JPH0610142B2 - Purification method of organic solvent - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying an organic solvent containing particles (fine particles) and water and having an azeotropic point with water.

[Conventional Technology and Problems] In processing semiconductor substrates such as silicone wafers,
Cleaning with an organic solvent is performed by the polishing treatment, the etching treatment, the water washing treatment or the like for the purpose of removing abrasive powder, particles such as suspended particles in the air, water and the like attached to the surface of the substrate. In the above cleaning, it is required to use an extremely high-purity organic solvent as the degree of integration of a semiconductor device using a semiconductor substrate increases. Therefore, when the organic solvent after cleaning is reused, a purification technique for removing impurities such as particles and water contained in the cleaning with extremely high accuracy is required. However, in the cleaning, in order to efficiently remove water, acid, etc. adhering to the surface of the semiconductor substrate,
When a polar organic solvent such as isopropyl alcohol (hereinafter referred to as IPA) is used, the organic solvent has an azeotropic point with water contained as impurities, and it is difficult to easily separate water by ordinary distillation. Becomes

Conventionally, as a method of selectively separating water from a liquid mixture of water and an organic solvent having an azeotropic point such as IPA and water, a cell divided into a treatment liquid chamber and a permeation vapor chamber by a separation membrane is used. The mixture is supplied to the treatment liquid chamber, and water that permeates the separation membrane is selectively taken out from the vapor permeation chamber as vapor.
The so-called pervaporation method is known.

However, in general, a separation membrane has a property that, when water is removed from a liquid mixture having a high organic solvent concentration, the ability to selectively remove the water, that is, the reduction of the separation coefficient becomes severe. Therefore, when trying to obtain a purified organic solvent by removing water from the waste liquid having a relatively high organic solvent concentration by such a method, the separation efficiency is extremely poor, and the loss amount of the organic solvent and the purification cost increase. There is a problem of inviting. Further, in the above method, since the organic solvent from which water has been separated is taken out from the processing liquid chamber, it is almost impossible to remove particles contained as impurities.

Therefore, it has been desired to develop a purification method for efficiently removing particles and water from an organic solvent containing the particles and water and having an azeotropic point with water.

[Means for Solving Problems] The inventors of the present invention have conducted extensive studies to solve the above problems. As a result, they have found that the above-mentioned organic solvent containing particles and water can be purified extremely efficiently by combining the pervaporation method and a specific distillation method, and completed the present invention.

The present invention is a crude organic solvent containing particles and water and having an azeotropic point with water (hereinafter, simply referred to as a crude organic solvent).
Is rectified to obtain an organic solvent from which water has been removed as a bottom liquid and an organic solvent containing water as a distillate, respectively. The distillate of the rectification step is subjected to a pervaporation method. A pervaporation step for treating and selectively removing water to obtain an organic solvent having a liquid composition in which the concentration of the organic solvent is higher than the azeotropic composition, and the organic solvent obtained by the pervaporation step is subjected to the rectification step. It is a method for purifying an organic solvent, which comprises a circulation step for circulation and a simple distillation step for obtaining a purified organic solvent from which particles have been removed as a distillate by simple distillation of the bottom liquid in the rectification step.

The crude organic solvent to be purified in the present invention is an organic solvent containing particles and water and having an azeotropic point with water. Typical examples of the organic solvent include alcohols such as IPA, ethanol, n-propanol, isobutanol, and isoamyl alcohol. Among the above-mentioned crude organic solvents, the one in which the method of the present invention is particularly effective is a crude organic solvent having a water content smaller than the azeotropic composition of the organic solvent and water. That is, when a crude organic solvent having a high organic solvent concentration is directly processed by the pervaporation method, the separation characteristics of the separation membrane generally decrease sharply with an increase in the concentration of the organic solvent. And increase the size of the device. In the present invention, as described below, such crude organic solvent is first rectified to reduce the concentration of the organic solvent to near the azeotropic composition, and then processed by the pervaporation method. A crude organic solvent having a high solvent concentration can be efficiently treated. As the crude organic solvent having a high organic solvent concentration, there is crude IPA obtained as a waste liquid in, for example, spray cleaning and immersion cleaning of a silicone wafer. In the above washing,
In order to obtain a sufficient cleaning effect, the water content in the waste liquid is generally suppressed to 10% by weight or less, preferably 5% by weight or less.

In the present invention, the crude organic solvent is first supplied to the rectification step. In the rectification step, a crude organic solvent is rectified using a rectification tower, and an organic solvent from which water has been removed is contained as a still liquid and an azeotropic composition or high-concentration water close to the azeotropic composition is contained as a distillate. This is a step of obtaining an organic solvent (hereinafter also referred to as a water-containing organic solvent). It is preferable to reduce the amount of water in the organic solvent taken out as the bottom liquid as much as possible in order to increase the purity of the finally obtained purified organic solvent, and generally 5% by weight or less, particularly 1% by weight. It is desirable to set the rectification conditions so as to be as follows. Further, the water-containing organic solvent taken out as a distillate, the rectification conditions should be set so that the water content is as close to an azeotropic composition as possible, while reducing the treatment amount in the next pervaporation step. It is preferable to increase the processing efficiency.

In the rectification step, a rectification column having a known structure is used without particular limitation. For example, tray towers, packed towers, etc. are common. Further, the number of stages of the rectification column, the height of the packed bed, the supply position of the liquid, and the like may be appropriately determined so that the above-mentioned pot residual liquid and distillate liquid have the desired organic solvent concentrations.

In the present invention, in the pervaporation step, the water-containing organic solvent obtained as a distillate from the rectification step is treated by a pervaporation method to selectively remove water, and the concentration of the organic solvent is higher than the azeotropic composition. This is a step of obtaining an organic solvent having a liquid composition. The higher the removal rate of water in the pervaporation step, the more the burden of the rectification step can be reduced. However, when the removal rate of water is increased, the separation characteristics deteriorate as the organic solvent concentration increases as described above. The problem arises. Therefore, it is desirable to determine the treatment conditions so that the organic solvent extracted from the pervaporation step has a water content of 85 to 99% by weight, preferably 90 to 95%.

In the pervaporation step, the pervaporation device may have a structure having a treatment liquid chamber and a permeation vapor chamber through a separation membrane, and known pervaporation devices are used without particular limitation. For example, a vertical type structure in which separation membranes are arranged in the vertical direction, a horizontal type structure in which separation membranes are arranged in the horizontal direction, and the like are common. The conditions of the pervaporation method are also not particularly limited, but are generally set so that the treatment liquid chamber temperature is 0 to 200 ° C., particularly room temperature to 100 ° C., and the permeation vapor chamber pressure is 1 to 100 Torr, particularly 1 to 50 Torr. It is desirable to do. When the specific gravity of the organic solvent in the water-containing organic solvent of the treatment liquid is smaller than that of water, a vertical pervaporation device can be used to supply the water-containing organic solvent from below the treatment liquid chamber and to take it out from above. It is preferable that the mixing due to the difference in the specific gravity of the liquid in the processing liquid chamber due to the removal of water can be prevented and the higher concentration organic solvent can be efficiently taken out.

The separation membrane used in the pervaporation device is not particularly limited as long as it is a membrane that can selectively permeate water with respect to the organic solvent. For example, a film having a cation exchange group or an anion exchange group, a polyvinyl film, a polyvinyl acetal film, a cellulose-based polymer film or the like is generally used. As the separation membrane, a known shape such as a sheet shape or a tubular shape is used according to the cell structure.

The organic solvent from which water has been removed in the pervaporation step is circulated to the rectification step by the circulation step. The circulation step may be configured by directly connecting a pervaporation step and a rectification step with a line, or may be configured by connecting a line for supplying a crude organic solvent to the rectification step with a line.

In the present invention, the simple distillation step is a step of simple distillation of the organic solvent substantially free of water, which is obtained as the bottom liquid of the rectification step. By the simple distillation step, a high-purity organic solvent from which particles and water have been removed is obtained as a distillate.

The simple distillation apparatus used in the simple distillation step is not particularly limited, and a known simple distillation apparatus can be used without limitation. Among them, those having a demister (spray filter) in the gas phase portion are preferable because particles entrained in the organic solvent vapor can be cut and the purification efficiency can be further improved. In addition, in order to remove particles accumulated in the residual liquid in the pot, a structure in which a filter such as a microfilter is installed outside and a part of the residual liquid in the pot is circulated does not require discarding the organic solvent in the residual pot. It is preferable since distillation can be carried out.

FIG. 1 is a flow sheet showing a typical embodiment of the method of the present invention. The crude organic solvent containing water and particles is supplied to the rectification step I from the line 1 and rectified in the rectification column 2, and the hydrous organic solvent is taken out as a distillate. The water-containing organic solvent is supplied to the treatment liquid chamber 6 of the pervaporation step II through the line 7, and the water that selectively permeates the separation membrane 5 is removed from the permeation vapor chamber 4 through the line 9.
The water-containing organic solvent supplied to the treatment liquid chamber 6 has particles removed in the rectification step, and has a merit that particles can be completely prevented from accumulating in the treatment liquid chamber due to long-term operation. . The high-concentration organic solvent taken out from the treatment liquid chamber 6 is circulated to the rectification step I by the circulation step III. On the other hand, the organic solvent obtained as a bottom liquid from the rectification step and containing substantially no water is supplied to the simple distillation step IV through the line 8 and simple distilled in the simple distillation apparatus 3 to remove particles and water as a distillate. A highly purified organic solvent containing no is obtained from the line 10.

[Effect] As can be understood from the above description, according to the present invention, a high-purity organic solvent is treated with a high-concentration crude organic solvent from an organic solvent containing particles and water and having an azeotropic point with water. In such a case, it is possible to prevent the separation characteristics from deteriorating in the pervaporation method and carry out the purification extremely efficiently.

[Examples] Examples will be shown below to more specifically describe the present invention, but the present invention is not limited thereto.

Example Hydrofluoric acid 100ppm and particles (0.5μ or more)
IPA containing 8000 pieces / cc and the evaporation residue is 7ppm
An IPA-water mixture having a concentration of 95% by weight was treated according to the flow sheet shown in FIG. First, the IPA-water mixture was supplied from the line 1 to the rectification column 2 having 44 theoretical plates in the rectification step I at the 10th plate from the top at a flow rate of 9.8 / hr for rectification. . The rectification is carried out under the conditions that the reflux ratio is 5, the amount of evaporate at the bottom of the column is 31.5 / hr, and the amount of condensate is 36.6 / hr, and the distillate with an IPA concentration of 90% by weight is 4.8 from the top of the column. / Hr. The distillate obtained from the rectification step was supplied through line 7 to the treatment liquid chamber 6 of the pervaporation step II for treatment. Pervaporation device is 20d
Using a vertical cell having a m ² pyridinium-type anion exchange membrane as the separation membrane 5, the treatment was performed under the conditions that the treatment liquid chamber temperature was 60 ° C. and the permeation vapor chamber 4 pressure was 10 Torr. From the treatment liquid chamber 6, an IPA-water mixed liquid having an IPA concentration of 95% by weight was 4.6.
The obtained IPA / water mixture was circulated to the rectification step I by the circulation step III. Further, from the permeated vapor chamber 4, an IPA-water mixed solution having an IPA concentration of 6.9% by weight is 0.2.
/ Hr.

On the other hand, IPA 5.1 / hr having an IPA concentration of 99.9% by weight was taken out from the rectification column 2 in the rectification step as a bottom liquid and supplied to the simple distillation apparatus 3 having a demister in the gas phase portion of the simple distillation step IV. , Simple distillation was performed. From the top of the simple distillation step 3,
High-purity IPA having an IPA concentration of 99.9% by weight, particles (0.5 μm or more) 93 particles / cc, hydrofluoric acid-trace, and an evaporation residue of 1 ppm or less was obtained at 5 / hr.

[Brief description of drawings]

FIG. 1 is a flow sheet showing a typical embodiment of the method of the present invention. In the figure, I is a rectification step, II is a pervaporation step, III is a circulation step, IV is a simple distillation step, 2 is a rectification column, 3 is a simple distillation apparatus, 4 is a permeation vapor chamber, 5
Is a separation membrane, 6 is a processing liquid chamber, and 1, 7, 8, 9 and 10 are lines.

Claims (1)

[Claims] 1. A crude organic solvent containing particles and water, which has an azeotropic point with water, is rectified to remove water as a bottom liquid, and an organic solvent containing water as a distillate. A rectification step to be obtained and a distillate of the rectification step are treated by a pervaporation method to selectively remove water to obtain an organic solvent having a liquid composition in which the concentration of the organic solvent is higher than the azeotropic composition. A vaporization step, a circulation step of circulating the organic solvent obtained from the pervaporation step to the rectification step, and a simple distillation of the bottom liquid of the rectification step to distill the organic solvent from which particles have been removed. The method for purifying an organic solvent, which comprises the simple distillation step as described in 1.