dimer 30 to 60% by mass, polymerization inhibitor (For example, hydroquinone) 5 to 15% by mass, maleic acid 3 to 10% by mass, and other high-boiling substances.

  The method of the present invention basically comprises the following steps. That is, a purification step, for example, crude acrylic acid containing acrylic acid dimer and maleic acid from a high boiling point impurity separation tower is introduced into an acrylic acid recovery tower, where acrylic acid in the acrylic acid is introduced from the top of the tower. Collect by evaporation. On the other hand, a can solution containing acrylic acid dimer and maleic acid is taken out from the bottom of the column, and this can solution A is introduced into a thermal decomposition tank, where the acrylic acid dimer is decomposed. At least part of the can B from the pyrolysis tank is circulated to the acrylic acid recovery tower, and acrylic acid obtained by thermal decomposition of the acrylic acid dimer in the can B is recovered from the top of the tower.

  The acrylic acid recovery tower used in the present invention is not particularly limited as long as crude acrylic acid containing acrylic acid dimer and maleic acid can be distilled. However, since acrylic acid obtained as a can of the high boiling point impurity separation tower in the acrylic acid production process has a high viscosity, when treating such acrylic acid, a distillation column equipped with a thin film evaporator Is preferably used.

  Therefore, separation of high boiling point impurities as a purification step in the process of catalytic vapor phase oxidation of propylene and / or acrolein as crude acrylic acid containing acrylic acid dimer and maleic acid, followed by azeotropic distillation to produce acrylic acid The present invention will be described in detail below, taking as an example the case of using a can liquid (high boiling point impurities) obtained from a tower and using a distillation tower equipped with a thin film evaporator as an acrylic acid recovery tower.

  FIG. 1 is a flow chart showing one embodiment of the method of the present invention. Crude acrylic acid containing acrylic acid dimer, maleic acid and the like obtained from the bottom of high boiling point impurity separation tower 1 is introduced into distillation tower 2 equipped with thin film evaporator 3, and acrylic acid is distilled and recovered. To do. At this time, the maleic acid content in the distilled acrylic acid is remarkably reduced. At this time, maleic acid in acrylic acid is 0 to 3%, preferably 0 to 1%. The acrylic acid recovered in this way is usually recycled to the previous step, for example, a purification step, specifically, a high boiling point impurity separation tower 1 to obtain product acrylic acid.

  It is preferable to select the type and operating conditions of the distillation column 2 so that the maleic acid can be efficiently separated as described above. Specifically, as the distillation column 2, a plate column having 1 to 5 theoretical plates, preferably 1 to 3 plates, and having a non-weir perforated plate is suitably used. Regarding the operating conditions, it is desirable to perform distillation under reduced pressure, preferably at an operating pressure of 10 to 100 mmHg, and under conditions where the bottom temperature of the distillation column 2 is 120 ° C. or lower, preferably 60 to 120 ° C. If the column bottom temperature is too high, precipitates that are thought to be caused by maleic acid are generated, making long-term safe operation difficult.

  In addition, there is no restriction | limiting in particular about the thin film evaporator 3, What is generally used as a thin film evaporator can be used.

  The can A from the thin film evaporator 3 is introduced into the next pyrolysis tank 4 where the acrylic acid dimer is pyrolyzed and converted to acrylic acid. There is no restriction | limiting in particular about the form of the thermal decomposition tank 4, Any can be used if it is suitable for thermally decomposing the acrylic acid dimer in the can liquid A to acrylic acid.

  The thermal decomposition temperature in the thermal decomposition tank 4 is usually 120 to 220 ° C, and it is particularly preferable to perform thermal decomposition in the range of 120 to 160 ° C. Since the residence time (thermal decomposition tank capacity / waste oil amount) varies depending on the thermal decomposition temperature, it cannot be specified unconditionally, but usually a residence time of about 20 to 50 hours is required. If the thermal decomposition is carried out at a high temperature for a short time, undesirable decomposition or polymerization may occur.

  In the pyrolysis tank 4, the acrylic acid dimer is thermally decomposed into acrylic acid. In order to recover the acrylic acid from the decomposition product, at least a part of the can B in the pyrolysis tank 4 is evaporated in a thin film. Circulate to vessel 3. The rest is discarded as waste liquid.

  In order to efficiently recover the acrylic acid in the can liquid B, the circulation amount of the can liquid B to the thin-film evaporator 3 may be increased. Usually, the crude acrylic containing acrylic acid dimer and maleic acid is used. It is good to set it as 1-20 mass times of an acid, Preferably it is 3-20 mass times. Although the can B may be circulated to the high boiling point impurity separation column 1, since the maleic acid is concentrated on the bottom of the high boiling point impurity separation column 1 and may be precipitated in some cases, the thin film evaporator It is good to circulate to 3.

  The acrylic acid recovered from the top of the distillation column 2 is usually recycled to the previous step, for example, the purification step, specifically the high boiling point impurity separation column 1 to obtain product acrylic acid. At this time, since the maleic acid content in the recovered acrylic acid is remarkably small, it is not concentrated in the purification step or the like, and the purity of the product acrylic acid is not lowered. In addition, since most of the maleic acid is separated and removed as a waste liquid, it is possible to remarkably reduce the occurrence of trouble due to the precipitation.

Hereinafter, the present invention will be specifically described with reference to examples.
(Example 1)
Acrylic acid was recovered according to the process chart shown in FIG. The distillation tower 2, thin film evaporator 3 and pyrolysis tank 4 used are as follows.
Distillation column 2: 15 plates, no weir perforated plate distillation column thin film evaporator 3: heat transfer area 7.5 m ² , horizontal pyrolysis tank 4: capacity 11 m ³
0.7 h / hr of crude acrylic acid containing maleic acid and an acrylic acid dimer obtained through a propylene catalytic vapor phase oxidation step, a collection step, an azeotropic separation step and a purification step (high boiling point impurity separation tower 1) Was introduced into the middle column of the distillation column 2 at a flow rate of

  In the distillation column 2, the thin film evaporator 3 is controlled so that the column bottom temperature becomes 85 ° C., and operated under the conditions of an operating pressure of 25 mmHg and a reflux ratio of 0.9, and acrylic acid is supplied from the top of the column at 0.5 t / It was recovered at a flow rate of hr (hereinafter, this acrylic acid is referred to as recovered acrylic acid).

  The can liquid from the thin film evaporator 3 is introduced into the pyrolysis tank 4, where pyrolysis is carried out under the conditions of an internal temperature of 140 ° C. and a residence time of 45 hours, and a part of the can liquid is put into the thin film evaporator 3. It was circulated. The circulation rate of this can was 2.8 t / hr, which was 4 times the mass of the crude acrylic acid containing acrylic acid and maleic acid. The rest was discarded as waste liquid.

  The composition of the crude acrylic acid including acrylic acid and maleic acid, the recovered acrylic acid and the waste liquid was as shown in Table 1.

  The above operation was continued for 6 months, but there was no problem such as precipitation and the operation was stable. The purification yield was 98%, and the decomposition rate of the acrylic acid dimer was 73.9%.

It is process drawing which shows one embodiment of the method of this invention.

Explanation of symbols

1 High boiling point impurity separation tower 2 Distillation tower 3 Thin film evaporator 4 Pyrolysis tank

Claims (5)

In recovering acrylic acid from crude acrylic acid including acrylic acid dimer and maleic acid,
(1) The crude acrylic acid is introduced into a distillation column having a theoretical plate number of 1 to 5 equipped with a thin film evaporator, and the concentration of maleic acid in the acrylic acid distillate from the top of the distillation column is 0. Distilled under conditions of ˜3 wt% (excluding 3 wt%), and recovered by distilling acrylic acid from the top of the column,
(2) The can A from the thin film evaporator is introduced into the pyrolysis tank, where the acrylic acid dimer in the can A is decomposed at a temperature in the range of 120 to 220 ° C., and (3) the above A method for recovering acrylic acid, characterized in that at least a part of the can liquid B from the thermal decomposition tank is circulated to the thin film evaporator of the distillation column. The method for recovering acrylic acid according to claim 1, wherein the distillation is performed at 10 to 100 mmHg and a column bottom temperature of 60 to 120 ° C in (1). The method for recovering acrylic acid according to claim 1 or 2, wherein the circulation amount of can B in the thermal decomposition tank is 1 to 20 times the amount of crude acrylic acid introduced into the distillation column. Acrylic acid-containing gas obtained by contact gas phase oxidation of propylene and / or acrolein is brought into contact with water, acrylic acid is collected as an aqueous acrylic acid solution, and the aqueous acrylic acid solution is separated with water in an azeotropic separation tower. In the process of distilling in the presence of an azeotropic solvent that forms an azeotrope and then purifying crude acrylic acid obtained from the bottom of the azeotropic separation tower in a high-boiling impurity separation tower, the high-boiling impurity separation tower In recovering acrylic acid from crude acrylic acid containing acrylic acid dimer and maleic acid from the bottom of
(1) The crude acrylic acid containing the acrylic acid dimer and maleic acid is introduced into a distillation column having a theoretical plate number of 1 to 5 provided with a thin film evaporator, where 10 to 100 mmHg and a column bottom temperature of 60 to Distilled under the condition of 120 ° C., distilled and recovered acrylic acid from the top of the column and recycled to the previous step,
(2) The can A from the thin film evaporator is introduced into the pyrolysis tank, where the acrylic acid dimer in the can A is decomposed at a temperature in the range of 120 to 220 ° C., and (3) the above Acrylic, characterized in that can liquid B from the pyrolysis tank is circulated in the thin film evaporator of the distillation tower at a ratio of 1 to 20 times that of crude acrylic acid containing acrylic acid dimer and maleic acid. Acid recovery method. The method for recovering acrylic acid according to claim 1 or 4 , wherein the concentration of acrylic acid dimer and maleic acid in the crude acrylic acid is at least 20 wt% and 3 to 10 wt%, respectively.

Images