Method for producing purified aqueous isopropanol solution

Abstract

The present invention provides a method for producing a purified aqueous isopropanol solution from a low-water-content isopropanol waste liquid containing toluene as an impurity, the method comprising a low-boiling-point distillation step in which the low-water-content isopropanol waste liquid is supplied to a raw material supply section of a distillation tower, and the low-boiling-point distillation step is performed in which the low-water-content isopropanol waste liquid is discharged from the distillation tower, and the low-boiling-point distillation step is performed in which the low-water-content isopropanol waste liquid is discharged from the distillation tower. In the method, a distillate containing toluene is extracted from the top of the distillation column, and a bottom solution containing isopropanol and water is extracted from the bottom of the distillation column, and the water content in the liquid phase in the raw material supply section of the distillation column is adjusted so as to be 70-95 mass%.

Description

Technical Field

[0001] This invention relates to a method for producing purified isopropanol aqueous solution and a method for producing purified isopropanol. Background Technology

[0002] Isopropanol (hereinafter referred to as "IPA") has the property of dissolving both water and organic solvents, and is widely used as a solvent for coatings and inks, as well as a raw material for various synthesis processes. In addition, high-purity IPA is also used extensively in the rinsing section of semiconductor substrates in semiconductor manufacturing equipment, and its usage is expected to increase in the future.

[0003] The high manufacturing cost of high-purity IPA contributes to increased costs in the rinsing sections of semiconductor substrates, where it is widely used. Furthermore, while used IPA wastewater is typically incinerated, this releases carbon dioxide, a contributor to global warming. Therefore, from an environmental protection perspective, there is a desire to reduce its waste volume. Consequently, the demand for the recovery, purification, and reuse of IPA wastewater discharged from such industrial equipment is constantly increasing (see, for example, Patent Document 1).

[0004] However, the rinsing section of the semiconductor substrate is generally located adjacent to the rear section of the cleaning section. The cleaning solution used in the cleaning section is typically ultrapure water or a high-aqueous liquid, causing moisture adhering to the surface of the semiconductor substrate in the cleaning section to flow back into the rinsing section. Therefore, the IPA waste liquid recovered from the rinsing section easily becomes a low-aqueous composition containing a small amount of water. Furthermore, IPA is frequently used in the developing section and the pre-wetting section, and water is also widely used in various parts of the semiconductor manufacturing apparatus. Therefore, low-aqueous IPA waste liquid is typically discharged from the semiconductor manufacturing apparatus equipped with the rinsing section; for example, in Patent Document 2, the water content in the low-aqueous IPA waste liquid is set to approximately 5% by mass.

[0005] On the other hand, toluene is sometimes used in cleaning and rinsing sections of semiconductor manufacturing equipment. Furthermore, toluene is widely used as a solvent for solids, such as a solvent component in photoresist materials used in the developing section, and a solvent component in adhesives used in various parts. In addition, most substrate treatment agents use compounds containing toluenesulfonyl groups, and if these compounds decompose, toluene is generated. Due to these circumstances, trace amounts of toluene are sometimes mixed into the recovered IPA waste liquid.

[0006] Therefore, sometimes IPA low-aqueous waste liquid (hereinafter simply referred to as "IPA low-aqueous waste liquid") containing toluene as an impurity is recovered from industrial equipment such as semiconductor manufacturing plants equipped with rinsing sections, and purification treatment of the IPA low-aqueous waste liquid is carried out. Generally speaking, conventional purification methods for organic solvents include distillation. For example, in Patent Document 3, a purification scheme using a distillation process is proposed for IPA low-aqueous waste liquid with a water content of 5-15% and which may contain toluene and other impurities.

[0007] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2017-144410 Patent Document 2: Japanese Patent Application Publication No. 2014-55120 Patent Document 3: Description of Chinese Patent Application Publication No. 112999679 Summary of the Invention

[0008] The problem that the invention aims to solve However, when IPA waste liquid containing toluene is present, current distillation methods are insufficient to remove toluene effectively. For example, in Patent Document 3, the purification process involves feeding IPA waste liquid into a distillation column for distillation, obtaining a fraction containing IPA from the top of the column. Furthermore, after cooling and liquefying the IPA-containing fraction, it is fed to a phase separation unit to remove the aqueous phase, and then further fed to a collection tank for heating, thereby fractionating it into a low-boiling fraction to be fed to a low-boiling tank and a purified IPA fraction to be recovered to a product tank. However, when this purification process was applied to the purification of IPA waste liquid containing toluene, satisfactory results were not obtained. This is because although the boiling point of toluene (110.6°C) is higher than that of IPA (82.4°C) and water, during distillation, due to the azeotropic reaction between toluene and IPA, and between IPA and water, a certain amount of toluene is carried in the IPA-containing fraction from the top of the distillation column. Because subsequent phase separation and fractionation operations using the aqueous phase cannot effectively remove toluene carried in the fraction containing IPA, it is impossible to obtain IPA with high purity.

[0009] Therefore, methods for producing highly purified isopropanol aqueous solutions and purified isopropanol by highly removing toluene from isopropanol waste liquid containing toluene as an impurity are unknown, and developing such methods is a major challenge.

[0010] Methods for solving problems The inventors of this application conducted in-depth research in view of the aforementioned problems. As a result, they discovered that for isopropanol waste liquid with low water content containing toluene as an impurity, by adjusting the water content within a specified range and then distilling, a highly toluene-free bottom liquid can be obtained from the bottom of the distillation column, thus completing the present invention.

[0011] That is, one aspect of the present invention is a method for producing a purified isopropanol aqueous solution, which is a method for producing a purified isopropanol aqueous solution from isopropanol low-aqueous waste liquid containing toluene as an impurity. The aforementioned method includes a low-boiling distillation step, in which the aforementioned isopropanol low-aqueous waste liquid is supplied to the feed section of a distillation column, a distillate containing toluene is drawn from the top of the aforementioned distillation column, and a bottom liquid containing isopropanol and water is drawn from the bottom of the aforementioned distillation column. In the aforementioned method, the water content in the liquid phase in the feed section of the aforementioned distillation column is adjusted to be 70% by mass or more and 95% by mass or less.

[0012] In the method for manufacturing the purified isopropanol aqueous solution, the preferred method is that the aforementioned isopropanol low-aqueous waste liquid is a waste liquid recovered from a semiconductor manufacturing apparatus having a rinsing section for a semiconductor substrate.

[0013] Alternatively, a preferred method is to adjust the water content in the liquid phase of the feed section of the aforementioned distillation column to be 80% by mass or more and 93% by mass or less.

[0014] Alternatively, a preferred method is that the toluene content in the aforementioned isopropanol low-aqueous waste liquid is between 1 ppm and 2000 ppm by mass relative to isopropanol.

[0015] In addition, another aspect of the present invention is a method for producing purified isopropanol, which is a method for producing purified isopropanol from a purified isopropanol aqueous solution obtained by the method for producing purified isopropanol aqueous solution, the aforementioned method including a dehydration step of dehydrating the aforementioned purified isopropanol aqueous solution.

[0016] In the method for producing purified isopropanol, the preferred method includes: an azeotropic mixture generation step, in which the aforementioned purified isopropanol aqueous solution is distilled to extract the azeotropic mixture of isopropanol and water in the form of distillate; and a dehydration step, in which an azeotropic agent is added to the aforementioned azeotropic mixture of isopropanol and water for distillation to extract the bottom liquid containing isopropanol, thereby performing dehydration.

[0017] Alternatively, a preferred method is to use the aforementioned purified isopropanol as a semiconductor solution. A particularly preferred method is to use the aforementioned semiconductor solution as a rinsing solution for a semiconductor substrate.

[0018] Alternatively, a preferred embodiment may include: a second low-boiling distillation step, in which the aforementioned dehydrated azeotropic mixture is subjected to low-boiling distillation to extract a bottom liquid containing isopropanol; and a high-boiling distillation step, in which the aforementioned bottom liquid containing isopropanol is subjected to high-boiling distillation to extract a distillate containing isopropanol.

[0019] Invention Effects According to the present invention, toluene can be removed to a high degree from IPA low-aqueous waste liquid containing toluene as an impurity. Therefore, IPA low-aqueous waste liquid can be easily regenerated into high-purity IPA, which can be reused as a semiconductor solution, especially as a rinsing solution for semiconductor substrates, and has great industrial value. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating a representative method of low-boiling distillation.

[0021] Figure 2 This is a graph showing the effect of moisture concentration on the relative volatility α of toluene and IPA. Detailed Implementation

[0022] The following is a reference to the appendix. Figure 1 The embodiments of the present invention will be described below.

[0023] [Method for preparing purified IPA aqueous solution] (IPA low-water-content waste liquid) In this embodiment, the distillation target liquid is IPA low-aqueous waste liquid containing toluene as an impurity. IPA low-aqueous waste liquid is mostly discharged from the manufacture of paints and inks, and from various industrial equipment using them. The recovered waste liquid can be used without restrictions, and the most suitable waste liquid for purification is the waste liquid recovered from semiconductor manufacturing equipment equipped with a rinsing section for semiconductor substrates. In particular, waste liquid recovered from the rinsing section is easily converted into a low-aqueous composition, which can be appropriately applied. Furthermore, developing solutions, pre-wetting solutions, etching solutions, cleaning solutions, stripping solutions, and drying solutions discharged from semiconductor manufacturing equipment can also be included in the IPA low-aqueous waste liquid.

[0024] The IPA content in the low-aqueous waste liquid containing IPA 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-aqueous waste liquid containing IPA is preferably 95% by mass or less, more preferably 85% by mass or less.

[0025] In this specification and claims, "low water content" means a water content of less than 50% by mass. The water content in IPA low-water waste liquid is preferably 40% by mass or less, more preferably 30% by mass or less. The water content in IPA low-water waste liquid is preferably 5% by mass or more, more preferably 15% by mass or more. When the water content in IPA low-water waste liquid is high, the equipment for recovering the IPA low-water waste liquid becomes bulky, and the cost of transporting the IPA low-water waste liquid increases.

[0026] Here, the water content in the low-water-content IPA waste liquid is determined using the Karl Fischer method. Additionally, the IPA content in the low-water-content IPA waste liquid is determined using gas chromatography.

[0027] The toluene content in the low-aqueous waste liquid of IPA is preferably 1 ppm to 2000 ppm by mass relative to isopropanol, more preferably 50 ppm to 1000 ppm. If the toluene content in the low-aqueous waste liquid of IPA is above the lower limit, the toluene removal effect can be significantly achieved. On the other hand, if the toluene content in the low-aqueous waste liquid of IPA is below the upper limit, toluene and IPA become less likely to azeotropic, making it easier to reduce the toluene content in the purified IPA aqueous solution.

[0028] IPA low-aqueous waste liquid may also contain low-boiling impurities other than toluene, which have a lower boiling point than IPA. Examples of low-boiling impurities include: alkenes such as butenes, pentenes, and hexenes; alkanes such as butanes, pentanes, and hexanes; aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, and butyraldehyde; 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-aqueous waste liquid, by mass ratio relative to IPA, is preferably 0.1 ppm to 10,000 ppm, more preferably 1 ppm to 100 ppm. As described below, the low-boiling impurities are distilled away at a high concentration from the top of the distillation column along with toluene.

[0029] In addition, IPA low-aqueous waste liquid may also contain high-boiling impurities other than toluene, which have higher boiling points than IPA. Specifically, when the IPA low-aqueous waste liquid is a waste liquid from semiconductor chemical solutions, especially cleaning solutions and drying solutions, high-boiling impurities include, for example: metals such as iron, chromium, nickel, copper, zinc, sodium, potassium, calcium, and magnesium; carboxylic acids such as formic acid, acetic acid, and propionic acid; salts with anions such as nitrate ions, nitrite ions, sulfate ions, chloride ions, and fluoride ions; aldehydes and ketones such as butylene aldehyde and 2-pentanone; and alcohols such as 1-propanol and 1-butanol. Ethers such as 1-methoxy-2-propanol, 1-(2-methoxypropoxy)propane-2-ol, and 1-(2-methoxy-2-methylethoxy)-2-propanol; aromatics 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. As described below, high-boiling impurities can be significantly removed by performing the purification process described later on on the bottom liquid drawn from the distillation column.

[0030] (Adjustment of water content in the liquid phase of the feed section of the distillation column) In this embodiment, when distilling the low-aqueous waste liquid of IPA recovered from the semiconductor manufacturing apparatus, the water content in the liquid phase of the feed section of the distillation column is adjusted to be 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 ensures that toluene, along with low-boiling impurities, is effectively distilled away from the top of the distillation column. In other words, a bottom liquid with significantly reduced toluene content can be drawn from the bottom of the distillation column.

[0031] Because toluene has a higher boiling point than IPA, it would be assumed that during distillation, considering only the boiling point difference, toluene would not distill from the top of the column but rather from the bottom. However, toluene exhibits azeotropic properties with IPA and water, and in such an azeotropic system, toluene is enriched in the gas phase. Moreover, regarding IPA waste liquid with low water content, the enrichment of toluene in the gas phase due to azeotropy with water is dominant. As a result, as... Figure 2 As shown, as the water concentration, i.e. the water content in the liquid phase, increases, the enrichment efficiency of toluene into the gas phase increases significantly.

[0032] However, in the case of low-aqueous waste liquid of IPA, due to the low water content, the enrichment efficiency of toluene azeotropically reacting with water into the gas phase is insufficient, and the amount of toluene distilled off the top of the distillation column is considered to be low. In this embodiment, by increasing the water content in the liquid phase of the feed section of the distillation column, the azeotropic reaction between toluene and water is activated during distillation, resulting in a higher amount of toluene distilled off the top of the distillation column, and consequently, a lower toluene content in the bottom liquid.

[0033] It should be noted that, as organic solvents with a higher boiling point than IPA (similar to toluene) and exhibiting azeotropic properties with both IPA and water, and which may also be present in waste liquid recovered from semiconductor manufacturing equipment, examples include xylene (ortho, meta, and para) and isopropyl acetate. By applying the method for producing purified IPA aqueous solution according to this embodiment, the same effect can be achieved with such organic solvents.

[0034] The method for adjusting the water content in the liquid phase of the feed section of a distillation column generally involves mixing water after measuring the water content in a waste liquid receiving tank that contains recovered low-water-content IPA waste liquid. In this case, for example, at least two waste liquid receiving tanks are provided, one for supplying the distillation column with the liquid whose water content has been adjusted, and the other for adjusting the water content. This allows for effective switching between the two tanks when the receiving capacity of the tank used to supply the distillation column is about to run out.

[0035] Regarding the determination of water content and mixing of water in IPA low-water-content waste liquid, it can be carried out in the piping supplying the IPA low-water-content waste liquid to the distillation column. If the IPA low-water-content waste liquid is transported to a waste liquid receiving tank at a distance, it can also be carried out in the transport container (e.g., transport vehicle, container, metal drum).

[0036] It should be noted that the water content in the liquid phase of the feed section of the distillation column can also be adjusted within the distillation column itself. That is, the low-water-content IPA waste liquid can be supplied directly to the feed section of the distillation column, or with water added at a water content of less than 70% by mass. Alternatively, water can be supplied to the distillation column from the outside. In this case, water can be supplied to the feed section of the distillation column, or water can be supplied to the section between the feed section and the top of the column.

[0037] When water is supplied to the section between the feed section and the top of the distillation column, the water content in the liquid phase of the feed section can be obtained, for example, 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 back to the distillation column, the water content in the liquid phase of the feed section of the distillation column can be calculated by considering the amount of water contained in the refluxed distillate. Furthermore, when the distillate drawn from the top of the distillation column is supplied to a second distillation column, water is added externally, and distillation is performed again, with the bottom liquid supplied to the distillation column, the water content in the liquid phase of the feed section of the distillation column can be calculated by considering the amount of water contained in the bottom liquid.

[0038] There is no restriction on the water content in the liquid phase of the feed section of the distillation column, as long as it is between 70% and 95% by mass. The hourly variation relative to the total content of the liquid phase (100% by mass) is preferably within 3% by mass, and more preferably within 1% by mass. If the hourly variation is small, the boiling point of toluene will not change significantly, and flooding is less likely to occur.

[0039] (Low-boiling distillation process) The method for producing purified IPA aqueous solution in this embodiment includes a low-boiling distillation step, in which IPA low-water-content waste liquid is distilled, a distillate containing toluene is drawn from the top of the distillation column, and a bottom liquid containing IPA and water is drawn from the bottom of the distillation column.

[0040] Figure 1 The diagram illustrates a representative method for a low-boiling-point distillation process. Specifically, two waste liquid receiving tanks 1 are provided. One tank supplies IPA (Isobaric Acid) waste liquid with adjusted water content to the low-boiling-point distillation column 2, while the other tank adjusts the water content of the IPA waste liquid. The functions of the two tanks are switched when the IPA waste liquid with adjusted water content becomes empty. IPA waste liquid with low water content is supplied to the waste liquid receiving tank 1 via a waste liquid supply pipe 3. Furthermore, water is supplied to the waste liquid receiving tank 1 via a water supply pipe 8, ensuring that the water content in the liquid phase of the feed section of the low-boiling-point distillation column 2 is between 70% and 95% by mass.

[0041] Thus, the IPA low-water-content waste liquid, with its water content adjusted, is supplied to the feed section of the low-boiling distillation column 2 via the distillate supply pipe 4 and distilled. A condenser 5 is installed at the top of the low-boiling distillation column 2. Of the condensate obtained in the condenser 5, a portion is refluxed, and the remainder is discharged as low-boiling distillate from the distillate discharge pipe 6. The toluene contained in the IPA low-water-content waste liquid is carried away in the low-boiling distillate and discharged. As a result, the bottom liquid, with toluene largely removed, is discharged from the bottom liquid discharge pipe 7 at the bottom of the low-boiling distillation column 2.

[0042] The low-boiling distillation column 2 can be either a plate column or a packed column, 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, more preferably 20 to 50. Examples of plates in a plate column include cross-flow plates and spray plates. Examples of packing materials in a packed column include Raschig rings and Luxing rings. Examples of materials used for the plate column, packed column, and packing material include iron, stainless steel, Hastelloy, borosilicate glass, quartz glass, and fluoropolymers (e.g., polytetrafluoroethylene).

[0043] In the low-boiling distillation column 2, the number of sections from the feed section to the bottom of the column, calculated in terms of theoretical plates, is preferably 5 or more, more preferably 10 or more, and even more preferably 20 or more. If the number of sections from the feed section to the bottom of the column is large, toluene is easier to remove. In this case, it is sufficient to set the feed section within the space up to the top of the column; however, from the viewpoint of reducing IPA waste, it is preferable to set the feed section at the top of the column. It should be noted that the top and bottom of the column are not included in the calculation of the theoretical plates in the feed section calculation. It is preferable to actually operate the low-boiling distillation column 2 and analyze the composition of the distillate to determine the number of theoretical plates of the low-boiling distillation column 2.

[0044] The mass of the gas phase at the top of the low-boiling distillation column 2 is preferably 0.1 to 10 relative to the total mass of the liquid supplied to the low-boiling distillation column 2.

[0045] Furthermore, the pressure (gauge pressure) at the top of the low-boiling distillation column 2 is not particularly limited, for example, it can be between 0.0 MPaG and 0.1 MPaG. In this case, the temperatures at the top and bottom of the low-boiling distillation column 2 can be appropriately set according to the pressure.

[0046] The low-boiling-point distillate removed from the top of the column is condensed using condenser 5, and a portion of the condensed low-boiling-point distillate is refluxed. The reflux ratio is preferably 10 to 10,000, more preferably 100 to 2,000, and even more preferably 300 to 1,500. By increasing the reflux ratio, the amount of distillate decreases, thus enabling the separation of toluene while reducing the amount of IPA removed during distillation.

[0047] In this way, the low-boiling distillate drawn from the top of the column can be discharged outside the system; alternatively, the low-boiling distillate can be supplied to the second distillation column, and after adding water from the outside, it can be distilled again, with the bottom liquid supplied to the upstream section of the low-boiling distillation column 2 to further improve the removal of toluene and low-boiling impurities. The low-boiling distillate discharged outside the system can also be reused, for example, as fuel.

[0048] (Purity of purified IPA aqueous solution) According to the method for manufacturing purified IPA aqueous solution of this embodiment, in the low-boiling distillation step, the content of toluene, which is an impurity, can be reduced to preferably 10 ppb or less, more preferably 0.001 ppb or more or 1 ppb or less, based on the mass ratio relative to IPA. Furthermore, low-boiling impurities can be significantly reduced; for example, in the case where the low-aqueous waste liquid of IPA contains low-aldehyde or propionaldehyde ketones, their respective contents can be reduced to preferably 10 ppb or less, more preferably 0.001 ppb or more or 1 ppb or less, based on the mass ratio relative to IPA.

[0049] [Method for manufacturing purified IPA] In the low-boiling distillation process, purified IPA can be produced by dehydrating the purified IPA aqueous solution, which is the bottom liquid drawn from the bottom of the low-boiling distillation column 2. To obtain purified IPA with higher purity, the following additional purification process is preferably implemented. That is, the additional purification process includes: an azeotropic mixture generation process, in which the purified IPA aqueous solution is distilled to extract an azeotropic mixture of IPA and water as distillate; and a dehydration process, in which the azeotropic mixture of IPA and water is dehydrated.

[0050] The additional purification process preferably includes a high-boiling distillation process, in which the dehydrated azeotropic mixture is distilled at high boiling point to extract the distillate containing isopropanol. Furthermore, to further remove low-boiling impurities, a second low-boiling distillation process may be included between the dehydration process and the high-boiling distillation process. In this second low-boiling distillation process, the dehydrated azeotropic mixture is distilled at low boiling point to extract the bottom liquid containing isopropanol. The various additional purification processes will be described below.

[0051] (Azeotropic mixture generation process) In the azeotropic mixture generation process, a purified IPA aqueous solution is supplied to the feed section of a distillation column and distilled. An azeotropic mixture of IPA and water is drawn from the top of the distillation column as distillate, and a bottom liquid containing high-boiling impurities with a boiling point higher than that of IPA is drawn from the bottom of the distillation column.

[0052] Specifically, since the azeotropic temperature of IPA and water is 80.1°C, the azeotropic mixture of IPA and water can be extracted from the top of the column by distilling the purified IPA aqueous solution at 80.1°C. On the other hand, the bottom liquid, containing high-boiling impurities and water, can be extracted from the bottom of the column. A portion of the water in the bottom liquid can also be used to adjust the water content in the liquid phase of the feed section in the low-boiling distillation process. This reduces water consumption and wastewater treatment costs, and the bottom liquid can be used without cooling, thereby reducing energy consumption.

[0053] Furthermore, the azeotropic mixture generation process can be carried out under the various conditions described in the low-boiling distillation process.

[0054] (Dehydration process) In the dehydration process, the azeotropic mixture of IPA and water obtained in the azeotropic mixture generation process is dehydrated.

[0055] There are no particular limitations on the dehydration method; examples include azeotropic distillation, adsorption, and membrane permeation. It should be noted that in the case of azeotropic distillation of an azeotropic mixture of IPA and water, water can be removed by adding an azeotropic agent. Examples of azeotropic agents include diethyl ether, benzene, toluene, trichloroethylene, dichloromethane, and hexenes.

[0056] (Second low-boiling distillation process) In the second low-boiling distillation step, the azeotropic mixture dehydrated in the dehydration step is subjected to low-boiling distillation again. That is, the second low-boiling distillation step is a process of drawing out the distillate containing low-boiling impurities from the top of the low-boiling distillation column and drawing out the bottom liquid containing IPA with further reduced low-boiling impurities from the bottom of the low-boiling distillation column, which can be implemented according to the desired purity of IPA.

[0057] (High-boiling distillation process) In the high-boiling distillation process, the azeotropic mixture that has been dehydrated by the dehydration process is subjected to high-boiling distillation. The bottom liquid containing high-boiling impurities is drawn from the bottom of the high-boiling distillation column, and the distillate containing IPA, which further reduces the high-boiling impurities, is drawn from the top of the high-boiling distillation column.

[0058] (Other processes) The distillate obtained from the high-boiling distillation process can be further purified by methods such as adsorption, as needed. Alternatively, filtration can be used to remove particles (e.g., metal particles, inorganic particles, organic particles), and ion exchange resins can be used to remove ions (e.g., metal ions).

[0059] (Purity of purified IPA) The purified IPA aqueous solution described above is dehydrated, and as needed, according to the method for manufacturing purified IPA with additional purification, the water content can be set to preferably 100 ppm by mass or less, more preferably 1 to 50 ppm by mass by performing the dehydration process. Furthermore, if a high-boiling distillation process is performed, high-boiling impurities other than toluene can be significantly reduced. Therefore, purified IPA with a purity of preferably 99.9% by mass or more, more preferably 99.99 to 99.999999% by mass (excluding water content) can be obtained.

[0060] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and the above embodiments can be appropriately modified within the scope of the spirit of the present invention.

[0061] Example The following describes embodiments of the present invention, but the present invention is not limited to these embodiments. Furthermore, in these embodiments, unless otherwise stated, % and ppm are based on mass.

[0062] <Analysis example 1> (Methods for determining water content) Instrument: Karl Fischer moisture analyzer CA-200 (manufactured by Mitsubishi Chemical Analysis Technology Co., Ltd.) For samples with a water content considered to exceed 1%, the sample is diluted with IPA before measurement. The water content in the IPA used for dilution has been pre-determined and confirmed to be 30 ppm. For samples with a water content considered to be less than 1%, the sample is analyzed without dilution. In cases where the water content is higher than expected, the measurement is only time-consuming and does not affect the measured value. A sample of 5 g or more is collected using a Terumo syringe in a glove box at a dew point below -60°C, and the water content in the IPA used for dilution is determined. This analytical method can quantify samples with a water content of 1 ppm or higher.

[0063] <Analysis example 2> (Method for determining the content of 1-methoxy-2-propanol) IPA 1L was concentrated to 1ml using an evaporator (water bath at 80℃ and 10kPa (absolute pressure)) and then analyzed by GC / MS. The limit of quantitation was calculated using standard substances, and the result showed that the limit of quantitation for 1-methoxy-2-propanol was 0.01ppb.

[0064] -Determination Conditions- Device: 7890A / 5975C (manufactured by Agilent Technologies) Analytical column: SUPELCO WAX-10 (60m × 0.25mm, 0.25μm) Column temperature: 35℃ (hold for 2 minutes) → increase at 5℃ / min → 100℃ → increase at 10℃ / min → 240℃ (hold for 6 minutes) Carrier gas: Helium Carrier gas flow rate: 2 mL / min Inlet temperature: 240℃ Injection volume: 5μl Sample injection method: Pulse-splitterless method Injection pulse pressure: 90 psi (2 minutes) Flow rate at the shunt: 50 mL / min (2 minutes) Use Gas Saver mode: 20 mL / min (5 minutes) Transmission line temperature: 240℃ Ion source temperature and quadrupole temperature: 230℃ and 150℃ respectively. Scanning ions: m / Z = 25~250 SIM (Selective Ion Detection): 75 (1-Methoxy-2-propanol) <Analysis example 3> (Determination methods for the content of toluene and isopropyl acetate) A: When the water content in IPA is above 1%. After setting the water content in the IPA to 95%, headspace gas chromatography-mass spectrometry (HS / GC / MS) was used to analyze the contents of toluene and isopropyl acetate. The detection limits for IPA with a water content of 5% (IPA 95%) in this method are 0.1 ppb for toluene and 0.1 ppb for isopropyl acetate. It should be noted that the SIM value can be arbitrarily set for each compound to be quantified.

[0065] -Determination Conditions- Apparatus: Gas chromatograph-mass spectrometer (GC / MS) 8890, 5977B (manufactured by Agilent Technologies), headspace sampler 8697 (manufactured by Agilent Technologies). Injection mode: No splitting Carrier gas: Helium Chromatographic column: J&W Scientific DB-1 (60m length, 0.32mm inner diameter, 5μm thickness) Column temperature: After maintaining at 30°C for 15 minutes, the temperature was increased to 250°C at a rate of 20°C / min, and then maintained at 250°C for another 10 minutes. Column flow rate: 1.4 ml / min Inlet pressure: 8.4 psi Inlet temperature: 200℃ Injection volume: 1 mL (gas phase section of the small glass vial in the headspace method) Ion source temperature: 230℃ Quadrupole temperature: 150℃ SIM (Selective Ion Detection): 61 (Isopropyl acetate), 91 (Toluene) Solvent heating temperature (headspace): 60℃ Solvent heating time (headspace): 15 minutes B: Cases where the water content in the 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] It should be noted that the SIM value can be arbitrarily set for each compound to be quantified. Toluene and isopropyl acetate are azeotropic with IPA, making it difficult to lower the detection limit using enrichment methods at atmospheric pressure. However, by using adsorbents such as activated carbon that readily adsorb low-polarity substances, the detection limit can be reduced to below 1 ppt.

[0067] -Determination Conditions- Apparatus: Gas Chromatography-Mass Spectrometry (GC / MS) 8890, 5977B (manufactured by Agilent Technologies) Injection mode: No splitting Carrier gas: Helium Chromatographic column: J&W Scientific DB-1 (60m length, 0.32mm inner diameter, 5μm thickness) Column temperature: After maintaining at 30°C for 15 minutes, the temperature was increased to 250°C at a rate of 20°C / min, and then maintained at 250°C for another 10 minutes. Column flow rate: 1.4 ml / min Inlet pressure: 8.4 psi Inlet temperature: 200℃ Injection volume: 5μL Ion source temperature: 230℃ Quadrupole temperature: 150℃ SIM (Selective Ion Detection): 59 (2-methyl-2-propanol), 61 (isopropyl acetate), 91 (toluene) <Example 1> (Low-boiling distillation process) Three days' worth of low-aqueous IPA waste liquid, recovered from a semiconductor manufacturing apparatus equipped with a semiconductor substrate rinsing section and collected in waste liquid receiving tank 1, is then processed... Figure 1 Purification is performed using the low-boiling distillation process shown. The IPA low-aqueous waste liquid contains 20% water (IPA content is 80%) by mass and 100 ppm toluene by mass relative to IPA. Water is supplied to waste liquid receiving tank 1 with a water content of 90% relative to the IPA low-aqueous waste liquid (IPA content is 10%) to obtain a water content adjustment solution for the low-boiling distillation process.

[0068] As a low-boiling distillation column 2 for distilling the water content adjustment solution, an Oldershaw-type low-boiling distillation column with 15 trays was installed, and the theoretical number of trays for the low-boiling distillation column 2 was confirmed to be 10 through experiments. Here, the bottom of the low-boiling distillation column 2 is a 2L container, and a condenser 5 is installed at the top. A portion of the distillate condensed in the condenser 5 is refluxed to the top of the low-boiling distillation column 2. The water content adjustment solution is supplied to the top of the low-boiling distillation column at a rate of 10L / h for distillation. At this time, the temperature at the top of the column is set to 75–85°C, and the pressure (gauge pressure) at the top of the column is set to 0–10 kPaG. Furthermore, the reflux rate is set to 10L / h, the reflux ratio is set to 1000, and the distillate is withdrawn from the distillate discharge pipe 6 at a rate of 10ml / h. In addition, the bottom liquid (purified IPA aqueous solution) is drawn out from the bottom liquid discharge pipe 7 at a rate of about 10L / h, while the liquid volume at the bottom of the column is maintained at about 1.5L.

[0069] The toluene content in the purified IPA aqueous solution was determined, and the results showed that it was less than 0.2 ppb relative to IPA by mass, below the detection limit, confirming that the toluene content was significantly reduced by the low-boiling distillation process. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was less than 1 ppb relative to IPA by mass.

[0070] (Additional purification process) The purified IPA aqueous solution obtained through the low-boiling distillation process is supplied to the feed section of the distillation column for the azeotropic mixture generation process. That is, the bottom liquid (purified IPA aqueous solution) drawn from the bottom liquid discharge pipe 7 is supplied to the feed section of the distillation column for distillation, and an azeotropic mixture of IPA and water (mass ratio of 87.5:12.5) is drawn from the top of the column.

[0071] Next, the azeotropic mixture of IPA and water is fed to a dehydration process using benzene as an azeotropic agent. The bottom liquid containing IPA, with its water content reduced to below 100 ppm, is drawn from the bottom of the column. Then, the bottom liquid containing IPA is fed to a second low-boiling distillation process, where a further reduced low-boiling impurities are extracted. The bottom liquid containing IPA is then fed to a high-boiling distillation process, where a further reduced high-boiling impurities are extracted, followed by cooling. The distillate containing IPA is then passed through an ion exchange resin and then through three filters (fluoropolymer filters with pore sizes of 50 nm, 10 nm, and 2 nm) to obtain purified IPA.

[0072] The toluene content in the purified IPA was less than 0.1 ppb by mass relative to the IPA, below the detection limit. Furthermore, the contents of isopropyl acetate and 1-methoxy-2-propanol are listed in Table 1.

[0073] <Comparative Example 1> (Low-boiling distillation process) Water was supplied to the waste liquid receiving tank 1 to obtain a water content adjustment solution, with the water content being 50% (IPA content being 50%) relative to the low-aqueous IPA waste liquid contained in the waste liquid receiving tank 1. Otherwise, the low-boiling distillation process was performed in the same manner as in Example 1. The toluene content in the purified IPA aqueous solution drawn from the bottom liquid discharge pipe 7 was measured, and the result was 8 ppb relative to the mass of IPA. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was 175 ppb relative to the mass of IPA.

[0074] (Additional purification process) Except for using the purified IPA aqueous solution obtained by low-boiling distillation, the additional purification process was performed in the same manner as in Example 1. The toluene content in the purified IPA obtained was 6 ppb relative to the mass of IPA. Furthermore, the contents of isopropyl acetate and 1-methoxy-2-propanol are described in Table 1.

[0075] <Comparative Example 2> (Low-boiling distillation process) Water was not supplied to the low-aqueous IPA waste liquid contained in waste liquid receiving tank 1. Instead of water content adjustment liquid, the low-aqueous IPA waste liquid was used. Otherwise, the low-boiling distillation process was performed in the same manner as in Example 1. The toluene content in the purified IPA aqueous solution drawn from the bottom liquid discharge pipe 7 was measured, and the result was 12400 ppb relative to IPA by mass. In addition, the isopropyl acetate content in the purified IPA aqueous solution was 6950 ppb relative to IPA by mass.

[0076] (Additional purification process) Except for using the purified IPA aqueous solution obtained by low-boiling distillation, the additional purification process was performed in the same manner as in Example 1. The toluene content in the purified IPA obtained was 100 ppb relative to the mass of IPA. Furthermore, the contents of isopropyl acetate and 1-methoxy-2-propanol are described in Table 1.

[0077] <Example 2> (Low-boiling distillation process) A water content adjustment solution was obtained by supplying water to the waste liquid receiving tank 1 such that the water content was 70% (IPA content was 30%) relative to the low-aqueous waste liquid of IPA contained in the waste liquid receiving tank 1. Otherwise, a low-boiling distillation process was performed in the same manner as in Example 1. The toluene content in the purified IPA aqueous solution drawn from the bottom liquid discharge pipe 7 was measured, and the result showed that it was less than 0.2 ppb relative to IPA by mass, below the detection limit, confirming that the toluene content was significantly reduced by the low-boiling distillation process. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was 1.2 ppb relative to IPA by mass.

[0078] (Additional purification process) Except for using the purified IPA aqueous solution obtained by low-boiling distillation, the additional purification process was performed in the same manner as in Example 1. The toluene content in the purified IPA thus obtained was less than 0.1 ppb by mass relative to the IPA, which was below the detection limit. Furthermore, the contents of 1-methoxy-2-propanol are listed together in Table 1.

[0079] <Example 3> (Low-boiling distillation process) A water content adjustment solution was obtained by supplying water to the waste liquid receiving tank 1 such that the water content was 80% (IPA content was 20%) relative to the low-aqueous IPA waste liquid contained in the waste liquid receiving tank 1. Otherwise, a low-boiling distillation process was performed in the same manner as in Example 1. The toluene content in the purified IPA aqueous solution drawn from the bottom liquid discharge pipe 7 was measured, and the result showed that it was 0.2 ppb or less by mass relative to IPA, below the detection limit, confirming that the toluene content was significantly reduced by the low-boiling distillation process. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was 1 ppb or less by mass relative to IPA.

[0080] (Additional purification process) Except for using the purified IPA aqueous solution obtained by low-boiling distillation, the additional purification process was performed in the same manner as in Example 1. The toluene content in the purified IPA thus obtained was less than 0.1 ppb by mass relative to the IPA, which was below the detection limit. Furthermore, the contents of isopropyl acetate and 1-methoxy-2-propanol are listed in Table 1.

[0081] <Example 4> (Low-boiling distillation process) As the low-boiling distillation column 2, an Oldershaw-type low-boiling distillation column with 60 trays was installed. Otherwise, the low-boiling distillation process was performed in the same manner as in Example 1. Experiments confirmed that the theoretical number of trays for the low-boiling distillation column 2 was 40. The toluene content in the purified IPA aqueous solution drawn from the bottom drain pipe 7 was measured, and the result showed that it was less than 0.2 ppb relative to IPA by mass, below the detection limit, confirming that the toluene content was significantly reduced by the low-boiling distillation process. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was less than 1 ppb relative to IPA by mass.

[0082] (Additional purification process) Except for using the purified IPA aqueous solution obtained by low-boiling distillation, the additional purification process was performed in the same manner as in Example 1. The toluene content in the purified IPA thus obtained was less than 0.1 ppb by mass relative to the IPA, which was below the detection limit. Furthermore, the contents of isopropyl acetate and 1-methoxy-2-propanol are listed in Table 1.

[0083] <Example 5> (Low-boiling distillation process) The IPA low-aqueous waste liquid used had a water content of 20% (IPA content of 80%) and a toluene content of 500 ppm (mass ratio of IPA). Otherwise, the low-boiling distillation process was performed in the same manner as in Example 4. The toluene content in the purified IPA aqueous solution drawn from the bottom drain pipe 7 was measured, and the result showed that it was less than 0.2 ppb (mass ratio of IPA), below the detection limit, confirming that the toluene content was significantly reduced by the low-boiling distillation process. Furthermore, the isopropyl acetate content in the purified IPA aqueous solution was less than 1 ppb (mass ratio of IPA).

[0084] (Additional purification process) Except for using the purified IPA aqueous solution obtained by low-boiling distillation, the additional purification process was performed in the same manner as in Example 1. The purified IPA obtained thus contained less than 0.1 ppb of toluene, which is below the detection limit. Furthermore, the contents of isopropyl acetate and 1-methoxy-2-propanol are described in Table 1.

[0085] [Table 1] It should be noted that in Table 1, the contents of toluene, isopropyl acetate, and 1-methoxy-2-propanol are mass ratios relative to IPA.

[0086] As shown in Table 1, in Examples 1-5, toluene was significantly removed from the low-aqueous IPA waste liquid, resulting in high purity of the purified IPA aqueous solution and purified IPA. In contrast, in Comparative Example 1, since the water content in the water content adjustment solution was 50%, toluene was not significantly removed from the low-aqueous IPA waste liquid, resulting in low purity of the purified IPA aqueous solution and purified IPA. Furthermore, in Comparative Example 2, since water was not supplied to the low-aqueous IPA waste liquid to adjust the water content, toluene was not significantly removed from the low-aqueous IPA waste liquid, resulting in low purity of the purified IPA aqueous solution and purified IPA.

[0087] Explanation of reference numerals in the attached figures 1: Waste liquid receiving tank 2: Low-boiling distillation column 3: Waste liquid supply pipe 4: Distillate supply tube 5: Condenser 6: Distillate discharge pipe 7: Bottom liquid discharge pipe 8: Water supply pipe

Claims

1. A method for preparing a purified isopropanol aqueous solution, comprising a method for preparing a purified isopropanol aqueous solution from isopropanol low-aqueous waste liquid containing toluene as an impurity. The method includes a low-boiling-point distillation step, in which the aforementioned isopropanol low-aqueous-content waste liquid is fed to the feed section of a distillation column, a distillate containing toluene is drawn from the top of the distillation column, and a bottom liquid containing isopropanol and water is drawn from the bottom of the distillation column. The water content in the liquid phase of the feed section of the aforementioned distillation column is adjusted to be between 70% and 95% by mass.

2. The method for preparing purified isopropanol aqueous solution as described in claim 1, wherein, The aforementioned isopropanol low-aqueous waste liquid is a waste liquid recovered from a semiconductor manufacturing apparatus equipped with a rinsing section for semiconductor substrates.

3. The method for producing purified isopropanol aqueous solution as described in claim 1 or 2, wherein, The water content in the liquid phase of the feed section of the aforementioned distillation column is adjusted to be between 80% and 93% by mass.

4. The method for producing purified isopropanol aqueous solution as described in claim 1 or 2, wherein, In the aforementioned isopropanol low-aqueous waste liquid, the toluene content, in terms of mass ratio relative to isopropanol, is between 1 ppm and 2000 ppm.

5. A method for producing purified isopropanol, comprising a method for producing purified isopropanol from an aqueous solution of purified isopropanol obtained using the method for producing an aqueous solution of purified isopropanol according to claim 1 or 2. The method includes a dehydration step of dehydrating the aforementioned purified isopropanol aqueous solution.

6. The method for producing purified isopropanol as described in claim 5, wherein the method comprises: In the azeotropic mixture generation process, the aforementioned purified isopropanol aqueous solution is distilled to extract the azeotropic mixture of isopropanol and water in the form of distillate. and, In the dehydration process, an azeotropic agent is added to the aforementioned azeotropic mixture of isopropanol and water to perform distillation, and the bottom liquid containing isopropanol is extracted, thereby achieving dehydration.

7. The method for producing purified isopropanol as described in claim 5, wherein, The aforementioned purified isopropanol is a semiconductor solution.

8. The method for producing purified isopropanol as described in claim 7, wherein, The aforementioned semiconductor solution is a rinsing solution for semiconductor substrates.

9. The method for producing purified isopropanol as described in claim 6, further comprising: The second low-boiling distillation step involves performing low-boiling distillation on the aforementioned dehydrated azeotropic mixture to extract the bottom liquid containing isopropanol. and, The high-boiling distillation process involves high-boiling distillation of the bottom liquid containing isopropanol to extract the distillate containing isopropanol.

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