Method for producing purified isopropyl alcohol aqueous solution

Abstract

Provided is a method for producing a purified aqueous isopropyl alcohol solution from a low-water-content isopropyl alcohol waste liquid containing toluene as an impurity, the method comprising a low-boiling distillation step of supplying the low-water-content isopropyl alcohol waste liquid to a raw material supply stage of a distillation tower, extracting a distillate containing toluene from the top of the distillation tower, and extracting a bottoms liquid containing isopropyl alcohol and water from the bottom of the distillation tower, and adjusting the water content in the liquid phase in the raw material supply stage of the distillation tower to be 70% by mass or more and 95% by mass or less.

Description

[Technical field]

[0001] The present invention relates to a method for producing a purified aqueous isopropyl alcohol solution and a method for producing purified isopropyl alcohol. [Background technology]

[0002] Isopropyl alcohol (hereinafter also abbreviated as "IPA") has the property of dissolving both water and organic solvents, and is widely used as a solvent for paints and inks, various synthetic raw materials, etc. Furthermore, high-purity IPA is also used in large quantities in the rinsing section of semiconductor substrates in semiconductor manufacturing equipment, and its usage is expected to continue to increase in the future.

[0003] The manufacturing cost of high-purity IPA is high, and it can be a factor in rising costs in the rinsing section of semiconductor substrates, where a large amount is used. In addition, IPA waste liquid after use is usually burned, but this process releases carbon dioxide, which is believed to be a cause of global warming, so from the perspective of environmental conservation, it has been desired to reduce the amount of IPA waste liquid disposed of. For this reason, there is an increasing demand to collect, purify, and reuse IPA waste liquid discharged from such industrial facilities (see, for example, Patent Document 1).

[0004] Incidentally, the semiconductor substrate rinsing section is generally provided adjacent to the rear stage of the semiconductor substrate cleaning section. The cleaning liquid used in the cleaning section is usually ultrapure water or a high water content liquid, so the rinsing section washes off the water adhering to the surface of the semiconductor substrate in the cleaning section. Therefore, the IPA waste liquid recovered from the rinsing section is likely to be a low water content composition containing a small amount of water. In addition, IPA is often used in the developing section and the pre-wet section, and water is often used in various parts of the semiconductor manufacturing equipment. Therefore, it is common for an IPA low water content waste liquid to be discharged from a semiconductor manufacturing equipment equipped with a rinsing section. For example, in Patent Document 2, the water content in the IPA low water content waste liquid is assumed to be about 5 mass %.

[0005] On the other hand, in semiconductor manufacturing equipment, toluene is sometimes used in the cleaning and rinsing sections, and toluene is also widely used as a solvent for solids, for example, as a solvent component of photoresist materials used in the developing section and as a solvent component of adhesives used in various parts. Furthermore, compounds containing toluenesulfonyl groups are often used in substrate processing agents, and when these compounds decompose, toluene can be produced. For these reasons, a small amount of toluene can also be mixed into the recovered IPA waste liquid.

[0006] Therefore, from industrial equipment such as semiconductor manufacturing equipment equipped with a rinsing section, IPA low water content waste liquid containing toluene as an impurity (hereinafter, also simply abbreviated as "IPA low water content waste liquid") may be recovered, and the IPA low water content waste liquid is subjected to purification treatment. In general, distillation is a conventional purification method for organic solvents, and for example, Patent Document 3 proposes purifying IPA low water content waste liquid, which may contain toluene and the like with a water content of 5 to 15% as an impurity, by a purification process using distillation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2017-144410 A [Patent Document 2] JP 2014-55120 A [Patent Document 3] China Patent Publication No. 112999679 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when toluene is contained in the IPA low-water waste liquid, it has been difficult to remove toluene to a high degree using the conventional distillation method. For example, in Patent Document 3, in a purification process, the IPA waste liquid is supplied to a rectification tower and rectified to obtain a fraction containing IPA from the top of the tower. The fraction containing IPA is then cooled and liquefied, and then supplied to a phase separation device to remove the aqueous phase, and then further supplied to a collection tank and heated, and is fractionated into a low boiling fraction supplied to a low boiling tank and a purified IPA fraction recovered in a product tank. However, when this purification process is applied to the purification of an IPA low-water waste liquid containing toluene, satisfactory results were not obtained. Although the boiling point of toluene (110.6°C) is higher than that of IPA (82.4°C) and the boiling point of water, toluene and IPA form an azeotrope during distillation, and further IPA and water form an azeotrope, so that a certain amount of toluene is entrained in the fraction containing IPA from the top of the rectification tower. Since it was difficult to thoroughly remove the toluene entrained in the fraction containing IPA through the subsequent phase separation or fractional distillation of the aqueous phase, high-purity IPA could not be obtained.

[0009] Therefore, a method for producing a highly purified isopropyl alcohol aqueous solution and purified isopropyl alcohol by removing toluene to a high degree from an isopropyl alcohol low-water-content waste liquid containing toluene as an impurity is not known, and it was a major challenge to develop this method. [Means for solving the problem]

[0010] The present inventors have been conducting intensive research in view of the above problems. As a result, they have found that by adjusting the water content of an isopropyl alcohol low-water-content waste liquid containing toluene as an impurity to a specific range and distilling it, a bottoms liquid from which toluene has been highly removed can be obtained from the bottom of the distillation column, and have completed the present invention.

[0011] That is, one aspect of the present invention is a method for producing a purified aqueous isopropyl alcohol solution from an isopropyl alcohol low-water-content waste liquid containing toluene as an impurity, and the isopropyl alcohol low-water-content waste liquid is supplied to a raw material supply stage of a distillation tower, and a distillate containing toluene is extracted from the top of the distillation tower. A low-boiling distillation step is included in which a bottom product containing isopropyl alcohol and water is extracted from the bottom of the distillation tower, and the water content in the liquid phase in the raw material supply stage of the distillation tower is adjusted to be 70% by mass or more and 95% by mass or less. This is a method for producing a purified aqueous isopropyl alcohol solution.

[0012] In the method for producing a purified aqueous isopropyl alcohol solution, it is preferable that the low water content isopropyl alcohol waste liquid is a waste liquid recovered from a semiconductor manufacturing apparatus having a rinsing section for semiconductor substrates.

[0013] In a preferred embodiment, the water content in the liquid phase at the raw material supply stage of the distillation column is adjusted to be 80% by mass or more and 93% by mass or less.

[0014] In a preferred embodiment, the isopropyl alcohol low water content waste liquid has a toluene content of 1 ppm or more and 2000 ppm or less in terms of mass ratio to isopropyl alcohol.

[0015] Furthermore, another aspect of the present invention is a method for producing purified isopropyl alcohol from a purified isopropyl alcohol aqueous solution obtained by the method for producing a purified isopropyl alcohol aqueous solution, and includes a dehydration step of dehydrating the purified isopropyl alcohol aqueous solution. This is a method for producing purified isopropyl alcohol.

[0016] In the method for producing purified isopropyl alcohol, the purified aqueous isopropyl alcohol solution is distilled to extract an azeotropic mixture of isopropyl alcohol and water as a distillate. An azeotropic mixture of isopropyl alcohol and water is distilled by adding an azeotropic agent, and the bottoms containing isopropyl alcohol are extracted. It is a preferable embodiment that the method includes the steps of:

[0017] In a preferred embodiment, the purified isopropyl alcohol is a semiconductor chemical liquid. In particular, the semiconductor chemical liquid is a rinse liquid for semiconductor substrates.

[0018] In addition, it is a preferred embodiment that the process further includes a second low-boiling distillation step in which the dehydrated azeotropic mixture is subjected to low-boiling distillation and a bottoms liquid containing isopropyl alcohol is extracted, and a high-boiling distillation step in which the bottoms liquid containing isopropyl alcohol is subjected to high-boiling distillation and a distillate containing isopropyl alcohol is extracted. Effect of the Invention

[0019] According to the present invention, toluene can be removed to a high degree from low-water-content IPA wastewater containing toluene as an impurity. Therefore, the low-water-content IPA wastewater can be easily regenerated into high-purity IPA, which can be reused as a semiconductor chemical, particularly as a rinsing liquid for semiconductor substrates, and is of great industrial value. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram showing a typical embodiment of a low boiling distillation process. [Diagram 2] 1 is a graph showing the effect of water concentration on the relative volatility α of toluene with respect to IPA. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0022] [Method of producing purified IPA aqueous solution] (IPA low water content waste liquid) In this embodiment, the liquid to be distilled is an IPA low-water waste liquid containing toluene as an impurity. IPA low-water waste liquid is often discharged from the manufacture of paints and inks or from various industrial facilities that use them, and recovered waste liquids can be used without restrictions, but the most suitable for purification is waste liquid recovered from a semiconductor manufacturing device equipped with a semiconductor substrate rinsing section. In particular, waste liquid recovered from the rinsing section is easily converted into a low-water composition and is preferably applicable. In addition, the IPA low-water waste liquid may contain a developing solution, a pre-wetting solution, an etching solution, a cleaning solution, a stripping solution, or a drying solution discharged from a semiconductor manufacturing device.

[0023] The content of IPA in the IPA low-water content waste liquid is preferably more than 50% by mass, more preferably 60% by mass or more, particularly preferably 70% by mass or more. The content of IPA in the IPA low-water content waste liquid is preferably 95% by mass or less, more preferably 85% by mass or less.

[0024] In this specification and claims, "low water content" means that the water content is less than 50 mass%. The water content in the IPA low water content waste liquid is preferably 40 mass% or less, more preferably 30 mass% or less. The water content in the IPA low water content waste liquid is preferably 5 mass% or more, more preferably 15 mass% or more. If the IPA low water content waste liquid has a high water content, the equipment for recovering the IPA low water content waste liquid becomes huge, and the cost of transporting the IPA low water content waste liquid increases.

[0025] Here, the water content in the IPA low-water waste liquid is a value measured by the Karl Fischer method, and the IPA content in the IPA low-water waste liquid is a value measured by gas chromatography.

[0026] The content of toluene in the IPA low-water waste liquid is preferably 1 ppm or more and 2000 ppm or less, more preferably 50 ppm or more and 1000 ppm or less, in terms of mass ratio to isopropyl alcohol. When the content of toluene in the IPA low-water waste liquid is equal to or more than the lower limit, the effect of removing toluene is significantly exhibited. On the other hand, when the content of toluene in the IPA low-water waste liquid is equal to or less than the upper limit, toluene and IPA are unlikely to form an azeotrope, and the content of toluene in the purified IPA aqueous solution is likely to be reduced.

[0027] The IPA low water waste liquid may further contain low boiling impurities having a boiling point lower than that of IPA as impurities other than toluene. Examples of low boiling impurities include olefins such as butenes, pentenes, and hexenes, alkanes such as butane, pentane, and hexane, aldehydes such as formaldehyde, acetaldehyde, propylene aldehyde, and butyl aldehyde, ketones such as acetone and butanone, alcohols such as methanol, ethanol, and 2-methyl-2-propanol, and chloroalkanes such as dichloromethane, chloroform, carbon tetrachloride, and vinyl chloride. The total content of low boiling impurities in the IPA low water waste liquid is preferably 0.1 ppm or more and 10,000 ppm or less, more preferably 1 ppm or more and 100 ppm or less, in terms of mass ratio to IPA. As described later, the low boiling impurities are highly distilled off together with toluene from the top of the distillation column.

[0028] Furthermore, the IPA low-water waste liquid may further contain high-boiling impurities having a boiling point higher than that of IPA as impurities other than toluene. Specifically, when the IPA low-water waste liquid is a waste liquid of a chemical liquid for semiconductors, particularly a cleaning liquid or drying liquid, the high-boiling impurities include, for example, metals such as iron, chromium, nickel, copper, zinc, sodium, potassium, calcium, magnesium, etc., carboxylic acids such as formic acid, acetic acid, propionic acid, etc., salts with anions such as nitrate ion, nitrite ion, sulfate ion, chloride ion, fluoride ion, etc., aldehydes and ketones such as crotonaldehyde and 2-pentanone, alcohols such as 1-propanol and 1-butanol, 1-methylethanol, etc., and the like. Examples of high boiling impurities include ethers such as 1-(2-methoxypropoxy)propan-2-ol, 1-(2-methoxy-2-methylethoxy)-2-propanol, aromatics such as toluene and xylene (ortho, meta, para), alkanes such as octane, decane, hexadecane, carboxylic acid esters such as isopropyl acetate, isopropyl propionate, butyl formate, phthalates such as dioctyl phthalate and dibutyl phthalate, and adipates such as dioctyl adipate. High boiling impurities can be removed to a high extent by subjecting the bottoms withdrawn from the bottom of the distillation column to a purification step described below, as will be described later.

[0029] (Adjustment of water content in liquid phase at raw material feed tray of distillation column) In this embodiment, for example, when distilling low-water IPA wastewater recovered from a semiconductor manufacturing device, the water content in the liquid phase at the raw material supply stage of the distillation tower is adjusted to 70% by mass to 95% by mass, more preferably 80% by mass to 93% by mass. This makes it possible to effectively distill off toluene together with low-boiling impurities from the top of the distillation tower. In other words, it becomes possible to extract a bottoms liquid with a highly reduced amount of toluene from the bottom of the distillation tower.

[0030] Since toluene has a higher boiling point than IPA, if we only consider the boiling point difference, it would be expected that toluene would not be distilled from the top of the column but would be discharged from the bottom of the column during distillation. However, toluene has the property of forming an azeotrope with IPA and water, and in such an azeotropic system, it is concentrated in the gas phase. In the case of IPA low water content waste liquid, toluene forms an azeotrope with water and is predominantly concentrated in the gas phase. As a result, as shown in Figure 2, as the water concentration, i.e., the water content in the liquid phase, increases, the efficiency of toluene concentration in the gas phase increases significantly.

[0031] However, in the case of low-water-content IPA waste liquid, the water content is low, so that the efficiency of concentrating toluene in the gas phase by azeotropy with water is insufficient, and it is considered that the amount of toluene distilled off from the top of the distillation tower is also low. In this embodiment, by increasing the water content in the liquid phase at the raw material supply stage of the distillation tower, the azeotropy with water is activated during distillation, and the amount of toluene distilled off from the top of the distillation tower is increased, and as a result, the toluene content in the bottoms is reduced.

[0032] As with toluene, organic solvents that have a higher boiling point than IPA, form an azeotrope with IPA and water, and may be contained in wastewater recovered from semiconductor manufacturing equipment include, for example, xylene (ortho, meta, para), isopropyl acetate, etc. By applying the method for producing a purified IPA aqueous solution of the present embodiment, the same effect can be achieved with respect to such organic solvents.

[0033] A common method for adjusting the water content in the liquid phase at the raw material supply stage of the distillation column is to measure the water content in a waste liquid receiving tank that contains the recovered IPA low water content waste liquid, and then mix water into the waste liquid. In this case, for example, at least two waste liquid receiving tanks are installed, one of which is used to supply the liquid with the adjusted water content to the distillation column, and the other is used to adjust the water content. In this case, it is efficient to switch the roles of the two tanks when the tank used to supply the distillation column becomes nearly empty.

[0034] The measurement of the water content in the IPA low-water content waste liquid and the mixing of water may be performed in the piping that supplies the IPA low-water content waste liquid to the distillation column, or may be performed in a transport vessel (e.g., a tanker, a container, or a drum) when the IPA low-water content waste liquid is transported to a remote waste liquid receiving tank.

[0035] The water content in the liquid phase at the raw material supply stage of the distillation tower may be adjusted within the distillation tower. That is, the low-water-content IPA waste liquid may be supplied to the raw material supply stage of the distillation tower as is or in a water-added state with a water content of less than 70% by mass, while water may be supplied to the distillation tower from the outside. In this case, water may be supplied to the raw material supply stage of the distillation tower, or water may be supplied to a stage between the raw material supply stage and the top of the distillation tower.

[0036] When water is supplied to a stage between the raw material supply stage and the top of the distillation tower, the water content in the liquid phase at the raw material supply stage can be calculated using process simulation software such as AspenPlus (manufactured by Aspen Technology) and PROII (manufactured by AVEVA). As described later, when the distillate from the top of the distillation tower is condensed in a condenser and a part of the condensed distillate is refluxed to the distillation tower, the water content in the liquid phase at the raw material supply stage of the distillation tower can be calculated taking into account the amount of water contained in the refluxed distillate. In addition, when the distillate extracted from the top of the distillation tower is supplied to a second distillation tower, water is added from the outside and the distillate is distilled again, and the bottoms are supplied to the distillation tower, the water content in the liquid phase at the raw material supply stage of the distillation tower can be calculated taking into account the amount of water contained in the bottoms.

[0037] The water content in the liquid phase at the feed tray of the distillation column is not limited as long as it is within the range of 70% by mass to 95% by mass, but the fluctuation per hour is preferably within 3% by mass, more preferably within 1% by mass, based on the total content (100% by mass) of the liquid phase. If the fluctuation per hour is small, the boiling point of toluene does not change significantly, and flooding is less likely to occur.

[0038] (Low boiling distillation process) The method for producing a purified IPA aqueous solution of the present embodiment includes a low-boiling distillation step of distilling an IPA low-water content waste liquid, extracting a distillate containing toluene from the top of a distillation column, and extracting a bottoms liquid containing IPA and water from the bottom of the distillation column.

[0039] A typical embodiment of the low boiling point distillation process is shown in Fig. 1. In Fig. 1, two waste liquid receiving tanks 1 are installed, one of which is used to supply the IPA low water content waste liquid with the adjusted water content to a low boiling point distillation tower 2, and the other is used to adjust the water content of the IPA low water content waste liquid, and when the IPA low water content waste liquid with the adjusted water content becomes empty, the roles of the two are switched. The IPA low water content waste liquid is supplied to the waste liquid receiving tank 1 through a waste liquid supply pipe 3. Then, water is supplied from a water supply pipe 8 to the waste liquid receiving tank 1 so that the water content in the liquid phase at the raw material supply stage of the low boiling point distillation tower 2 is 70 mass% or more and 95 mass% or less.

[0040] The IPA low-water waste liquid, the water content of which has been adjusted in this manner, is supplied to the raw material supply stage of the low-boiling distillation column 2 through the distilled liquid supply pipe 4 and distilled. A condenser 5 is installed at the top of the low-boiling distillation column 2, and a portion of the condensed liquid condensed in the condenser 5 is refluxed, while the remainder is discharged from the distillate discharge pipe 6 as a low-boiling distillate. Toluene contained in the IPA low-water waste liquid is discharged together with the low-boiling distillate. As a result, the bottoms from which toluene has been largely removed are discharged from the bottoms discharge pipe 7 from the bottoms of the low-boiling distillation column 2.

[0041] The low boiling distillation column 2 may be either a plate column or a packed column, but is preferably a plate column. The theoretical number of plates of the low boiling distillation column 2 is not particularly limited, but is preferably 10 to 200 plates, more preferably 20 to 50 plates. Examples of the plates in the plate column include cross-flow trays and shower trays. Examples of the packing in the packed column include Raschig rings and Lessing rings. Examples of the materials for the plate column, packed column, and packing include iron, stainless steel, Hastelloy, borosilicate glass, quartz glass, and fluororesin (e.g., polytetrafluoroethylene).

[0042] In the low boiling distillation column 2, the number of stages from the raw material supply stage to the bottom of the column is preferably 5 stages or more, more preferably 10 stages or more, and even more preferably 20 stages or more, in terms of theoretical plate number. If the number of stages from the raw material supply stage to the bottom of the column is large, toluene is easily removed. In this case, the raw material supply stage may be installed between the top of the column, but since the amount of IPA waste is reduced, it is preferable to install the raw material supply stage at the top of the column. In addition, the bottom and the top of the column are not included in the theoretical plate in the calculation of the raw material supply stage. It is preferable to confirm the theoretical plate number of the low boiling distillation column 2 by actually operating the low boiling distillation column 2 and analyzing the composition of the distillate.

[0043] The amount of substance in the vapor phase at the top of the low boiling distillation column 2 is preferably 0.1 to 10 relative to the amount of substance in the entire liquid phase supplied to the low boiling distillation column 2.

[0044] Furthermore, the pressure (gauge pressure) at the top of the low boiling distillation column 2 is not particularly limited, but is, for example, 0.0 MPaG or more and 0.1 MPaG or less. At this time, the temperatures at the top and bottom of the low boiling distillation column 2 are appropriately set according to the pressure.

[0045] The low boiling point distillate distilled from the top of the column is condensed by the condenser 5, and a part of the condensed low boiling point distillate is refluxed. In this case, the reflux ratio is preferably from 10 to 10,000, more preferably from 100 to 2,000, and further preferably from 300 to 1,500. By increasing the reflux ratio, the distillate is reduced, and therefore it becomes possible to separate toluene while reducing the amount of IPA distilled off.

[0046] The low boiling point distillate thus extracted from the top of the column may be discharged outside the system, or may be supplied to a second distillation column, where water is added from the outside and distilled again, and the bottoms are supplied to the upstream part of the low boiling point distillation column 2 to further enhance the removal of toluene and low boiling point impurities. The low boiling point distillate discharged outside the system may be reused, for example, as fuel.

[0047] (Degree of purification of purified IPA aqueous solution) According to the method for producing a purified IPA aqueous solution of this embodiment, it is possible to reduce the content of toluene contained as an impurity in the low boiling point distillation step to preferably 10 ppb or less, more preferably 0.001 ppb to 1 ppb, in terms of mass ratio to IPA. Low boiling point impurities can also be significantly reduced. For example, when low-temperature aldehydes and ketones such as acetaldehyde and propionaldehyde are contained in the IPA low-water-content waste liquid, it is possible to reduce the content of each of them to preferably 10 ppb or less, more preferably 0.001 ppb to 1 ppb, in terms of mass ratio to IPA.

[0048] [Production method of purified IPA] In the low boiling distillation step, purified IPA can be produced by dehydrating the purified IPA aqueous solution, which is the bottoms withdrawn from the bottom of the low boiling distillation column 2. In order to obtain purified IPA with a higher purity, it is preferable to carry out the following additional purification step. That is, the additional purification step includes an azeotrope generation step in which the purified IPA aqueous solution is distilled and an azeotrope of IPA and water is withdrawn as a distillate, and a dehydration step in which the azeotrope of IPA and water is dehydrated.

[0049] The additional purification step preferably further includes a high boiling distillation step of distilling the dehydrated azeotropic mixture at a high boiling point and extracting a distillate containing isopropyl alcohol. In addition, between the dehydration step and the high boiling distillation step, a second low boiling distillation step of distilling the dehydrated azeotropic mixture at a low boiling point and extracting a bottoms liquid containing isopropyl alcohol may be interposed in order to remove low boiling impurities to a higher degree. Each additional purification step will be described below.

[0050] (Azeotrope generation process) In the azeotrope producing step, the purified aqueous IPA solution is supplied to the raw material supply tray of a distillation column and distilled. An azeotropic mixture of IPA and water is extracted as a distillate from the top of the distillation column, and a bottoms liquid containing high-boiling impurities having a higher boiling point than IPA is extracted from the bottom of the distillation column.

[0051] Specifically, since the azeotropic temperature of IPA and water is 80.1°C, by distilling the purified IPA aqueous solution at 80.1°C, an azeotropic mixture of IPA and water is withdrawn from the top of the tower. Meanwhile, bottoms containing high boiling impurities and water are withdrawn from the bottom of the tower. A part of the water in the bottoms can be used to adjust the water content in the liquid phase at the raw material supply stage of the low boiling distillation process. This not only reduces the amount of water used and the cost of wastewater treatment, but also reduces energy by using the bottoms without cooling them.

[0052] In addition, the azeotropic mixture producing step may be carried out in accordance with the conditions explained in the low boiling point distillation step.

[0053] (Dehydration process) In the dehydration step, the azeotropic mixture of IPA and water obtained in the azeotropic mixture formation step is dehydrated.

[0054] The dehydration method is not particularly limited, but examples thereof include azeotropic distillation, adsorption, and membrane permeation. When azeotropic distillation is performed on an azeotropic mixture of IPA and water, water can be removed by adding an azeotropic agent and distilling. Examples of the azeotropic agent include diethyl ether, benzene, toluene, trichloroethylene, dichloromethane, and hexenes.

[0055] (Second low boiling distillation process) In the second low boiling distillation step, the azeotropic mixture dehydrated in the dehydration step is again subjected to low boiling distillation. That is, the second low boiling distillation step is a step of extracting a distillate containing low boiling impurities from the top of the low boiling distillation column and extracting a bottoms liquid containing IPA with further reduced low boiling impurities from the bottom of the low boiling distillation column, and may be performed according to the desired purity of IPA.

[0056] (High boiling point distillation process) In the high boiling distillation step, the azeotropic mixture dehydrated in the dehydration step is high boiling distilled, and a bottoms liquid containing high boiling impurities is extracted from the bottom of the high boiling distillation tower, while a distillate containing IPA in which high boiling impurities have been further reduced is extracted from the top of the high boiling distillation tower.

[0057] (Other processes) The distillate obtained in the high boiling distillation step may be further purified by a method such as adsorption, if necessary. In addition, particles (e.g., metal particles, inorganic particles, organic particles) may be removed by filtration, and ions (e.g., metal ions) may be removed by an ion exchange resin.

[0058] (Degree of purification of purified IPA) According to the above-described method for producing purified IPA, in which the aqueous solution of purified IPA is dehydrated and, if necessary, further purified, the dehydration step can reduce the water content to preferably 100 mass ppm or less, more preferably 1 to 50 mass ppm. Furthermore, if a high-boiling point distillation step is performed, high-boiling point impurities other than toluene can also be significantly reduced. Therefore, it is possible to obtain purified IPA having a purity of preferably 99.9 mass % or more, more preferably 99.99 to 99.999999 mass %, excluding the water content.

[0059] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and the above embodiment may be modified as appropriate within the scope of the spirit of the present invention. EXAMPLES

[0060] Examples of the present invention will be described below, but the present invention is not limited to these examples. In the examples, % and ppm are by mass unless otherwise specified.

[0061] <Analysis example 1> (Method of measuring water content) Equipment: Karl Fischer moisture meter CA-200 (Mitsubishi Chemical Analytical) Samples thought to have a water content of more than 1% were diluted with IPA before measurement. The water content of the IPA used for dilution was measured in advance and confirmed to be 30 ppm. Samples thought to have a water content of 1% or less were analyzed without dilution. If there is more water than expected, it will just take longer to measure, but will not affect the measured value. The water content of the IPA used for dilution was measured by taking a measurement sample of 5g or more with a thermo syringe in a glove box with a dew point of -60°C or less, and this analytical method is capable of quantifying water contents of 1 ppm or more.

[0062] <Analysis example 2> (Method for measuring 1-methoxy-2-propanol content) After concentrating 1 L of IPA to 1 ml using an evaporator (water bath 80°C, 10 kPa (absolute pressure)), analysis was performed using GC / MS. The lower limit of quantification was calculated using a standard substance, and the lower limit of quantification for 1-methoxy-2-propanol was found to be 0.01 ppb. -Measurement conditions- Equipment: 7890A / 5975C (Agilent Technologies) Analytical column: SUPELCO WAX-10 (60 m x 0.25 mm, 0.25 μm) Column temperature: 35°C (held for 2 minutes) → 5°C / min heating → 100°C → 10°C / min heating → 240°C (held for 6 minutes) Carrier gas: Helium Carrier gas flow rate: 2mL / min Inlet temperature: 240℃ Injection volume: 5μl Sample injection method: Pulsed splitless method Injection pulse pressure: 90 psi (2 min) Split vent flow rate: 50mL / min (2 min) Gas saver use: 20mL / min (5 min) Transfer line temperature: 240℃ Ion source, quadrupole temperature: 230℃, 150℃ Scan ion: m / Z=25~250 SIM (selected ion detection): 75 (1-methoxy-2-propanol)

[0063] <Analysis example 3> (Method for measuring the content of toluene and isopropyl acetate) A: When the water content in IPA is 1% or more After adjusting the water content in IPA to 95%, the contents of toluene and isopropyl acetate were analyzed by headspace gas chromatography mass spectrometry (HS / GC / MS). The detection limits in IPA with a water content of 5% (IPA 95%) in this method were 0.1 ppb for toluene and 0.1 ppb for isopropyl acetate. The SIM value can be set arbitrarily for each compound to be quantified.

[0064] -Measurement conditions- Equipment: Gas chromatograph mass spectrometer (GC / MS) 8890, 5977B (Agilent Technologies), Headspace Sampler 8697 (Agilent Technologies) Injection mode: splitless Carrier: Helium Column: J&W Scientific DB-1 (length 60 m, inner diameter 0.32 mm, thickness 5 μm) Column temperature: Maintain at 30°C for 15 min, then increase to 250°C at 20°C / min, and maintain at 250°C for 10 min. Column flow rate: 1.4 ml / min Inlet pressure: 8.4psi Inlet temperature: 200℃ Injection volume: 1 mL (viale gas phase in headspace method) Ion source temperature: 230℃ Quadrupole temperature: 150℃ SIM (selected ion detection): 61 (isopropyl acetate) 91 (toluene) Solvent heating temperature (headspace): 60℃ Solvent heating time (headspace): 15 minutes

[0065] B: When the water content in IPA is less than 1% The contents of toluene and isopropyl acetate were analyzed by gas chromatography mass spectrometry (GC / MS). The detection limits of this method were 1 ppb for toluene and 1 ppb by mass for isopropyl acetate.

[0066] The SIM value can be set arbitrarily for each compound to be quantified. Toluene and isopropyl acetate form an azeotrope with IPA, so it is difficult to lower the detection limit using the normal pressure concentration method. By using an adsorbent that easily adsorbs low-polarity substances, such as activated carbon, it is possible to lower the detection limit to 1 ppt or less.

[0067] -Measurement conditions- Equipment: Gas chromatograph mass spectrometer (GC / MS) 8890, 5977B (Agilent Technologies) Injection mode: splitless Carrier: Helium Column: J&W Scientific DB-1 (length 60 m, inner diameter 0.32 mm, thickness 5 μm) Column temperature: Maintain at 30°C for 15 min, then increase to 250°C at 20°C / min, and maintain at 250°C for 10 min. Column flow rate: 1.4 ml / min Inlet pressure: 8.4psi Inlet temperature: 200℃ Injection volume: 5μL Ion source temperature: 230℃ Quadrupole temperature: 150℃ SIM (selected ion detection): 59 (2-methyl-2-propanol), 61 (isopropyl acetate), 91 (toluene)

[0068] <Example 1> (Low boiling distillation process) IPA low-water content waste liquid was collected from a semiconductor manufacturing device equipped with a semiconductor substrate rinsing section, and three days' worth of the waste liquid was collected in waste liquid receiving tank 1 and purified by the low boiling point distillation process shown in Fig. 1. The IPA low-water content waste liquid had a water content of 20% by mass (IPA content: 80%) and a toluene content of 100 ppm by mass relative to IPA. Water was supplied to the waste liquid receiving tank 1 so that the water content of the IPA low-water content waste liquid became 90% (IPA content: 10%), and a water content-adjusted liquid to be subjected to the low boiling point distillation process was obtained.

[0069] An Oldershaw-type low boiling distillation column with 15 plates was installed as the low boiling distillation column 2 for distilling the water content adjustment liquid, and it was confirmed by an experiment that the theoretical number of plates of the low boiling distillation column 2 was 10. Here, the low boiling distillation column 2 has a 2L container at the bottom, a condenser 5 is installed at the top, and a part of the distillate condensed in the condenser 5 is refluxed to the top of the low boiling distillation column 2. The water content adjustment liquid was supplied to the top of the low boiling distillation column 2 at 10 L / h and distilled. At this time, the temperature of the top was 75 to 85°C, and the pressure (gauge pressure) of the top was 0 to 10 kPaG. In addition, the reflux amount was 10 L / h, the reflux ratio was about 1000, and the distillate was extracted from the distillate discharge pipe 6 at 10 ml / h. Furthermore, the bottoms (purified IPA aqueous solution) were extracted from the bottoms discharge pipe 7 at about 10 L / h so that the amount of liquid at the bottom of the column was maintained at about 1.5 L.

[0070] The toluene content in the purified IPA solution was measured and found to be below the detection limit of 0.2 ppb by mass relative to IPA, confirming that the toluene content was significantly reduced by the low boiling point distillation process. Also, the isopropyl acetate content in the purified IPA solution was below 1 ppb by mass relative to IPA.

[0071] (Additional purification process) The purified IPA aqueous solution obtained by the low boiling point distillation step was supplied to the raw material supply tray of the distillation column for the azeotropic mixture production step. That is, the bottoms (purified IPA aqueous solution) extracted from the bottoms discharge pipe 7 was supplied to the raw material supply tray of the distillation column and distilled, and an azeotropic mixture of IPA and water (mass ratio 87.5:12.5) was extracted from the top of the column.

[0072] Next, the azeotropic mixture of IPA and water was subjected to a dehydration step, and benzene was used as an entrainer, and the bottoms containing IPA, in which the water content was reduced to 100 ppm or less, were extracted from the bottom of the column. Thereafter, the bottoms containing IPA were subjected to a second low boiling distillation step, and the bottoms containing IPA in which low boiling impurities were further reduced were extracted, and then the bottoms containing IPA were subjected to a high boiling distillation step, and the distillate containing IPA in which high boiling impurities were further reduced was extracted and cooled. The distillate containing IPA was passed through an ion exchange resin, and then passed through three types of filters (fluororesin filters with pore sizes of 50 nm, 10 nm, and 2 nm) to obtain purified IPA.

[0073] The toluene content in the purified IPA was below the detection limit of 0.1 ppb by mass relative to IPA. The contents of isopropyl acetate and 1-methoxy-2-propanol are shown in Table 1.

[0074] <Comparative Example 1> (Low boiling distillation process) A low boiling point distillation step was carried out in the same manner as in Example 1, except that water was supplied to the waste liquid receiving tank 1 so that the water content of the low-water-content IPA waste liquid contained in the waste liquid receiving tank 1 was 50% (IPA content: 50%), and a water content-adjusted liquid was obtained. The toluene content in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured and found to be 8 ppb in mass ratio to IPA. The isopropyl acetate content in the purified IPA aqueous solution was 175 ppb in mass ratio to IPA.

[0075] (Additional purification process) The additional purification step was carried out in the same manner as in Example 1, except that the purified IPA aqueous solution obtained by the low boiling point distillation step was used. The toluene content in the purified IPA obtained in this manner was 6 ppb in terms of mass ratio to IPA. The contents of the other components, including isopropyl acetate and 1-methoxy-2-propanol, are shown in Table 1.

[0076] <Comparative Example 2> (Low boiling distillation process) A low boiling point distillation step was carried out in the same manner as in Example 1, except that water was not supplied to the IPA low-water content waste liquid contained in the waste liquid receiving tank 1, and the IPA low-water content waste liquid was used instead of the water content adjusting liquid. The toluene content in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured and found to be 12,400 ppb in mass ratio to IPA. The isopropyl acetate content in the purified IPA aqueous solution was 6,950 ppb in mass ratio to IPA.

[0077] (Additional purification process) The additional purification step was carried out in the same manner as in Example 1, except that the purified IPA aqueous solution obtained by the low boiling point distillation step was used. The toluene content in the purified IPA obtained in this manner was 100 ppb in terms of mass ratio to IPA. The contents of the other components, including isopropyl acetate and 1-methoxy-2-propanol, are shown in Table 1.

[0078] <Example 2> (Low boiling distillation process) The low boiling point distillation step was carried out in the same manner as in Example 1, except that water was supplied to the waste liquid receiving tank 1 so that the water content of the IPA low-water-content waste liquid contained in the waste liquid receiving tank 1 was 70% (IPA content was 30%) to obtain a water content-adjusted liquid. The toluene content in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured and found to be 0.2 ppb or less in mass ratio to IPA, which was below the lower detection limit, and it was confirmed that the toluene content was significantly reduced by the low boiling point distillation step. The isopropyl acetate content in the purified IPA aqueous solution was 1.2 ppb in mass ratio to IPA.

[0079] (Additional purification process) The additional purification step was carried out in the same manner as in Example 1, except that the purified IPA aqueous solution obtained by the low boiling point distillation step was used. The toluene content in the purified IPA thus obtained was 0.1 ppb or less, which is below the detection limit, in terms of mass ratio to IPA. The other contents are shown in Table 1, together with the content of 1-methoxy-2-propanol.

[0080] <Example 3> (Low boiling distillation process) The low boiling point distillation step was carried out in the same manner as in Example 1, except that water was supplied to the waste liquid receiving tank 1 so that the water content of the IPA low-water-content waste liquid contained in the waste liquid receiving tank 1 was 80% (IPA content was 20%) to obtain a water content-adjusted liquid. The toluene content in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured and found to be 0.2 ppb or less in mass ratio to IPA, which was below the lower detection limit, and it was confirmed that the toluene content was significantly reduced by the low boiling point distillation step. In addition, the isopropyl acetate content in the purified IPA aqueous solution was 1 ppb or less in mass ratio to IPA.

[0081] (Additional purification process) The additional purification step was carried out in the same manner as in Example 1, except that the purified IPA aqueous solution obtained by the low boiling point distillation step was used. The toluene content in the purified IPA thus obtained was 0.1 ppb or less, which is below the detection limit, in terms of mass ratio to IPA. The contents of isopropyl acetate and 1-methoxy-2-propanol are also shown in Table 1.

[0082] <Example 4> (Low boiling distillation process) The low boiling distillation step was carried out in the same manner as in Example 1, except that an Oldershaw type low boiling distillation column with 60 plates was installed as the low boiling distillation column 2. It was confirmed by experiment that the theoretical number of plates of the low boiling distillation column 2 was 40. When the content of toluene in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured, it was 0.2 ppb or less in mass ratio to IPA, which was below the lower detection limit, and it was confirmed that the content of toluene was greatly reduced by the low boiling distillation step. In addition, the content of isopropyl acetate in the purified IPA aqueous solution was 1 ppb or less in mass ratio to IPA.

[0083] (Additional purification process) The additional purification step was carried out in the same manner as in Example 1, except that the purified IPA aqueous solution obtained by the low boiling point distillation step was used. The toluene content in the purified IPA thus obtained was 0.1 ppb or less, which is below the detection limit, in terms of mass ratio to IPA. The contents of isopropyl acetate and 1-methoxy-2-propanol are also shown in Table 1.

[0084] <Example 5> (Low boiling distillation process) A low boiling point distillation step was carried out in the same manner as in Example 4, except that an IPA low-water content waste liquid was used in which the water content was 20% by mass (IPA content was 80%) and the toluene content was 500 ppm by mass relative to IPA. The toluene content in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured and found to be 0.2 ppb or less by mass relative to IPA, which was below the lower detection limit, and it was confirmed that the toluene content was significantly reduced by the low boiling point distillation step. In addition, the isopropyl acetate content in the purified IPA aqueous solution was 1 ppb or less by mass relative to IPA.

[0085] (Additional purification process) The additional purification step was carried out in the same manner as in Example 1, except that the purified IPA aqueous solution obtained by the low boiling point distillation step was used. The toluene content in the purified IPA obtained in this manner was 0.1 ppb or less, which was below the detection limit. The contents of isopropyl acetate and 1-methoxy-2-propanol are also shown in Table 1.

[0086] [Table 1] In Table 1, the contents of toluene, isopropyl acetate and 1-methoxy-2-propanol are expressed as mass ratios relative to IPA.

[0087] From Table 1, it can be seen that in Examples 1 to 5, toluene was removed to a high extent from the low-water-content IPA waste liquid, and the purity of the purified IPA aqueous solution and purified IPA was high. In contrast, in Comparative Example 1, the water content in the water content adjusting liquid was 50 mass %, so toluene was not removed to a high extent from the low-water-content IPA waste liquid, and the purity of the purified IPA aqueous solution and purified IPA was low. In Comparative Example 2, water was not supplied to the low-water-content IPA waste liquid, and the water content was not adjusted, so toluene was not removed to a high extent from the low-water-content IPA waste liquid, and the purity of the purified IPA aqueous solution and purified IPA was low. [Explanation of symbols]

[0088] 1. Waste liquid receiving tank 2. Low boiling distillation tower 3. Waste liquid supply pipe 4; Distillate supply pipe 5; Condenser 6; Distillate drain pipe 7;Bottled liquid discharge pipe 8;Water supply pipe

Claims

1. A method for producing a purified aqueous isopropyl alcohol solution from an isopropyl alcohol low-water-content waste liquid containing toluene as an impurity, comprising: The method includes a low-boiling distillation step of supplying the isopropyl alcohol low-water-containing waste liquid to a raw material supply stage of a distillation column, extracting a distillate containing toluene from the top of the distillation column, and extracting a bottoms containing isopropyl alcohol and water from the bottom of the distillation column, The water content in the liquid phase at the raw material supply stage of the distillation column is adjusted to 70% by mass or more and 95% by mass or less.

2. The method for producing a purified isopropyl alcohol aqueous solution according to claim 1, wherein the isopropyl alcohol low water content waste liquid is a waste liquid recovered from a semiconductor manufacturing apparatus equipped with a semiconductor substrate rinsing section.

3. The method for producing a purified isopropyl alcohol aqueous solution according to claim 1 or 2, wherein the water content in the liquid phase in the raw material supply stage of the distillation column is adjusted to be 80% by mass or more and 93% by mass or less.

4. The method for producing a purified isopropyl alcohol aqueous solution according to claim 1 or 2, wherein the isopropyl alcohol low water content waste liquid has a toluene content of 1 ppm or more and 2000 ppm or less in terms of mass ratio to isopropyl alcohol.

5. A method for producing purified isopropyl alcohol from a purified isopropyl alcohol aqueous solution obtained by the method for producing a purified isopropyl alcohol aqueous solution according to claim 1 or 2, A method for producing purified isopropyl alcohol, comprising a dehydration step of dehydrating the purified isopropyl alcohol aqueous solution.

6. An azeotrope generating step of distilling the purified isopropyl alcohol aqueous solution and extracting an azeotrope of isopropyl alcohol and water as a distillate; The method for producing purified isopropyl alcohol according to claim 5, further comprising a dehydration step of adding an azeotropic agent to the azeotropic mixture of isopropyl alcohol and water, distilling the mixture, and extracting a bottoms solution containing isopropyl alcohol.

7. The method for producing purified isopropyl alcohol according to claim 5, wherein the purified isopropyl alcohol is a semiconductor chemical liquid.

8. The method for producing purified isopropyl alcohol according to claim 7, wherein the semiconductor chemical liquid is a rinse liquid for a semiconductor substrate.

9. A second low-boiling distillation step in which the dehydrated azeotropic mixture is subjected to low-boiling distillation and a bottoms liquid containing isopropyl alcohol is extracted; The method for producing purified isopropyl alcohol according to claim 6, further comprising a high boiling distillation step of high boiling distilling the bottoms containing isopropyl alcohol and extracting a distillate containing isopropyl alcohol.