Method and device for producing purified isopropyl alcohol

Abstract

Provided is a method for producing purified isopropyl alcohol by dehydrating crude isopropyl alcohol containing water as an impurity, the method comprising: a phase separation step in which a mixed liquid of the crude isopropyl alcohol and an azeotropic agent is accommodated in a phase separation tank and phase-separated into an upper-phase liquid containing the azeotropic agent, water, and isopropyl alcohol and a lower-phase liquid containing water; and an azeotropic distillation step in which the upper-phase liquid is subjected to azeotropic distillation in an azeotropic distillation column, and a distillate containing an azeotropic mixture of the azeotropic agent and water and a bottom product containing isopropyl alcohol are extracted, wherein the distillate is supplied to the phase separation tank.

Description

Purified isopropyl alcohol manufacturing method and manufacturing apparatus

[0001] The present invention relates to a method and apparatus for producing purified isopropyl alcohol by dehydrating crude isopropyl alcohol containing water as an impurity.

[0002] Isopropyl alcohol (hereinafter also abbreviated as "IPA") has the property of dissolving both water and organic solvents, and is widely used as a solvent for paints, inks, and various synthetic raw materials. Furthermore, high-purity IPA is used in large quantities in the rinsing section of semiconductor substrates in semiconductor manufacturing equipment, and its usage is expected to continue to increase in the future.

[0003] A known method for synthesizing IPA is, for example, the direct hydration of propylene. The crude IPA synthesized in this manner is typically purified by distillation, but to obtain high-purity IPA, a combination of multiple distillation steps is required. Specifically, taking into account the boiling points of organic impurities contained in the crude IPA, a low-boiling distillation step is performed to remove low-boiling impurities with a boiling point lower than that of IPA from the top of a distillation column, followed by a high-boiling distillation step to remove high-boiling impurities with a boiling point higher than that of IPA from the bottom of the distillation column. Furthermore, since the distillate extracted from the top of the distillation column in the high-boiling distillation step contains an azeotropic mixture of IPA and water, an azeotropic distillation step is performed in which an azeotropic agent such as benzene is added to the distillate and the azeotropic distillation is performed (see, for example, Patent Document 1).

[0004] Furthermore, since high-purity IPA has a high manufacturing cost, its use in semiconductor manufacturing contributes to an increase in the manufacturing cost of semiconductors. IPA waste liquid recovered from semiconductor manufacturing equipment is generally burned, but this process releases carbon dioxide, which is believed to be a cause of global warming. Therefore, from the perspective of environmental conservation, it has been desirable to reduce the amount of IPA waste liquid disposed of.

[0005] For this reason, there is an increasing demand for purifying and reusing IPA waste liquid. A method of purifying IPA waste liquid by combining multiple distillation steps is also being applied (see, for example, Patent Document 2). In this case, too, there is a strong demand for obtaining high-purity IPA at the lowest possible production cost.

[0006] International Publication No. 2020 / 071481 JP 10-109948 Publication

[0007] For these reasons, it is desirable to efficiently purify crude IPA and IPA waste liquid by distillation at low production costs. Among these methods, the azeotropic distillation process consumes a large amount of heat. Therefore, it would be extremely beneficial to efficiently produce purified IPA from crude IPA containing water as an impurity with a small amount of heat.

[0008] The present inventors have conducted extensive research in light of the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by azeotropically distilling an upper phase liquid containing an azeotropic agent, water, and isopropyl alcohol obtained by phase separation in the presence of an azeotropic agent, rather than directly azeotropically distilling crude IPA containing water as an impurity, and have thus completed the present invention.

[0009] That is, one aspect of the present invention is a method for producing purified isopropyl alcohol by dehydrating crude isopropyl alcohol containing water as an impurity, and a mixed liquid of the crude isopropyl alcohol and an azeotropic agent is placed in a phase separation tank. An azeotropic distillation step for separating the mixed liquid into an upper phase liquid containing the azeotropic agent, water, and isopropyl alcohol and a lower phase liquid containing water, and an azeotropic distillation step for extracting the distillate containing an azeotropic mixture of the azeotropic agent and water and the bottoms containing isopropyl alcohol, and supplying the distillate to the phase separation tank. This is a method for producing purified isopropyl alcohol.

[0010] Another aspect of the present invention is an apparatus for producing purified isopropyl alcohol by dehydrating crude isopropyl alcohol containing water as an impurity, the apparatus comprising: a phase separation tank that accommodates a mixture of the crude isopropyl alcohol and an azeotropic agent and separates the mixture into an upper phase liquid containing the azeotropic agent, water, and isopropyl alcohol, and a lower phase liquid containing water; and an azeotropic distillation column that azeotropically distills the upper phase liquid. The phase separation tank is provided with a first supply pipe that supplies the crude isopropyl alcohol to the phase separation tank, and a second supply pipe that supplies the upper phase liquid to the phase separation tank. A second supply pipe that supplies the raw material to the raw material supply stage of the azeotropic distillation tower is connected, a third supply pipe that supplies a distillate containing an azeotropic mixture of the entrainer and water to the phase separation tank is connected to the top of the azeotropic distillation tower, and a withdrawal pipe that withdraws a bottom product containing isopropyl alcohol is connected to the bottom of the azeotropic distillation tower. A fourth supply pipe that supplies the entrainer is connected to any one of the first supply pipe, the phase separation tank, the second supply pipe, the azeotropic distillation tower, and the third supply pipe. This is an apparatus for producing purified isopropyl alcohol.

[0011] According to the present invention, purified IPA can be efficiently produced from crude IPA containing water as an impurity with a small amount of heat.

[0012] 1 is a schematic diagram showing an apparatus for producing purified IPA according to an embodiment of the present invention.

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as necessary.

[0014] [Crude IPA] The crude IPA is not particularly limited as long as it contains water as an impurity. Examples include crude IPA obtained by a synthetic method such as direct hydration of propylene, and IPA waste liquid recovered from various industrial facilities. Among these, IPA waste liquid recovered from a semiconductor substrate manufacturing apparatus is preferred. Specifically, IPA waste liquid recovered from the development unit and pre-wet unit of a semiconductor substrate manufacturing apparatus is applicable. Furthermore, a semiconductor substrate manufacturing apparatus is provided with a rinse unit that removes moisture adhering to the surface of the substrate after the cleaning unit that cleans the substrate with an aqueous cleaner, and a large amount of IPA is used as the rinse liquid. In this embodiment, IPA waste liquid recovered from the rinse unit is also suitable.

[0015] Although crude IPA and IPA waste liquid can be used as the crude IPA, it is preferable to use aqueous IPA obtained by purifying the crude IPA and IPA waste liquid. The water content of the crude IPA is usually 1% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 20% by mass or less.

[0016] Distillation is a suitable method for purifying the crude IPA product and IPA waste liquid. Examples of distillation include removing high-boiling impurities from the bottom of a high-boiling distillation column. It is preferable to apply the distillate containing an azeotropic mixture of IPA and water (IPA 88% by mass, water 12% by mass) extracted from the top of the high-boiling distillation column to the crude IPA. Prior to distillation in the high-boiling distillation column, low-boiling impurities may usually be removed from the top of a low-boiling distillation column.

[0017] [Azeotropic Agent] In this embodiment, the upper phase liquid obtained by phase separation of a mixture of crude IPA and an azeotropic agent is subjected to azeotropic distillation. That is, azeotropic distillation is a distillation method in which an azeotropic agent is added to form an azeotropic mixture to separate a mixture of liquids that are difficult or impossible to separate by conventional distillation. In this embodiment, an azeotropic agent is used to remove water from the upper phase liquid. As the azeotropic agent, a compound that has a boiling point lower than that of IPA and forms an azeotropic mixture with water is used. Furthermore, as the azeotropic agent, a compound that forms an upper phase containing the azeotropic agent, water, and IPA and a lower phase containing water when the mixture of crude IPA and an azeotropic agent is phase separated is used. Examples of azeotropic agents include benzene, toluene, cyclohexane, and isopropyl ether. Among these, benzene is particularly preferred.

[0018] The amount of the azeotropic agent added is preferably 50 parts by mass or more and 1000 parts by mass or less, and more preferably 80 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of crude IPA.

[0019] [Dehydration Method] In this embodiment, crude IPA is mixed with an azeotropic agent and placed in a phase separation tank before azeotropic distillation. The upper phase liquid formed in the phase separation tank, containing the azeotropic agent, water, and IPA, is then separated and subjected to azeotropic distillation. Conventional methods for purifying crude IPA involve direct azeotropic distillation of the crude IPA (see, for example, Patent Document 2). However, in this case, since a large amount of crude IPA is azeotropically distilled, not only does the amount of heat increase, but the diameter of the azeotropic distillation column also increases, making it difficult to efficiently produce purified IPA.

[0020] In contrast, in this embodiment, the crude IPA is not directly supplied to the azeotropic distillation column, but is contained in a phase separation tank in a state where it is mixed with an azeotropic agent. That is, by being contained in the phase separation tank, the crude IPA is separated into an upper phase liquid containing an azeotropic agent, water, and IPA, and a lower phase liquid containing water. Therefore, by separating the upper phase liquid and supplying it to the azeotropic distillation column, the total amount and water content of the upper phase liquid to be azeotropically distilled can be reduced relative to the crude IPA, thereby reducing the amount of heat consumed during azeotropic distillation. For example, the water content of the upper phase liquid obtained from crude IPA with a water content of 12% by mass, which corresponds to an azeotropic mixture of IPA and water, can be reduced to 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 4% by mass or less.

[0021] The method for producing crude IPA according to this embodiment will be described in more detail with reference to FIG.

[0022] (Phase Separation Tank) In FIG. 1 , the first supply pipe 1 for supplying crude IPA, the liquid to be treated, is connected to the phase separation tank 4 rather than the azeotropic distillation column 2. As a result, the crude IPA is temporarily stored inside the phase separation tank 4. At this time, the crude IPA is supplied to the injection point described below, and the crude IPA and the azeotropic agent are mixed together and stored in the phase separation tank 4. As a result, in the phase separation tank 4, phase separation occurs into an upper phase liquid 5 containing the azeotropic agent, water, and IPA, and a lower phase liquid 6 containing water. In this embodiment, the upper phase liquid 5 formed by phase separation is supplied to the raw material supply stage of the azeotropic distillation column 2 via the second supply pipe 7 and subjected to azeotropic distillation.

[0023] The phase separation tank 4 is not particularly limited as long as it is capable of phase separation into an upper phase liquid 5 and a lower phase liquid 6 due to the difference in specific gravity, and a known decanter, settler, or the like may be appropriately selected and used. The phase separation tank 4 preferably has a structure shown in FIG. 2. In this case, the phase separation tank 4 is divided into the following chambers: a) a phase separation chamber 8 that accommodates a mixture of crude IPA and an azeotropic agent and undergoes phase separation into an upper phase liquid 5 and a lower phase liquid 6; b) an upper phase liquid storage chamber 10 that is adjacent to the phase separation chamber 8 on one side via a first partition wall 9a and accommodates the upper phase liquid 5 that overflows the first partition wall 9a and flows in from the phase separation chamber 8; and c) a lower phase liquid storage chamber 11 that is adjacent to the phase separation chamber 8 on the other side via a second partition wall 9b and accommodates the lower phase liquid 6 that is delivered from the phase separation chamber 8 via a liquid delivery pipe 14. That is, when the upper phase liquid 5 overflows and separates from the lower phase liquid 6, the separation of the upper phase liquid 5 can be further enhanced, which is preferable. At this time, since the upper end of the first partition wall 9a is lower than the upper end of the second partition wall 9b, the inflow of the upper phase liquid 5 into the lower phase liquid storage chamber 11 is suppressed. In addition, the second supply pipe 7 is connected to the lower end region of the upper phase liquid storage chamber 10.

[0024] The liquid feed pipe 14 is a communicating pipe having a first open end communicating with the lower phase liquid 6 contained in the phase separation chamber 8 and a second open end communicating with the lower phase liquid storage chamber 11. The communicating pipe has an upward bent portion 12 including a second open end, and a third open end communicating with the gas phase portion of the phase separation tank 4 at a position higher than the upper end of the first partition wall 9a, and a branch portion 13 branching off from the upward bent portion 12. As a result, the lower phase liquid 6 contained in the phase separation chamber 8 is sucked in from the first open end of the communicating pipe, and the lower phase liquid 6 is discharged from the second open end into the lower phase liquid storage chamber 11.

[0025] Here, in the liquid feed pipe 14, the height of the upward bent portion 12 (the height of the highest part of the pipe peripheral wall) corresponds to the height of the upper end region of the first partition wall 9a, so that the inflow rate of the upper phase liquid 5 and the feed rate of the lower phase liquid 6 are well balanced. The height of the upward bent portion 12 may be any height as long as it maintains a good balance between the inflow rate of the upper phase liquid 5 and the feed rate of the lower phase liquid 6 and maintains the desired volumes of the phase separation chamber 8 and the lower phase liquid storage chamber 11. The height of the upward bent portion 12 is usually a height that is spaced downward by a distance that is 1 / 9, preferably 1 / 10, of the length from the upper end of the first partition wall 9a to the lower end of the first partition wall 9a.

[0026] Furthermore, since the branch section 13 is provided in the liquid feed pipe 14, destabilization due to the siphon effect is prevented when the lower phase liquid 6 is fed. Here, the pressure of the gas phase section of the phase separation tank 4 to which the third open end communicates is not particularly limited, but from the viewpoints of preventing air from being mixed in and improving separation performance during distillation, it is preferably 900 hPa or more and 4013 hPa or less, and more preferably 1013 hPa or more and 2013 hPa or less.

[0027] To prevent the release of harmful substances and the inclusion of air, the third open end is connected to the gas phase of the phase separation tank 4, as shown in Fig. 2. The third open end is located at a position 40 cm or more, preferably 50 cm or more, higher than the upper end of the first partition wall 9a. The third open end may also be connected to the outside of the phase separation tank 4.

[0028] From the viewpoint of stably separating the upper phase liquid 5 and the lower phase liquid 6, it is preferable to maintain a state in which the lower phase liquid 6 is held at a constant height in the phase separation chamber 8. For this reason, it is preferable to previously store a constant amount of water in the phase separation chamber 8, specifically, an amount of water that enables the residence time of the mixture of crude IPA and the azeotropic agent in the phase separation chamber 8 to be 10 minutes or more and 90 minutes or less. The amount of water previously stored in the phase separation chamber 8 is generally an amount corresponding to a height of 50 cm or more and 300 cm or less from the bottom of the phase separation chamber 8.

[0029] When supplying crude IPA to the phase separation chamber 8, it is preferable to insert the open end of the first supply pipe 1 to a certain depth into the lower phase liquid 6 and reduce the flow rate of the crude IPA so as not to disturb the phase separation of the mixture of crude IPA and azeotropic agent contained in the phase separation chamber 8. The flow rate of the crude IPA is preferably 0.1 m / s or more and 2 m / s or less, more preferably 0.3 m / s or more and 1 m / s or less.

[0030] In this embodiment, the mixture of crude IPA and the azeotropic agent is phase-separated before azeotropic distillation, and therefore a significantly larger amount of the mixture is supplied to the phase separation tank 4 than when the phase separation occurs after azeotropic distillation. In this case, use of the phase separation tank 4 having the structure shown in Fig. 2 is particularly effective because it provides excellent separability between the upper phase liquid 5 and the lower phase liquid 6 and minimizes contamination with components of other phases.

[0031] (Azeotropic Distillation Column) An upper phase liquid 5 is supplied from an upper phase liquid storage chamber 10 to a raw material supply tray of the azeotropic distillation column 2 via a second supply pipe 7. A first distillate containing an azeotropic mixture of an entrainer and water and IPA, which is extracted from the top of the azeotropic distillation column 2 via a condenser 3, is supplied to a phase separation tank 4 via a third supply pipe 15. On the other hand, a first bottoms product containing IPA is extracted from the bottom of the azeotropic distillation column 2 via a first extraction pipe 16. At this time, the first bottoms product may be used as purified IPA, or, as described below, the first bottoms product may be purified and used as purified IPA.

[0032] Here, the first distillate preferably has an entrainer content of 40% by mass to 80% by mass, a water content of 1% by mass to 10% by mass, and an IPA content of 14% by mass to 54% by mass, and more preferably has an entrainer content of 40% by mass to 50% by mass, a water content of 2% by mass to 8% by mass, and an IPA content of 40% by mass to 50% by mass.

[0033] The azeotropic distillation column 2 may be either a plate column or a packed column, but is preferably a plate column. The number of theoretical plates in the azeotropic distillation column 2 is preferably 10 to 200, more preferably 20 to 50. Examples of the plates in a plate column include cross-flow trays and shower trays. Examples of packing materials in a packed column include Raschig rings and Lessing rings. Examples of materials for the column and packing materials include iron, stainless steel, Hastelloy, borosilicate glass, quartz glass, and fluororesins (e.g., polytetrafluoroethylene).

[0034] In this embodiment, the upper phase liquid 5, which has a reduced water content compared to crude IPA, is subjected to azeotropic distillation, so the amount of heat consumed can be significantly reduced, and the azeotropic distillation column 2 can be made smaller than when crude IPA is azeotropically distilled.

[0035] The number of theoretical plates of the azeotropic distillation column 2 to which the raw material is supplied up to the bottom of the column is usually 5 or more, more preferably 10 to 30. The total number of theoretical plates of the azeotropic distillation column 2 is preferably confirmed by actually operating the column and analyzing the composition.

[0036] The gauge pressure at the top of the azeotropic distillation column 2 is not particularly limited, but is, for example, 0.0 MPaG or more and 0.1 MPaG or less. In this case, the temperatures at the top and bottom of the azeotropic distillation column 2 may be appropriately set according to the gauge pressure.

[0037] The water content of the first bottoms product varies depending on the type of entrainer used, but is usually 1% by mass or less, preferably 1,000 ppm to 1 ppm. The purity of the first bottoms product (excluding the water content) is usually 99.9% by mass or more, preferably 99.99% by mass to 99.999999% by mass.

[0038] (Supply of First Distillate to Phase Separation Tank) In this embodiment, the first distillate is supplied to and circulated in the phase separation tank 4 via the third supply pipe 15. That is, the azeotropic agent, water, and IPA contained in the first distillate are again phase-separated into an upper phase liquid 5 and a lower phase liquid 6, and the upper phase liquid 5 is azeotropically distilled, thereby increasing the recovery rate of IPA.

[0039] Here, the third supply pipe 15 is provided in parallel with the first supply pipe 1 , but the third supply pipe 15 may be connected to the first supply pipe 1 .

[0040] In order to separate the phases of the crude IPA supplied to the phase separation tank 4, a fourth supply pipe 17 is provided to supply an azeotropic agent to the phase separation tank 4. The fourth supply pipe 17 may be connected to any of the first supply pipe 1, the second supply pipe 7, the azeotropic distillation column 2, and the third supply pipe 15.

[0041] (IPA Recovery Distillation Column) The lower phase liquid 6 contains water and IPA. Specifically, the IPA content in the lower phase liquid 6 is 5% by mass or more and 50% by mass or less, preferably 10% by mass or more and 30% by mass or less. Therefore, the lower phase liquid 6 is supplied to the raw material supply stage of the IPA recovery distillation column 19 via the fifth supply pipe 18, and a side cut liquid containing an azeotropic mixture of IPA and water is extracted from the upper side of the IPA recovery distillation column 19. The side cut liquid is then supplied to the phase separation tank 4 via the sixth supply pipe 20 and circulated. That is, the water and IPA contained in the side cut liquid are phase-separated again into the upper phase liquid 5 and the lower phase liquid 6, and the upper phase liquid 5 is azeotropically distilled, thereby increasing the IPA recovery rate. The lower phase liquid 6 may be disposed of without being distilled. Alternatively, the second distillate may be extracted from the top of the column.

[0042] On the other hand, a second bottoms liquid containing water is withdrawn from the bottom of the IPA recovery distillation column 19 via a second withdrawal pipe 21 .

[0043] Here, in the IPA recovery distillation column 19, distillation can be performed under conditions that are similar to the distillation conditions in the azeotropic distillation column 2, and that allow the second distillate containing an azeotropic mixture of IPA and water to be efficiently extracted from the top or upper side of the column.

[0044] When crude IPA is derived from IPA waste liquid discharged and recovered from various industrial facilities, it often has a complex composition containing various organic impurities in addition to water. Typically, most of the organic impurities are removed by low-boiling point distillation, high-boiling point distillation, or the like, but completely removing the organic impurities is not easy. In particular, IPA waste liquid recovered from the rinse section of a semiconductor substrate manufacturing apparatus may contain low-boiling point impurities such as methanol and ethanol. In this case, a third distillate containing low-boiling point impurities is extracted from the top of the IPA recovery distillation column 19 via a third extraction pipe 22. In this case, the third distillate may be disposed of.

[0045] [Other Purification Steps] The first bottoms may be purified by adsorption or the like. Alternatively, the first bottoms may be purified by filtration to remove metal particles, inorganic particles, organic particles, etc. Furthermore, the first bottoms may be purified by an ion exchange resin or the like to remove metal ions, etc.

[0046] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and the above-described embodiments may be modified as appropriate within the scope of the spirit of the present invention.

[0047] Examples of the present invention will be described below, but the present invention is not limited to these examples. In these examples, % and ppm are by mass unless otherwise specified. In the following examples and comparative examples, the contents of components in samples were measured by the following methods.

[0048] (Method for measuring water content in a sample) Instrument: Karl Fischer moisture meter CA-200 (Mitsubishi Chemical Analytical). When the water content of the sample was expected to exceed 1%, the sample was diluted with IPA and the water content of the diluted sample was measured. The water content of the IPA used for dilution was measured in advance and confirmed to be 100 ppm or less. When the water content of the sample was expected to be 1% or less, the water content of the sample was measured without dilution. Note that if the water content of the sample is higher than expected, it will simply take longer to measure but will not affect the measured value. Furthermore, when the water content of the sample was 100 ppm or less, 5 g or more of the sample was collected using a thermosyringe in a glove box with a dew point of -60°C or less, and the water content of the sample was measured. This analytical method was capable of quantifying water content in samples with a water content of 1 ppm or more.

[0049] (Method for measuring the benzene and IPA contents in a sample) The benzene and IPA contents in a sample were measured by gas chromatography analysis. Apparatus: Gas chromatography analyzer GC-8A (Shimadzu Corporation) Detector: TCD Carrier: Hydrogen Column: Porapak T Column temperature: 130°C Injection port temperature: 150°C Injection volume: 5 μL

[0050] Example 1 Purified IPA was obtained by purifying crude IPA derived from an aqueous IPA waste liquid recovered from a semiconductor manufacturing apparatus equipped with a semiconductor substrate rinsing section using an apparatus that was a partial modification of the purified IPA manufacturing apparatus shown in Figures 1 and 2. The crude IPA used was an azeotropic mixture (88% by mass of IPA, 12% by mass of water) obtained by subjecting the IPA waste liquid to low-boiling distillation from the top of a column to remove low-boiling impurities, and then subjecting the IPA waste liquid to high-boiling distillation from the bottom of the column.

[0051] Here, the capacity of the phase separation chamber 8 was 24 L, the capacity of the upper phase liquid storage chamber 10 was 15 L, and the capacity of the lower phase liquid storage chamber 11 was 15 L. The height of the upper end of the first partition wall 9a was 30 cm lower than the height of the second partition wall 9b, and was spaced apart by 1 / 5 of the length from the upper end to the lower end of the second partition wall 9b.

[0052] Furthermore, one open end of the liquid feed pipe 14 was connected to the bottom of the phase separation chamber 8 and communicated with the lower phase liquid 6, and the other open end of the liquid feed pipe 14 communicated with the lower phase liquid storage chamber 11. Furthermore, the height of the upward bent portion 12 of the liquid feed pipe 14 (the height of the highest part of the pipe peripheral wall) was a height spaced downward by 1 / 10 of the length from the upper end of the first partition wall 9a to the lower end of the first partition wall 9a. Furthermore, the open end of the branch portion 13 communicated with the gas phase portion of the phase separation tank 4 at a position 50 cm higher than the upper end of the first partition wall 9a.

[0053] After adding water to the phase separation chamber 8 so that the height from the bottom of the chamber was 120 cm, crude IPA was supplied to the phase separation chamber 8 through the first supply pipe at a flow rate of 0.3 m / s. The residence time of the mixture of crude IPA and the azeotropic agent in the phase separation chamber 8 was 25 minutes.

[0054] In addition, benzene as an azeotropic agent was supplied via a fourth supply pipe 17 in an amount of 90 parts by mass per 100 parts by mass of crude IPA supplied to the phase separation chamber 8, causing phase separation into an upper phase liquid 5 containing the azeotropic agent, water, and IPA, and a lower phase liquid 6 containing water and IPA.

[0055] The upper phase liquid 5 formed in the phase separation chamber 8 overflowed the upper end of the first partition wall 9a and flowed into the upper phase liquid storage chamber 10. On the other hand, the lower phase liquid 6 formed in the phase separation chamber 8 was sent to the lower phase liquid storage chamber 11 via the liquid sending pipe 14.

[0056] The upper phase liquid 5 flowing into the upper phase liquid storage chamber 10 had a composition of 26 mass % IPA and 1 mass % water, and the water content was significantly reduced compared to the crude IPA. The upper phase liquid 5 was supplied to the raw material supply tray of the azeotropic distillation column 2 via the second supply pipe at a flow rate of 59 L / h, and azeotropic distillation was carried out.

[0057] Here, the azeotropic distillation column 2 is a packed column with a packing height of 100 cm, and it was confirmed through experiments that the theoretical number of plates is 35. A condenser 3 is provided at the top of the azeotropic distillation column 2. Taking into account the flow rate of the upper phase liquid 5, the azeotropic distillation column 2 is designed to be small, with a diameter of 10 cm.

[0058] In the azeotropic distillation column 2, the temperature at the top of the column was 68°C, and the gauge pressure at the top of the column was 0 kPaG. Furthermore, a first distillate containing an azeotropic mixture of benzene and water and IPA was supplied and circulated from the top of the azeotropic distillation column 2 to the phase separation tank 4 via the third supply pipe 15, and the reflux rate of the first distillate was 59 L / h. Here, the composition of the first distillate was 68 mass% benzene, 6 mass% water, and 26 mass% IPA.

[0059] In addition, the lower phase liquid 6 sent to the lower phase liquid storage chamber 11 was supplied to the IPA recovery distillation column 19 at a rate of 4 L / h via the fifth supply pipe 18 and distilled. At this time, a second distillate containing an azeotropic mixture of IPA and water was extracted from the top of the IPA recovery distillation column 19 at a rate of 1.7 L / h and supplied to the phase separation tank 4 via a separately provided supply pipe. That is, in this example, the second distillate was not extracted from the upper side of the IPA recovery distillation column 19. In addition, a third distillate containing low-boiling impurities was not extracted from the top of the IPA recovery distillation column 19 via the third extraction pipe 22. Meanwhile, a second bottoms product containing water was extracted from the bottom of the IPA recovery distillation column 19 via the second extraction pipe 21. In the IPA recovery distillation column 19, the temperature at the top was 85°C, and the gauge pressure at the top was 10 kPaG.

[0060] As a result of the above purification of the crude IPA, the purified IPA extracted from the first extraction pipe 16 had a water content of 30 ppm and a purity (excluding the water content) of 99.99% by mass, and was of high quality as anhydrous IPA.

[0061] On the other hand, when crude IPA was not supplied to the phase separation tank 4 but was directly supplied to the raw material supply stage of the azeotropic distillation column 2 for azeotropic distillation, the flow rate of crude IPA was calculated to be 62 L / h, which was larger than the flow rate of the upper phase liquid 5 (59 L / h) in Example 1. The amount of heat consumed in the azeotropic distillation column 2 was calculated to be 32.8 MJ / h, which was significantly larger than the amount of heat consumed in the azeotropic distillation column 2 in Example 1 (23.7 MJ / h). The diameter of the azeotropic distillation column 2 was also calculated to be 12 cm, which was larger than the diameter of the azeotropic distillation column 2 in Example 1 (10 cm).

[0062] 1; First supply pipe 2; Azeotropic distillation column 3; Condenser 4; Phase separation tank 5; Upper phase liquid 6; Lower phase liquid 7; Second supply pipe 8; Phase separation chamber 9a; First partition wall 9b; Second partition wall 10; Upper phase liquid storage chamber 11; Lower phase liquid storage chamber 12; Upward bent portion 13; Branch portion 14; Liquid transfer pipe 15; Third supply pipe 16; First withdrawal pipe 17; Fourth supply pipe 18; Fifth supply pipe 19; IPA recovery distillation column 20; Sixth supply pipe 21; Second withdrawal pipe 22; Third withdrawal pipe

Claims

1. A method for producing purified isopropyl alcohol by dehydrating crude isopropyl alcohol containing water as an impurity, comprising: a phase separation step of placing a mixture of the crude isopropyl alcohol and an azeotropic agent in a phase separation tank and separating the mixture into an upper phase liquid containing the azeotropic agent, water, and isopropyl alcohol, and a lower phase liquid containing water; and an azeotropic distillation step of azeotropically distilling the upper phase liquid in an azeotropic distillation tower and extracting a distillate containing an azeotropic mixture of the azeotropic agent and water, and a bottoms liquid containing isopropyl alcohol, and supplying the distillate to the phase separation tank.

2. The phase separation tank is divided into: a) a phase separation chamber in which the mixed liquid is accommodated and phase-separated into the upper phase liquid and the lower phase liquid; b) an upper phase liquid accommodation chamber adjacent to the phase separation chamber via a first partition wall on one side of the phase separation chamber and accommodating the upper phase liquid that overflows the first partition wall and flows in from the phase separation chamber; and c) a lower phase liquid accommodation chamber adjacent to the phase separation chamber via a second partition wall on the other side of the phase separation chamber and accommodating the lower phase liquid delivered from the phase separation chamber via a liquid delivery pipe; and the liquid delivery pipe is a communicating pipe having a first opening end connected to the lower phase liquid accommodated in the phase separation chamber and a second opening end connected to the lower phase liquid accommodation chamber, The communicating pipe has a maximum height corresponding to the upper end region of the first partition wall, an upward bent portion including the second opening end, and a third opening end that is connected to the gas phase portion of the phase separation tank at a position higher than the upper end of the first partition wall and has a branch portion branched from the upward bent portion, the upper phase liquid storage chamber is connected to a supply pipe that supplies the upper phase liquid to a raw material supply stage of the azeotropic distillation tower, the lower phase liquid storage chamber is connected to a discharge pipe that discharges the lower phase liquid, and the upper end of the first partition wall is lower than the upper end of the second partition wall. The method for producing purified isopropyl alcohol according to claim 1.

3. The method for producing purified isopropyl alcohol according to claim 1 or 2, wherein the azeotropic agent is benzene.

4. The method for producing purified isopropyl alcohol according to claim 1 or 2, further comprising the steps of: distilling the lower phase liquid in an isopropyl alcohol recovery distillation column to extract a second distillate containing an azeotropic mixture of isopropyl alcohol and water, and a second bottoms liquid containing water; and supplying the second distillate to the phase separation tank.

5. The method for producing purified isopropyl alcohol according to claim 4, wherein the second distillate is extracted from the upper side of the isopropyl alcohol recovery distillation column, and low boiling impurities are extracted from the top of the isopropyl alcohol recovery distillation column and disposed of.

6. An apparatus for producing purified isopropyl alcohol by dehydrating crude isopropyl alcohol containing water as an impurity, comprising: a phase separation tank for accommodating a mixture of the crude isopropyl alcohol and an azeotropic agent and for phase-separating the mixture into an upper phase liquid containing the azeotropic agent, water, and isopropyl alcohol, and a lower phase liquid containing water; and an azeotropic distillation tower for azeotropically distilling the upper phase liquid, wherein a first supply pipe for supplying the crude isopropyl alcohol to the phase separation tank and a second supply pipe for supplying the upper phase liquid to a raw material supply stage of the azeotropic distillation tower are connected to the phase separation tank; a third supply pipe for supplying a distillate containing an azeotropic mixture of the azeotropic agent and water to the phase separation tank is connected to the top of the azeotropic distillation tower; and a withdrawal pipe for withdrawing a bottoms liquid containing isopropyl alcohol is connected to the bottom of the azeotropic distillation tower. A fourth supply pipe for supplying the azeotropic agent is connected to any one of the first supply pipe, the phase separation tank, the second supply pipe, the azeotropic distillation column, and the third supply pipe.

7. The phase separation tank is divided into the following compartments: a) a phase separation chamber in which the mixed liquid is accommodated and phase-separated into the upper phase liquid and the lower phase liquid; b) an upper phase liquid accommodation chamber adjacent to the phase separation chamber via a first partition wall on one side of the phase separation chamber and accommodating the upper phase liquid that overflows the first partition wall and flows in from the phase separation chamber; and c) a lower phase liquid accommodation chamber adjacent to the phase separation chamber via a second partition wall on the other side of the phase separation chamber and accommodating the lower phase liquid delivered from the phase separation chamber via a liquid delivery pipe; and the liquid delivery pipe is a communicating pipe having a first opening end connected to the lower phase liquid accommodated in the phase separation chamber and a second opening end connected to the lower phase liquid accommodation chamber, The communicating pipe has a highest portion at a height corresponding to the upper end region of the first partition wall, an upward bent portion including the second opening end, and a branch portion having a third opening end that is connected to the gas phase portion of the phase separation tank at a position higher than the upper end of the first partition wall and branches off from the upward bent portion, the second supply pipe is connected to the upper phase liquid storage chamber, a discharge pipe that discharges the lower phase liquid is connected to the lower phase liquid storage chamber, and the upper end of the first partition wall is lower than the upper end of the second partition wall.

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