How is purified isopropyl alcohol produced?

Abstract

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

Description

[Technical field]

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

[0002] Isopropyl alcohol (hereinafter also abbreviated as "IPA") has the property of dissolving both water and organic solvents, and is widely used as a paint solvent, ink solvent, and various synthetic raw materials. Furthermore, high-purity IPA is used in large quantities in the rinsing section of semiconductor substrates in semiconductor manufacturing equipment, and its usage is expected to increase in the future. Distillation purification is known as a method of purifying crude IPA to produce high-purity IPA. (See Non-Patent Document 1)

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

[0004] Incidentally, the semiconductor substrate rinsing section is generally provided adjacent to the rear stage of the semiconductor substrate cleaning section. Since ultrapure water or a highly water-containing liquid is usually used as the cleaning liquid used in the semiconductor substrate cleaning section, the semiconductor substrate rinsing section performs an operation to remove the moisture attached to the surface of the semiconductor substrate in the semiconductor substrate cleaning section. Therefore, the IPA waste liquid recovered from the semiconductor substrate rinsing section becomes a low water-containing liquid. In addition, IPA is also used in large quantities in the developing section and the pre-wet section of the semiconductor manufacturing equipment, and further, water is often used for various purposes in the semiconductor manufacturing equipment. Therefore, an IPA water-containing waste liquid is discharged from a semiconductor manufacturing equipment equipped with a semiconductor substrate rinsing section. For example, Patent Document 2 assumes that the water content of the IPA water-containing waste liquid is about 5 mass%. As a method for recovering IPA from such an IPA water-containing waste liquid, for example, Patent Document 3 proposes distilling and purifying an IPA water-containing waste liquid having a water content of 5 to 15%. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-144410 A [Patent Document 2] JP 2014-55120 A [Patent Document 3] China Patent Publication No. 112999679 [Non-patent literature]

[0006] [Non-Patent Document 1] Organic Synthesis, Vol. 35, No. 9, 1977, pp. 762-766 Summary of the Invention [Problem to be solved by the invention]

[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 the solvent components of photoresist materials used in the developing section and the solvent components of adhesives used for various purposes. Therefore, the IPA waste liquid discharged from 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 pure purified IPA from crude IPA containing butyl formate as an impurity. [Means for solving the problem]

[0009] In view of the above problems, the present inventors have investigated the separation and removal of butyl formate by distillation purification of crude IPA, and as a result, have found that it is difficult to produce purified IPA. Specifically, when the crude IPA does not contain water but contains butyl formate, an azeotropic mixture of butyl formate and IPA is obtained, so that it is difficult to separate and remove butyl formate even when distilled under non-pressurized conditions. On the other hand, when the crude IPA contains water and butyl formate, it is possible to separate and remove butyl formate as a low-boiling impurity by distillation under non-pressurized conditions. However, since an azeotropic mixture of IPA and water is obtained, azeotropic distillation is necessary, which makes the production of purified IPA complicated. Furthermore, it has been found that when the crude IPA further contains formic acid or 1-butanol, butyl formate is generated again by dehydrating the crude IPA.

[0010] Based on the above findings, the present inventors investigated a method for producing purified IPA when 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 thus completed 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 the above-mentioned one aspect of the present invention, it is preferable to take the following aspect.

[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) subjecting the crude isopropyl alcohol to pressure distillation under conditions in which the absolute pressure is 120 kPa or more and 1000 kPa or less. (3) 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. (4) The ratio of formate ions to isopropyl alcohol in the undiluted solution of the crude isopropyl alcohol 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 raw solution of crude isopropyl alcohol is 10 ppb by mass or more and 100,000 ppb by mass or less. (6) The raw solution of crude isopropyl alcohol is a waste liquid recovered from semiconductor manufacturing equipment. Effect of the Invention

[0013] According to the present invention, it is possible to produce a highly pure purified IPA from a crude IPA containing butyl formate as an impurity. Therefore, it is possible to easily regenerate IPA waste liquid recovered from a semiconductor manufacturing device or the like equipped with a semiconductor substrate rinsing section into high-purity IPA, and the high-purity IPA can be used as a semiconductor chemical, particularly as a semiconductor substrate rinsing liquid, and is of great industrial value. [Brief description of the drawings]

[0014] [Figure 1A]FIG. 1 is a full view of a graph showing the mole fraction of liquid phase IPA and vapor phase IPA versus pressure. [Figure 1B] FIG. 2 is an enlarged view of the range of high mole fractions in a graph showing the mole fractions of liquid-phase IPA and gas-phase IPA at different pressures. [Diagram 2] FIG. 1 is a schematic diagram showing a low boiling point distillation column used in Example 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The method for producing purified IPA of this embodiment is a method for producing purified IPA from crude IPA containing butyl formate as an impurity, and includes a pressurized distillation step of pressurizing and distilling the crude IPA. The details of why butyl formate can be removed to a high degree from crude IPA containing butyl formate as an impurity by the method for producing purified IPA of this embodiment are unclear, but the present inventors speculate as follows. As described above, water and butyl formate may be contained in the IPA waste liquid discharged from a semiconductor manufacturing device. In this case, it is possible to separate and remove butyl formate by distillation under non-pressurized conditions. On the other hand, if water is not contained in the IPA waste liquid, even if it is distilled under non-pressurized conditions, it is impossible to separate and remove butyl formate because it becomes an azeotrope of butyl formate and IPA. On the other hand, if it is above the boiling point of IPA, particularly above 100°C, the saturated vapor pressure difference between IPA and butyl formate becomes large, and it becomes difficult to form an azeotrope of butyl formate and IPA. For this reason, it is speculated that if it is distilled under pressurized conditions, it is possible to separate and remove butyl formate without forming an azeotrope of butyl formate and IPA.

[0016] In this specification, unless otherwise specified, the notation "A to B" for the numerical values ​​A and B means "A or more and B or less." In addition, in such notation, when a unit is added only to the numerical value B, the unit is also applied to the numerical value A. In the following description, unless otherwise specified, the concentrations "ppm," "ppb," and "ppt" are all based on mass, including 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 the present embodiment, crude IPA containing butyl formate as an impurity is distilled under pressure. Butyl formate has a boiling point of about 106° C. at normal pressure. The crude IPA is not particularly limited, and may be a reaction product obtained by reacting propylene with water by a propylene process, a reaction product obtained by reducing acetone, or an 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, it is possible to remove butyl formate by adjusting the pressure distillation conditions described later.

[0019] The crude IPA may contain other components (e.g., water, acetone, 1-propanol). In this case, if the content of IPA 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 content of IPA in the crude IPA is preferably 95% or more, and more preferably 99% or more. When the content of IPA 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 content of IPA in the crude IPA can be measured by gas chromatography.

[0020] In addition, water may be contained in the crude IPA. However, when a large amount of water is contained in the crude IPA, the separation and removal efficiency of butyl formate tends to decrease. Therefore, the method for producing purified IPA according to this embodiment may further include a dehydration step of dehydrating a stock solution of crude IPA containing water to obtain crude IPA. Accordingly, 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. Examples of the method for dehydrating the stock solution of crude IPA 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 stock solution of crude IPA is not particularly limited. Hereinafter, the method for preparing crude IPA when using IPA waste liquid as the stock solution of crude IPA will be described in detail. Note that, as the stock solution of crude IPA, a solution obtained by diluting the IPA waste liquid with water may be used.

[0022] <IPA waste liquid> IPA waste liquid is often discharged from various industrial facilities such as the production and use of paints and inks, and these recovered liquids can also be applied without limitation. However, the most suitable is the waste liquid recovered from a semiconductor manufacturing apparatus equipped with a rinse section for a semiconductor substrate. In particular, the waste liquid recovered from the rinse section of a semiconductor substrate is likely to have a composition suitable for the production of purified IPA and is preferably applied. In addition, the IPA waste liquid may contain a developing solution, a pre-wet solution, an etching solution, a cleaning solution, a stripping solution, a drying solution, etc. discharged from a semiconductor manufacturing apparatus.

[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. When the water content in the IPA waste liquid is high, the equipment tends to be huge and the transportation cost increases.

[0024] The 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. The cause of contamination with butyl formate and 1-butanol may be, for example, use in a pre-process of a semiconductor cleaning process, or contamination as an impurity such as butyl acetate. In addition, the cause of contamination with formate ions may be, for example, use in a pre-process of a semiconductor cleaning process, or contamination as an impurity of acetic acid or methanol. In addition, the 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 IPA produces formic acid when exposed to air, and formic acid is particularly likely to be produced in the presence of water.

[0025] The IPA waste liquid may further contain low-boiling impurities having a boiling point 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, 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 waste liquid of semiconductor chemicals, particularly waste liquid of cleaning liquid or waste liquid of drying liquid, the IPA waste liquid contains metals such as iron, chromium, nickel, copper, zinc, sodium, potassium, calcium, magnesium, carboxylic acids such as formic acid, acetic acid, propionic acid, salts having anions such as nitrate ion, nitrite ion, sulfate ion, chloride ion, fluoride ion, aldehyde-ketones such as crotonaldehyde, 2-pentanone, alcohols such as 1-propanol, 2-butanol, 1-butanol, ethers such as 1-methoxy-2-propanol, 1-(2-methoxypropoxy)propan-2-ol, 1-(2-methoxy-2-methylethoxy)-2-propanol, aromatics such as toluene, xylene (ortho, meta, para), alkanes such as octane, decane, hexadecane, carboxylic acid esters such as isopropyl acetate, isopropyl propionate, phthalic acid esters such as dioctyl phthalate, dibutyl phthalate, adipic acid esters such as dioctyl adipate, etc., and often further contains high-boiling impurities.

[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 after extracting a distillate containing an azeotropic mixture of IPA and water from the top of a high-boiling distillation column, the distillate is subjected to azeotropic distillation, and a bottoms liquid containing IPA is extracted to obtain crude IPA. At this time, a part of the low-boiling impurities and high-boiling impurities can also be separated and removed.

[0028] <Method for removing low-boiling impurities and high-boiling impurities in IPA waste liquid> When the IPA waste liquid contains low-boiling impurities and high-boiling impurities, the IPA waste liquid is distilled to extract a first bottoms liquid containing IPA and water, and then the water in the first bottoms liquid is removed as described above, and the second bottoms liquid containing the extracted IPA is distilled to obtain crude IPA as the bottoms liquid. By subjecting the crude IPA to pressure distillation, it is possible to highly remove impurities.

[0029] At this time, the ratio of butyl formate to IPA in the second bottoms may be greater than the ratio of butyl formate to IPA in the first bottoms. This is presumably because butyl formate is generated during removal of water from the first bottoms. That is, when the IPA waste liquid contains formate ions and 1-butanol, it is presumed that butyl formate is generated by 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. In addition, 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. 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 method described above.

[0032] <Pressure distillation of crude IPA> In the method for producing purified IPA of this embodiment, crude IPA is distilled under pressure. Specifically, crude IPA is distilled under a pressurized condition where the absolute pressure is equal to or higher than atmospheric pressure. Since butyl formate has a higher boiling point than IPA, it can be extracted as a bottom product 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) for each pressure. Here, when a mixture of IPA and butyl formate is distilled, the sum of the molar fractions is 1 because it is a two-component gas-liquid equilibrium. When the pressure (absolute pressure) is 101 kPa, when the molar fraction of IPA is 0.96 or more, it overlaps with the diagonal line (the line where the molar fractions of IPA in the liquid phase and the gas phase are the same) (see Figure 1B). That is, it shows that the concentrations of IPA and butyl formate in the liquid phase and the gas phase 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 the 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 may be appropriately set at 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 about 100°C.

[0034] The pressure distillation tower may be either a plate tower or a packed tower, but is preferably a plate tower. The theoretical number of plates of the pressure distillation tower is preferably 10 to 200 plates, more preferably 20 to 100 plates. Examples of the plates in the plate tower include cross-flow trays and shower trays. Examples of the packing in the packed tower include Raschig rings and Lessing rings. Examples of the materials of the tower and packing include iron, stainless steel, Hastelloy, borosilicate glass, quartz glass, and fluororesin (e.g., polytetrafluoroethylene).

[0035] In the pressurized distillation tower, the number of theoretical plates of the raw material supply stage to the bottom of the tower is preferably 5 or more, and the number of theoretical plates to the top of the tower is preferably 5 or more. In addition, in the calculation of the raw material supply stage, the bottom and the top of the tower are not included in the theoretical plates. It is preferable to confirm the total theoretical plates of the pressurized distillation tower by actually operating it and analyzing the composition.

[0036] It is preferable to reflux a part of the purified IPA distilled off from the top of the pressure distillation tower, and extract the remaining part 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 becomes possible to separate and remove butyl formate while reducing the amount of IPA extracted from the bottom of the tower as much as possible, and it becomes possible to obtain 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 of the present embodiment, it is possible to remove butyl formate and high-boiling impurities having a higher boiling point than IPA contained in the crude IPA. The high-boiling impurities are not particularly limited as long as they have a higher boiling point than IPA, but 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-pentanal. Examples of the solvent 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, phthalic acid esters, such as dioctyl phthalate and dibutyl phthalate, and adipic acid esters, such as dioctyl adipate. According to the method for producing purified IPA of the present embodiment, it is possible to highly remove high-boiling impurities.

[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 utilized for other purposes or may be reused as fuel or the like.

[0040] <Other processes> The purified IPA may be further purified by adsorption or the like as necessary. For example, the purified IPA may have metal particles, inorganic particles, organic particles, etc. removed by filter filtration, or metal ions, etc. removed by an ion exchange resin or the like.

Examples

[0041] Examples of the present invention will be described below, but the present invention is not limited to the examples. In these examples, % and ppm are based on mass unless otherwise specified. Also, the content of impurities in the sample was analyzed by the following method.

[0042] (Method for measuring the water content in the sample) Equipment: Karl Fischer moisture meter CA-200 (manufactured by Mitsubishi Chemical Analytic) When it is assumed that the water content in the sample exceeds 1%, the sample was diluted with IPA, and then the water content in the diluted sample was measured. The water content in the IPA used for dilution was measured in advance and confirmed to be 100 ppm or less. When it is assumed that the water content in the sample is 1% or less, the water content in the sample was measured without dilution. Also, if the water content in the sample is more than assumed, it only takes more time for the measurement and does not affect the measured value. Further, when the water content in the sample is 100 ppm or less, it is preferable to collect 5 g or more of the sample with a Terumo syringe in a glove box with a dew point of -60°C or lower and measure the water content in the sample. This analysis method can be quantified if the water content in the sample is 1 ppm or more.

[0043] (Method for measuring the ratio of butyl formate to IPA in the sample) <A: When the water content in the sample is 1 mass% or more> After setting the water content in the sample 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). In addition, this analytical method can also analyze 1-butanol, trimethylsilylated IPA, etc. with high sensitivity. The detection limits of this analytical method were 1 ppb for butyl formate, 1 ppb for 1-butanol, and 1 ppb for trimethylsilylated IPA. The SIM values can be arbitrarily set for each compound to be quantified.

[0044] -Measurement conditions- Equipment: 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 Scientifuic) Column temperature: Maintained at 30 °C for 15 minutes, then heated at 20 °C / min to 250 °C, and further maintained at 250 °C for 10 minutes. Column flow rate: 1.4 ml / min Inlet pressure: 8.4 psi Inlet temperature: 200 °C Injection volume: 1 mL (vial gas phase part in the headspace method) Ion source temperature: 230 °C Quadrupole temperature: 150 °C SIM (Selected 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 samples was measured using gas chromatography mass spectrometry (GC / MS). This analytical method can also analyze other substances such as 1-butanol and trimethylsilylated IPA 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 set arbitrarily for each compound to be quantified. Butyl formate forms an azeotrope with IPA, so it is difficult to further lower the detection limit by a concentration method at normal pressure. As in the method for producing purified IPA of this embodiment, by concentrating under pressurized conditions or using an adsorbent that easily adsorbs substances with low polarity, such as activated carbon, the detection limit can be further lowered, and it is also possible to make it 1 ppt or less.

[0046] -Measurement conditions- Equipment: 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: After maintaining at 30°C for 15 minutes, the temperature is increased to 250°C at 20°C / min, and then maintained at 250°C for 10 minutes. Column flow rate: 1.4 ml / min Inlet pressure: 8.4psi Inlet temperature: 200℃ Injection volume: 5μL Ion source temperature: 230℃ Quadrupole temperature: 150℃ SIM (selected ion detection): 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 the samples were identified and their ratios to IPA were evaluated by concentrated ion chromatography using the measurement equipment and conditions shown below.

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

[0049] <Example 1> A 1-inch SUS tube was attached to an autoclave (made by Nippon Taiatsu Glass Co., Ltd.), a SUS Helipak (made by Tohto Enji Co., Ltd.) was placed in the SUS tube to a height of 50 cm, the top of the tower was cooled with tap water, and a pressurized distillation tower was installed with a structure that allowed the refluxed liquid to be extracted. 1000 g of crude IPA, which had been adjusted so that the ratio of butyl formate (made by Fujifilm Wako Pure Chemical Industries, Ltd.) to IPA was 10,000 ppb, was placed in the autoclave, and refluxed at normal pressure for 30 minutes to extract the gas in the system. Next, the autoclave was sealed, the temperature of the tower bottom was set to 110°C, and the crude IPA was distilled under pressure. At this time, the absolute pressure when the temperature of the tower bottom reached 110°C was about 280 kPa. In addition, about 10 g of purified IPA was extracted from the top of the tower as a distillate every 30 minutes, and a total of 100 g was extracted. The ratio of butyl formate to IPA in the purified IPA was analyzed and found to be 90 ppb. The theoretical number of plates in the pressure distillation column was estimated to be 12.

[0050] <Comparative Example 1> The crude IPA was distilled under pressure in the same manner as in Example 1, except that the autoclave was not sealed and the temperature of the column bottom was set to 83° C., to obtain purified IPA. The ratio of butyl formate to IPA in the purified IPA was analyzed and found to be 10,000 ppb.

[0051] <Example 2> A simulation of pressurized distillation was performed 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 tower with 80 plates. The pressure distillation tower was provided with a condenser at the top (top plate) of the tower, and a portion of the purified IPA condensed in the condenser was refluxed to the top of the tower, 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 fed at 10 L / h to the feed tray 30 trays below the top of the pressure distillation tower, and the crude IPA was pressure-distilled. At this time, the temperature of the top of the tower was 93°C, and the absolute pressure of the top of the tower was 155 kPa. The reflux amount 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 from the bottom of the tower at about 10 mL / h so that the liquid volume at the bottom 3 of the tower 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 pressurized distillation was carried out in the same manner as in Example 2, except that the temperature at the top of the column was set to 101° C. and the absolute pressure at the top of the column was set to 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 pressurized distillation was carried out in the same manner as in Example 2, except that the temperature at the top of the column was set to 110° C. and the absolute pressure at the top of the column was set to 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 pressurized 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 aqueous waste liquid was collected from a semiconductor manufacturing device equipped with a semiconductor substrate rinse section, and three days' worth of it was stored in a waste liquid receiving tank. The IPA aqueous waste liquid had a water content of 80% and an IPA content of 20%, and the ratios of impurities to 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 aqueous waste liquid was 90% and the IPA content was 10%, and a water content-adjusted solution was obtained as a stock solution of crude isopropyl alcohol.

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

[0059] When the ratio of butyl formate to IPA in the first bottoms was measured, it was found to be less than 1 ppb, which is below the detection limit, indicating that butyl formate was removed by the low boiling point 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 supply tray of the high boiling distillation column and distilled, and the first distillate containing an azeotropic mixture of IPA and water (mass ratio 87.5:12.5) was extracted from the top of the column.

[0061] The first distillate was fed to the feed tray of the azeotropic distillation column and azeotropically distilled. At this time, 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. The second bottoms, which contained IPA and had a water content of 100 ppm or less, were extracted 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. 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 the low boiling distillation column 1 was used as the low boiling distillation column, and the second bottoms were distilled, low boiling impurities were extracted from the top of the column, and crude IPA from which the low boiling impurities had been removed was obtained as the bottoms from the bottom of 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, which was below the 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 types of filters: a 100 nm pore size filter, a 10 nm pore size filter, a cation exchange filter, and a 2 nm pore size filter (Integris), 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. [Explanation of symbols]

[0066] 1: Low boiling distillation tower 2: Condenser 3: Bottom of the tower 4: Water content adjustment liquid 5: Distillate 6: Canned liquid

Claims

1. A method for producing purified isopropyl alcohol from crude isopropyl alcohol containing butyl formate as an impurity, comprising the steps of: A method for producing purified isopropyl alcohol, 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 an absolute pressure of 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 raw solution of crude isopropyl alcohol 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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