JPH1135504A - Recovery of isopropyl alcohol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover isopropyl alcohol in a high yield with suppressing the decomposition of dimethyl sulfoxide, by maintaining the liquid contact part of a heater for a distillation column for distilling isopropyl alcohol contaminated with dimethyl sulfoxide at a specific temperature. SOLUTION: In this method for recovering isopropyl alcohol contaminated with dimethyl sulfoxide, the liquid contact part of a heater for a distillation column is maintained at <=220 deg.C. Preferably the concentration of dimethyl sulfoxide in a liquid in the heater for the distillation column is made <=10 wt.% and the temperature of the condensing face of a condenser at the top of the distillation column is maintained at a temperature (>=37.3 deg.C) not to condense dimethyl sulfide as the decomposition product of dimethyl sulfoxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recovering isopropyl alcohol by distilling isopropyl alcohol contaminated with dimethyl sulfoxide. In particular, the present invention relates to a method of purifying isopropyl alcohol contaminated with dimethyl sulfoxide discharged from a process of performing fine processing using a photoresist by distillation.

[0002]

2. Description of the Related Art In a process of performing fine processing using a photoresist, it is necessary to peel off the photoresist after finishing the processing. There are several known photoresist stripping methods, but the mainstream is a method of treating with an organic solvent, washing with isopropyl alcohol, and completely replacing the organic solvent used as a stripping agent. . Dimethyl sulfoxide is often used in combination with an amine such as monoethanolamine as a stripping agent, but isopropyl alcohol contaminated with this stripping agent is currently discarded. The main reason is that
Dimethyl sulfoxide is apt to cause self-decomposition exothermic reaction, and it is considered that it is difficult and dangerous to recover isopropyl alcohol of high purity by distillation and purification of isopropyl alcohol contaminated with dimethyl sulfoxide. Since the exothermic self-decomposition reaction of dimethyl sulfoxide is promoted by an acid, dimethyl sulfoxide coexisting with amines should be relatively stable, but still causes an exothermic self-decomposition reaction depending on conditions. When dimethyl sulfoxide is decomposed in the distillation column, dimethyl sulfide (boiling point 37.3) is obtained.
C) and methyl mercaptan (boiling point 6 ° C.), which reach the top with isopropyl alcohol and contaminate the recovered isopropyl alcohol.

[0003]

However, with the increasing use of photoresist, the amount of dimethylsulfoxide-contaminated isopropyl alcohol discharged from this process is also increasing. Therefore, there is a demand for the development of a technology for recovering and recycling this isopropyl alcohol with high purity. The present invention addresses such a need.

[0004]

According to the present invention, when distilling and recovering isopropyl alcohol contaminated with dimethyl sulfoxide, the temperature of the liquid contact portion of the heater of the distillation column is maintained at 220 ° C. or lower. Thereby, decomposition of dimethyl sulfoxide can be suppressed and isopropyl alcohol can be recovered with high purity.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Isopropyl alcohol contaminated with dimethyl sulfoxide, which is a target of the present invention, is discharged from a process of stripping a photoresist using dimethyl sulfoxide in a process of processing mainly using a photoresist. It was done. Since dimethyl sulfoxide is often used in combination with amines such as monoethanolamine when the photoresist is stripped, the isopropyl alcohol discharged from this step must be contaminated with both dimethyl sulfoxide and amines. There are many. However, amines are more stable to heat than dimethyl sulfoxide, so that when examining distillation conditions, attention should be paid exclusively to dimethyl sulfoxide.

According to the study of the present inventors, the onset of exothermic temperature of dimethyl sulfoxide measured by using ARC (manufactured by Scientific, Columbia) is 226 ° C., to which amine or isopropyl alcohol is mixed. However, the heat generation start temperature does not decrease so much. For example,
The exothermic onset temperature of the composition containing 10% by weight of dimethyl sulfoxide, 23% by weight of monoethanolamine and 67% by weight of isopropyl alcohol was 221 ° C. Further, this composition does not generate heat at 200 ° C. unless a long time elapses. Further, in these experiments, since the exothermic onset temperature and the pressure increase onset temperature coincided with each other, it was confirmed that self-decomposition exothermic reaction had occurred.

In the present invention, the distillation is carried out while preventing the self-decomposition exothermic reaction.
Keep below 0 ° C. Considering the possibility that components that promote decomposition heat generation may be mixed in the liquid, the temperature change inevitably occurring in the heater, and the local retention of the liquid, the temperature of the liquid contact part of the heater is 200 ° C or less. It is particularly preferable to maintain the temperature at 150 ° C. or lower.

[0008] If dimethyl sulfoxide is concentrated to a high concentration in the heater, it is generally considered that the risk of self-decomposition exothermic reaction increases. Therefore, the concentration of dimethyl sulfoxide in the liquid in the heater is reduced. It is preferred to keep it below 10% by weight. If distillation is performed while maintaining the temperature of the liquid-contact part of the heater of the distillation column and the concentration of dimethyl sulfoxide in the liquid under the above conditions, high-purity isopropyl alcohol can be recovered from the top of the column. Since isopropyl alcohol azeotropes with water, if water is contained in isopropyl alcohol contaminated with dimethyl sulfoxide supplied to the distillation column, water is also contained in isopropyl alcohol distilled from the top of the column. Come in. Therefore, when it is desired to recover anhydrous isopropyl alcohol, the distilled isopropyl alcohol may be dehydrated by contact with a dehydrating agent, or may be dehydrated by pervaporation.

According to the present invention, the decomposition of dimethyl sulfoxide in the distillation column can be almost completely suppressed, but in some cases, a slight decomposition occurs to generate by-products such as dimethyl sulfide, thereby contaminating the recovered isopropyl alcohol. May be. Contamination by these decomposed products is very small and hardly hinders when the recovered isopropyl alcohol is used for normal use. However, when the recovered isopropyl alcohol is reused for removing the photoresist, a small amount of contamination by these decomposed products is also likely to be an obstacle, so that the recovered isopropyl alcohol is not contaminated by these decomposed products. It is desirable to operate it. One method is to use a difference in boiling point with isopropyl alcohol to discharge these decomposition products out of the system without condensing them in a condenser at the top of the tower. That is, the boiling point of isopropyl alcohol is 8
Although the boiling point of dimethyl sulfide, which is the decomposition product of dimethyl sulfoxide, is 37.3 ° C and the boiling point of methyl mercaptan is 6 ° C, the temperature of the condensation surface of the condenser is maintained at 37.3 ° C or higher. This can prevent these decomposition products from condensing and mixing into isopropyl alcohol. If the concentration of the decomposition product in the gas phase of the condenser is low, the condensation can be prevented even if the temperature of the condensation surface is further lowered. Also, when the gas of these decomposition products accumulates in the condenser and its concentration increases, they dissolve in the condensed isopropyl alcohol and cause pollution. Therefore, it is preferable to maintain the concentration of the decomposition product gas in the condenser low by distilling the gas of the non-condensed decomposition product out of the system from the gas phase part of the condenser. In order to discharge the gas of the decomposition product out of the system, the temperature of the condenser may be increased and the gas may be discharged out of the system together with a part of the isopropyl alcohol vapor flowing in.

[0010]

The present invention will be described more specifically with reference to the following examples. Example 1 A packed column type distillation column was charged with a composition of 5% by weight of dimethyl sulfoxide, 11.7% by weight of monoethanolamine and 83.3% by weight of isopropyl alcohol, and the temperature of the liquid contact surface of the heater was set to 150 ° C. ± 3 ° C. The distillation was performed with a reflux ratio of 0.5 and a cooling water temperature of 25 ° C. supplied to the condenser. The condenser effluent was pumped back to the distillation column heater. After operating under these conditions for 3 hours, the smell of dimethyl sulfide was not felt in the gas collected from the gas phase of the condenser. When the condensate was analyzed by gas chromatography, the concentrations of dimethyl sulfoxide and monoethanolamine were each 50 ppm or less, and dimethyl sulfide was below the detection limit, and was a high-purity product that could withstand the use in the photoresist stripping process. there were.

Comparative Example 1 Distillation was carried out for 1 hour and 20 minutes in the same manner as in Example 1 except that the heat transfer area of the heater was reduced by half and the temperature of the liquid contact surface was set to 220 ° C. ± 5 ° C. went. The gas collected from the condenser had a strong odor of dimethyl sulfide. When the condensate was analyzed by gas chromatography, the concentrations of dimethyl sulfoxide and monoethanolamine were each 50 ppm or less, but the concentration of dimethyl sulfide was 210 ppm.

Claims (5)

[Claims] 1. A method for recovering isopropyl alcohol, comprising maintaining a temperature of a liquid contact portion of a heater of a distillation column at 220 ° C. or lower when distilling and purifying isopropyl alcohol contaminated with dimethyl sulfoxide. 2. The temperature of the liquid-contact part of the heater of the distillation column is 200
The method for recovering isopropyl alcohol according to claim 1, wherein the temperature is maintained at a temperature of not more than ℃. 3. The method for recovering isopropyl alcohol according to claim 1, wherein the concentration of dimethyl sulfoxide in the liquid in the heater of the distillation column is maintained at 10% by weight or less. 4. The recovery of isopropyl alcohol according to claim 1, wherein the distillation is performed while exhausting gas components not condensed in the condenser at the top of the distillation column to the outside of the system. Method. 5. The method according to claim 1, wherein the temperature of the condensation surface of the condenser at the top of the distillation column is maintained at a temperature at which dimethyl sulfide in the gas present in the gas phase of the condenser does not condense. The method for recovering isopropyl alcohol according to any one of the above.