JP2002161067A - Method for extracting and recovering polymerization inhibitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for extracting and recovering a polymerization inhibitor, by which the polymerization inhibitor can efficiently be recovered from the can liquid of a distillation tower close to the final site of a process for distilling crude acrylic acid. SOLUTION: This method for extracting and recovering the polymerization inhibitor, comprises mixing 100 pts.wt. of the can liquid having an acrylic acid content of <15 wt.% and containing acrylic acid and acrylic acid dimer in a total amount of <60 wt.% with >=50 pts.wt. of an organic solvent immiscible with the can liquid, and then leaving to stand the mixture to separate the mixture into two phases. The present invention can be applied to a can liquid having a viscosity of >=1,800 cp at 50 deg.C and a specific gravity of >=1.25. The organic solvent is preferably isopropyl acetate, methyl acetate, methyl isobutyl ketone, and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for extracting and recovering a polymerization inhibitor used in a process for producing acrylic acid. More specifically, the present invention relates to a process for producing acrylic acid by catalytic vapor phase oxidation of propylene, propane or acrolein. The present invention relates to a method for extracting and recovering a polymerization inhibitor from a distillation bottom liquid of crude acrylic acid.

[0002]

2. Description of the Related Art Usually, acrylic acid is produced by a process of cooling and collecting acrylic acid produced by catalytic vapor phase oxidation of propylene, propane (hereinafter collectively referred to as propylene or the like) or acrolein together with water, and then a collecting liquid. Extracting acrylic acid from water using an extraction solvent (or a dehydration azeotropic step of removing a water by adding a solvent azeotropic with water to a collected liquid) and a step of distilling off the extraction solvent from the extracted acrylic acid Further, it is industrially manufactured through a step of distilling off acetic acid produced as a by-product, a step of purifying the crude acrylic acid thus obtained by a plurality of distillations, and the like.

[0003] Acrylic acid is extremely polymerizable, and polymerization occurs even during the above-mentioned production process.
Each manufacturing facility, such as a pipe, an extraction tower, and a distillation tower, is easily clogged.
In order to avoid this problem, it has been customary to coexist a polymerization inhibitor in each step after the production of propylene or the like or acrolein by catalytic gas phase oxidation.

[0004] The polymerization inhibitor is concentrated each time it goes through each production process, and a part of the bottom liquid in the distillation step, which is the final purification step, is consumed to prevent polymerization, while the remaining large amount of polymerization inhibitor is consumed. The agent is included. However, usually, the can solution is difficult to handle due to its high viscosity, and furthermore, the process of recovering the polymerization inhibitor from the can solution becomes complicated, so the incineration treatment is performed without recovering the polymerization inhibitor from the can solution. ing.

However, this large amount of polymerization inhibitor is recovered,
Reuse is preferable from the viewpoint of reduction in production cost and resource saving, and methods for recovering the polymerization inhibitor have been studied.

For example, Japanese Patent Application Laid-Open No. 51-91208 discloses a method in which a bottom of a rectification column is evaporated by 60 to 80% by a thin film evaporator to recover a polymerization inhibitor and reuse the same. . However, the recovery rate of the polymerization inhibitor by this method is low, and most of them are not recovered and are discarded.

Japanese Patent Application Laid-Open No. 54-52038 discloses a method in which a polymerization inhibitor is extracted and recovered with water from an evaporation residue obtained by evaporating a rectification column solution of acrylic acid. However, in the extraction method using water, the water-insoluble polymerization inhibitor is not recovered, and there is a problem that the number of steps for treating wastewater generated by the extraction operation increases.

[0008] In addition to acrylic acid, a technique for extracting and recovering a phenolic polymerization inhibitor in a distillation residue (styrene tar) produced when distilling and refining styrene with a water-soluble oxygen-containing compound such as methanol or acetone. However, JP 63
No. 2,306,659. In this extraction and recovery technology, styrene tar 100 parts by weight,
If 100 to 600 parts by weight of an oxygen-containing compound such as methanol is not used, there is a problem that the recovery rate of the polymerization inhibitor decreases, and the use of such a large amount of solvent has problems in operation and energy cost. Further, it is described that the extraction system is easily emulsified, and in this case, the emulsion is destroyed by adding water to the extraction system.
However, the addition of water raises new problems as described above.

[0009]

The present inventors have studied various extraction solvents and extraction conditions in order to solve the above-mentioned problems. I found that it could be collected well. The present invention has been completed based on the above findings, and an object of the present invention is to extract and collect various polymerization inhibitors in a can solution by using a predetermined ratio of an organic solvent that does not mix with the can solution. Is to provide.

[0010]

The present invention to achieve the above object is as described below.

[1] produced by distillation of crude acrylic acid,
A polymerization inhibitor, the acrylic acid content is less than 15% by mass, and the total amount of acrylic acid and acrylic acid dimer is 6%
After adding at least 50 parts of an organic solvent that is immiscible with the can solution per 100 parts by mass of 0% by mass of the can solution, and mixing the two, the mixture is allowed to stand and subjected to two-phase separation to polymerize the polymer contained in the can solution. A method for extracting and recovering a polymerization inhibitor, wherein the polymerization inhibitor is extracted toward the organic solvent.

[2] The viscosity of the can solution is 18 at 50 ° C.
The method for extracting and recovering a polymerization inhibitor according to [1], which is at least 00 cp.

[3] The method for extracting and recovering a polymerization inhibitor according to [1] or [2], wherein the specific gravity of the can solution is 1.25 or more.

[4] The method for extracting and recovering a polymerization inhibitor according to any one of [1] to [3], wherein the organic solvent is an oxygen-containing compound.

[5] The organic solvent is any one of isopropyl acetate, methyl acetate, methyl isobutyl ketone or a mixture thereof, or a mixture of these with another solvent [1] to [4]. A method for extracting and recovering a polymerization inhibitor according to the above item.

[6] The method for extracting and recovering a polymerization inhibitor according to [5], wherein the other solvent is benzene, toluene or heptane.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention generates crude acrylic acid which is an intermediate product of a process for producing acrylic acid by catalytic vapor phase oxidation of propylene or the like or acrolein through various steps. The present invention relates to a method for extracting and recovering various polymerization inhibitors in a distillation column can solution. The purification of the crude acrylic acid is usually carried out by a dehydration step using a rectification column,
It is performed through the above-mentioned distillation step (crude acrylic acid purification tower) and the like.

Thereafter, the crude acrylic acid purification tower can solution is sent to a facility for decomposing an acrylic acid dimer represented by the following formula (1), where it is heated to decompose a high-boiling compound higher than the acrylic acid dimer. Then, acrylic acid is further recovered. Since the can solution of the dimer decomposition equipment has undergone the above steps, a high viscosity containing the following components,
It is often a high specific gravity can solution.

[0019]

CH ₂ = CHCOOCH ₂ CH ₂ COOH (1) Therefore, when the polymerization inhibitor is usually recovered from the above-mentioned can solution by liquid-liquid extraction, the can solution and the extraction solvent are mixed. For this reason, liquid-liquid extraction has conventionally been considered difficult. These can solutions often have a specific gravity of 1.5 or more and a viscosity at 50 ° C. of 1800 cp or more. Further, the above-mentioned can solution has a total amount of acrylic acid and acrylic acid dimer of less than 60% by mass, more preferably less than 45% by mass, and acrylic acid of less than 15% by mass, more preferably less than 8%.

The can solution to be used in the present invention is a can solution having the above-mentioned composition, and this can solution may be prepared in any manner.

The polymerization inhibitor contained in the above can solution includes:
There is no particular limitation, and any of the polymerization inhibitors usually used in the production process of acrylic acid may be contained. Specific examples include quinone-based polymerization inhibitors such as hydroquinone and hydroquinone monomethyl ether, and phenothiazine.

In the present invention, the polymerization inhibitor in the above can solution is extracted and recovered using an organic solvent.

As the organic solvent, any organic solvent that does not mix with the can solution can be used. The organic solvent may be used alone or as a mixture of organic solvents. Specific examples include saturated hydrocarbons such as hexane and heptane, aromatic compounds such as benzene, toluene, xylene and ethylbenzene, ketones such as methyl isobutyl ketone (MIBK), and esters such as methyl acetate and isopropyl acetate. it can.

Particularly preferred organic solvents are oxygenated compounds such as methyl acetate, isopropyl acetate, and methyl isobutyl ketone. Further, once an acrylic acid aqueous solution is obtained in the acrylic acid production process, the organic solvent used for extracting and separating acrylic acid from the aqueous solution is preferably the same as the organic solvent for extracting the polymerization inhibitor. . The polymerization inhibitor can be efficiently extracted and recovered whether these oxygen-containing compounds are used alone or as a mixture thereof. When used as a mixture, each component can be mixed in any proportion.

Further, a mixture of the oxygen-containing compound or a mixture thereof with another solvent such as an aliphatic hydrocarbon or an aromatic hydrocarbon is also a preferable extraction solvent. As the other solvent, the above-mentioned heptane, benzene, toluene and the like are particularly preferable. The mixing ratio of the other solvent is desirably 20% by mass or less. If it exceeds 20% by mass, the extraction efficiency decreases.

The mixing ratio of the can solution and the solvent is preferably at least 50 parts by mass of the solvent with respect to 100 parts by mass of the can solution.
The solvent is more preferably 50 to 500 parts by mass with respect to 0 parts by mass, and particularly preferably 50 to 100 parts by mass with respect to 100 parts by mass of the can solution. 50 parts of solvent per 100 parts by weight of can liquid
If the amount is less than 2 parts by mass, the can solution and the organic solvent are
Phase separation becomes difficult, and the polymerization inhibitor cannot be recovered at a high recovery rate.

The extraction temperature is not particularly limited, but is preferably in a temperature range in which the vapor pressure of an organic solvent generally used does not become too high.

There is no particular limitation on the extraction method,
After mixing and stirring the can solution and the organic solvent, the mixture is allowed to stand and separated into two phases over time. The standing time is preferably 10 minutes or more, particularly preferably 1 to 3 hours. Next, an organic solvent phase containing a polymerization inhibitor is obtained from the two separated phases, and the polymerization inhibitor can be recovered by distilling off or concentrating the solvent. Also, if there is no problem with mixing the organic solvent into the process,
The organic solvent phase can be used as it is to prevent polymerization in the process.

As the extraction device, a known mixer settler or the like can be used, but since this extraction system is easily emulsified, strong stirring and mixing are not preferred. A preferred mixing method is a method in which a solvent and a can solution are mildly mixed using a static mixer.

The collected polymerization inhibitor can be recycled and reused in each step of the acrylic acid production process.

[0031]

Example 1 A 500 ml separating funnel was charged with 100 g of a can solution having the composition shown in Table 1 (can solution of a crude acrylic acid purification tower) and 50 g of isopropyl acetate. This separating funnel was shaken for 10 minutes using a shaker and then allowed to stand for 15 minutes. The upper phase (organic solvent phase) separated into two phases was separated and analyzed for composition. The results are shown in Table 2.

Comparative Example 1 As Comparative Example 1, the same operation as in Example 1 was carried out using a can solution having the composition shown in Table 1. The shaker was allowed to settle but did not separate into two phases. It is presumed that the reason why Comparative Example 1 did not separate into two phases was that the ratio of other components to the total amount of acrylic acid and acrylic acid dimer was different. That is, if the low molecular weight acid (acrylic acid, dimer) is relatively large, it is well mixed with the organic solvent (extraction solvent),
It is thought that it is difficult to dissolve in an organic solvent when the amount of the polymer acid (acrylic acid trimer or more) is large.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

According to the present invention, since the organic solvent is added at a specific ratio to the can solution when extracting the polymerization inhibitor from the can solution, two-phase separation between the can solution and the organic solvent is good. . For this reason, various polymerization inhibitors can be simultaneously and efficiently extracted and recovered in the organic solvent phase. The collected polymerization inhibitor can be returned to each step of the production of acrylic acid and reused, thereby contributing to a reduction in the production cost of acrylic acid.

Claims (6)

[Claims] 1. A mass of a can solution containing a polymerization inhibitor, produced by distillation of crude acrylic acid, having an acrylic acid content of less than 15% by mass and a total amount of acrylic acid and acrylic acid dimer of less than 60% by mass. Per part, after adding 50 parts or more of an organic solvent that does not mix with the can solution, and mixing the two, the polymerization inhibitor contained in the can solution is allowed to stand and subjected to two-phase separation to the organic solvent side. A method for extracting and recovering a polymerization inhibitor to be extracted. 2. The viscosity of a can solution at 50 ° C. is 1800 c.
The method for extracting and recovering a polymerization inhibitor according to claim 1, wherein the number is p or more. 3. The method for extracting and recovering a polymerization inhibitor according to claim 1, wherein the specific gravity of the can solution is 1.25 or more. 4. The method according to claim 1, wherein the organic solvent is an oxygen-containing compound.
4. The method for extracting and recovering a polymerization inhibitor according to any one of claims 1 to 3. 5. The method according to claim 1, wherein the organic solvent is any one of isopropyl acetate, methyl acetate and methyl isobutyl ketone, or a mixture thereof, or a mixture thereof with another solvent. Extraction and recovery method of polymerization inhibitor. 6. The method for extracting and recovering a polymerization inhibitor according to claim 5, wherein the other solvent is benzene, toluene or heptane.