High purity isopropanol and method for making same

Abstract

Provided is high-purity isopropanol in which the concentration of an acetal compound having 7 to 12 carbon atoms is 100 ppb or less on a mass basis, and in the case where an accelerated test is performed in which the isopropanol is heated at 80°C for 4 hours in a nitrogen atmosphere, the increase in the concentration of the acetal compound relative to the value before the heating is within 30 times, and the value is maintained at 100 ppb or less on a mass basis. Also provided is a method for producing high-purity isopropanol as described above.

Description

Technical Field

[0001] This invention relates to high-purity isopropanol and its manufacturing method. Background Technology

[0002] Isopropanol (also known as 2-propanol) is an organic solvent used in a variety of applications. It is manufactured by methods such as hydration, which involves hydrating propylene.

[0003] Typically, isopropanol is manufactured in petrochemical complexes that supply propylene as a feedstock. After production, it is transported to the point of demand and stored in storage tanks. In this way, isopropanol is often stored for a considerable period after production until use. Therefore, the increase in impurities in isopropanol during long-term storage becomes a serious problem.

[0004] In particular, if isopropanol, which has become contaminated with impurities due to long-term storage, is used for cleaning electronic devices such as semiconductor equipment, residues of impurities from the isopropanol may remain on the surface of the electronic devices after cleaning and drying.

[0005] For example, Patent Document 1 describes the following: Organic impurities dissolved in isopropanol condense as isopropanol evaporates, becoming larger particles. These particles remain in the treated body, generating particulate contamination (particulate defects).

[0006] Thus, residues after cleaning and drying become a major cause of defects in electronic devices. Therefore, it is desirable to minimize the concentration of organic impurities in the isopropanol used as a cleaning fluid, especially the concentration of organic impurities with boiling points higher than isopropanol that contribute to the residues after treatment. Furthermore, it is desirable that the organic impurities contributing to the residues after cleaning and drying do not increase even with long-term storage of isopropanol.

[0007] Regarding the increase of impurities during the storage of isopropanol, for example, Patent Document 2 describes the following: by having an electron donor for the peroxide free radical generated by the oxidation reaction of isopropanol present in isopropanol, the oxidative degradation can be highly suppressed, and the ketones generated during the storage of isopropanol can be significantly reduced.

[0008] Furthermore, Patent Document 3 describes removing impurities with higher boiling points than isopropanol by distillation. It also describes removing organic impurities with lower boiling points than isopropanol by distillation in combination with the removal of high-boiling-point impurities. Additionally, Patent Document 3 suggests that these impurities in isopropanol can remain on the wafer during semiconductor manufacturing processes, thus becoming defects.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2016-004902

[0012] Patent Document 2: Japanese Patent Application Publication No. 2016-179956

[0013] Patent Document 3: International Publication No. 01 / 094284 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] However, Patent Document 3 does not specify the exact types of high-boiling-point impurities and low-boiling-point organic impurities, nor does it indicate what substances of these impurities interact to cause adverse conditions in the aforementioned semiconductor applications. Therefore, the removal of organic impurities remains at the level of obtaining isopropanol of general quality, only considering atmospheric distillation performed in typical industrial processes. As a result, the total amount of organic impurities becomes a large amount, ranging from 200 to 500 ppm (see paragraph

[0018] ).

[0016] The inventors of this application conducted research and found that if only electron donors for peroxide radicals are present in isopropanol, there are impurities whose concentration cannot be suppressed from increasing. In particular, it has been found that even when manufacturing and quality control are carried out in a manner that meets the management value of impurities with a boiling point of 120°C or higher required in recent years for isopropanol used in the electronics industry, i.e., a range of 50 ppb or less on a mass basis, the concentration of impurities from organic matter can sometimes increase during transportation and storage.

[0017] Furthermore, the inventors of this application conducted research and found that the impurities from the organic matter mentioned above contain acetal compounds formed by the condensation of aldehyde compounds and alcohol compounds, and these acetal compounds increase over time during storage.

[0018] The objective of this invention is to provide high-purity isopropanol with low concentrations of acetal compounds as impurities, suppression of the time-dependent increase in the concentration of the acetal compounds, and excellent long-term storage stability, as well as a method for manufacturing the same.

[0019] Methods for solving problems

[0020] The inventors of this application conducted in-depth research to solve the aforementioned problems. As a result, they discovered that the above problems could be solved, thus completing the present invention, by not only directly reducing the acetal compounds present as impurities in isopropanol (composition), but also controlling the concentration of aldehyde compounds with 1 to 6 carbon atoms to below 1500 ppb by mass. Furthermore, the inventors of this application also discovered that by controlling the concentration of ketone compounds with 3 to 6 carbon atoms to below 2000 ppb by mass, the concentration of acetal compounds can be reduced more significantly. It is believed that aldehyde compounds with 1 to 6 carbon atoms, or aldehyde compounds and ketone compounds with 3 to 6 carbon atoms, can transform into acetal compounds during storage due to certain influences. By reducing these impurities, the time-dependent increase of acetal compounds can be suppressed, resulting in isopropanol with a low concentration of acetal compounds.

[0021] It was previously believed that aldehydes and ketones with 1 to 6 carbon atoms, especially those with 1 to 3 carbon atoms, generally have lower boiling points than isopropanol and would not remain in the treated material, even when used for cleaning electronic equipment. Therefore, in reality, their content was not strictly regulated; only the amount removed by atmospheric distillation, a common industrial process for removing low-boiling-point organic impurities, was reduced.

[0022] Under these circumstances, the inventors of this application have for the first time successfully discovered isopropanol as described below: by highly removing high-boiling-point organic impurities, the concentration of the acetal compound is reduced to a low concentration of less than 100 ppb by mass, and the substances that cause the formation of the acetal compound during storage are also highly removed, so that even after accelerated testing for long-term storage as envisioned, the concentration of the acetal compound can be maintained at a low concentration of less than 100 ppb by mass.

[0023] The specific means used to solve the above problems include the following implementation methods.

[0024] <1> High-purity isopropanol, wherein the concentration of acetal compounds with 7-12 carbon atoms is below 100 ppb on a mass basis.

[0025] When an accelerated test is conducted under a nitrogen atmosphere and heated at 80°C for 4 hours, the concentration of the aforementioned acetal compound increases by no more than 30 times compared to the value before heating, and remains below 100 ppb on a mass basis.

[0026] <2> According to <1>, the high-purity isopropanol, in which an accelerated test was conducted at 120°C for 4 hours under a nitrogen atmosphere, showed that the concentration of the aforementioned acetal compound increased by no more than 30 times compared to the value before heating, and remained below 100 ppb on a mass basis.

[0027] <3> The high-purity isopropanol according to <1> or <2> contains an aldehyde compound with 1 to 6 carbon atoms at a concentration of less than 1500 ppb on a mass basis.

[0028] <4> The high-purity isopropanol according to any one of <1> to <3>, wherein the concentration of the ketone compound having 3 to 6 carbon atoms is less than 2000 ppb on a mass basis.

[0029] <5> High-purity isopropanol according to any one of <1> to <4>, wherein the water content is 0.1 to 100 ppm by mass.

[0030] <6> High-purity isopropanol according to any one of <1> to <5>, wherein the isopropanol is obtained by direct hydration of propylene.

[0031] The method for producing high-purity isopropanol as described in <7> <1> involves performing the following steps on the crude isopropanol mixture:

[0032] The vacuum distillation process removes low-boiling-point components by vacuum distillation, thereby purifying the compound until the concentration of aldehydes with 1 to 6 carbon atoms is reduced to below 1500 ppb on a mass basis; and

[0033] The atmospheric distillation process uses atmospheric distillation to remove the bottom liquid from the column, thereby purifying the product until the concentration of acetal compounds with 7 to 12 carbon atoms is reduced to below 100 ppb on a mass basis.

[0034] <8> The method for manufacturing high-purity isopropanol according to <7>, wherein in the aforementioned vacuum distillation process, purification is carried out to reduce the concentration of ketone compounds with 3 to 6 carbon atoms to below 2000 ppb by mass.

[0035] <9> The method for producing high-purity isopropanol according to <7> or <8>, wherein the aforementioned crude isopropanol is obtained by direct hydration of propylene.

[0036] Invention Effects

[0037] According to the present invention, a method for producing high-purity isopropanol and a method thereof can be provided, which has a low concentration of acetal compounds as impurities, suppresses the time-dependent increase in the concentration of the acetal compounds, and exhibits excellent long-term storage stability.

[0038] Since acetal compounds have higher boiling points than isopropanol, using isopropanol containing acetal compounds as a cleaning solution may result in residues after cleaning and drying. To address this, the high-purity isopropanol of this invention maintains the concentration of acetal compounds with 7 to 12 carbon atoms at 100 ppb or less by mass, making it particularly suitable for use as a cleaning solution in semiconductor manufacturing processes. Detailed Implementation

[0039] The embodiments of the present invention will now be described in detail. In the following description, including the examples, the terms “%”, “ppm”, and “ppb” indicating concentration are all mass references.

[0040] High-purity isopropanol

[0041] Regarding the high-purity isopropanol involved in this embodiment, the concentration of the acetal compound with 7 to 12 carbon atoms is 100 ppb or less. Furthermore, in the case of an accelerated test conducted by heating at 80°C for 4 hours under a nitrogen atmosphere, the concentration of the aforementioned acetal compound increased by less than 30 times compared to the value before heating, and remained at 100 ppb or less.

[0042] Here, the concentrations of acetal compounds (total concentration of acetal compounds), aldehyde compounds (total concentration of aldehyde compounds), ketone compounds (total concentration of ketone compounds), and water content are based on the total amount of high-purity isopropanol. These concentrations or amounts are determined using the methods described later.

[0043] It should be noted that the high-purity isopropanol involved in this embodiment refers to an isopropanol concentration of 99.99% or higher, preferably 99.999% or higher, expressed as a concentration after water removal using gas chromatography-mass spectrometry (GC / MS).

[0044] (Impurities; acetal compounds)

[0045] The acetal compound in this embodiment is a compound represented by formula (1), which is generated by the condensation of an aldehyde compound with 1 to 6 carbon atoms and a ketone compound with 3 to 6 carbon atoms with an alcohol under an acid catalyst or a base catalyst. For example, an acetal compound with 9 carbon atoms is generated from propionaldehyde and isopropanol.

[0046] [Chemical Formula 1]

[0047]

[0048] (where R is in the formula) 1 and R 2Each can be used independently to represent an alkyl group. R 3 and R 4 Each can independently represent a hydrogen atom or an alkyl group.

[0049] Specific examples of acetal compounds with 7 to 12 carbon atoms include dimethyl acetone, diisopropanol acetone, diisopropanol acetaldehyde, diisopropanol propionaldehyde, diisopropanol butyraldehyde, diisopropanol pentanaldehyde, diisopropanol hexaaldehyde, diisopropanol acetone, diisopropanol butanol, diisopropanol 2-pentanol, and diisopropanol 2-methyl-3-pentanol.

[0050] Regarding the high-purity isopropanol involved in this embodiment, the total concentration of such acetal compounds is 100 ppb or less, preferably 50 ppb or less, and more preferably 20 ppb or less. When using the high-purity isopropanol involved in this embodiment as a cleaning solution in a semiconductor manufacturing process, from the perspective of ensuring that no residue remains on the treated body after cleaning and drying, it is preferable to have as few acetal compounds as possible (i.e., closer to 0 ppb). However, considering the industrial manufacturing, storage, and transportation of isopropanol, the lower limit of the total concentration of acetal compounds is preferably 0.1 ppb, and more preferably 0.5 ppb.

[0051] Regarding the high-purity isopropanol involved in this embodiment, not only is the concentration of acetal compounds with 7 to 12 carbon atoms low (below 100 ppb), but the causative agents of these acetal compounds during storage are also significantly reduced. In an accelerated test conducted under a nitrogen atmosphere at 80°C for 4 hours, the concentration of the aforementioned acetal compounds increased by less than 30 times compared to the value before heating, and remained below 100 ppb. Here, the accelerated test is almost equivalent to the severity of the effect on the increase of acetal compounds experienced by isopropanol when stored at room temperature (25°C) in the dark for 6 months.

[0052] Furthermore, the high-purity isopropanol involved in this embodiment is preferably characterized by an increase in the concentration of the aforementioned acetal compound of less than 30 times compared to the value before heating, and maintained at less than 100 ppb, even after an accelerated test was conducted at 120°C for 4 hours under a nitrogen atmosphere. The property of suppressing the increase of acetal compounds even under such stringent conditions means that even after isopropanol is subjected to high-temperature transport in summer and long-term storage, the concentration of the aforementioned acetal compounds can be suppressed to a low level, which can greatly improve the adverse effects caused by residues when used for cleaning electronic devices such as semiconductor equipment.

[0053] In this embodiment, the increase in the concentration of the acetal compound after the accelerated test is preferably within 10 times, more preferably within 5 times, compared to the value before heating.

[0054] The concentration of the acetal compound after the accelerated test was determined using the following method: 10 mL of high-purity isopropanol was added to approximately 20 mL of stainless steel (SUS) tube, and nitrogen was supplied at a rate of 100 mL / min for 30 minutes to deoxygenate the tube. After deoxygenation, the tube was sealed to prevent oxygen from entering, and then heated in an oil bath at 80°C or 120°C for 4 hours. After the accelerated test, the concentration of the acetal compound in the isopropanol in the SUS tube was measured.

[0055] Even with such rigorous accelerated testing, the acetal properties in isopropanol do not significantly increase. This is achieved by reducing aldehydes with 1 to 6 carbon atoms, or aldehydes combined with ketones with 3 to 6 carbon atoms. Acetals are believed to be formed from aldehydes with 1 to 6 carbon atoms, or aldehydes combined with ketones with 3 to 6 carbon atoms, which are unavoidably present during the manufacture of isopropanol, and their concentration increases over time after manufacture. Therefore, by significantly reducing these specific low-boiling-point organic impurities, the properties described in the accelerated testing can be satisfied.

[0056] (Impurities; aldehydes and ketones)

[0057] In this embodiment, considering the suppression of acetal compound formation, the total concentration of aldehyde compounds with 1 to 6 carbon atoms contained in high-purity isopropanol is preferably 1500 ppb or less, more preferably 500 ppb or less, and even more preferably 150 ppb or less. Furthermore, it is believed that the lower the lower limit of the aldehyde compound concentration, the better the suppression of acetal compound formation; therefore, 0 ppb is preferred. However, considering the industrial production of isopropanol, the lower limit is preferably 1 ppb, more preferably 10 ppb, and even more preferably 50 ppb.

[0058] Furthermore, in this embodiment, considering the suppression of acetal compound formation, the total concentration of ketone compounds with 3 to 6 carbon atoms contained in high-purity isopropanol is preferably 2000 ppb or less, more preferably 1000 ppb or less, and even more preferably 500 ppb or less. Additionally, it is believed that the lower the lower limit of the ketone compound concentration, the better the suppression of acetal compound formation; therefore, 0 ppb is preferred. However, considering the industrial production of isopropanol, the lower limit is preferably 10 ppb, more preferably 50 ppb, and even more preferably 100 ppb. It should be noted that ketone compounds are less likely to transform into acetal compounds than aldehyde compounds, and even at the same concentration, the amount of acetal compound formed is usually less than 1 / 10.

[0059] In this embodiment, it is preferable that the aldehyde compound and the ketone compound do not coexist, and even if they coexist, their concentrations are preferably low.

[0060] Previously, even when aldehydes and ketones (especially aldehydes) were contained in isopropanol, these impurities, which are substances with lower boiling points than isopropanol, were not considered to cause adverse effects, even when used in cleaning solutions. However, according to the research of the inventors of this application, it is known that if the concentration of these compounds, especially aldehydes, is within the aforementioned range, the increase of acetals can be suppressed, and even under accelerated testing, the concentration of the acetal can be easily controlled below 100 ppb. For the same reason, it is preferable to set the concentration of ketones within the aforementioned range.

[0061] As mentioned above, aldehydes are more likely to form acetals than ketones, therefore managing the concentration range of aldehydes is particularly important. Specific examples of aldehydes with 1 to 6 carbon atoms include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, pentanal, 2-methylbutyraldehyde, isovaleraldehyde, and hexanal.

[0062] In addition, specific examples of ketone compounds with 3 to 6 carbon atoms include acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl isopropyl ketone, 4-methyl-2-pentanone, 3-methyl-2-pentanone, 2-methyl-3-pentanone, etc.

[0063] Isopropanol is typically produced by methods such as the acetone reduction method (synthesizing isopropanol by reducing acetone), the indirect hydration method (synthesizing isopropanol by esterification of propylene with concentrated sulfuric acid followed by hydrolysis), and the direct hydration method (synthesizing isopropanol by directly hydrating propylene using a catalyst). In this embodiment, isopropanol obtained using methods and raw materials that readily generate aldehyde compounds is preferred. Specifically, isopropanol produced using the direct hydration method is preferred.

[0064] Isopropanol produced by direct hydration contains, before purification, more than 100 ppb of acetal compounds with 7 to 12 carbon atoms, and approximately more than 300 ppb of acetal compounds with 7 to 12 carbon atoms. It also contains more than 1500 ppb of aldehyde compounds with 1 to 6 carbon atoms, and approximately more than 3000 ppb of aldehyde compounds with 1 to 6 carbon atoms. Furthermore, it contains more than 2000 ppb of ketone compounds with 3 to 6 carbon atoms, and approximately more than 4000 ppb of ketone compounds with 3 to 6 carbon atoms.

[0065] The main reasons for the presence of aldehydes with 1 to 6 carbon atoms and / or ketones with 3 to 6 carbon atoms in isopropanol can be listed as "impurities contained in propylene / acetone, which are raw materials for isopropanol", "byproducts of the synthesis reaction of isopropanol", and "alcohol compounds contained in the manufactured isopropanol".

[0066] For these main reasons, industrially produced isopropanol inevitably contains aldehydes with 1 to 6 carbon atoms and ketones with 3 to 6 carbon atoms.

[0067] For example, ethylene, present as an impurity in the raw material propylene, is oxidized to produce ethanol. It is believed that ethanol is oxidized by dissolved oxygen in isopropanol, transforming into acetaldehyde, which is then contained within isopropanol as an aldehyde compound. Furthermore, it is believed that alcohols such as 1-propanol, 1-butanol, 2-butanol, 2-pentanol, 4-methyl-2-pentanol, 3-methyl-2-pentanol, and 2-methyl-3-pentanol inevitably exist as reaction byproducts, and that propionaldehyde, butyraldehyde, methyl ethyl ketone, methyl propyl ketone, 4-methyl-2-pentanone, 3-methyl-2-pentanone, and 2-methyl-3-pentanone are produced as oxidation products of these alcohols.

[0068] Thus, aldehydes and ketones, being byproducts of the reaction and impurities generated during reaction, purification, and storage oxidation, are present in large quantities in isopropanol, and therefore their concentration ranges have not been strictly controlled to date.

[0069] However, based on the research of the inventors of this application, it is believed that: for example, if isopropanol contains an aldehyde compound, then isopropanol reacts with the aldehyde compound as shown in the following reaction formula, and the acetal compound increases over time. It should be noted that the following reaction formula is in the acetal compound shown in the above formula (1) where R... 1 and R 2 Example when it becomes isopropyl.

[0070] [Chemical Formula 2]

[0071]

[0072] According to the above reaction formula, by managing the concentration of acetaldehyde contained in isopropanol, it is possible to suppress the increase of acetal compounds with 8 carbon atoms.

[0073] In addition, isopropanol contains aldehyde compounds with different numbers of carbon atoms besides acetaldehyde. Therefore, for example, in the reaction of propionaldehyde with 3 carbon atoms and isopropanol, the carbon acetal compound with 9 carbon atoms increases over time.

[0074] Therefore, it is presumed that by controlling the concentration of aldehydes with 1 to 6 carbon atoms in isopropanol within a specific range, the aging effect of acetals can be suppressed. It is believed that R in the above formula (1)... 3 and R 4 In the case of alkyl groups, impurities used as raw materials will become ketone compounds, but in this case, acetal compounds will also increase due to the same reaction mechanism.

[0075] It should be noted that sometimes aldehyde compounds present as impurities condense with each other to form high-boiling-point organic compounds during storage. These condensates may also become residues after cleaning and drying. Therefore, by managing the concentration of aldehyde compounds with 1 to 6 carbon atoms within a specific range, the condensation of aldehyde compounds with each other can be prevented.

[0076] (Other impurities)

[0077] The high-purity isopropanol described in this embodiment may contain other impurities that are unavoidably introduced during manufacturing. Examples of unavoidably introduced impurities include water, organic impurities, and inorganic impurities. Among these, organic impurities are those that are not separated during the distillation process of isopropanol and are thus introduced.

[0078] (water)

[0079] The water content of the high-purity isopropanol involved in this embodiment is preferably 0.1 to 100 ppm. It is believed that water in isopropanol can contribute to residues and watermarks after cleaning and drying, and may also act as a catalyst. Therefore, the water content is preferably 100 ppm or less. On the other hand, it is believed that since the reaction that forms acetal compounds is a dehydration reaction, the presence of water in isopropanol can suppress the formation of acetal compounds, considering chemical equilibrium. Therefore, the water content is preferably 0.1 ppm or more. From the perspective of using it as a cleaning solution for high-purity isopropanol and suppressing the formation of acetal compounds, the water content is more preferably 1 to 50 ppm, and even more preferably 3 to 25 ppm.

[0080] Furthermore, the total mass of aldehyde and ketone compounds and the water content contained in the high-purity isopropanol involved in this embodiment preferably satisfy the following relationship. Specifically, the ratio p shown in formula (I) is preferably 0.001 to 1, more preferably 0.01 to 0.1.

[0081] p = (Total mass of aldehydes and ketones) / (Water content) ... (I)

[0082] As described above, the reaction that produces acetals is a dehydration reaction. Considering chemical equilibrium, it is believed that the water present in isopropanol can be used to suppress the formation of acetals. On the other hand, it is believed that the water present in isopropanol causes it to be oxidized, thereby supplying aldehydes and ketones, which are the raw materials for acetals. Therefore, it is believed that if the ratio p is greater than 1, there is a tendency for less water and an increase in the formation of acetals. On the other hand, if the ratio p is less than 0.001, there is a tendency for an increase in aldehydes, which may ultimately lead to an increase in acetals.

[0083] Based on the above reasons, it is believed that by managing the ratio p to the range of 0.001 to 1 in the high-purity isopropanol involved in this embodiment, the formation of acetal compounds can be further suppressed.

[0084] The high-purity isopropanol described in this embodiment exhibits superior stability by controlling the moisture content, enabling long-term transportation and storage. Furthermore, it is suitable, for example, for use as a cleaning solution in semiconductor manufacturing processes.

[0085] (Other impurities: free acid)

[0086] It is presumed that free acids act as catalysts in the formation of acetal compounds. Therefore, the concentration of organic acids in the high-purity isopropanol involved in this embodiment is preferably 10 ppm or less, more preferably 100 ppb or less, and even more preferably 10 ppb or less. The lower the lower limit, the more preferred; however, considering industrial manufacturing, storage, and transportation, it is generally 0.1 ppb or more.

[0087] <Method for manufacturing high-purity isopropanol>

[0088] The high-purity isopropanol involved in this embodiment can be manufactured by any method as long as isopropanol satisfying the above-mentioned properties can be obtained. As a suitable manufacturing method, a method of performing the following steps on the crude isopropanol composition can be listed: a vacuum distillation step, in which low-boiling-point components are removed by vacuum distillation, thereby purifying until the concentration of aldehyde compounds with 1 to 6 carbon atoms is reduced to below 1500 ppb by mass; and an atmospheric distillation step, in which the bottom liquid is removed by atmospheric distillation, thereby purifying until the concentration of acetal compounds with 7 to 12 carbon atoms is reduced to below 100 ppb by mass.

[0089] As described above, the inventors of this application first discovered that acetal compounds with 7 to 12 carbon atoms exist as impurities in isopropanol. While distillation purification during the production of isopropanol is known, as described in Patent Document 3, etc., since this acetal compound was not recognized as a harmful organic impurity that should be removed, no operation was performed to reduce it to a negligible level beyond what is typically achieved through distillation. Furthermore, it was unknown that aldehyde compounds with 1 to 6 carbon atoms also exist in isopropanol, and it was also unknown that ketone compounds with 3 to 6 carbon atoms (excluding acetone) also exist in isopropanol. Moreover, it was not known that these aldehyde compounds with 1 to 6 carbon atoms and ketone compounds with 3 to 6 carbon atoms could be contributing factors to the formation of acetal compounds. Therefore, no operation was performed to reduce these contributing factors to a negligible level beyond what is typically achieved through distillation.

[0090] Furthermore, aldehydes with 1 to 6 carbon atoms exhibit high compatibility with isopropanol, making them difficult to remove completely by distillation under atmospheric pressure. Therefore, even repeated atmospheric distillation of crude isopropanol fails to reduce the concentration of these aldehydes below 1500 ppb. In particular, butyraldehyde shows significantly reduced separability from isopropanol during atmospheric distillation, making it extremely difficult to achieve low concentrations. Similarly, ketones with 3 to 6 carbon atoms also exhibit high compatibility with isopropanol, and atmospheric distillation fails to reduce their concentrations below 2000 ppb. Methyl propyl ketone, in particular, shows significantly reduced separability from isopropanol, making it extremely difficult to achieve low concentrations.

[0091] In contrast, when isopropanol is subjected to vacuum distillation, it is known that aldehydes with 1 to 6 carbon atoms and ketones with 3 to 6 carbon atoms can be removed with high efficiency. That is, by removing low-boiling-point components through vacuum distillation, aldehydes with 1 to 6 carbon atoms and ketones with 3 to 6 carbon atoms can be reduced to the aforementioned concentrations.

[0092] The pressure for vacuum distillation is preferably 20 kPa or less, more preferably 10 kPa or less, and even more preferably 5 kPa or less. From the viewpoint of confidentiality and economy of the apparatus, the lower limit of the pressure is preferably 1 kPa or more, and more preferably 3 kPa or more.

[0093] The distillation column used for vacuum distillation can be any distillation column known in the art, with plate columns or packed columns being preferred examples. Vacuum distillation aims to reduce the amount of substances that cause acetal compounds (aldehydes with 1 to 6 carbon atoms and ketones with 3 to 6 carbon atoms), and since atmospheric and vacuum distillation are performed separately, a smaller number of plates can be set. There is no limitation on the number of plates in a plate column, or the equivalent number of plates in a distillation column converted to a plate column; however, if there are too many, the cost of the distillation equipment increases. Therefore, 2 to 30 plates are preferred, 3 to 20 plates are more preferred, and 5 to 10 plates are even more preferred.

[0094] There are no restrictions on the reflux ratio in vacuum distillation; however, a higher ratio increases the cost of the distillation equipment. Therefore, a ratio of 1 to 100 is preferred, more preferably 5 to 50, and even more preferably 10 to 20. As a plate column, through-flow plates, spray plates, etc., can be used. Known packing materials such as Raschig rings and Lessing rings can be used when using a packed column. There are no restrictions on the material of the column or the packing material; various metals and resins such as iron, SUS, Hastelloy, borosilicate glass, quartz glass, and fluoropolymers (e.g., polytetrafluoroethylene) can be used.

[0095] Furthermore, regarding the aforementioned method for producing high-purity isopropanol, in the atmospheric distillation process, the concentration of acetal compounds with 7 to 12 carbon atoms must be reduced to below 100 ppb by removing the bottom liquid. Without atmospheric distillation, it is impossible to remove acetal compounds with 7 to 12 carbon atoms to a high degree.

[0096] There is no limitation on the number of trays in the distillation column, or the equivalent number of trays in the distillation column converted to a tray column, but it is preferably 10 to 300. Furthermore, there is no limitation on the circulation ratio in atmospheric distillation, but it is preferably 0.5 to 50, more preferably 1 to 10. In addition, the conditions for atmospheric distillation are the same as those described in vacuum distillation.

[0097] There are no restrictions on the order in which vacuum distillation and atmospheric distillation are performed, as long as they are combined. Vacuum distillation can be performed first, followed by atmospheric distillation, or vice versa. However, considering the leaching of the materials used and the introduction of impurities during vacuum distillation, it is preferable to perform vacuum distillation first, followed by atmospheric distillation.

[0098] It should be noted that in the vacuum distillation process, by removing low-boiling-point components through distillation, not only is the concentration of aldehydes (and ketones with 3 to 6 carbon atoms) reduced, but the high-boiling-point components, such as the bottom liquid, are also removed simultaneously. In this case, the purified isopropanol can simply be taken out from the side of the distillation column. Even with the removal of the high-boiling-point components from the bottom liquid in the vacuum distillation process, acetals with 7 to 12 carbon atoms cannot be removed to a high degree; therefore, an atmospheric distillation process is necessary.

[0099] Furthermore, in the atmospheric distillation process, by removing the bottom liquid, not only is the concentration of acetals with 7 to 12 carbon atoms reduced, but low-boiling-point components can also be removed by distillation. In this case, high-purity isopropanol can simply be taken out from the side of the distillation column. Even with this removal of low-boiling-point components by distillation in the atmospheric distillation process, aldehydes with 1 to 6 carbon atoms (and ketones with 3 to 6 carbon atoms) cannot be removed to a high degree, therefore a vacuum distillation process is required.

[0100] Example

[0101] The present invention will be described in more detail below with reference to embodiments; however, the present invention is not limited to these embodiments.

[0102] First, the analytical and quantitative methods for impurities will be explained.

[0103] (Determination methods for acetal compounds; qualitative analysis)

[0104] The acetal compounds contained in isopropanol were determined using GC-MS under the determination conditions shown below.

[0105] -Determination Conditions-

[0106] Device: 7890A / 5975C (manufactured by Agilent Technologies Co., Ltd.)

[0107] Analytical column: SUPELCO WAX-10 (60m × 0.25mm, 0.25μm)

[0108] Column temperature: 35℃ (hold for 2 minutes) → increase at 5℃ / minute → 100℃ → increase at 10℃ / minute → 240℃ (hold for 6 minutes)

[0109] Carrier gas: Helium

[0110] Carrier gas flow rate: 2 mL / min

[0111] Inlet temperature: 240℃

[0112] Sample injection method: Pulse-type splitless method

[0113] Injection pulse pressure: 90 psi (2 minutes)

[0114] Flow rate of the diversion orifice: 50 mL / min (2 minutes)

[0115] Use the seasonal mode: 20 mL / minute (5 minutes)

[0116] Transmission line temperature: 240℃

[0117] Ion source and quadrupole temperatures: 230℃ and 150℃

[0118] Scanning ions: m / Z = 25–250

[0119] If no peak is detected in the region with a longer retention time than isopropanol in the spectrum obtained under the above conditions without concentrating isopropanol, the concentration of the acetal compound can be evaluated as being below the detection limit of 500 ppb.

[0120] (Determination methods for acetal compounds; quantitative analysis)

[0121] When a peak is identified in the spectrum obtained using the qualitative analysis method described above, a spectral library search is performed on the mass spectra of that peak to identify its structure. Next, a standard substance for the identified acetal compound is prepared, and its peak area is compared with that of a pre-quantified standard substance. The concentration of the acetal compound detected in the qualitative analysis is then quantified using selected ion detection (SIM).

[0122] -SIM monitoring of ions-

[0123] Group 1 start time: 12.7 minutes, m / Z: 101, 131, 145 (duel 60)

[0124] (Determination methods for aldehyde compounds; qualitative analysis)

[0125] The aldehyde compounds contained in isopropanol were determined using GC-MS under the determination conditions shown below.

[0126] -Determination Conditions-

[0127] Device: 7890A / 5975C (manufactured by Agilent Technologies Co., Ltd.)

[0128] Analytical column: SUPELCO WAX-10 (60m × 0.25mm, 0.25μm)

[0129] Column temperature: 35℃ (hold for 2 minutes) → increase at 5℃ / minute → 100℃ → increase at 10℃ / minute → 240℃ (hold for 6 minutes)

[0130] Carrier gas: Helium

[0131] Carrier gas flow rate: 2 mL / min

[0132] Inlet temperature: 240℃

[0133] Sample injection method: split method

[0134] Flow split ratio: 1:10

[0135] Transmission line temperature: 240℃

[0136] Ion source and quadrupole temperatures: 230℃ and 150℃

[0137] Scanning ions: m / Z = 25–250

[0138] If no peak is detected in the region with a shorter retention time than isopropanol in the spectrum obtained under the above conditions without concentrating isopropanol, the concentration of the aldehyde compound can be evaluated as being below the detection limit of 5000 ppb.

[0139] (Determination methods for aldehyde compounds; quantitative analysis)

[0140] Similar to the quantitative analysis of acetal compounds, when a peak is identified in the spectrum obtained according to the qualitative analysis method described above, a spectral library search is performed on the mass spectra of that peak to identify its structure. Next, a standard substance for the identified aldehyde compound is prepared, and its peak area is compared with that of a pre-quantified standard substance. The concentration of the aldehyde compound detected in the qualitative analysis is then quantified using selected ion detection (SIM).

[0141] -SIM monitoring of ions-

[0142] m / Z: 29 (acetaldehyde analysis)

[0143] m / Z: 58 (Acetone and propionaldehyde analysis)

[0144] m / Z: 72 (Analysis of butyraldehyde and methyl ethyl ketone)

[0145] (Methods for determining moisture content)

[0146] Equipment: Karl Fischer moisture meter AQ-7 (manufactured by Hiranuma Sangyo Co., Ltd.)

[0147] Method: 0.25 g of the sample and 0.75 g of dehydrated acetonitrile were mixed in a glove box with a dew point below -80°C. 0.5 g of the mixed solution was collected in the glove box using thoroughly dried TERUMO Syringe (trade name, 2.5 mL) and determined using a Karl Fischer moisture meter.

[0148] <Example 1>

[0149] To prepare isopropanol for the electronics industry from TOKUYAMA Co., Ltd. (an operation was performed to remove the bottom liquid using atmospheric distillation), the distillation operation shown below was carried out.

[0150] (Distillation process)

[0151] A 2L flask was placed in a water bath, and a 2m long packed column containing glass beads was set up. 2L of isopropanol was added to the flask. The pressure was reduced to 5kPa, and distillation was performed under the following conditions: water bath temperature 50℃, column top temperature 15–25℃, and cooler temperature -5–0℃. After distillation, the aldehydes were determined according to the above-described method, and acetaldehyde, propionaldehyde, and butyraldehyde were detected as aldehydes. The combined concentration of acetaldehyde, propionaldehyde, and butyraldehyde was below 100 ppb. It is assumed that acetaldehyde, propionaldehyde, and butyraldehyde were discharged from the system without condensation.

[0152] Furthermore, the isopropanol purified by distillation contains 5 ppm of water. In addition, the free acid (calculated as acetic acid) in the isopropanol is 2 ppm.

[0153] Next, in order to confirm the storage stability of isopropanol purified by distillation, an accelerated test was conducted under the conditions shown below.

[0154] (Accelerated Testing)

[0155] A 10 mL sample, obtained by distillation, with a combined concentration of acetaldehyde, propionaldehyde, and butyraldehyde below 100 ppb, was placed in a 20 mL SUS tube. Nitrogen gas was supplied at a rate of 100 mL / min for 30 minutes to deoxygenate the sample. After deoxygenation, the tube was sealed to prevent oxygen from entering. The SUS tube was then heated in an oil bath at 120°C for 4 hours. After the accelerated test, the concentration of acetal compounds was determined according to the method described above, and the result was 20 ppb (Table 1).

[0156] Isopropanol, with its combined concentration of acetaldehyde, propionaldehyde, and butyraldehyde reduced to below 100 ppb, still exhibits an acetal concentration of 20 ppb even after accelerated testing, demonstrating excellent long-term storage stability.

[0157] <Comparative Example 1>

[0158] Industrial isopropanol from TOKUYAMA Co., Ltd. was used. Acetaldehyde, propionaldehyde, and butyraldehyde were not distilled. Otherwise, the same accelerated testing as in Example 1 was performed, and the acetal compounds were evaluated. The result was that the concentration of the acetal compounds increased to 2000 ppb (Table 1).

[0159] Accelerated testing of isopropanol without reducing the concentrations of acetaldehyde, propionaldehyde, and butyraldehyde resulted in an acetal concentration of 2000 ppb, indicating poor long-term storage stability.

[0160] Table 1

[0161]

[0162] <Example 2>

[0163] (Preparation of crude isopropanol)

[0164] Propylene as feedstock was prepared containing the following substances as impurities: 39,972 ppm propane, 20 ppm ethane, 8 ppm butene, less than 0.1 ppm pentene, and less than 0.1 ppm hexene. Water as feedstock was prepared by adding phosphotungstic acid as an acid catalyst to adjust the pH to 3.0. The water was fed into a reactor with a volume of 10 L at a flow rate of 18.4 kg / h (due to a density of 920 kg / m³). 3 Therefore, water heated to 110°C was added at a supply rate of 20 L / h, and propylene was added at a supply rate of 1.2 kg / h.

[0165] The reaction temperature in the reactor was set to 280°C and the reaction pressure to 250 atm, allowing propylene to react with water to produce isopropanol. The reaction product containing the generated isopropanol was cooled to 140°C and the pressure was reduced to 18 atm, thereby recovering the propylene dissolved in water in the reaction product as a gas. The recovered propylene was fed into a propylene recovery tank for reuse as a feedstock. At this point, the conversion rate of the supplied propylene was 84.0%, and the selectivity for converting propylene to isopropanol was 99.2%.

[0166] Next, the product was dehydrated by distillation to obtain crude isopropanol with a concentration of 99%. The concentrations of acetal, aldehyde, and ketone compounds in the obtained crude isopropanol were determined, and the results are shown in Table 2.

[0167] Table 2

[0168]

[0169]

[0170] (Purification of crude isopropanol)

[0171] A 2L flask was placed in a water bath, and a 2m long packed column containing glass beads was prepared (equivalent to 10 plates in a plate column). 2L of crude isopropanol was added to the flask. Vacuum distillation was performed under the following conditions: pressure 20 kPa, reflux ratio 3, water bath temperature 70°C, column top temperature 35–45°C, and cooler temperature -5–0°C, to remove low-boiling-point components. Next, similarly, a 2L flask was placed in a water bath, and a 3m long packed column containing glass beads was prepared (equivalent to 20 plates in a plate column). The isopropanol obtained from the vacuum distillation was added to the flask. Atmospheric distillation was performed under the following conditions: reflux ratio 3, oil bath temperature 120°C, column top temperature 82°C, and cooler temperature 25°C. The concentration of isopropanol in the bottom effluent was determined by GC / MS, and the result showed a high purity of over 99.999% after water removal. The concentrations of acetal, aldehyde, and ketone compounds in the obtained high-purity isopropanol were determined, and the results are shown in Tables 3 to 5. Additionally, the water content in the obtained high-purity isopropanol was determined, and the results are also shown in Table 3.

[0172] (Accelerated Testing)

[0173] The high-purity isopropanol obtained using the above method was subjected to an accelerated test at a heating temperature of 80°C, similar to that in Example 1, and the acetal compounds were evaluated. The result was that the concentration of acetal compounds was 90 ppb (Table 6). Alternatively, the SUS tube containing the high-purity isopropanol was stored at room temperature (25°C) for 6 months, and the result for the acetal compounds was 85 ppb. This confirms that the accelerated test at 80°C is almost equivalent to the severity of the increase in acetal compounds caused by isopropanol stored in the dark at room temperature (25°C) for 6 months.

[0174] Furthermore, the same accelerated test was carried out by changing the heating temperature in the oil bath of the SUS tube to 120°C, and the concentration of acetal compound was 350 ppb (Table 7).

[0175] <Example 3>

[0176] Except for changing the vacuum distillation conditions in Example 2 (purification of crude isopropanol) to a pressure of 10 kPa, a reflux ratio of 3, a water bath temperature of 70°C, a column top temperature of 28–38°C, and a cooler temperature of -5–0°C, high-purity isopropanol with a concentration of 99.999% or higher after water removal was produced in the same manner as in Example 2. The concentrations of acetals, aldehydes, and ketones in the obtained high-purity isopropanol were determined, and the results are shown in Tables 3–5. Additionally, the water content in the obtained high-purity isopropanol was determined, and the results are also shown in Table 3.

[0177] (Accelerated Testing)

[0178] The high-purity isopropanol obtained using the above method was subjected to accelerated testing at various temperature conditions of 80°C and 120°C, similar to Example 1, and the acetal compound was evaluated. The results showed that the concentration of the acetal compound was 40 ppb at 80°C (Table 6) and 85 ppb at 120°C (Table 7).

[0179] <Example 4>

[0180] Except for changing the vacuum distillation conditions in Example 2 (purification of crude isopropanol) to a pressure of 5 kPa, a reflux ratio of 6, a water bath temperature of 50°C, a column top temperature of 15–25°C, and a cooler temperature of -5–0°C, high-purity isopropanol with a concentration of 99.999% by mass or higher after water removal was produced in the same manner as in Example 2. The concentrations of acetals, aldehydes, and ketones in the obtained high-purity isopropanol were determined, and the results are shown in Tables 3–5. Additionally, the water content in the obtained high-purity isopropanol was determined, and the results are also shown in Table 3.

[0181] (Accelerated Testing)

[0182] The high-purity isopropanol obtained using the above method was subjected to accelerated testing at various temperature conditions of 80°C and 120°C, similar to Example 1, and the acetal compound was evaluated. The results showed that the concentration of the acetal compound was 19 ppb at 80°C (Table 6) and 27 ppb at 120°C (Table 7).

[0183] <Example 5>

[0184] Except for changing the vacuum distillation conditions in Example 2 (purification of crude isopropanol) to a pressure of 5 kPa, a reflux ratio of 9, a water bath temperature of 50°C, a column top temperature of 15–25°C, and a cooler temperature of -5–0°C, high-purity isopropanol with a concentration of 99.999% by mass or higher after water removal was produced in the same manner as in Example 2. The concentrations of acetals, aldehydes, and ketones in the obtained high-purity isopropanol were determined, and the results are shown in Tables 3–5. Additionally, the water content in the obtained high-purity isopropanol was determined, and the results are also shown in Table 3.

[0185] (Accelerated Testing)

[0186] The high-purity isopropanol obtained using the above method was subjected to accelerated tests at various temperature conditions of 80°C and 120°C, similar to Example 1, and the acetal compound was evaluated. The results showed that the concentration of the acetal compound was 11 ppb at 80°C (Table 6) and 15 ppb at 120°C (Table 7).

[0187] <Example 6>

[0188] Except for changing the atmospheric distillation conditions in Example 2 (purification of crude isopropanol) to 10 trays, a reflux ratio of 1, an oil bath temperature of 120°C, a column top temperature of 82°C, and a cooler temperature of 25°C, high-purity isopropanol with a concentration of 99.999% by mass or higher after water removal was produced in the same manner as in Example 2. The concentrations of acetals, aldehydes, and ketones in the obtained high-purity isopropanol were determined, and the results are shown in Tables 3 to 5. Additionally, the water content in the obtained high-purity isopropanol was determined, and the results are also shown in Table 3.

[0189] (Accelerated Testing)

[0190] The high-purity isopropanol obtained using the above method was subjected to accelerated tests at various temperature conditions of 80°C and 120°C, similar to Example 1, and the acetal compound was evaluated. The results showed that the concentration of the acetal compound was 89 ppb at 80°C (Table 6) and 100 ppb at 120°C (Table 7).

[0191] <Comparative Example 2>

[0192] Except that the vacuum distillation in Example 2 (purification of crude isopropanol) was changed to atmospheric distillation under the conditions of a reflux ratio of 3, an oil bath temperature of 120°C, a column top temperature of 82°C, and a cooler temperature of 25°C, high-purity isopropanol with a concentration of 99.999% by mass or higher after water removal was produced in the same manner as in Example 2. The concentrations of acetals, aldehydes, and ketones in the obtained high-purity isopropanol were determined, and the results are shown in Tables 3 to 5. In addition, the water content in the obtained high-purity isopropanol was determined, and the results are also shown in Table 3.

[0193] (Accelerated Testing)

[0194] The high-purity isopropanol obtained using the above method was subjected to accelerated testing at various temperature conditions of 80°C and 120°C, similar to Example 1, and the acetal compound was evaluated. The results showed that the concentration of the acetal compound was 270 ppb at 80°C (Table 6) and 900 ppb at 120°C (Table 7).

[0195] <Comparative Example 3>

[0196] Except that the atmospheric distillation in Example 2 (purification of crude isopropanol) was changed to vacuum distillation under the conditions of 20 kPa pressure, 10 trays, reflux ratio of 3, water bath temperature of 70°C, top temperature of 35–45°C, and cooler temperature of -5–0°C, high-purity isopropanol with a concentration of 99.999% by mass or higher after water removal was produced in the same manner as in Example 2. The concentrations of acetals, aldehydes, and ketones in the obtained high-purity isopropanol were determined, and the results are shown in Tables 3–5. In addition, the water content in the obtained high-purity isopropanol was determined, and the results are also shown in Table 3.

[0197] (Accelerated Testing)

[0198] The high-purity isopropanol obtained using the above method was subjected to accelerated testing at various temperature conditions of 80°C and 120°C, similar to Example 1, and the acetal compound was evaluated. The results showed that the concentration of the acetal compound was 200 ppb at 80°C (Table 6) and 190 ppb at 120°C (Table 7).

[0199] Table 3

[0200]

[0201] Table 4

[0202]

[0203] Table 5

[0204]

[0205] Table 6

[0206]

[0207] Table 7

[0208]

[0209]

[0210] The entire disclosure of Japanese Application 2018-188017, filed on October 3, 2018, is incorporated herein by reference.

Claims

1. A method for manufacturing high-purity isopropanol, wherein the concentration of an acetal compound having 7 to 12 carbon atoms in the high-purity isopropanol is 100 ppb or less by mass, and in the case of an accelerated test conducted by heating at 80°C for 4 hours under a nitrogen atmosphere, the increase in the concentration of the acetal compound relative to the value before heating is within 30 times, and the concentration is maintained at 100 ppb or less by mass. In the manufacturing method, the crude isopropanol composition obtained by direct hydration of propylene is subjected to the following steps: The vacuum distillation process removes low-boiling-point components by vacuum distillation, thereby purifying the compound until the concentration of aldehydes with 1 to 6 carbon atoms is reduced to below 1500 ppb on a mass basis; and The atmospheric distillation process uses atmospheric distillation to remove the bottom liquid from the column, thereby purifying the product until the concentration of acetal compounds with 7 to 12 carbon atoms is reduced to below 100 ppb on a mass basis.

2. The method for manufacturing high-purity isopropanol according to claim 1, wherein, In the vacuum distillation process, purification is carried out to reduce the concentration of ketone compounds with 3 to 6 carbon atoms to below 2000 ppb by mass.

Images