Method for producing purified isopropyl alcohol

Abstract

Provided is a method for producing isopropyl alcohol from crude isopropyl alcohol containing butyl formate as an impurity, the method comprising a pressure distillation step for pressure-distilling crude isopropyl alcohol.

Description

Method for producing purified isopropyl alcohol

[0001] The present invention relates to a method for producing purified isopropyl alcohol from crude isopropyl alcohol containing butyl formate as an impurity.

[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, inks, and various synthetic raw materials. Furthermore, high-purity IPA is also used in large quantities in the rinsing section of semiconductor substrates in semiconductor manufacturing equipment, and its usage is expected to continue to increase in the future. Distillation purification is known as a method for purifying crude IPA to produce high-purity IPA. (See Non-Patent Document 1)

[0003] Because high-purity IPA has a high manufacturing cost, the semiconductor substrate rinsing section, which uses a large amount of high-purity IPA, can contribute to increased semiconductor manufacturing costs. Furthermore, IPA waste liquid recovered after use in the semiconductor substrate rinsing section is typically burned, which releases carbon dioxide, a cause of global warming. Therefore, from the perspective of environmental conservation, it is desirable to reduce the amount of IPA waste liquid disposed of. For this reason, there is a growing demand for purifying and reusing IPA waste liquid (see, for example, Patent Document 1).

[0004] Incidentally, a semiconductor substrate rinsing unit is typically located adjacent to the downstream of a semiconductor substrate cleaning unit. Because ultrapure water or a highly water-rich solution is typically used as the cleaning liquid in the semiconductor substrate cleaning unit, the semiconductor substrate rinsing unit performs an operation to remove moisture adhering to the surface of the semiconductor substrate. Therefore, the IPA waste liquid recovered from the semiconductor substrate rinsing unit is a low-water-content liquid. Furthermore, IPA is also used in large quantities in the developing unit and pre-wet unit of semiconductor manufacturing equipment. Furthermore, water is often used for various purposes in semiconductor manufacturing equipment. Therefore, an IPA-containing waste liquid is discharged from semiconductor manufacturing equipment equipped with a semiconductor substrate rinsing unit. For example, Patent Document 2 assumes that the water content of the IPA-containing waste liquid is approximately 5% by mass. Patent Document 3, for example, proposes a method for recovering IPA from such IPA-containing waste liquid by distillation and purification of IPA-containing waste liquid with a water content of 5 to 15%.

[0005] Japanese Patent Publication No. 2017-144410 Japanese Patent Publication No. 2014-55120 Chinese Patent Publication No. 112999679

[0006] Organic Synthetic Chemistry, Vol. 35, No. 9, 1977, pp. 762-766

[0007] On the other hand, in semiconductor manufacturing equipment, various compounds other than IPA are used in the cleaning and rinsing sections. Examples of various compounds other than IPA include solvent components of photoresist materials used in the developing section and solvent components of adhesives used for various purposes. Therefore, the IPA waste liquid discharged from the semiconductor manufacturing equipment after passing through the cleaning and rinsing sections contains these solvent components in addition to water.

[0008] The present inventors have investigated the production of high-purity IPA that can be used in semiconductor manufacturing equipment by purifying IPA waste liquid, and have found that butyl formate is a solvent component that is difficult to remove from IPA waste liquid. Therefore, an object of the present invention is to provide a method for producing highly purified IPA from crude IPA that contains butyl formate as an impurity.

[0009] In view of the above-mentioned problems, the present inventors investigated the separation and removal of butyl formate by distillation purification of crude IPA, and found that the production of purified IPA is difficult. Specifically, when crude IPA contains no water but contains butyl formate, an azeotropic mixture of butyl formate and IPA is obtained, making it difficult to separate and remove butyl formate even by distillation under non-pressurized conditions. On the other hand, when crude IPA contains water and butyl formate, distillation under non-pressurized conditions allows for the separation and removal of butyl formate as a low-boiling impurity. However, since an azeotropic mixture of IPA and water is obtained, azeotropic distillation is required, making the production of purified IPA complicated. Furthermore, it was found that when crude IPA further contains formic acid or 1-butanol, butyl formate is regenerated by dehydrating the crude IPA.

[0010] Based on the above findings, the present inventors investigated a method for producing purified IPA in the case where crude IPA does not contain water but does contain butyl formate. As a result, they found that by distilling crude IPA under pressure, purified IPA from which butyl formate has been highly removed can be obtained as a distillate from the top of a distillation column, and this finding led to the completion of the present invention.

[0011] That is, one aspect of the present invention is a method for producing purified isopropyl alcohol from crude isopropyl alcohol containing butyl formate as an impurity, which includes a pressure distillation step of pressure-distilling the crude isopropyl alcohol. In one aspect of the present invention, the following aspect is preferably taken.

[0012] (1) The ratio of butyl formate to isopropyl alcohol in the crude isopropyl alcohol is 10 ppb by mass or more and 100,000 ppb by mass or less. (2) The crude isopropyl alcohol is pressure-distilled under conditions of an absolute pressure of 120 kPa or more and 1,000 kPa or less. (3) The method further includes a dehydration step of dehydrating a crude isopropyl alcohol stock solution containing formate ions, 1-butanol, and water to obtain the crude isopropyl alcohol. (4) The ratio of formate ions to isopropyl alcohol in the crude isopropyl alcohol stock solution is 10 ppb by mass or more and 100,000 ppb by mass or less. (5) The ratio of 1-butanol to isopropyl alcohol in the crude isopropyl alcohol stock solution is 10 ppb by mass or more and 100,000 ppb by mass or less. (6) The crude isopropyl alcohol stock solution is a waste liquid recovered from semiconductor manufacturing equipment.

[0013] According to the present invention, highly purified IPA can be produced from crude IPA containing butyl formate as an impurity. Therefore, IPA waste liquid recovered from semiconductor manufacturing equipment equipped with a semiconductor substrate rinsing section can be easily recycled into high-purity IPA. The high-purity IPA can be used as a semiconductor chemical, particularly as a semiconductor substrate rinsing liquid, and is of great industrial value.

[0014] 1 is a schematic diagram showing a low-boiling point distillation column used in Example 6. It is an overall view of a graph showing the molar fraction of liquid-phase IPA and gas-phase IPA for each pressure. It is an enlarged view of the range where the molar fraction is high in the graph showing the molar fraction of liquid-phase IPA and gas-phase IPA for each pressure. It is a schematic diagram showing a low-boiling point distillation column used in Example 6.

[0015] The method for producing purified IPA according to the present embodiment is a method for producing purified IPA from crude IPA containing butyl formate as an impurity, and includes a pressure distillation step of pressurizing and distilling the crude IPA. While the details of why the method for producing purified IPA according to the present embodiment enables a high level of butyl formate removal from crude IPA containing butyl formate as an impurity are unclear, the inventors speculate as follows. As described above, IPA waste liquid discharged from semiconductor manufacturing equipment may contain water and butyl formate. In this case, distillation under non-pressurized conditions makes it possible to separate and remove butyl formate. On the other hand, if the IPA waste liquid does not contain water, distillation under non-pressurized conditions will result in an azeotrope of butyl formate and IPA, making it impossible to separate and remove butyl formate. On the other hand, above the boiling point of IPA, particularly above 100°C, the difference in saturated vapor pressure between IPA and butyl formate becomes large, making it difficult to form an azeotrope of butyl formate and IPA. Therefore, it is speculated that distillation under pressurized conditions will prevent the formation of an azeotrope of butyl formate and IPA, making it possible to separate and remove butyl formate.

[0016] In this specification, unless otherwise specified, the notation "A to B" for numerical values ​​A and B means "greater than or equal to A and less than or equal to B." Furthermore, in such notation, when a unit is assigned only to numerical value B, the unit also applies to numerical value A. In the following description, unless otherwise specified, the concentrations "ppm," "ppb," and "ppt" are all based on mass, including in the examples. The method for producing purified IPA of this embodiment will be described in detail below.

[0017] <Crude IPA> In the method for producing purified IPA of this embodiment, crude IPA containing butyl formate as an impurity is distilled under pressure. Butyl formate has a boiling point of approximately 106°C at atmospheric pressure. The crude IPA is not particularly limited and may be a reaction product obtained by reacting propylene with water using a propylene process, a reaction product obtained by a reduction reaction of acetone, or IPA waste liquid.

[0018] The ratio of butyl formate to isopropyl alcohol in the crude IPA is not particularly limited, but is preferably 10 to 100,000 ppb, more preferably 100 to 10,000 ppb. When the ratio of butyl formate to isopropyl alcohol in the crude IPA is within the above range, the effect of separating and removing butyl formate in this embodiment is significantly exhibited. On the other hand, even if the ratio of butyl formate to isopropyl alcohol in the crude IPA exceeds 100,000 ppb, butyl formate can be removed by adjusting the pressure distillation conditions described below.

[0019] The crude IPA may contain other components (e.g., water, acetone, 1-propanol). In this case, if the IPA content in the crude IPA is low, the production of purified IPA requires many steps, which is inefficient, and the efficiency of separating and removing butyl formate tends to decrease. Therefore, the IPA content in the crude IPA is preferably 95% or more, and more preferably 99% or more. When the IPA content in the crude IPA is low, it is preferable to remove impurities by a known method before subjecting the crude IPA to the method for producing purified IPA of this embodiment. The IPA content in the crude IPA can be measured by gas chromatography.

[0020] The crude IPA may also contain water. However, if the crude IPA contains a large amount of water, the efficiency of separating and removing butyl formate tends to decrease. For this reason, the method for producing purified IPA of this embodiment may further include a dehydration step in which the crude IPA stock solution containing water is dehydrated to obtain the crude IPA. Therefore, the water content in the crude IPA is preferably 1000 ppm or less, more preferably 100 ppm or less, and even more preferably 1 to 50 ppm. Methods for dehydrating the crude IPA stock solution containing water include distillation, adsorption, and membrane permeation. The water content in the crude IPA can be measured by the Karl Fischer method.

[0021] <Method for Preparing Crude IPA> The crude IPA stock solution is not particularly limited. Hereinafter, a method for preparing crude IPA in the case where IPA waste liquid is used as the crude IPA stock solution will be described in detail. Note that a liquid obtained by diluting IPA waste liquid with water may also be used as the crude IPA stock solution.

[0022] <IPA waste liquid> IPA waste liquid is often discharged from various industrial facilities for the production and use of paints and inks, and recovered liquids from these can also be used without any restrictions, but the most suitable is waste liquid recovered from a semiconductor manufacturing apparatus equipped with a semiconductor substrate rinsing section. In particular, waste liquid recovered from a semiconductor substrate rinsing section is likely to have a composition suitable for producing purified IPA and is therefore preferably used. In addition, the IPA waste liquid may also contain developing solutions, pre-wetting solutions, etching solutions, cleaning solutions, stripping solutions, drying solutions, and the like discharged from semiconductor manufacturing apparatuses.

[0023] The IPA content in the IPA waste liquid is preferably 5% by mass or more and 95% by mass or less, more preferably 10 to 80% by mass, and particularly preferably 15 to 30% by mass. On the other hand, the water content in the IPA waste liquid is preferably less than 95% by mass, more preferably 20 to 90% by mass, and particularly preferably 70 to 85% by mass. If the IPA waste liquid has a high water content, the equipment required will be large, and transportation costs will tend to increase.

[0024] IPA waste liquid may contain formate ions, butyl formate, and 1-butanol. The ratio of the total amount of formate ions, butyl formate, and 1-butanol to IPA in the IPA waste liquid is preferably 100 to 1,000,000 ppb, more preferably 1,000 to 100,000 ppm. When the ratio of the total amount of formate ions, butyl formate, and 1-butanol to IPA in the IPA waste liquid is within the above range, the effect of separating and removing butyl formate is significantly exhibited. Possible causes of contamination with butyl formate and 1-butanol include, for example, use in a pre-processing step of a semiconductor cleaning process or contamination as an impurity such as butyl acetate. Possible causes of contamination with formate ions include, for example, use in a pre-processing step of a semiconductor cleaning process or contamination as an impurity in acetic acid or methanol. In addition, IPA waste liquid is usually not controlled for air contamination, and formic acid may be generated due to oxygen in the air. It is known that when IPA comes into contact with air, formic acid is produced, and in particular, formic acid is easily produced in the presence of water.

[0025] The IPA waste liquid may further contain low-boiling impurities with boiling points lower than that of IPA, such as olefins such as butene, pentene, and hexene, alkanes such as butane, pentane, and hexane, aldehydes such as formaldehyde, acetaldehyde, and propylene aldehyde, ketones such as acetone and butanone, alcohols such as methanol, ethanol, and 2-methyl-2-propanol, chloroalkanes such as dichloromethane, chloroform, carbon tetrachloride, and vinyl chloride, and silylated alcohols such as trimethylsilylated IPA and trimethylsilylated ethanol. The ratio of the total amount of low-boiling impurities to IPA in the IPA waste liquid is preferably 0.1 to 10,000 ppm, and more preferably 1 to 100 ppm.

[0026] Furthermore, the IPA waste liquid may further contain high-boiling impurities having a boiling point higher than that of IPA. Specifically, in the case of semiconductor chemical waste liquid, particularly cleaning liquid or drying liquid waste liquid, the IPA waste liquid may contain 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 crotonaldehyde and 2-pentanone, alcohols such as 1-propanol, 2-butanol, and 1-butanol, 1-methoxy- They often further contain high-boiling impurities such as ethers such as 2-propanol, 1-(2-methoxypropoxy)propan-2-ol, and 1-(2-methoxy-2-methylethoxy)-2-propanol; aromatics such as toluene and xylene (ortho, meta, para); alkanes such as octane, decane, and hexadecane; carboxylic acid esters such as isopropyl acetate and isopropyl propionate; phthalic acid esters such as dioctyl phthalate and dibutyl phthalate; and adipic acid esters such as dioctyl adipate.

[0027] <Method for Dehydrating IPA Waste Liquid> When a large amount of water is contained in the IPA waste liquid, it is preferable to dehydrate the IPA waste liquid. Specifically, the IPA waste liquid is distilled, and a distillate containing an azeotropic mixture of IPA and water is withdrawn from the top of a high-boiling distillation column. The distillate is then azeotropically distilled, and a bottom product containing IPA is withdrawn to obtain crude IPA. At this time, low-boiling impurities and a portion of high-boiling impurities can also be separated and removed.

[0028] <Method for Removing Low-Boiling-Point Impurities and High-Boiling-Point Impurities from IPA Waste Liquid> When IPA waste liquid contains low-boiling-point impurities and high-boiling-point impurities, it is preferable to distill the IPA waste liquid to extract a first bottoms product containing IPA and water, and then distill the second bottoms product containing IPA extracted by removing the water from the first bottoms product as described above to obtain crude IPA as a bottoms product. By distilling the crude IPA under pressure, it is possible to remove impurities to a high degree.

[0029] In this case, the ratio of butyl formate to IPA in the second bottoms may be higher than the ratio of butyl formate to IPA in the first bottoms. This is presumably due to butyl formate being generated during the removal of water from the first bottoms. That is, when formate ions and 1-butanol are contained in the IPA waste liquid, it is presumed that butyl formate is generated through dehydration condensation of the formate ions and 1-butanol. From the viewpoint of reducing the ratio of butyl formate to IPA in the purified IPA as much as possible, the ratio of formate ions to IPA in the IPA waste liquid is preferably 10 to 100,000 ppb, more preferably 100 to 10,000 ppb. Furthermore, the ratio of 1-butanol to IPA in the IPA waste liquid is preferably 10 to 100,000 ppb, more preferably 100 to 10,000 ppb.

[0030] The ratio of formate ions to IPA in the IPA waste liquid can be measured by ion chromatography, and the ratios of butyl formate and 1-butanol to IPA in the IPA waste liquid can be measured by GC / MS.

[0031] Crude IPA can be prepared by the above method.

[0032] <Pressure Distillation of Crude IPA> In the method for producing purified IPA according to this embodiment, crude IPA is distilled under pressure. Specifically, crude IPA is distilled under pressurized conditions where the absolute pressure is equal to or greater than atmospheric pressure. Because butyl formate has a higher boiling point than IPA, it can be extracted as bottoms if azeotropy does not occur during distillation. Figures 1A and 1B are graphs showing the molar fractions of liquid-phase IPA (X-axis) and gas-phase IPA (Y-axis) at various pressures. Here, when a mixture of IPA and butyl formate is distilled, a two-component vapor-liquid equilibrium is reached, resulting in a sum of the molar fractions equal to 1. When the pressure (absolute pressure) is 101 kPa, when the IPA molar fraction is 0.96 or greater, it overlaps with the diagonal line (the line where the liquid and gas phase IPA molar fractions are the same) (see Figure 1B). This indicates that the concentrations of IPA and butyl formate in the liquid and gas phases are the same. Thus, when the pressure (absolute pressure) is 101 kPa, butyl formate and IPA form an azeotrope, making it difficult to separate and remove butyl formate from crude IPA.

[0033] On the other hand, when the pressure (absolute pressure) is 200 kPa and 300 kPa (see FIG. 1B), butyl formate and IPA do not form an azeotrope, and butyl formate can be extracted as the bottoms during pressure distillation. The absolute pressure during pressure distillation is preferably 120 to 1000 kPa, more preferably 150 to 800 kPa, and even more preferably 200 to 500 kPa. If the absolute pressure during pressure distillation is less than 120 kPa, butyl formate cannot be sufficiently separated and removed, and if it exceeds 1000 kPa, the equipment becomes expensive. The temperature during pressure distillation can be appropriately set based on the boiling point of IPA at the desired absolute pressure. For example, the boiling point of IPA when the absolute pressure is 200 kPa is approximately 100°C.

[0034] The pressure distillation column may be either a plate column or a packed column, but is preferably a plate column. The number of theoretical plates in the pressure distillation column is preferably 10 to 200, more preferably 20 to 100. Examples of the 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 the column and packing materials include iron, stainless steel, Hastelloy, borosilicate glass, quartz glass, and fluororesins (e.g., polytetrafluoroethylene).

[0035] In the pressure distillation column, the number of theoretical plates to the bottom of the column is preferably 5 or more, and the number of theoretical plates to the top of the column is preferably 5 or more. In calculating the number of theoretical plates to be fed, the bottom and top of the column are not included in the number of theoretical plates. It is preferable to confirm the total number of theoretical plates of the pressure distillation column by actually operating the column and analyzing the composition.

[0036] It is preferable to reflux a portion of the purified IPA distilled off from the top of the pressure distillation column, and extract the remainder of the purified IPA as a distillate. That is, the reflux ratio (reflux amount / distillate amount) is preferably 1.1 to 100, more preferably 1.2 to 10, and even more preferably 1.5 to 5. By adjusting the reflux ratio, the number of theoretical plates, and the absolute pressure, it is possible to separate and remove butyl formate while minimizing the amount of IPA extracted from the bottom of the column, thereby obtaining purified IPA with reduced butyl formate as a high-boiling impurity. The ratio of butyl formate to IPA in the purified IPA is preferably 100 ppb or less, more preferably 10 ppb or less, and even more preferably 0.1 ppb or less.

[0037] In the method for producing purified IPA of the present embodiment, the pressure distillation step is preferably carried out as the final distillation step when other distillation steps are included.

[0038] In the pressure distillation step in the method for producing purified IPA according to the present embodiment, it is possible to remove butyl formate and high-boiling impurities contained in crude IPA that have a boiling point higher than that of IPA. The high-boiling impurities are not particularly limited as long as they have a boiling point higher than that of IPA. Examples of high-boiling impurities include 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 having 4 to 8 carbon atoms such as 2-pentanone, 3-methyl-2-pentanone, 4-methyl-2-pentanone, butanal, 3-methylbutanal, and 3-methylpentanal; 1-propanol, 1-butanol, 2-butanol, 1-pentanol, 2-pentanol, 2-methyl-3-pentanol, and 3-methyl-3-pentanol. Examples of suitable solvents include alcohols having 3 to 8 carbon atoms, such as ethanol, 1-methyl-2-pentanol, 1-heptanol, 2-methylhexanol, 1-octanol, and 2-methylheptanol, ethers such as 1-methoxy-2-propanol, 1-(2-methoxypropoxy)propan-2-ol, and 1-(2-methoxy-2-methylethoxy)-2-propanol, alkanes having 8 to 20 carbon atoms, such as octane, decane, and hexadecane, carboxylic acid esters, such as isopropyl acetate, isopropyl propionate, isopropyl formate, and butyl formate, phthalates, such as dioctyl phthalate and dibutyl phthalate, and adipates, such as dioctyl adipate. According to the method for producing purified IPA of this embodiment, it is possible to remove high-boiling impurities to a high degree.

[0039] The high boiling impurities thus extracted from the bottom of the column are discharged to the outside of the system, and the high concentration impurities are separated and may be used for other purposes or may be reused as fuel or the like.

[0040] <Other Steps> The purified IPA may be further purified, as necessary, by adsorption, etc. For example, the purified IPA may be filtered to remove metal particles, inorganic particles, organic particles, etc., or may be treated with an ion exchange resin to remove metal ions, etc.

[0041] 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. The content of impurities in the samples was analyzed by the following method.

[0042] (Method for measuring water content in a sample) Instrument: Karl Fischer moisture meter CA-200 (manufactured by Mitsubishi Chemical Analytical). When the water content of the sample was expected to exceed 1%, the sample was diluted with IPA and the water content of the diluted sample was measured. The water content of the IPA used for dilution was measured in advance and confirmed to be 100 ppm or less. When the water content of the sample was expected to be 1% or less, the water content of the sample was measured without dilution. Note that if the water content of the sample is higher than expected, it will simply take longer to measure but will not affect the measured value. Furthermore, when the water content of the sample is 100 ppm or less, it is preferable to collect 5 g or more of the sample with a thermosyringe in a glove box with a dew point of -60°C or less and measure the water content of the sample. This analytical method is capable of quantifying water content in samples with a water content of 1 ppm or more.

[0043] (Method for Measuring the Ratio of Butyl Formate to IPA in a Sample) <A: When the Water Content of the Sample is 1% by Mass or More> After the water content of the sample was adjusted to 95% by mass, the ratio of butyl formate to IPA in the sample was analyzed by headspace gas chromatography mass spectrometry (HS / GC / MS). This analytical method can also be used to analyze 1-butanol, trimethylsilylated IPA, and other compounds with high sensitivity. The lower detection limits of this analytical method were 1 ppb for butyl formate, 1-butanol, and trimethylsilyl IPA, respectively. The SIM value can be arbitrarily set for each compound to be quantified.

[0044] -Measurement conditions- Apparatus: Gas chromatograph mass spectrometer (GC / MS) 8890, 5977B (manufactured by Agilent Technologies), headspace sampler 8697 (manufactured by 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 a further 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 (selective ion detection): 56 (butyl formate, 1-butanol), 117 (trimethylsilylated IPA) Solvent heating temperature (headspace): 60°C Solvent heating time (headspace): 15 minutes <B: When the water content in the sample is less than 1% by mass> The ratio of butyl formate to IPA in the sample was measured by gas chromatography-mass spectrometry (GC / MS). This analytical method can also be used to analyze 1-butanol, trimethylsilylated IPA, and other compounds with high sensitivity. The detection limits of this analytical method were 0.1 ppb for butyl formate, 0.1 ppb for 1-butanol, and 0.1 ppb for trimethylsilylated IPA.

[0045] The SIM value can be arbitrarily set for each compound to be quantified. Because butyl formate forms an azeotrope with IPA, it is difficult to further lower the detection limit by a concentration method under atmospheric pressure. As in the method for producing purified IPA of this embodiment, by concentrating under pressurized conditions or using an adsorbent that easily adsorbs low-polarity substances, such as activated carbon, the detection limit can be further lowered, even to 1 ppt or less.

[0046] -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) (J&W Scientific) Column temperature: Maintain at 30°C for 15 minutes, then increase the temperature to 250°C at 20°C / min and maintain 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): 56 (butyl formate, 1-butanol), 117 (trimethylsilylated IPA)

[0047] (Method for measuring the ratio of formate ions to IPA in a sample) The organic acid ions and various anions contained in a sample were identified and their ratio to IPA evaluated by concentrated ion chromatography using the measurement device and under the measurement conditions shown below.

[0048] Device name: ICS2100 (manufactured by Thermo Fisher Scientific) for anion analysis. Detector: Electrical conductivity detector. Column: IonPacAS18. Flow rate: 1 ml / min. Temperature condition: 30°C. Gradient condition: 2 mM KOH → 15 minutes, 5 mM KOH → 25 minutes, 40 mM KOH → 40 minutes, 40 mM KOH. Concentration column: UTAC-LP2. Injection volume: 20 ml. Detection limit: 10 ppt (formate ions, acetate ions, propionate ions, butyrate ions, isobutyrate ions, fluoride ions, chloride ions, bromide ions, iodide ions, nitrate ions, nitrite ions, sulfate ions).

[0049] Example 1 A 1-inch stainless steel tube was attached to an autoclave (manufactured by Nippon Taiatsu Glass Co., Ltd.), and a stainless steel Helipak (manufactured by Tohto Enji Co., Ltd.) was placed in the SUS tube to a height of 50 cm. The top of the column was cooled with tap water to allow reflux, and a pressure distillation column was installed with a structure that allowed the refluxed liquid to be extracted. 1,000 g of crude IPA, adjusted to a ratio of butyl formate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to IPA of 10,000 ppb, was placed in the autoclave, and refluxed at normal pressure for 30 minutes, and the gas in the system was extracted. Next, the autoclave was sealed, the temperature at the bottom of the column was set to 110°C, and the crude IPA was pressure-distilled. At this time, the absolute pressure when the temperature at the bottom of the column reached 110°C was approximately 280 kPa. In addition, about 10 g of purified IPA was withdrawn as a distillate from the top of the column every 30 minutes, for a total of 100 g, and the ratio of butyl formate to IPA in the purified IPA was analyzed, resulting in a value of 90 ppb. The theoretical number of plates in the pressure distillation column was estimated to be 12.

[0050] Comparative Example 1 Crude IPA was distilled under pressure in the same manner as in Example 1, except that the autoclave was not sealed and the column bottom temperature was set to 83° C. Purified IPA was obtained by analyzing the ratio of butyl formate to IPA in the purified IPA, which was 10,000 ppb.

[0051] Example 2 A simulation of pressure distillation was carried out using process simulation software AspenPlus (manufactured by Aspen Technology).

[0052] Specifically, the bottoms were extracted from the bottom (2 L container) of a pressure distillation column having 80 plates. The pressure distillation column was provided with a condenser at the top (the top plate of the column), and a portion of the purified IPA condensed in the condenser was refluxed to the top of the column, and the remainder of the purified IPA was extracted as a distillate.

[0053] Crude IPA containing 10,000 ppb of butyl formate as an impurity was supplied at 10 L / h to the feedstock stage 30 stages below the top of the pressure distillation column, and the crude IPA was pressure-distilled. The temperature at the top of the column was 93 ° C., and the absolute pressure at the top of the column was 155 kPa. The reflux rate was 2.5 L / h, the reflux ratio was about 1.5, and the distillate was extracted from the condenser at 40 mL / h. Furthermore, the bottoms were extracted at about 10 mL / h so that the liquid volume at the bottom 3 of the column was maintained at about 1.5 L. The ratio of butyl formate to IPA in the purified IPA was analyzed and found to be 10 ppb.

[0054] Example 3 A simulation of pressure distillation was carried out in the same manner as in Example 2, except that the temperature at the top of the column was 101°C and the absolute pressure at the top of the column was 200 kPa. The ratio of butyl formate to IPA in the purified IPA was analyzed and found to be 0.1 ppb or less.

[0055] Example 4 A simulation of pressure distillation was carried out in the same manner as in Example 2, except that the temperature at the top of the column was 110°C and the absolute pressure at the top of the column was 275 kPa. The ratio of butyl formate to IPA in the purified IPA was analyzed and found to be 0.1 ppb or less.

[0056] Example 5 A simulation of pressure distillation was carried out in the same manner as in Example 2, except that the temperature at the top of the column was 85°C and the absolute pressure at the top of the column was 110 kPa. The ratio of butyl formate to IPA in the purified IPA was analyzed and found to be 1000 ppb.

[0057] Example 6: IPA-containing waste liquid was collected from a semiconductor manufacturing device equipped with a semiconductor substrate rinsing section, and three days' worth of the collected waste liquid was stored in a waste liquid receiving tank. The IPA-containing waste liquid had a water content of 80% and an IPA content of 20%, and the impurity ratios relative to the IPA were butyl formate 100 ppb, formate ion 21,000 ppb, 1-butanol 5000 ppb, and trimethylsilylated IPA 5000 ppb, respectively. Water was supplied to the waste liquid receiving tank so that the water content of the IPA-containing waste liquid was 90% and the IPA content was 10%, to obtain a water-content-adjusted solution as a crude isopropyl alcohol stock solution.

[0058] A water content-adjusted liquid 4 was distilled using the low-boiling distillation column 1 shown in FIG. 2, which had 20 theoretical plates, a 2-L container at the bottom 3, and a condenser 2 at the top. The water content-adjusted liquid 4 was supplied to the top of the low-boiling distillation column 1 at a rate of 10 L / h and distilled. At this time, the temperature at the top of the column was 75 to 85 ° C., and the absolute pressure at the top of the column was 101 kPa. The reflux rate was 10 L / h, the reflux ratio was about 1000, and the distillate 5 was discharged from the condenser 2 at a rate of 10 ml / h and incinerated. Furthermore, a first bottoms solution containing IPA and water was extracted as the bottoms solution 6 at a rate of about 10 L / h so that the liquid volume at the bottoms solution 3 was maintained at about 1.5 L.

[0059] The ratio of butyl formate to IPA in the first bottoms was measured and found to be 1 ppb or less, which is below the detection limit, indicating that butyl formate was removed by the low-boiling distillation column.

[0060] The first bottoms were distilled using the same distillation column as the low-boiling distillation column 1 as the high-boiling distillation column. Specifically, the first bottoms were supplied to the raw material feed tray of the high-boiling distillation column and distilled, and a first distillate containing an azeotropic mixture of IPA and water (mass ratio 87.5:12.5) was withdrawn from the top of the column.

[0061] The first distillate was fed to the feed tray of an azeotropic distillation column and subjected to azeotropic distillation. Benzene was used as an entrainer, and the benzene and water distilled from the top of the column were separated. The water was discharged, and the benzene was returned to the azeotropic distillation column. A second bottoms product containing IPA and having a water content of 100 ppm or less was withdrawn from the bottom of the column.

[0062] The ratio of butyl formate to IPA in the second bottoms was measured and found to be 1000 ppb. This is presumably due to the formation of butyl formate during the removal of water from the first bottoms. Furthermore, the ratio of trimethylsilylated IPA to IPA in the second bottoms was measured and found to be 2500 ppb.

[0063] The same distillation column as low-boiling distillation column 1 was used as the low-boiling distillation column, and the second bottoms were distilled. Low-boiling impurities were withdrawn from the top of the column, and crude IPA from which low-boiling impurities had been removed was obtained as the bottoms from the column. The ratio of butyl formate to IPA in the crude IPA was measured to be 1000 ppb. The ratio of trimethylsilyl IPA to IPA in the crude IPA was measured to be less than 1 ppb, below the lower detection limit.

[0064] Except for using the obtained crude IPA, the crude IPA was distilled under pressure and a second distillate was extracted in the same manner as in Example 1. The ratio of butyl formate to IPA in the second distillate was analyzed and found to be 8 ppb.

[0065] The second distillate was filtered through four filters: a 100 nm pore size filter, a 10 nm pore size filter, a cation exchange filter, and a 2 nm pore size filter (manufactured by Entegris) to obtain purified IPA. The ratios of impurities to IPA in the purified IPA were butyl formate 8 ppb, formate ion 0.5 ppb, 1-butanol 2 ppb, and trimethylsilyl IPA less than 0.1 ppb, respectively.

[0066] 1: Low boiling point distillation column 2: Condenser 3: Column bottom 4: Water content adjusting liquid 5: Distillate 6: Bottoms

Claims

1. A method for producing purified isopropyl alcohol from crude isopropyl alcohol containing butyl formate as an impurity, comprising a pressure distillation step of pressure-distilling the crude isopropyl alcohol.

2. The method for producing purified isopropyl alcohol according to claim 1, wherein the ratio of butyl formate to isopropyl alcohol in the crude isopropyl alcohol is 10 ppb by mass or more and 100,000 ppb by mass or less.

3. The method for producing purified isopropyl alcohol according to claim 1 or 2, wherein the crude isopropyl alcohol is pressure-distilled under conditions in which the absolute pressure is 120 kPa or more and 1000 kPa or less.

4. The method for producing purified isopropyl alcohol according to claim 1, further comprising a dehydration step of dehydrating a stock solution of crude isopropyl alcohol containing formate ions, 1-butanol, and water to obtain the crude isopropyl alcohol.

5. The method for producing purified isopropyl alcohol according to claim 4, wherein the ratio of formate ions to isopropyl alcohol in the crude isopropyl alcohol stock solution is 10 ppb by mass or more and 100,000 ppb by mass or less.

6. The method for producing purified isopropyl alcohol according to claim 4 or 5, wherein the ratio of 1-butanol to isopropyl alcohol in the raw solution of crude isopropyl alcohol is 10 ppb by mass or more and 100,000 ppb by mass or less.

7. The method for producing purified isopropyl alcohol according to claim 4, wherein the raw solution of crude isopropyl alcohol is a waste liquid recovered from a semiconductor manufacturing device.

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