Method for producing purified isopropyl alcohol aqueous solution

Abstract

The present invention provides a method for producing a purified isopropyl alcohol aqueous solution from a low water content isopropyl alcohol waste liquid that contains toluene as an impurity, the method including a low-boiling distillation step in which the low water content isopropyl alcohol waste liquid is supplied to a starting material supply stage of a distillation column, and a liquid distillate that contains toluene is extracted from the column top of the distillation column, while extracting a column bottom liquid that contains isopropyl alcohol and water from the column bottom of the distillation column. In this method for producing a purified isopropyl alcohol aqueous solution, the water content in the liquid phase at the starting material supply stage of the distillation column is adjusted to be within the range of 70 mass% to 95 mass% inclusive.

Description

Method for producing purified isopropyl alcohol aqueous solution

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

[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, as a raw material for various synthetic processes, etc. Furthermore, high-purity IPA is also used in large quantities in the semiconductor substrate rinsing section of 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, which can lead to increased costs when used in large quantities for rinsing semiconductor substrates. Furthermore, used IPA waste is typically burned, which releases carbon dioxide, a cause of global warming. Therefore, reducing the amount of IPA waste is desirable from the perspective of environmental conservation. Therefore, there is a growing demand for recovering, purifying, and reusing IPA waste from such industrial facilities (see, for example, Patent Document 1).

[0004] Incidentally, a semiconductor substrate rinsing section is typically located adjacent to a semiconductor substrate cleaning section. Because the cleaning liquid used in the cleaning section is typically ultrapure water or a highly water-rich liquid, the rinsing section washes away moisture adhering to the surface of the semiconductor substrate. Therefore, the IPA waste liquid recovered from the rinsing section tends to be a low-water composition containing a small amount of water. IPA is also frequently used in the developing section and pre-wetting section, and water is often used in various parts of semiconductor manufacturing equipment. Therefore, semiconductor manufacturing equipment equipped with a rinsing section typically discharges low-water IPA waste liquid. For example, Patent Document 2 predicts that the water content of low-water IPA waste liquid is approximately 5% by 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 for photoresist materials used in the developing section and as a solvent component for adhesives used in various parts. Furthermore, compounds containing toluenesulfonyl groups are often used in substrate processing agents, and decomposition of these compounds can produce toluene. For these reasons, trace amounts of toluene may be mixed into the recovered IPA waste liquid.

[0006] Therefore, low-water-content IPA waste liquid containing toluene as an impurity (hereinafter simply referred to as "low-water-content IPA waste liquid") may be recovered from industrial equipment such as semiconductor manufacturing equipment equipped with a rinse unit, and the low-water-content IPA waste liquid is subjected to a purification process. Generally, distillation is a conventional purification method for organic solvents. For example, Patent Document 3 proposes purifying low-water-content IPA waste liquid, which may contain toluene and other impurities with a water content of 5 to 15%, by a purification process using distillation.

[0007] Japanese Patent Publication No. 2017-144410 Japanese Patent Publication No. 2014-55120 Chinese Patent Application Publication No. 112999679

[0008] However, when toluene is contained in low-water-content IPA waste liquid, it has been difficult to thoroughly remove toluene using conventional distillation techniques. For example, in Patent Document 3, in a purification process, IPA waste liquid is supplied to a rectification column and rectified, and a fraction containing IPA is obtained from the top of the column. The IPA-containing fraction is then cooled and liquefied, then supplied to a phase separation device to remove the aqueous phase, and then further supplied to a collection tank and heated, where it is fractionated into a low-boiling-point fraction supplied to a low-boiling-point tank and a purified IPA fraction recovered in a product tank. However, when this purification process was applied to the purification of low-water-content IPA 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 that of water, toluene and IPA form an azeotrope during distillation, and further, IPA and water form an azeotrope, so a certain amount of toluene is entrained in the IPA-containing fraction from the top of the rectification column. Since it is difficult to thoroughly remove the toluene entrained in the fraction containing IPA by subsequent phase separation of the aqueous phase or fractional distillation, IPA with high purity could not be obtained.

[0009] Therefore, a method for producing a highly purified isopropyl alcohol aqueous solution and purified isopropyl alcohol by highly removing toluene 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.

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

[0011] That is, one aspect of the present invention is a method for producing a purified aqueous isopropyl alcohol solution from a low-water isopropyl alcohol waste liquid containing toluene as an impurity, wherein the low-water isopropyl alcohol waste liquid is supplied to a raw material supply stage of a distillation column, and a distillate containing toluene is extracted from the top of the distillation column. 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 column, and the water content in the liquid phase in the raw material supply stage of the distillation column 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, the low-water-content isopropyl alcohol waste liquid is preferably a waste liquid recovered from a semiconductor manufacturing apparatus equipped with a rinsing section for semiconductor substrates.

[0013] In a preferred embodiment, the water content in the liquid phase at the raw material supply tray of the distillation column is adjusted to 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 a mass ratio relative 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 the purified isopropyl alcohol aqueous solution is dehydrated. 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 azeotrope generation step, and an azeotropic mixture of isopropyl alcohol and water are added to the azeotropic mixture, distilled, and a bottoms liquid containing isopropyl alcohol are extracted. It is a preferred embodiment that the method includes the following steps:

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

[0018] Moreover, the dehydrated azeotropic mixture is subjected to low-boiling distillation and a bottoms liquid containing isopropyl alcohol is extracted. A second low-boiling distillation step, and the bottoms liquid containing isopropyl alcohol are subjected to high-boiling distillation and a distillate containing isopropyl alcohol are extracted. It is a preferred embodiment that the method further includes a high-boiling distillation step.

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

[0020] 1 is a schematic diagram showing a typical embodiment of a low-boiling point distillation process. 2 is a graph showing the effect of water concentration on the relative volatility α of toluene with respect to IPA.

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

[0022] [Method for Producing Purified IPA Aqueous Solution] (Low-Water IPA Wastewater) In this embodiment, the liquid to be distilled is a low-water IPA wastewater containing toluene as an impurity. Low-water IPA wastewater is often discharged from the production of paints and inks or from various industrial facilities that use these materials. Any recovered wastewater can be used, but the wastewater most suitable for purification is that recovered from a semiconductor manufacturing apparatus equipped with a semiconductor substrate rinse unit. In particular, wastewater recovered from a rinse unit is easily converted into a low-water composition and is therefore suitable for use. In addition, the low-water IPA wastewater may contain a developer, pre-wet liquid, etching liquid, cleaning liquid, stripping liquid, or drying liquid discharged from a semiconductor manufacturing apparatus.

[0023] The IPA content in the low-water IPA waste liquid is preferably more than 50% by mass, more preferably 60% by mass or more, and particularly preferably 70% by mass or more. The IPA content in the low-water IPA waste liquid is preferably 95% by mass or less, and 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% by mass. The water content in the IPA low-water content waste liquid is preferably 40% by mass or less, more preferably 30% by mass or less. The water content in the IPA low-water content waste liquid is preferably 5% by mass or more, more preferably 15% by 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 will be large, and the cost of transporting the IPA low-water content waste liquid will increase.

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

[0027] The IPA low-water waste liquid may further contain low-boiling impurities other than toluene, which have a boiling point lower than that of IPA. 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 butylaldehyde; 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 to 10,000 ppm, more preferably 1 ppm to 100 ppm, by mass relative to IPA. As described below, the low-boiling impurities are distilled off together with toluene from the top of the distillation column.

[0028] Furthermore, the IPA low-water waste liquid may further contain, as impurities other than toluene, high-boiling impurities having a boiling point higher than that of IPA. Specifically, when the IPA low-water waste liquid is a waste liquid of a semiconductor chemical, particularly a cleaning liquid or a 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 / ketones such as crotonaldehyde, 2-pentanone, etc., alcohols such as 1-propanol, 1-butanol, 1-methylpropanol, etc., and the like. Examples of high-boiling impurities include ethers such as 2-propanol, 1-(2-methoxypropoxy)propan-2-ol, and 1-(2-methoxy-2-methylethoxy)-2-propanol; aromatic compounds such as toluene and xylene (ortho-, meta-, and para-); alkanes such as octane, decane, and hexadecane; carboxylic acid esters such as isopropyl acetate, isopropyl propionate, and 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, as described below.

[0029] (Adjustment of Water Content in the Liquid Phase at the Raw Material Supply Stage of the Distillation Column) In this embodiment, for example, when distilling low-water IPA wastewater recovered from a semiconductor manufacturing apparatus, 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, more preferably 80% by mass or more and 93% by mass or less. This makes it possible to efficiently distill off toluene together with low-boiling impurities from the top of the distillation column. In other words, it becomes possible to extract a bottoms product from the bottom of the distillation column in which toluene has been highly reduced.

[0030] Because toluene has a higher boiling point than IPA, if we only consider the difference in boiling points, it would be expected that toluene would not be distilled from the top of the column but would be discharged from the bottom. However, toluene exhibits 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 low-water-content IPA waste liquid, toluene forms an azeotrope with water, and concentration in the gas phase becomes dominant. 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 the efficiency of concentrating toluene into the gas phase by azeotropy with water is insufficient, and it is thought that the amount of toluene distilled off from the top of the distillation column is also low. In this embodiment, by increasing the water content in the liquid phase at the raw material feed tray of the distillation column, the azeotropy with water is activated during distillation, and the amount of toluene distilled off from the top of the distillation column is increased, resulting in a lower toluene content in the bottoms.

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

[0033] A common method for adjusting the water content in the liquid phase at the raw material feed stage of a distillation column is to measure the water content in a waste liquid receiving tank that contains the recovered IPA low-water 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 carried out in the piping that supplies the IPA low-water-content waste liquid to the distillation column, or may be carried out 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 feed tray of the distillation column may be adjusted within the distillation column. That is, the low-water IPA waste liquid may be supplied to the feed tray of the distillation column directly or in a water-added state with a water content of less than 70% by mass, while water may be supplied to the distillation column from outside. In this case, water may be supplied to the feed tray of the distillation column, or water may be supplied to a tray between the feed tray and the top of the distillation column.

[0036] When water is supplied to a stage between the raw material supply stage and the top of the distillation column, the water content in the liquid phase at the raw material supply stage can be determined using process simulation software such as AspenPlus (manufactured by Aspen Technology) or PROII (manufactured by AVEVA). As described below, when the distillate from the top of the distillation column is condensed in a condenser and a portion of the condensed distillate is refluxed to the distillation column, the water content in the liquid phase at the raw material supply stage of the distillation column 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 column is supplied to a second distillation column, and water is added from the outside, and the bottom product is supplied to the distillation column, the water content in the liquid phase at the raw material supply stage of the distillation column can be calculated taking into account the amount of water contained in the bottom product.

[0037] The water content in the liquid phase at the feed tray of the distillation column is not particularly limited as long as it is within the range of 70% by mass or more and 95% by mass or less, but the fluctuation per hour is preferably within 3% by mass, more preferably within 1% by mass, of the total content (100% by mass) of the liquid phase. When 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 point distillation step) The method for producing a purified IPA aqueous solution of this embodiment includes a low-boiling point distillation step of distilling a low-water-content IPA 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] Figure 1 shows a typical embodiment of a low-boiling point distillation step. Specifically, two waste liquid receiving tanks 1 are installed in Figure 1. One is used to supply IPA low-water-content waste liquid, the water content of which has been adjusted, to a low-boiling point distillation column 2, and the other is used to adjust the water content of the IPA low-water-content waste liquid. The roles of the two tanks are switched when the IPA low-water-content waste liquid, the water content of which has been adjusted, becomes empty. IPA low-water-content waste liquid is supplied to the waste liquid receiving tank 1 via a waste liquid supply pipe 3. Water is then supplied to the waste liquid receiving tank 1 via a water supply pipe 8 so that the water content in the liquid phase at the raw material supply stage of the low-boiling point distillation column 2 is 70% by mass or more and 95% by 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 point distillation column 2 via the distilled liquid supply pipe 4 and distilled. A condenser 5 is installed at the top of the low-boiling point distillation column 2, and a portion of the condensed liquid condensed in the condenser 5 is refluxed, while the remainder is discharged as a low-boiling point distillate from a distillate discharge pipe 6. Toluene contained in the IPA low-water waste liquid is discharged together with the low-boiling point distillate. As a result, the bottoms from which toluene has been largely removed are discharged from the bottoms of the low-boiling point distillation column 2 via a bottoms discharge pipe 7.

[0041] The low-boiling distillation column 2 may be either a plate column or a packed column, but is preferably a plate column. The number of theoretical plates in 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 plates in a plate column include cross-flow trays and shower trays. Examples of packing materials in a packed column include Raschig rings and Lessing rings. Examples of materials for plate columns, packed columns, and packing materials include iron, stainless steel, Hastelloy, borosilicate glass, quartz glass, and fluororesins (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 or more, more preferably 10 or more, and even more preferably 20 or more, in terms of the theoretical number of stages. The greater the number of stages from the raw material supply stage to the bottom of the column, the easier it is to remove toluene. In this case, the raw material supply stage may be installed between the top of the column and the column, but since this reduces the amount of IPA waste, it is preferable to install the raw material supply stage at the top of the column. Note that, in calculating the number of raw material supply stages, the bottom and top of the column are not included in the theoretical plates. It is preferable to confirm the number of theoretical stages 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 in a condenser 5, and a portion of the condensed low boiling point distillate is refluxed. In this case, the reflux ratio is preferably 10 or more and 10,000 or less, more preferably 100 or more and 2,000 or less, and even more preferably 300 or more and 1,500 or less. By increasing the reflux ratio, the amount of distillate decreases, and 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 may be supplied to the upstream portion of the low boiling point distillation column 2, thereby further enhancing 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] (Purity of purified IPA aqueous solution) According to the method for producing a purified IPA aqueous solution of this embodiment, the content of toluene contained as an impurity in the low-boiling point distillation step can be reduced to preferably 10 ppb or less, more preferably 0.001 ppb or more and 1 ppb or less, in terms of mass ratio relative to IPA. Low-boiling point impurities can also be significantly reduced. For example, when the low-water IPA waste liquid contains low-aldehyde ketones such as acetaldehyde and propionaldehyde, the content of each can be reduced to preferably 10 ppb or less, more preferably 0.001 ppb or more and 1 ppb or less, in terms of mass ratio relative to IPA.

[0048] [Method for Producing Purified IPA] In the low-boiling distillation step, purified IPA can be produced by dehydrating the purified IPA aqueous solution as 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 perform the following additional purification step. That is, the additional purification step includes an azeotrope production step in which the purified IPA aqueous solution is distilled and an azeotropic mixture of IPA and water is extracted as a distillate, and a dehydration step in which the azeotropic mixture of IPA and water is dehydrated.

[0049] The additional purification step preferably further includes a high-boiling distillation step in which the dehydrated azeotropic mixture is subjected to high-boiling distillation and a distillate containing isopropyl alcohol is extracted. Furthermore, between the dehydration step and the high-boiling distillation step, a second low-boiling distillation step in which the dehydrated azeotropic mixture is subjected to low-boiling distillation and a bottoms product containing isopropyl alcohol is extracted in order to more thoroughly remove low-boiling impurities. Each of the additional purification steps is described below.

[0050] (Azeotrope Formation Step) In the azeotrope formation step, the purified aqueous IPA solution is supplied to a raw material supply tray of a distillation column and distilled, and an azeotrope 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 boiling point higher than that of 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 column. Meanwhile, a bottom product containing high-boiling impurities and water is withdrawn from the bottom of the column. A portion of the water in the bottom product can be used to adjust the water content in the liquid phase in the raw material supply stage of the low-boiling distillation step. This not only reduces the amount of water used and the cost of wastewater treatment, but also reduces energy consumption by using the bottom product without cooling it.

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

[0053] (Dehydration Step) 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 azeotropically distilling 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 point distillation step) In the second low-boiling point distillation step, the azeotropic mixture dehydrated in the dehydration step is again subjected to low-boiling point distillation. That is, the second low-boiling point distillation step is a step of withdrawing a distillate containing low-boiling point impurities from the top of the low-boiling point distillation column and withdrawing a bottoms product containing IPA in which the low-boiling point impurities have been further reduced from the bottom of the low-boiling point distillation column. This step may be performed depending on the desired purity of IPA.

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

[0057] (Other Steps) 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, and organic particles) may be removed by filtration, or ions (e.g., metal ions) may be removed by an ion exchange resin.

[0058] (Purity of Purified IPA) According to the method for producing purified IPA described above, in which an aqueous solution of purified IPA is dehydrated and, if necessary, further purified, the dehydration step can reduce the water content to preferably 100 ppm by mass or less, more preferably 1 to 50 ppm by mass. Furthermore, by performing a high-boiling point distillation step, 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% by mass or more, more preferably 99.99 to 99.999999% by mass (excluding the water content).

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

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

[0061] <Analysis Example 1> (Method for measuring water content) Equipment: Karl Fischer moisture meter CA-200 (manufactured by Mitsubishi Chemical Analytical) Samples thought to have a water content of more than 1% were diluted with IPA and then measured. 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 the water content is higher than expected, it will simply take longer to measure, but will not affect the measured value. The water content of the IPA used for dilution was measured by collecting 5 g or more of the measurement sample with a thermosyringe 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) 1 L of IPA was concentrated to 1 ml using an evaporator (water bath 80°C, 10 kPa (absolute pressure)), and then analyzed by GC / MS. The lower limit of quantitation was calculated using a standard substance, and the lower limit of quantitation for 1-methoxy-2-propanol was found to be 0.01 ppb. - Measurement conditions - Apparatus: 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) → Heat at 5°C / min → 100°C → Heat at 10°C / min → 240°C (held for 6 minutes) Carrier gas: Helium Carrier gas flow rate: 2 mL / min Injection port temperature: 240°C Injection volume: 5 μl Sample injection method: Pulsed splitless method Pulse pressure during injection: 90 psi (2 minutes) Split vent flow rate: 50 mL / min (2 minutes) Gas saver used: 20 mL / min (5 minutes) Transfer line temperature: 240°C Ion source, quadrupole temperature: 230°C, 150°C Scan ion: m / Z = 25 to 250 SIM (selective ion detection): 75 (1-methoxy-2-propanol)

[0063] <Analysis Example 3> (Method for measuring the contents 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). In this method, the detection limits in IPA with a water content of 5% (IPA 95%) were 0.1 ppb for toluene and 0.1 ppb for isopropyl acetate. The SIM value can be arbitrarily set for each compound to be quantified.

[0064] -Measurement conditions- Apparatus: Gas chromatograph mass spectrometer (GC / MS) 8890, 5977B (Agilent Technologies), headspace sampler 8697 (Agilent Technologies) Injection mode: Splitless Carrier: Helium Column: DB-1 (length 60 m, inner diameter 0.32 mm, thickness 5 μm) manufactured by J&W Scientific Column temperature: After maintaining at 30°C for 15 minutes, the temperature was increased to 250°C at 20°C / min, and then maintained at 250°C for 10 minutes Column flow rate: 1.4 ml / min Injection port pressure: 8.4 psi Injection port temperature: 200°C Injection volume: 1 mL (vapor phase of vial in headspace method) Ion source temperature: 230°C Quadrupole temperature: 150°C SIM (selected ion detection): 61 (isopropyl acetate) 91 (toluene) Solvent heating temperature (headspace): 60°C Solvent heating time (headspace): 15 minutes

[0065] B: When the water content in IPA was 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, making it difficult to lower the detection limit using atmospheric pressure concentration methods. By using an adsorbent that easily adsorbs low-polarity substances, such as activated carbon, the detection limit can be reduced to 1 ppt or less.

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

[0068] Example 1 (Low-boiling point distillation step) A low-water-content IPA waste liquid collected from a semiconductor manufacturing apparatus equipped with a semiconductor substrate rinsing section and collected in a waste liquid receiving tank 1 for three days was purified by the low-boiling point distillation step 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%), thereby obtaining a water-content-adjusted liquid to be subjected to the low-boiling point distillation step.

[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-adjusted liquid, and it was confirmed through experiments that the theoretical number of plates of the low-boiling distillation column 2 was 10. Here, the low-boiling distillation column 2 had a 2-L vessel at the bottom, a condenser 5 was installed at the top, and a portion of the distillate condensed in the condenser 5 was refluxed to the top of the low-boiling distillation column 2. The water content-adjusted 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. Furthermore, the reflux rate was 10 L / h, the reflux ratio was approximately 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 approximately 10 L / h so that the liquid volume at the bottoms was maintained at approximately 1.5 L.

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

[0071] The purified aqueous IPA solution obtained in the low-boiling point distillation step was supplied to the raw material feed tray of a distillation column for the azeotrope production step. That is, the bottoms (purified aqueous IPA solution) extracted from the bottoms discharge pipe 7 were supplied to the raw material feed 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, an azeotropic mixture of IPA and water was subjected to a dehydration step, using benzene as an entrainer, and a bottoms product containing IPA, in which the water content had been reduced to 100 ppm or less, was withdrawn from the bottom of the column. The bottoms product containing IPA was then subjected to a second low-boiling point distillation step, in which a bottoms product containing IPA with even lower boiling points was withdrawn. The bottoms product containing IPA was then subjected to a high-boiling point distillation step, in which a distillate containing IPA with even lower boiling points was withdrawn 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 0.1 ppb or less, which is below the detection limit, in terms of mass ratio to IPA. This is also shown in Table 1, along with the contents of isopropyl acetate and 1-methoxy-2-propanol.

[0074] Comparative Example 1 (Low-boiling point distillation step) 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 by mass relative to IPA. The isopropyl acetate content in the purified IPA aqueous solution was 175 ppb by mass relative to IPA.

[0075] (Additional Purification Step) 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 relative to IPA. This is also shown in Table 1, along with the contents of isopropyl acetate and 1-methoxy-2-propanol.

[0076] Comparative Example 2 (Low-boiling point distillation step) 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 low-water-content IPA waste liquid contained in the waste liquid receiving tank 1 and that the low-water-content IPA waste liquid was used instead of the water content adjusting liquid. The toluene content in the purified aqueous IPA 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 aqueous IPA solution was 6,950 ppb in mass ratio to IPA.

[0077] (Additional Purification Step) 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 relative to IPA. This is also shown in Table 1, along with the contents of isopropyl acetate and 1-methoxy-2-propanol.

[0078] Example 2 (Low-boiling point distillation step) 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 low-water-content IPA waste liquid contained in the waste liquid receiving tank 1 was 70% (IPA content: 30%), thereby obtaining a water-content-adjusted solution. The toluene content in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured, and the mass ratio relative to IPA was 0.2 ppb or less, below the lower detection limit, confirming that the toluene content was significantly reduced by the low-boiling point distillation step. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was 1.2 ppb, relative to IPA, by mass.

[0079] (Additional Purification Step) 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 is below the lower detection limit, in terms of mass ratio to IPA. The toluene content and the 1-methoxy-2-propanol content are also shown in Table 1.

[0080] Example 3 (Low-boiling point distillation step) 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 low-water-content IPA waste liquid contained in the waste liquid receiving tank 1 was 80% (IPA content: 20%), thereby obtaining a water-content-adjusted solution. 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, below the lower detection limit, in terms of mass ratio to IPA. This confirmed that the toluene content was significantly reduced by the low-boiling point distillation step. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was 1 ppb or less, in terms of mass ratio to IPA.

[0081] (Additional Purification Step) 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 is below the lower detection limit, in terms of mass ratio to IPA. The content of isopropyl acetate and 1-methoxy-2-propanol is also shown in Table 1.

[0082] Example 4 (Low-boiling point distillation step) The low-boiling point distillation step was carried out in the same manner as in Example 1, except that an Oldershaw-type low-boiling point distillation column with 60 plates was installed as the low-boiling point distillation column 2. It was confirmed by experiment that the theoretical number of plates in the low-boiling point distillation column 2 was 40. When the toluene content in the purified IPA aqueous solution extracted from the bottoms discharge pipe 7 was measured, it was found to be 0.2 ppb or less in mass ratio to IPA, which was below the lower detection limit, confirming that the toluene content was significantly reduced by the low-boiling point 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 Step) 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 is below the lower detection limit, in terms of mass ratio to IPA. The content of isopropyl acetate and 1-methoxy-2-propanol is also shown in Table 1.

[0084] Example 5 (Low-boiling point distillation step) The low-boiling point distillation step was carried out in the same manner as in Example 4, except that a low-water IPA 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 was found to be 0.2 ppb or less by mass relative to IPA, below the lower detection limit. This confirmed that the toluene content was significantly reduced by the low-boiling point distillation step. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was 1 ppb or less by mass relative to IPA.

[0085] (Additional Purification Step) 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 is below the lower detection limit. This is also shown in Table 1, along with the contents of isopropyl acetate and 1-methoxy-2-propanol.

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

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

[0088] 1; Waste liquid receiving tank 2; Low boiling point distillation column 3; Waste liquid supply pipe 4; Distillate supply pipe 5; Condenser 6; Distillate discharge pipe 7; Bottoms discharge pipe 8; Water supply pipe

Claims

1. A method for producing a purified aqueous isopropyl alcohol solution from a low-water-content isopropyl alcohol waste liquid containing toluene as an impurity, 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.

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

3. The method for producing a purified aqueous isopropyl alcohol solution according to claim 1 or 2, wherein 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.

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

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

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 semiconductor substrates.

9. The method for producing purified isopropyl alcohol according to claim 6, further comprising: 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.

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