JPH0511100B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for recovering lower alkyl esters of acrylic acid or methacrylic acid (hereinafter referred to as (meth)acrylic acid). To explain in detail, (meta)
A lower alkyl ester mixture of (meth)acrylic acid containing acrylic acid, lower alcohol, water, etc. is extracted with water, the acid and alcohol are dropped into the extraction water phase, and the water phase is sent to an alcohol recovery distillation column to extract alcohol. This relates to a method in which a part of the aqueous solution at the bottom of the tower is side-cut and recycled as a distillate to the extraction process.

(Prior art) (Meth)acrylic acid in the presence of sulfuric acid, para-toluenesulfonic acid, strongly acidic ion exchange resin, etc.
Crude ester, which is a reaction product of (meth)acrylic acid and lower alcohol obtained as a distillate when esterified with a lower alcohol, usually contains (meth)acrylic acid, lower alcohol, and water in addition to the ester. contains. A known method for recovering ester from this crude ester is to bring the crude ester into countercurrent contact with water, extract and separate the (meth)acrylic acid and lower alcohol in the crude ester into an aqueous phase, and then remove the raffinate ester phase. Dehydration distillation followed by distillation as an ester product. Therefore, the extracted aqueous phase is supplied together with the distilled water phase of the ester synthesis step and/or the dehydration distillation step, or alone to the middle stage of the alcohol recovery distillation column, and the lower alcohol distilled from the top of the column is recovered. and recycled for use in the ester synthesis process. The bottom liquid of the alcohol recovery distillation column is normally sent to the activated sludge treatment process as wastewater (Kirk-Othmer: Encyclopedia
of Chemical Technology.Third Ed.Vol.1,
p341-342). In addition, the crude ester, which is a reaction product of the process for producing methyl ester of methacrylic acid using the acetone cyanohydrin method, similarly contains methacrylic acid, methanol, and water. The phases are extracted and separated, and the raffinate ester phase is sent to a low-boiling removal column and then to a purification column to recover purified methyl methacrylate as a distillate. The extracted aqueous phase is introduced into the middle stage of the methanol recovery distillation column, where methanol is recovered from the top of the column, and the bottom liquid is mainly sent to the activated sludge treatment process as wastewater. (Edited by the Chemical Engineering Society: Chemical Process Collection p619).

(Problems to be Solved by the Invention) As described above, wastewater generated during recovery of acrylic esters or methacrylic esters (hereinafter referred to as (meth)acrylic esters) is sent to an activated sludge treatment process.

When the bottom liquid of the alcohol recovery distillation column is recycled to the top of the extraction column as an extraction solvent for acid and alcohol, polymers such as (meth)acrylic acid, (meth)acrylic acid ester, and high-boiling by-product unsaturated compounds are produced. It accumulates in the circulating water, and usually a large amount of scum is generated in the extraction tower or becomes emulsified, making it difficult to separate the water and oil phases and making continuous operation impossible. Stand up. Therefore, as mentioned above,
While constantly supplying a large amount of fresh water to the extraction tower, it was necessary to simultaneously draw out a large amount of waste water from the bottom of the alcohol recovery distillation tower.

(Means for Solving the Problems) As a result of intensive research into improving the defects of the above-mentioned conventional method, the present inventors found that (meth)acrylic acid and (meth)acrylic acid contained in the extracted aqueous phase of the crude ester extraction tower While acid esters and high-boiling byproducts are circulated between the bottom of the alcohol recovery distillation column and the reboiler, or while they remain at the bottom of the column, they are heated and transformed into polymers, which are converted into polymers as the bottom liquid of the recovery distillation column. The present invention was achieved based on the discovery that the ester is brought into an emulsified state when the ester is recycled.

That is, the present invention involves extracting the lower alcohol and acrylic acid or methacrylic acid with water from a lower alkyl ester of acrylic acid or methacrylic acid, an ester mixture containing acrylic acid or methacrylic acid, a lower alcohol, and water, and converting the extract into alcohol. The lower alcohol is recovered from the top of the recovery distillation column, and a portion of the aqueous solution flowing down to the bottom of the column is extracted as a side cut and used as water for extracting the lower alcohol and acrylic acid or methacrylic acid from the ester mixture. The present invention relates to a method for recovering acrylic ester or methacrylic ester.

In the present invention, examples of the lower alkyl ester of acrylic acid or methacrylic acid include methyl ester, ethyl ester, n-propyl ester, and isopropyl ester of acrylic acid or methacrylic acid.

Ester mixtures include (meth)acrylic acid and lower alcohols (methanol, ethanol, n
-Propanol, isopropanol, etc.) in the presence of an acidic catalyst (e.g. sulfuric acid, para-toluenesulfonic acid, strongly acidic ion exchange resin, etc.) or methyl methacrylate obtained by the acetone cyanohydrin method. Examples include ester-containing reaction products.

The ester mixture obtained in this way usually contains (meth)acrylic acid lower alkyl ester.
55-85% by weight, (meth)acrylic acid 0-5% by weight, lower alcohol 5-30% by weight, water 5-15% by weight.
Contains % by weight.

The amount of water used to extract the lower alcohol and (meth)acrylic acid from the ester mixture is preferably about 30 to 150% by weight of the ester mixture.

At this time, salt, sodium carbonate, caustic soda, etc. may be added to the water used as the extraction agent.

When extraction is performed by bringing the ester mixture into contact with water, aromatic hydrocarbons (benzene, toluene, xylene, ethylbenzene, etc.) or saturated hydrocarbons (hexane, heptane, etc.) are used as extractants for lower alkyl (meth)acrylic esters. , octane, isooctane, etc.) can also be used in combination.

When a part of the aqueous solution flowing down to the bottom of the alcohol recovery distillation column is extracted as a side cut, the extraction point can be anywhere above the bottom liquid level at the bottom of the alcohol recovery distillation column, but the liquid flowing down from the bottom tray of the distillation column Particularly preferably, a portion of the liquid is removed as a side cut before it reaches the bottom liquid level.

The amount of the aqueous solution taken out as a side cut is determined by the extraction conditions, and is usually about 50 to 90% by weight of the aqueous solution flowing down to the bottom of the column.

Of the liquid flowing down from the bottom tray of the distillation column, the remaining liquid that was not taken out as a side cut is allowed to flow down to the bottom of the column and circulated between the reboiler and the bottom of the column as a bottom circulation liquid, and a part of it is used as a circulation liquid. A concentrated aqueous solution of polymers, etc. is extracted from the water and sent to a waste liquid treatment process.

Next, details of the present invention will be explained with reference to the drawings. In Figure 1, 1 is the reaction product (crude ester) obtained when (meth)acrylic acid is esterified with a lower alcohol in the presence of a strong acidic catalyst or the reaction product obtained by the acetocyanhydrin method. This is a (crude ester) introduction line, and alcohol, (meth)acrylic acid, high boiling point impurities, etc. in the crude ester are extracted with water from the line 26 in the extraction column 2. The raffinate ester phase is transferred from line 3 to low boiling point separation column 5.
The azeotropic mixture of ester and water is distilled out through line 6, condensed in condenser 7, and separated into oil and water phases in decanter 8. The entire oil phase is refluxed through line 9 to column 5, alcohol and some The aqueous phase containing dissolved ester is extracted from line 10 and introduced into alcohol recovery distillation column 15. 11 indicates the boiler, 12 indicates the bottom circulation line of the column 5, and 13
The more dehydrated (meth)acrylic acid ester is extracted.

The extracted water phase from the extraction column 2 passes through line 4 and is introduced into the middle stage of alcohol recovery distillation column 15 from line 14 together with the alcohol-containing water from line 10 .
The distilled alcohol passes through line 16, condenser 17, receiver 18, and is recovered from line 20.
A portion is refluxed to column 15 via line 19. At the bottom of the tower, high-boiling substances are concentrated through a bottom circulation line 22 and a reboiler 21, and are extracted as waste liquid through a line 23. 24 is a distributor for the liquid flowing down from the lowermost tray, and a predetermined amount of liquid is extracted from line 25 as a side cut and recycled to the extraction column 2. The remainder of the flowing liquid flows down to the bottom of the column. From line 27 or 28, in order to neutralize the (meth)acrylic acid contained in the crude ester,
This line introduces an aqueous solution such as soda carbonate.

(Example) Next, the present invention will be explained with reference to examples.

Example 1 Crude methyl methacrylate obtained by esterifying methacrylic acid using a strongly acidic ion exchange resin as a catalyst (methanol 11wt%, methacrylic acid 0.5wt%, water 5.1wt)
% content) is introduced into the lower part of the rotating disk extraction tower 2 of 74 mmφ x 40 stages, 5.0 Kg/H of water is introduced from the upper part, methanol and methacrylic acid are extracted with water, and methanol is extracted from line 3. A raffinate ester phase of 10.3 Kg/H containing 1.45 wt%, methacrylic acid 0.6 wt%, and water 1.45 wt% was obtained, and an extracted aqueous phase of 6.70 kg/H was obtained from line 4.
Kg/H was obtained. The extracted aqueous phase 6.70Kg/H is 200mmφ
The methanol was supplied to the middle stage of the 25-stage distillation column 15, and 1.35 kg/H of methanol containing 4.8 wt% methyl methacrylate and 2.9 wt% water was recovered from the top of the column. After dividing the liquid flowing down from the bottom tray of the distillation column 15 into two and extracting 5 kg/H as a side cut through the line 25, the entire amount of water to be supplied to the extraction column 2 is from the line 25, and the remaining liquid flowing down is After circulating through the bottom of the distillation column, reboiler 21, and line 22, 0.44 kg/H was extracted from line 23 as waste liquid. The circulating water to the extraction column is not heated at the bottom of the alcohol recovery distillation column, so the polymer content is 0.28wt.
%, and stable operation was possible without the occurrence of scum or emulsified state in the extraction column.

Example 2 Crude ethyl acrylate obtained by esterifying acrylic acid using sulfuric acid as a catalyst (contains 0.259 wt% ethanol, 0.054 wt% acrylic acid, and 0.143 wt% water) 9 Kg/H
was introduced into the lower part of a 74 mmφ x 40 stage rotating disk extraction tower 2, 8.0 kg/H of water was introduced from the upper part, ethanol and acrylic acid were extracted with water, and 0.31 wt% ethanol and acrylic acid were added through line 3. 0.004wt%, water
A raffinate ester phase of 5.26 Kg/H containing 1.56 wt% was obtained, and an extracted aqueous phase of 11.78 Kg/H was obtained from line 4.
The extracted aqueous phase 11.8Kg/H was transferred to a 200mmφ×40-stage distillation column 1.
5, and ethyl acrylate is added from the top of the column.
Ethanol 2.82 containing 11.26wt%, water 8.20wt%
Kg/H was recovered. The liquid flowing down from the bottom tray of the distillation column 15 is divided into two parts, and 8 kg/H is taken out as a side cut through the line 25.Then, the entire amount of water to be supplied to the extraction column 2 is from the line 25, and the remaining liquid flowing down is After circulating through the bottom of the distillation column, reboiler 21, and line 22, 0.97 kg/H was extracted from line 23 as waste liquid. In this case, the polymer content of the circulating water to the extraction tower was as low as about 0.25 wt%, and stable operation was possible without the occurrence of scum or emulsified state in the extraction tower.

Comparative Example 1 In the alcohol recovery distillation column 15, the entire amount from the lowest tray was allowed to flow down to the bottom of the column without side cutting, and after circulating through the reboiler 21 and line 22, a portion of the liquid extracted from line 23, 5.0 kg/
The operation was the same as in Example 1 except that H was recycled to the extraction column 2 from the line 26. Ten hours after the start of circulation of the bottom liquid of the alcohol recovery tower, the interior of the extraction tower became emulsified, making it difficult to continue the extraction.

However, in the examples, recovery of crude ester obtained by esterifying (meth)acrylic acid was explained as an example.
Of course, the crude methyl methacrylate used in the acetone-cyanhydrin method is a mixture containing methyl methacrylate, methacrylic acid, methanol and water, and can be carried out in the same manner.

In addition, a method in which aromatic hydrocarbons such as benzene, toluene, xylene, and ethylbenzene or saturated hydrocarbons such as hexane, heptane, octane, and isooctane are used together as an organic phase in the extraction and washing step of the crude ester, that is, an extraction column A process in which the raffinate oil phase is a mixture containing (meth)acrylic acid ester and a hydrocarbon solvent as main components, and the ester is purified by dehydration, solvent removal, and distillation of purified (meth)acrylic acid ester. Of course, the present invention can also be applied to.

(Effects of the Invention) As described above, according to the method of the present invention, there is no need to add new water to the extraction process, the amount of waste liquid to be treated is greatly reduced, and stable operation is possible. .

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing an example of an embodiment of the present invention. 2...extraction column, 5...low boiling point separation column, 15...alcohol recovery distillation column, 24...distributor.

Claims (1)

[Claims] 1 Lower alkyl ester of acrylic acid or methacrylic acid, lower alcohol and acrylic acid or methacrylic acid are extracted with water from an ester mixture containing acrylic acid or methacrylic acid, lower alcohol and water, and the extract is supplied to an alcohol recovery distillation column. and collect the lower alcohol from the top of the tower.
A method for recovering acrylic esters or methacrylic esters, characterized in that a part of the aqueous solution flowing down to the bottom of the tower is extracted as a side cut and used as water for extracting lower alcohol and acrylic acid or methacrylic acid from the ester mixture.