How is isopropyl alcohol purified?

Abstract

The present invention provides a method for producing isopropyl alcohol, comprising the steps of: cooling a reaction product and supplying the cooled reaction product to an absorption tower; and supplying a bottom discharge stream from the absorption tower containing isopropyl alcohol from the absorption tower to an isopropyl alcohol purification section including first to fourth columns, and supplying an upper discharge stream from the absorption tower containing propylene to a gas purification section including fifth and sixth columns, wherein all or a portion of the reaction product is cooled by heat exchange with one or more of the bottom discharge stream from the fourth column and the side discharge stream from the fifth column, the upper discharge stream from the second column is heat exchanged with the bottom discharge stream from the sixth column, and the upper discharge stream from the third column is heat exchanged with one or more of the bottom discharge stream from the first column and the bottom discharge stream from the second column.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0158482 filed on November 15, 2023 and Korean Patent Application No. 10-2024-0147824 filed on October 25, 2024, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for purifying isopropyl alcohol, and more particularly to a method that can reduce energy consumption and process costs when purifying isopropyl alcohol from a reaction product in the production process of isopropyl alcohol. [Background technology]

[0003] Isopropyl alcohol (IPA) is recognized as an excellent solvent in various industries and applications due to its ability to dissolve a wide range of substances, fast evaporation, and relatively low toxicity. Isopropyl alcohol is an essential substance in a variety of manufacturing, healthcare, and consumer applications.

[0004] In the process of producing isopropyl alcohol, for example, propylene and water are used as raw materials. At this time, the propylene and water react to produce isopropyl alcohol. In addition to isopropyl alcohol, unreacted propylene monomer, and unreacted water, the reaction products in the process of producing isopropyl alcohol contain various impurities or by-products such as diisopropyl ether (DIPE), acetone, n-propyl alcohol (NPA), and hexanol.

[0005] In order to obtain isopropyl alcohol from the reaction product, a purification process of isopropyl alcohol is necessarily required. Therefore, in order to obtain high-purity isopropyl alcohol, the purification process of isopropyl alcohol needs to be highly efficient, and an improved design is required from the economic point of view of reducing energy consumption, operating costs, and equipment costs. Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide an isopropyl alcohol purification method that can obtain high-purity isopropyl alcohol and reduce energy consumption and improve operating costs / equipment costs in order to solve the problems mentioned in the background art of the invention described above.

[0007] However, the problems to be solved by the present application are not limited to those mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0008] According to one embodiment of the present invention for solving the above-mentioned problems, the present invention provides a method for producing isopropyl alcohol, comprising the steps of: reacting propylene monomer with water to prepare a reaction product containing propylene and isopropyl alcohol; cooling the reaction product and supplying the cooled reaction product to an absorption tower; and supplying a bottom discharge stream from the absorption tower containing isopropyl alcohol from the absorption tower to an isopropyl alcohol purification section including first to fourth columns, and supplying an upper discharge stream from the absorption tower containing propylene to a gas purification section including fifth and sixth columns, wherein the isopropyl alcohol contained in the bottom discharge stream from the absorption tower supplied to the isopropyl alcohol purification section is separated from the bottom discharge stream from the first column, the first side discharge stream from the second column, the second side discharge stream from the third column, and the isopropyl alcohol contained in the top discharge stream from the absorption tower supplied to the isopropyl alcohol purification section. the propylene contained in the upper discharge stream of the absorption tower supplied to the gas purification section is obtained by sequentially passing through the upper discharge stream of the fifth column and the side discharge stream of the sixth column; all or a portion of the reaction product is cooled by heat exchange with one or more of the lower discharge stream of the fourth column and the side discharge stream of the fifth column; the upper discharge stream of the second column is heat exchanged with the lower discharge stream of the sixth column; and the upper discharge stream of the third column is heat exchanged with one or more of the lower discharge stream of the first column and the lower discharge stream of the second column. [Effects of the Invention]

[0009] According to the method for purifying isopropyl alcohol of the present invention, a feed containing isopropyl alcohol, water, and various by-products as a reaction product of propylene and water can be effectively purified to finally obtain high-purity isopropyl alcohol. In addition, unreacted propylene contained in the reaction product can be recovered in high purity and reused in the reaction for producing isopropyl alcohol.

[0010] By performing the processes that are conventionally performed using at least two distillation columns in the isopropyl alcohol purification section using a single distillation column, it is possible to reduce the reboiler energy required to operate at least two distillation columns, and to achieve a reduction in the capital and operating costs of the equipment by reducing the number of distillation columns.

[0011] Furthermore, after the reaction of propylene with water, heat exchange is performed between the distillation columns throughout the entire process for producing isopropyl alcohol, including the isopropyl alcohol purification section for recovering isopropyl alcohol and the gas purification section for recovering unreacted propylene. This reduces the amount of heat energy required to operate the distillation columns. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a process flow diagram showing all steps of a method for producing isopropyl alcohol according to one embodiment of the present invention. [Figure 2] FIG. 1 is a process flow diagram showing the steps between a reactor and an absorption tower in a process for producing isopropyl alcohol according to one embodiment of the present invention. [Figure 3] FIG. 1 is a process flow diagram showing a process related to an isopropyl alcohol purification unit in a process for producing isopropyl alcohol according to one embodiment of the present invention. [Figure 4] FIG. 1 is a process flow diagram showing a process related to a gas purification unit in a process for producing isopropyl alcohol according to one embodiment of the present invention. [Figure 5] FIG. 1 is a process flow diagram of a method for purifying isopropyl alcohol according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0013] The terms and words used in the description of the present invention and the claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0014] In connection with the description of the drawings, like reference numerals may be used for like or related components.

[0015] The singular form of a noun referring to an item can include one or more of said items unless the relevant context clearly dictates otherwise.

[0016] In this disclosure, each phrase such as "A or B," "at least one of A and B," "at least one of A or B," "A, B, or C," "at least one of A, B, and C," and "at least one of A, B, or C" can include any one or all possible combinations of the items listed in the corresponding phrase.

[0017] The term "and / or" includes combinations of the associated listed elements or any elements of the associated listed elements.

[0018] Terms such as "first," "second," or "first" or "second" may be used merely to distinguish a component from other components and do not limit the component in other respects (e.g., importance or order).

[0019] Furthermore, terms such as "front," "rear," "top," "bottom," "side," "left side," "right side," "upper," and "lower" used in this application are defined based on the drawings, and do not limit the shape or position of each component.

[0020] Terms such as "comprise" or "have" specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in this disclosure, but do not preclude the presence or possible addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0021] When a component is said to be "connected," "coupled," "supported," or "in contact with" another component, this includes not only cases where the components are directly connected, coupled, supported, or in contact, but also cases where the components are indirectly connected, coupled, supported, or in contact via a third component.

[0022] When a component is said to be located "on" another component, this includes not only the case where the component is in contact with the other component, but also the case where there is another component between the two components.

[0023] The term "stream" as used herein refers to the flow of fluid within a process, and may also refer to the fluid itself flowing through a pipe. Specifically, the term "stream" may refer to both the fluid itself and the flow of fluid flowing through a pipe connecting each device. The fluid may contain one or more components of gas, liquid, and solid.

[0024] Unless otherwise specified, the term "upper portion" used in this application means a point 0% to 10% below the top of the apparatus, specifically the top (top of the column), and the term "lower portion" means a point 90% to 100% below the top of the apparatus, specifically the bottom (bottom of the column).

[0025] Furthermore, "pressure" referred to in this application means gauge pressure measured under atmospheric pressure conditions.

[0026] On the other hand, unless otherwise specified in this application, the operating pressure of a column means the pressure at the top of the column, and the operating temperature of a column means the temperature at the bottom of the column.

[0027] One embodiment of the present invention relates to a method for purifying isopropyl alcohol (IPA). Hereinafter, the method for purifying isopropyl alcohol of the present invention will be described in detail with reference to the drawings.

[0028] Fig. 1 is a process flow diagram showing all steps of a method for producing isopropyl alcohol according to one embodiment of the present invention. Fig. 2 is a detailed process flow diagram showing steps between a reactor and an absorption tower in the method for producing isopropyl alcohol according to one embodiment of the present invention.

[0029] 1 and 2, the reaction product containing isopropyl alcohol can be produced by the reaction of propylene and water in a reactor. A feed containing propylene and water is supplied to the reactor, and the reaction product produced in the reactor may include isopropyl alcohol, unreacted propylene, unreacted water, and various by-products. In this case, the isopropyl alcohol must be separated and recovered from the reaction product, while the unreacted propylene monomer must be recovered and reused in the isopropyl alcohol production process.

[0030] Specifically, the reactor may be operated under optimal conditions for efficiently producing isopropyl alcohol through the gas phase reaction of propylene monomer and water. For example, the operating pressure of the reactor may be 10 kg / cm. 2 g~50kg / cm 2 g, 25 kg / cm 2 g~50kg / cm 2 g, or 35 kg / cm 2 g~45kg / cm 2The operating temperature can be 150°C to 220°C, 165°C to 220°C, or 180°C to 215°C. By operating the reactor at pressures and temperatures within the above ranges, isopropyl alcohol can be effectively produced by a gas-phase reaction using propylene monomer and water.

[0031] The reaction product produced under the operating conditions of the reactor may be a high-temperature, gas-phase reaction product. Meanwhile, the feed containing propylene and water, which are necessary reactants for the reaction, must be preheated to a temperature range suitable for supply to the reactor and then supplied to the reactor. Therefore, according to one embodiment of the present invention, the feed may be first supplied to heat exchanger 90 and primarily preheated by heat exchange with the reaction product. By exchanging heat between the feed and the reaction product discharged from the reactor in this manner, the high-temperature reaction product discharged from the reactor can be cooled to a temperature suitable for supply to absorber 10, and the feed can be preheated to a temperature suitable for supply to the reactor. This reduces the thermal energy required to heat the feed.

[0032] The feed preheated in the heat exchanger 90 can be additionally heated and fed to the reactor, if necessary.

[0033] On the other hand, the propylene contained in the feed may include propylene newly supplied for the reaction, propylene supplied from the top of the absorption tower 10, and propylene recovered at high purity from the gas purification section described below.

[0034] Propylene recycled within the process and supplied to the reactor is reused as a raw material for the gas-phase reaction. Therefore, to produce high-purity isopropyl alcohol, it is necessary to recover high-purity propylene after the reaction. Specifically, as described above, it is preferable that the propylene (C3H6) supplied to the reactor as a raw material has high purity. However, if the raw propylene contains impurities such as other unsaturated hydrocarbons (e.g., ethylene, butene, pentene), ethane, propane, or carbon dioxide, by-products (e.g., ethanol) with a boiling point similar to that of isopropyl alcohol may be produced during the reaction of propylene with water. Therefore, it is preferable that the propylene supplied to the reactor as a reactant contains 97 wt% or more, for example, 97 to 99.8 wt%, of propylene based on its total weight, and that the impurity content is less than 3 wt%.

[0035] However, only a portion of the propylene supplied to the reactor is used in the reaction. Therefore, the reaction product may contain unreacted propylene and unreacted water in addition to the isopropyl alcohol produced by the reaction of propylene monomer and water. For example, the reaction product may contain 65 to 85 wt% propylene monomer, 4 to 8 wt% isopropyl alcohol, and 5 to 30 wt% water. The reaction product may also contain at least two or more light and heavy by-products. Specifically, the reaction product may contain diisopropyl ether (DIPE) as a first light by-product, acetone as a second light by-product, and n-propyl alcohol (NPA) and hexanol as heavy by-products. Therefore, a process is required to separate the unreacted propylene from the reaction product and purify the isopropyl alcohol from the various by-products.

[0036] Meanwhile, there are various methods for recovering propylene from the reaction product. Among them, a method for recovering high-purity propylene and circulating it to the reactor where the gas-phase reaction is carried out will be exemplified.

[0037] According to one embodiment of the present invention, recovery of propylene in the reaction product can be carried out by a gas purification unit including an absorption tower, a flash drum, and at least a fifth column and a sixth column, while purification of isopropyl alcohol in the reaction product can be carried out by an isopropyl alcohol purification unit including an absorption tower, a flash drum, and at least a first to fourth column.

[0038] The method for producing isopropyl alcohol according to one embodiment of the present invention may include the step of cooling the reaction product and supplying the cooled reaction product to an absorber 10.

[0039] The cooling condenses and liquefies some components of the gas phase reaction product, while other components remain in the gas phase in the reaction product and can be supplied to the absorber 10. For example, isopropyl alcohol to be discharged to the lower discharge stream of the absorber 10 is preferably present in the liquid phase, and propylene and other gas components to be discharged to the upper discharge stream of the absorber 10 are preferably present in the gas phase. In other words, the phase change of some components due to the cooling can improve the efficiency of component separation in the absorber.

[0040] Specifically, if isopropyl alcohol is discharged to the top of the absorption tower and then re-introduced into the reactor, it will adversely affect the isopropyl alcohol production reaction taking place in the reactor, so it is preferable to recover isopropyl alcohol at the bottom of the absorption tower as much as possible. Also, if propylene and gas components are discharged to the bottom of the absorption tower, an additional gas purification column is required to recover the unreacted propylene or gas components discharged to the bottom, which increases energy consumption, so it is preferable to recover these unreacted propylene and gas components at the top of the absorption tower as much as possible.

[0041] Furthermore, in the absorption tower, water introduced into the upper part of the absorption tower absorbs isopropyl alcohol as it descends downward, and the reaction product can be supplied to the absorption tower 10 by adjusting the temperature range in which the absorption efficiency of isopropyl alcohol by water in the absorption tower 10 is highest by the cooling. That is, the cooling of the reaction product of the present invention can achieve the effect of improving the absorption efficiency of isopropyl alcohol in the absorption tower 10 by controlling the phase change of some components of the reaction product and the temperature of the reaction product.

[0042] From this point of view, the temperature of the cooled reaction product introduced into the absorber 10 may be 90 to 99°C, specifically 90 to 95°C. In this case, the efficiency of absorbing isopropyl alcohol by water in the absorber 100 is further improved, and propylene discharged to the bottom of the absorber can be minimized.

[0043] Meanwhile, all or a portion of the reaction product passing through the heat exchanger 90 may be cooled by heat exchange with one or more of the bottom discharge stream of the fourth column 400 and the side discharge stream of the fifth column 500.

[0044] Referring to FIGS. 2 to 4, which illustrate an embodiment of the present invention, the reaction product is heat exchanged in one or more of a fourth column first reboiler 410 provided at the bottom of the fourth column 400 in the isopropyl alcohol purification section and a fifth column first reboiler (side reboiler) 510 provided on the side of the fifth column 500 in the gas purification section, thereby enabling efficient energy use.

[0045] Specifically, first, by supplying the thermal energy of the high-temperature reaction product to one or more of the fourth column 400 and the fifth column 500, the thermal energy required to operate these columns can be reduced. In other words, most of the thermal energy required to operate one or more of the fourth column 400 and the fifth column 500 can be replaced by utilizing waste heat. Second, the amount of refrigerant used, which was previously required to cool the reaction product, can be reduced. Third, to improve the purification efficiency of the fifth column 500 in the gas purification section, it is essential to achieve a gentle temperature profile in the column. By supplying the thermal energy of the reaction product to the middle and lower sections of the fifth column 500, a gentle temperature profile can be achieved across the lower and middle sections of the fifth column.

[0046] Meanwhile, according to one embodiment of the present invention, the cooling of the reaction product may include a first cooling step in which all or a part of the reaction product stream is subjected to heat exchange with one or more of the bottom discharge stream of the fourth column 400 and the side discharge stream of the fifth column 500, and a second cooling step in which the first cooled reaction product stream (high temperature medium) is subjected to heat exchange with a refrigerant (low temperature medium).

[0047] 2, the reaction product stream may be branched into a first branch stream 50, a second branch stream 60, and a third branch stream 70. Here, the first branch stream 50 may be a stream that exchanges heat with the bottom discharge stream of the fourth column, and the second branch stream 60 may be a stream that exchanges heat with the side discharge stream of the fifth column. Meanwhile, the third branch stream 70 may be a stream that does not exchange heat with the fourth and fifth columns.

[0048] Specifically, the first branch stream 50 may be a stream that is heat exchanged with the bottom discharge stream of the fourth column 400 in the first reboiler 410 of the fourth column. That is, referring to Figures 2 and 3, heat exchanger A in Figure 2 is the first reboiler 410 of the fourth column. Meanwhile, the second branch stream 60 may be a stream that is heat exchanged with the side discharge stream of the fifth column 500 in the first reboiler 510 of the fifth column. That is, referring to Figures 2 and 4, heat exchanger B in Figure 2 is the first reboiler 510 of the fifth column.

[0049] In this case, the first cooling may be performed by heat exchange between the first branch stream 50 and the bottom discharge stream of the fourth column, and heat exchange between the second branch stream 60 and the side discharge stream of the fifth column.

[0050] The first cooled first and second branch streams 50 and 60 and the first uncooled third branch stream 70 are combined to form a combined stream, which may be additionally cooled by a refrigerant in a heat exchanger 80. Here, the refrigerant may be cooling water (CW).

[0051] Furthermore, the mass flow ratio of the first to third branch streams, i.e., the ratio of the mass flow rate of the first branch stream 50 to the mass flow rate of the second branch stream 60 to the mass flow rate of the third branch stream 70, may be in the range of 1:0.2-0.4:0.4-0.7. When the ratio is in the above range, the maximum amount of heat can be supplied compared to the sizes of the first reboiler 410 of the fourth column and the first reboiler 510 of the fifth column, and the sizes of the auxiliary reboiler 415 provided at the bottom of the fourth column 400 and the second reboiler 520 of the fifth column 500 provided at the bottom of the fifth column can be minimized. The reaction product cooled by the primary and secondary cooling processes can then be supplied to the absorber 10. Here, the cooled reaction product can be supplied to the absorber 10 as a gas-liquid mixed phase. In the absorber 10, a bottom discharge stream from the absorber containing isopropyl alcohol and an top discharge stream from the absorber containing propylene can be separated.

[0052] The reaction product may be supplied to the lower part of the absorber 10, and water may be supplied to the upper part of the absorber 10. The water supplied to the upper part dissolves isopropyl alcohol contained in the reaction product and is separated in the lower part of the absorber 10, and a stream containing propylene may be separated in the upper part.

[0053] The water supplied to the upper part of the absorption tower 10 may be a stream 230 that is branched and supplied from the bottom discharge stream of the second column 200 of the isopropyl alcohol purification unit.

[0054] The bottom discharge stream from the absorber 10 is supplied to a flash drum 20, and propylene and gas components present in the bottom discharge stream from the absorber 10 can be separated into the upper part of the flash drum 20 and re-supplied to the absorber 10. As a result, propylene and gas components can be eliminated or minimized in a bottom discharge stream 30 from the flash drum 20. The bottom discharge stream 30 from the flash drum 20 can be introduced into an isopropyl alcohol purifying section.

[0055] Meanwhile, the top discharge stream from the absorber 10 may contain propylene and gas components. After the top discharge stream from the absorber 10 is compressed by a compressor, a portion of the stream 40 may be supplied to a gas purifying section (described later), and the remaining stream may be mixed with newly supplied propylene and water, introduced into the heat exchanger 90 as described above, and then recycled to the reactor.

[0056] According to one embodiment of the present invention, the isopropyl alcohol purification unit may include first to fourth columns. The isopropyl alcohol contained in the bottom discharge stream of the absorption tower, preferably the bottom discharge stream 30 of the flash drum 20, may be obtained by sequentially passing through the bottom discharge stream of the first column, the first side discharge stream of the second column, the bottom discharge stream of the first region of the third column, and the top discharge stream of the fourth column. The purification process performed in the isopropyl alcohol purification unit will now be described with reference to FIG. 3.

[0057] According to one embodiment of the present invention, at least one of the bottom discharge stream from the absorber 10, the bottom discharge stream from the flash drum 20, and the bottom discharge streams from the fifth and sixth columns of the gas purification section can be supplied to the first column as a feed for the isopropyl alcohol purification section. Specifically, the feed stream supplied to the first column can be the bottom discharge stream 30 from the flash drum 20. The feed stream supplied to the first column can include isopropyl alcohol, water, a first light by-product, a second light by-product, and a heavy by-product.

[0058] The feed stream 30 to be supplied to the first column may be introduced into the first column 100 at a point 30 to 50% below the top of the column.

[0059] According to one embodiment of the present invention, the first light by-product contained in the feed 30 may be first separated and removed by the first column 100 and the layer separator 120 connected to the upper portion of the first column 100.

[0060] Specifically, as a result of the distillation in the first column 100, an upper discharge stream from the first column containing isopropyl alcohol, water, a first light by-product, and optionally a second light by-product, and a lower discharge stream from the second column containing isopropyl alcohol, water, a second light by-product, and a heavy by-product, may be discharged from the top and bottom of the first column 100, respectively.

[0061] The top discharge stream from the first column 100 may be supplied to a condenser, cooled, and liquefied after being discharged from the first column 100. The liquefied top discharge stream from the first column may be supplied to a phase separator 120 and subjected to liquid-liquid separation. After liquid-liquid separation, an aqueous phase stream containing isopropyl alcohol, water, and optionally a second light by-product may be refluxed to the first column, and an oil phase stream containing the first light by-product may be discharged to the system. The amount of the first light by-product discharged to the system may be 97% by weight or more, 99% by weight or more, or specifically 100% by weight, based on the content of the first light by-product contained in the feed stream 30 supplied to the first column as 100% by weight.

[0062] In order for the first light by-product to be easily separated by distillation in the first column 100 and liquid-liquid separation in the phase separator 120 installed at the top of the first column, at least the first light by-product should be an oily component that is not dissolved in water. That is, the first column 100 is operated under operating conditions that do not vaporize the heavy by-product, and the phase separator 120 separates the first light by-product from essentially water and isopropyl alcohol dissolved in water, thereby enabling efficient separation of the first light by-product.

[0063] According to one embodiment of the present invention, the first light by-product may be diisopropyl ether (DIPE), which is insoluble in water, and the second light by-product may be acetone, which is soluble in water. Because the boiling point of acetone is lower than that of diisopropyl ether, the top discharge stream from the first column may contain water, isopropyl alcohol, acetone, and diisopropyl ether (DIPE). The isopropyl alcohol contained in the top discharge stream from the first column is separated from the first light by-product (oil phase) by liquid-liquid separation performed in phase separator 120, and the water, isopropyl alcohol, and acetone contained in the aqueous phase are returned to first column 100. Therefore, the phase separator 120 installed at the top of first column 100 can minimize the amount of isopropyl alcohol lost at the top of first column 100.

[0064] Meanwhile, the first light by-product contained in the feed stream 30 supplied to the first column can be almost entirely discharged to the outside of the system. To achieve this, the operating conditions of the first column 100 should be controlled so that almost entirely the first light by-product contained in the feed 30 is discharged to the top discharge stream of the first column 100.

[0065] Specifically, the operating temperature of the first column 100 may be 75°C or more, 80°C or more, and 95°C or less, 90°C or less. The operating temperature may refer to the temperature at the bottom of the first column 100. Meanwhile, the operating pressure of the first column 100 is 1 kg / cm. 2 ·g or less, 0.5kg / cm 2 The operating pressure may be 0.1 g or less. The operating pressure may refer to the pressure at the top of the first column 100. When the first column 100 is operated at the above-described operating temperature and operating pressure, the first light by-product can be separated as much as possible into the top discharge stream of the first column. This prevents the first light by-product from flowing into the bottom discharge stream of the first column and, as a result, remaining as an impurity in the isopropyl alcohol produced. Furthermore, when the operating temperature and operating pressure of the first column 100 are as described above, efficient energy utilization is possible through heat exchange with the top discharge stream of the third column, which will be described later.

[0066] Meanwhile, in order to effectively recover isopropyl alcohol contained in the upper discharge stream of the first column and return it to the first column through the liquid-liquid separation performed in the layer separator 120, water should be supplied to the upper part of the first column. The water supplied to the upper part of the first column is supplied to the first column separately from the water contained in the feed stream 30 supplied to the first column. The water supplied to the upper part of the first column may be water contained in stream 220, which is a circulated stream obtained by branching off a portion of the water-containing lower discharge stream 250 of the second column, as described below.

[0067] Specifically, the stream discharged to the bottom of the second column 200 is branched into a reflux stream supplied to the first reboiler 210 of the second column 200, and the remaining stream may be branched into stream 230 supplied to the top of the absorber 10, stream 240 containing water discharged to the outside of the system, and stream 220 circulated to the top of the first column. That is, the branched stream 220 obtained by branching a portion of the water-containing discharge stream from the bottom of the second column 200 may be a branched stream obtained by branching a portion of stream 250 obtained by branching a stream to be refluxed to the first reboiler 210 of the second column 200 from the stream immediately after being discharged to the bottom of the second column 200.

[0068] Meanwhile, according to one embodiment of the present invention, the mass flow rate of the branch stream 220 of the bottom discharge stream 250 of the second column, which is recycled to the top of the first column, needs to be controlled in consideration of the amount of isopropyl alcohol lost in the layer separator 120 and the amount of energy consumed in the first column 100. Specifically, the mass flow rate of the branch stream 220 of the bottom discharge stream 250 of the second column relative to the mass flow rate of the feed stream 30 supplied to the first column 100 may be 0.4 to 1.2, 0.4 to 1.0, or 0.5 to 0.8. If the flow rate of water supplied to the top of the first column is greater than 1.2, the amount of energy required in the first column may increase excessively. On the other hand, if the flow rate of water supplied to the top of the first column is less than 0.4, it may be difficult to supply sufficient water to the layer separator 120, which may result in the loss of isopropyl alcohol as an oil phase or an excessive increase in the amount of loss.

[0069] Meanwhile, in the layer separator 120 installed at the top of the first column 100, isopropyl alcohol should be contained in the aqueous phase and refluxed together with water to the first column 100. If the isopropyl alcohol is contained in the oil phase, loss of isopropyl alcohol occurs in the layer separator 120. To prevent this loss of isopropyl alcohol, a sufficient amount of water should be secured in the layer separator 120. The amount of water in the layer separator 120 is affected by the amount of water introduced into the first column 100.

[0070] According to one embodiment of the present invention, the water introduced into the first column 100 may be water contained in the feed stream 30 supplied to the first column and water contained in the stream 220, which is a circulating stream formed by branching off a portion of the bottom discharge stream 250 from the second column. To minimize the loss of isopropyl alcohol in the phase separator 120, the sum of the mass flow rate of the water contained in the feed stream 30 and the mass flow rate of the water contained in the stream 220, which is a circulating stream formed by branching off a portion of the bottom discharge stream 250 from the second column, is preferably maintained at a ratio of 12 to 15 (mass flow rate ratio of isopropyl alcohol to water) relative to the mass flow rate of the isopropyl alcohol contained in the feed stream 30. In this case, a sufficient amount of water can be supplied to the phase separator 120, thereby preventing the loss of isopropyl alcohol as an oil phase in the phase separator 120 and optimizing the energy consumption required to operate the first column 100.

[0071] That is, when the mass flow ratio of the isopropyl alcohol to water supplied to the first column is less than 12, it is difficult to secure a sufficient amount of water in the layer separator 120, resulting in a loss of isopropyl alcohol as an oil phase and making it difficult to achieve a desired recovery rate of isopropyl alcohol. Furthermore, in this case, a problem may occur in that a portion of the first light by-product, which should be removed as an oil phase in the layer separator 120, is included in the aqueous phase and introduced into the second column 200. If such a first light by-product is introduced into the second column 200, it will be included in the first side discharge stream of the second column containing a mixture of isopropyl alcohol and water, resulting in a decrease in the purity of the isopropyl alcohol recovered from the second column.

[0072] Furthermore, if the mass flow ratio of the isopropyl alcohol to water supplied to the first column is greater than 15, the loss of isopropyl alcohol in the layer separator 120 can be prevented, but the amount of water circulating through the first column 100 and the second column 200 becomes excessively large, which increases the energy consumption of the two columns.

[0073] Furthermore, in order to minimize the loss of isopropyl alcohol in the layer separator 120 and reduce the amount of energy used in the first and second columns, the mass flow rate of water contained in the stream 220, which is a portion of the bottom discharge stream 250 of the second column branched off and recycled, may be 58% to 90% of the mass flow rate of water contained in the feed stream 30.

[0074] Meanwhile, a first reboiler 110 is provided at the bottom of the first column 100 to supply heat energy required for the operation of the first column. The reflux stream of the discharge stream from the bottom of the first column is introduced into the first reboiler 110 of the first column and is heat exchanged with a high-temperature heat source, and then may be introduced back into the bottom of the first column 100. The first reboiler 110 of the first column supplies the first column 100 with heat energy required for the operation of the first column.

[0075] According to one embodiment of the present invention, the heat source of the first reboiler 110 of the first column, i.e., the heat source exchanging heat with the reflux stream of the lower discharge stream of the first column, may be the upper discharge stream 330 of the third column 300, as described below. Specifically, all or a portion of the upper discharge stream 330 of the third column may be heat exchanged with the reflux stream of the lower discharge stream of the first column in the first reboiler 110 of the first column before being introduced into the condenser 380 or layer separator 340 provided at the top of the third column 300. In this way, the thermal energy of the upper discharge stream 330 of the third column 300 can be supplied to the first column 100.

[0076] Meanwhile, according to one embodiment of the present invention, if the thermal energy of the upper discharge stream 330 of the third column 300 alone cannot replace all of the reboiler energy required to operate the first column 100, an auxiliary reboiler 115 may be provided at the bottom of the first column 100, in addition to the first reboiler 110 of the first column.

[0077] According to one embodiment of the present invention, the bottom effluent stream of the first column is introduced into a second column 200 and separated into a second light by-product, a mixture of isopropyl alcohol and water, a heavy by-product, and water according to boiling point.

[0078] Specifically, the bottom effluent stream from the first column, which includes the isopropyl alcohol, water, a second light by-product, and a heavy by-product, may be supplied to a second column 200, and separated into a top effluent stream from the second column containing the second light by-product, a first side effluent stream from the second column 290 containing a mixture of the isopropyl alcohol and water, a second side effluent stream from the second column 280 containing the heavy by-product, and a bottom effluent stream from the second column 250 containing the water.

[0079] The second light by-product is a by-product having the lowest boiling point relative to the other components to be separated. The second light by-product may be a compound having a boiling point of 50 to 70°C, specifically acetone. The acetone may be a by-product produced during the gas-phase reaction to produce isopropyl alcohol, or may be a by-product produced by oxidation of isopropyl alcohol in a subsequent process after the gas-phase reaction. The top discharge stream from the second column may contain 60 wt% or more, 70 wt% or more, 90 wt% or more, and 100 wt% or less of the second light by-product, with the remainder being a mixture of isopropyl alcohol and water. After being discharged from the second column, the top discharge stream from the second column may pass through a condenser, with a portion of the second light by-product being refluxed back to the second column and the remainder being discharged to the outside of the system.

[0080] Meanwhile, according to one embodiment of the present invention, the upper discharge stream of the second column 200 may be heat-exchanged with the lower discharge stream of the sixth column 600. Specifically, referring to FIGS. 3 and 4, the upper discharge stream of the second column 200 may be heat-exchanged with the lower discharge stream of the sixth column 600 in a first reboiler 610 for the sixth column 600 provided at the bottom of the sixth column 600 before being introduced into a condenser 280 provided at the top of the second column 200. In this case, the heat exchanger D provided at the top of the second column 200 may be the first reboiler 610 for the sixth column. This allows the thermal energy of the upper discharge stream of the second column 200 to be supplied to the sixth column 600. The upper discharge stream of the second column 200 that has been heat-exchanged with the lower discharge stream of the sixth column 600 may be refluxed to the second column 200 via a condenser 280 provided at the top of the second column 200 or discharged to the outside of the system.

[0081] Meanwhile, the mixture of isopropyl alcohol and water may be an azeotrope of isopropyl alcohol and water. That is, water, which has a boiling point of about 100° C., and isopropyl alcohol, which has a boiling point of about 82.3° C., form an azeotrope at an azeotropic temperature of about 81° C. The boiling point of the azeotrope of isopropyl alcohol and water is higher than the boiling point of the second light by-product but lower than the boiling point of the heavy by-product.

[0082] Thus, a portion of the water introduced into the second column forms an azeotrope with the isopropyl alcohol and is discharged into the first side draw stream 290 of the second column, and the remaining water is discharged into the bottom draw stream 250 of the second column.

[0083] A second column first reboiler 210 is provided at the bottom of the second column 200 to supply heat energy required for the operation of the second column. The reflux stream from the bottom discharge stream of the second column is introduced into the second column first reboiler 210 and is heat exchanged with a high-temperature heat source, and then the reflux stream is introduced back into the bottom of the second column 200. The second column first reboiler 210 can supply the second column 200 with heat energy required for the operation of the second column 200.

[0084] According to one embodiment of the present invention, the heat source of the first reboiler 210 of the second column, i.e., the heat source that exchanges heat with the reflux stream of the lower discharge stream of the second column, may be the upper discharge stream 330 of the third column 300, as described below. Specifically, all or a portion of the upper discharge stream 330 of the third column may be heat exchanged with the reflux stream of the lower discharge stream of the second column in the second reboiler 230 before being introduced into the condenser 380 or layer separator 340 provided at the top of the third column 300. In this way, the thermal energy of the upper discharge stream of the third column 300 can be supplied to the second column 200.

[0085] According to one embodiment of the present invention, if the thermal energy of the upper discharge stream 330 of the third column 300 alone cannot replace all of the reboiler energy required to operate the second column 200, an auxiliary reboiler 215 may be provided at the bottom of the second column 200, in addition to the first reboiler 210 of the second column.

[0086] Meanwhile, a water-containing bottom discharge stream 250 from the second column, specifically, a branch stream 220 obtained by branching off a portion of the stream 250 discharged from the bottom of the second column 200 that is not supplied to the reboiler 210, may be recycled to the top of the first column. The water recycled from the second column 200 may be used to replenish a sufficient amount of water to facilitate the phase separation of the aqueous phase and the oil phase in the phase separator 120 provided at the top of the first column 100.

[0087] Meanwhile, the heavy by-products may include n-propyl alcohol (NPA) and hexanol, and such heavy by-products may be discharged into the second side draw stream 280 of the second column.

[0088] In one embodiment of the present invention, the second column 200 includes a dividing wall spaced apart from the bottom and extending along the length of the column, and the second column may be a distillation column divided by the dividing wall into a top region, a bottom region, a supply region, and a discharge region.

[0089] 3, the top region is a region located above the upper end of the separation wall and is a region where the upper discharge stream of the second column is discharged, and the bottom region is a region located below the lower end of the separation wall and is a region where the lower discharge stream 250 of the second column is discharged. Meanwhile, the lower discharge stream of the first column can be supplied to the supply region.

[0090] The first side discharge stream 290 of the second column and the second side discharge stream 280 of the second column may be discharged from a discharge region within the region partitioned by the partition wall. Specifically, the first side discharge stream 290 may be discharged from a discharge region above the second side discharge stream 280.

[0091] That is, according to one embodiment of the present invention, a composition containing at least four components, such as isopropyl alcohol, water, a second light by-product, and a heavy by-product (the bottom discharge stream of the first column) is separated and discharged into an upper section, a first side section, a second side section, and a lower section by a single column (the second column) equipped with a separating wall, thereby reducing the number of distillation columns conventionally required for separating these components.

[0092] Specifically, referring to FIG. 5, in which a distillation column without a separating wall is used as the C2 column, although it is not impossible to discharge separated products through the top, bottom, first, and second sides of the C2 column, in particular, because the side discharge stream from which heavy by-products are separated contains a large amount of isopropyl alcohol and water, additional purification of the side discharge stream is required to increase the isopropyl alcohol yield. That is, a process was required in which the side discharge stream was introduced into a C3 column, an additional stream containing isopropyl alcohol was recovered from the top, and this was then fed back to the C2 column. That is, referring to FIG. 5, according to the present invention, the same functions performed by the conventional C2 and C3 columns can be performed by a single distillation column equipped with a separating wall, thereby reducing the number of columns and the energy consumption (e.g., steam consumption) required for column operation. Furthermore, by using a second column equipped with a separating wall, separation is first performed in the feed region and final purification is performed in the discharge region, thereby achieving a reduction in energy consumption greater than simply operating two columns together.

[0093] Meanwhile, the upper end of the separation wall may be located at a point 3% to 30% of the height downward from the top of the second column 200, and the lower end of the separation wall may be located at a point 70% to 95% of the height downward from the top of the second column 200.

[0094] Furthermore, the first side draw stream 290 may be discharged from a point 5 to 33% below the top of the second column, and the second side draw stream 280 may be discharged from a point 40 to 80% below the top of the second column.

[0095] The location of the separator wall and the discharge points of the first and second side streams described above allow for reduced energy consumption compared to a conventional two-column system while providing four streams of desired purity from the second column.

[0096] The operating temperature and pressure in the top and bottom regions of the second column 200 must also be controlled in view of the purity of the components separated along with the isopropyl alcohol and the energy required to separate these components.

[0097] Specifically, the operating temperature of the top region of the second column 200 may be 90°C or less, 85°C or less, or 80°C or less, and the operating pressure of the top region may be 2 kg / cm 2 ·g or less, 1kg / cm 2 ·g or less, 0.05kg / cm 2 The operating temperature of the bottom region of the second column 200 may be 85°C or higher, or 88°C or higher, and 105°C or lower, or 103°C or lower. The operating pressure of the bottom region may be 1.0 kg / cm 2 ·g or less, 0.5kg / cm 2 ·g or less.

[0098] When the operating temperature and pressure of the second column 200 are as described above, efficient energy utilization is possible through heat exchange between the lower discharge stream of the second column and the upper discharge stream of the third column in the first reboiler 210 of the second column, and efficient energy utilization is possible through heat exchange between the lower discharge stream of the sixth column and the upper discharge stream of the second column in the first reboiler 610 of the sixth column.

[0099] A method for producing isopropyl alcohol according to one embodiment of the present invention can include feeding a first side draw stream 290 from a second column, the first side draw stream 290 comprising a mixture of isopropyl alcohol and water, to a third column 300 and performing azeotropic distillation in the presence of an azeotroping agent.

[0100] The third column 300 may be a dividing wall distillation column including a dividing wall connected to the bottom and extending in the column longitudinal direction, and divided by the dividing wall into a first region, a second region opposite the first region, and an upper region located above the upper end of the dividing wall. Specifically, the dividing wall may be connected to (coupled with) the bottom of the third distillation column 300 and extend upward in the longitudinal direction of the third distillation column 300. In this case, the first region and the second region are defined to face each other across the dividing wall, and the second region is a region opposite the first region. Meanwhile, the upper region is a region located above the upper end of the dividing wall.

[0101] Specifically, the first side draw stream 290 of the second column 200 can include a mixture of isopropyl alcohol and water, specifically an azeotropic mixture of isopropyl alcohol and water. More specifically, the first side draw stream 290 of the second column can include 80-90 wt% isopropyl alcohol and 10-20 wt% water.

[0102] Meanwhile, azeotropic distillation can be performed in the third distillation column 300 in the presence of an azeotropic agent. A portion of the isopropyl alcohol and a portion of the water contained in the first side discharge stream 290 of the second column 200 can form an azeotrope. Because these components cannot be completely separated by conventional distillation, an azeotropic agent is typically used to remove the azeotropic relationship between the isopropyl alcohol and water, after which the isopropyl alcohol and water can be separated with high purity. The azeotropic agent of the present invention that performs this function can be one or more selected from the group consisting of cyclohexane, benzene, toluene, and isopropyl acetate.

[0103] The azeotropic agent is a substance added separately from the feed components for azeotropic distillation. However, since the azeotropic agent is an impurity in terms of isopropyl alcohol, etc., the azeotropic agent should be separated using a separate distillation column or the like, and from an economical point of view, the separated azeotropic agent should be recycled.

[0104] 5, a conventional method for separating isopropyl alcohol and water from a feed containing an isopropyl alcohol-water azeotrope and by-products involves azeotropic distillation using a conventional azeotropic distillation column C4 without a separating wall in the presence of an azeotropic agent. The top discharge stream containing water and azeotropic agent is then phase-separated in a layer separator, and the oil phase containing the azeotropic agent is then refluxed back to the azeotropic distillation column C4. However, because the aqueous phase still contains a large amount of azeotropic agent in addition to water, the aqueous phase is introduced into the azeotropic agent recovery column C5, where the azeotropic agent and water are separated by distillation. The recovered azeotropic agent is then introduced back into the azeotropic distillation column C4, while the water is discharged outside the system. Separating the azeotropic agent and water by distillation in the azeotropic agent recovery column C5 requires the supply of a large amount of energy via a reboiler installed at the bottom of the azeotropic agent recovery column C5.

[0105] Meanwhile, in the prior art, the azeotropic distillation column C4 receives heat energy required for its operation from a reboiler installed at the bottom. When the top discharge stream of the azeotropic distillation column C4 contains water and an azeotropic agent, the bottom discharge stream of the azeotropic distillation column C4 contains isopropyl alcohol and by-products. The bottom discharge stream of the azeotropic distillation column C4 is supplied to an isopropyl alcohol recovery column C6, and isopropyl alcohol is obtained from the top of the isopropyl alcohol recovery column C6, and by-products are separated from the bottom of the isopropyl alcohol recovery column C6.

[0106] However, referring to Figures 1 and 3, which illustrate a method for producing isopropyl alcohol according to one embodiment of the present invention, the present invention provides a dividing wall in the third distillation column 300 where azeotropic distillation is performed, and optimally designs the reflux point of the aqueous and oil phases refluxed from the layer separator 340. This allows for the production of high-purity isopropyl alcohol without the need for an azeotropic agent recovery column C5, which is used to separate the azeotropic agent from the water. This not only reduces the thermal energy required to operate the conventional azeotropic agent recovery column C5 via a reboiler, but also reduces the cooling energy required to operate the condenser installed above the azeotropic agent recovery column C5. Furthermore, in addition to the energy savings achieved by not using the azeotropic agent recovery column C5, the energy consumption required to operate the distillation column can also be reduced when comparing the third distillation column 300 of the present invention, which is a dividing wall distillation column, with the conventional azeotropic distillation column C4.

[0107] To this end, according to one embodiment of the present invention, the first region provided at the bottom of the third distillation column 300 may be provided with a reboiler 310 connected to the bottom of the first region, and the second region may be provided with a reboiler 315 connected to the bottom of the second region. Here, the term "bottom" refers to a point 90% to 100% below the top (highest point) of the third distillation column 300. The first and second regions may receive thermal energy from reboilers 310 and 315, respectively, and the operating conditions of the first and second regions may be adjusted by adjusting the thermal energy supplied by the reboilers 310 and 315, respectively.

[0108] According to one embodiment of the present invention, the thermal energy supplied by the reboiler 310 connected to the lower part of the first zone may be 1.5 to 3 times, more specifically 1.8 to 2.5 times, the thermal energy supplied by the reboiler 315 connected to the lower part of the second zone. As a result, isopropyl alcohol of a desired purity can be separated into a bottom discharge stream from the first zone of the third distillation column, and pure water can be separated into a bottom discharge stream from the second zone.

[0109] The temperature at the bottom of the first zone can be 135°C or higher, 137°C or higher, and 150°C or lower, 148°C or lower. The temperature at the bottom of the second zone can be 155°C or higher, 158°C or higher, and 170°C or lower, 168°C or lower. Here, each bottom temperature is the operating temperature in the first and second zones at a point 90% to 100% below the top (top) of the column 300. By controlling the temperatures at the bottom of the first and second zones in this manner, it is possible to reduce the energy required for distillation in the third distillation column 300, as well as to obtain isopropyl alcohol of a desired purity from the bottom of the first zone and separate pure water from the bottom of the second zone.

[0110] Meanwhile, the first zone lower effluent stream discharged from the first zone of the third distillation column 300 may include isopropyl alcohol and heavy by-products. Here, the heavy by-products may include n-propyl alcohol (NPA). A portion of the first zone lower effluent stream may be heat exchanged in a reboiler 310 connected to the lower portion of the first zone and then refluxed back to the first zone, and the remainder of the first zone lower effluent stream may be supplied to the fourth column 400.

[0111] Meanwhile, the second zone lower discharge stream discharged from the second zone may contain water. A portion of the second zone lower discharge stream may be heat exchanged in a reboiler 315 connected to the lower part of the second zone and then returned to the second zone, and the remainder of the second zone lower discharge stream may be discharged to the outside of the system.

[0112] As described above, the region above the upper end of the separation wall in the third distillation column 300 may constitute the upper region. The separation wall extends from the bottom of the column, and the upper end of the separation wall may be located at a height of 10 to 45%, or more specifically, 15 to 30%, below the top of the third distillation column 300. This maximizes the separation efficiency of the third distillation column 300, allowing isopropyl alcohol of a desired purity to be obtained from the bottom of the first region and pure water to be separated from the bottom of the second region.

[0113] From the top of the upper region, a top effluent stream 330 comprising water and entrainer can be discharged.

[0114] According to one embodiment of the present invention, the upper discharge stream 330 of the third column may be heat exchanged with one or more of the lower discharge stream of the first column and the lower discharge stream of the second column in one or more of the first reboiler 110 of the first column 100 and the first reboiler 210 of the second column 200. Thus, by supplying heat from the upper discharge stream 330 of the third column to one or more of the first column and the second column, the thermal energy required to operate one or more of the first column and the second column can be reduced.

[0115] 3, the heat exchanger C provided at the top of the third column may be one or more of the first reboiler 110 of the first column and the first reboiler 210 of the second column. The upper discharge stream 330 of the third column is discharged from the third column 300 and then transferred to one or more of the first reboiler 110 of the first column and the first reboiler 210 of the second column, thereby supplying the heat energy contained therein to one or more of the first column 100 and the second column 200. In this case, the upper discharge stream 330 of the third column may be heat exchanged with the first reboiler 110 of the first column or the first reboiler 210 of the second column, or may be heat exchanged with both the first reboiler 110 of the first column and the first reboiler 210 of the second column. When the top discharge stream 330 of the third column is heat exchanged with both the first reboiler 110 of the first column and the first reboiler 210 of the second column, the top discharge stream 330 of the third column can be split into two streams, and each split stream can be heat exchanged with the first reboiler 110 of the first column and the first reboiler 210 of the second column, respectively. In this case, heat exchanger C in FIG. 1 can refer to both the first reboiler 110 of the first column and the first reboiler 210 of the second column.

[0116] After the upper discharge stream 330 of the third column is heat exchanged with one or more of the first reboiler 110 of the first column and the first reboiler 210 of the second column, the heat-exchanged upper discharge stream 330 of the third column may be transferred to a condenser 380 provided at the top of the third column 300. When the upper discharge stream 330 of the third column is branched and heat-exchanged with both the first reboiler 110 of the first column and the first reboiler 210 of the second column, the respective branched streams may be combined after heat exchange and transferred to the condenser 380.

[0117] The operating pressure at the top of the third column 300 may be 4.9 barg to 5.1 barg. When the operating pressure at the top of the third column is 4.9 barg or higher, the temperature of the upper discharge stream 330 of the third column is at least 10°C higher than the temperature at the bottom of the first and second columns, making it possible to maintain a temperature difference for heat exchange between the first reboiler 110 of the first column and the first reboiler 210 of the second column.

[0118] In particular, if the operating pressure at the top of the third column 300 is greater than 5.1 barg, a high temperature of the third column's upper discharge stream 330 can be achieved, and there is no problem with the heat supply to the first column 100 and the second column 200, but the separation performance of the third column 300 is reduced. In this case, additional energy must be supplied to the third column 300 to separate the components to the desired purity, which is undesirable from the perspective of reducing energy consumption. Conversely, if the operating pressure at the top of the third column 300 is less than 4.9 barg, it becomes difficult to maintain a high temperature of the third column's upper discharge stream 330, and it is difficult to ensure a sufficient temperature difference to enable heat exchange between the first reboiler 110 of the first column and the first reboiler 210 of the second column.

[0119] Meanwhile, the operating temperature of the upper portion of the third column 300, specifically the upper portion of the upper region of the third column 300, may be 120° C. or higher, specifically 122° C. or higher. In this case, a suitable temperature difference (e.g., a temperature difference of at least 10° C.) required for heat exchange with the lower portions of the first column 100 and the second column 200 can be ensured, thereby enabling efficient energy supply to the first column 100 and the second column 200 via the upper discharge stream 330 of the third column.

[0120] Furthermore, when the upper discharge stream 330 of the third column is heat exchanged with both the first reboiler 110 of the first column and the first reboiler 210 of the second column, the upper discharge stream 330 of the third column may be branched to form a branch stream supplied to the first reboiler 110 of the first column and a branch stream supplied to the first reboiler 210 of the second column. In this case, the ratio of the mass flow rate of the branch stream supplied to the first reboiler 110 of the first column to the mass flow rate of the branch stream supplied to the first reboiler 210 of the second column may be 1:5 to 1:7. This ratio maximizes the logarithmic mean temperature difference (LMTD) between the low-temperature medium (the lower discharge streams of the first and second columns) and the high-temperature medium (the upper discharge stream of the third column) that are heat exchanged in the first reboiler 110 of the first column and the first reboiler 210 of the second column, thereby enabling efficient design and operation of the first reboiler 110 of the first column and the first reboiler 210 of the second column. Furthermore, the sizes of the auxiliary reboilers 115, 215 of the first and second columns can be minimized.

[0121] The upper discharge stream 330 of the third column 300 may be condensed into a liquid phase in whole or in part while being cooled after heat exchange with one or more of the lower discharge stream of the first column and the lower discharge stream of the second column in one or more of the first reboiler 110 of the first column and the first reboiler 210 of the second column. The condensed upper discharge stream 330 of the third column 300 may be introduced into a condenser 380 provided at the top of the third column and may undergo additional condensation until the desired condensation conditions are reached.

[0122] The discharge stream from the condenser 380 after the additional condensation may be introduced into the layer separator 340 provided at the top of the third column. The layer separator 340 is a device that separates fluids based on density differences, and may separate the fluid into an aqueous phase containing water and an oil phase containing an entrainer. The oil phase stream containing the entrainer may be refluxed to the upper region, and the aqueous phase stream containing water may be refluxed to the second region.

[0123] That is, after the top discharge stream 330 is separated into an oil phase and an aqueous phase by the layer separator 340, the separated oil phase and aqueous phase are returned to the third distillation column 300. Therefore, the mass flow rate of the top discharge stream 330 from the third distillation column may be equal to the sum of the mass flow rates of the aqueous phase stream and the oil phase stream returned to the third distillation column 300 via the layer separator 340. That is, the top discharge stream 330 from the third distillation column 300 is discharged from the third column 300, supplied to one or more of the first reboiler 110 of the first column and the first reboiler 210 of the second column, and subsequently supplied to the condenser 380. After passing through the layer separator 340, the entire amount is returned to the third distillation column 300.

[0124] The entrainer contained in the oil phase stream is reused for the azeotropic distillation carried out in the third distillation column 300. By refluxing the entire separated oil and aqueous phases to the third distillation column 300 and optimizing the reflux point, the first zone bottom discharge stream and the second zone bottom discharge stream can be separated with high purity.

[0125] The reflux point of the aqueous phase to the second zone can be 10% to 50% of the height of the separation wall from the bottom of the column, specifically 25% to 40%, thereby minimizing the energy required for distillation and separating pure water at the bottom of the second zone.

[0126] More specifically, when the position of the upper end of the separation wall and the position of the reflux point of the aqueous phase to the second zone are set as described above, an azeotropic distillation zone for separating isopropyl alcohol from water using an azeotropic agent and a distillation zone for purifying isopropyl alcohol can be sufficiently secured simultaneously within the third distillation column 300. Furthermore, by sharing the upper zone above the separation wall between the first and second zones, the amount of energy required in the condenser 380 can be reduced, and by optimally distributing the liquid reflux stream, which is branched from the bottom of the upper zone to the first and second zones and flows downward, to the first and second zones, the amount of heat required in the reboiler in each zone can be minimized.

[0127] Meanwhile, according to one embodiment of the present invention, the first zone lower discharge stream discharged from the first zone may be supplied to a fourth column 400 for recovering isopropyl alcohol. The first zone lower discharge stream contains isopropyl alcohol and a small amount of heavy by-products, and isopropyl alcohol may be finally obtained from the top of the fourth column 400, and the heavy by-products may be separated from the bottom of the fourth column.

[0128] The fourth column 400 includes a fourth column first reboiler 410 located at the bottom, and as described above, the fourth column bottom discharge stream may be heat exchanged with the reaction product stream before being introduced into the absorption tower in the fourth column first reboiler 410. Specifically, referring to Figures 2 and 3, the first branch stream 50 of the branch stream of the reaction product stream may be heat exchanged with the fourth column bottom discharge stream in the fourth column first reboiler 410 (heat exchanger A in Figure 2).

[0129] Meanwhile, if the thermal energy of the first branch stream 50 alone cannot replace all of the reboiler energy required to operate the fourth column 400, an auxiliary reboiler 415 may be provided at the bottom of the fourth column 400, in addition to the first reboiler 410 of the fourth column.

[0130] As described above, the top discharge stream from the absorber 10 contains propylene and gas components, and after the top discharge stream from the absorber 10 is compressed by a compressor, a portion of the stream 40 can be supplied to a gas purifying section, which will be described later. Hereinafter, the recovery process performed in the gas purifying section will be described with reference to Figures 1 and 4.

[0131] Specifically, the stream supplied to the gas purification unit may be supplied to a feed stream 40 of a fifth column 500 of the gas purification unit. The feed stream 40 of the fifth column 500 includes propylene and gas components, including light gas components with a boiling point lower than that of propylene and heavy gas components with a boiling point higher than that of propylene. The feed stream 40 of the fifth column 500 may also include small amounts of isopropyl alcohol, water, and light by-product diisopropyl ether, and heavy by-product n-propyl alcohol, which were not completely separated in the lower part of the absorption tower 100. The fifth column 500 allows for the recovery of propylene recycled to the reactor with higher purity, and allows for the complete recovery of isopropyl alcohol from the lower part, which may have been lost to the upper part of the fifth column 500.

[0132] As described above, the side stream of the fifth column 500 may be heat exchanged with all or a portion of the reaction product supplied to the absorber 10. To this end, the fifth column 500 may include a first reboiler 510 connected to the side of the fifth column 500. That is, heat exchange between the reaction product and the side stream of the fifth column 500 may occur in the first reboiler 510 of the fifth column 500. Specifically, referring to FIGS. 2 and 4, the second branch stream 60 of the branch streams of the reaction product stream may be heat exchanged with the side discharge stream of the fifth column 500 in the first reboiler 510 of the fifth column (heat exchanger B in FIG. 2).

[0133] More specifically, the side draw stream from the fifth column 500 may be discharged from a point 55 to 85% below the top of the fifth column 500 and may be heat exchanged with the reaction product. For example, if the side draw stream is discharged from a point less than 55% below the top, there is a problem that the contact zone where certain components are vaporized and simultaneously contacted with the refluxed liquid phase components, i.e., the distillation zone where actual distillation and purification occur, is shortened. On the other hand, if the side draw stream is discharged from a point more than 85% below the top, the temperature of the side draw stream is too high, making it difficult to exchange heat with the reaction product or resulting in no heat exchange effect (cooling the reaction product and heating the side stream).

[0134] Meanwhile, the side discharge stream of the fifth column 500, which has been heat exchanged with the reaction product in the first reboiler 510 of the fifth column, may be re-supplied to the stage corresponding to the height point of the fifth column 500 from which the side stream was discharged.

[0135] In addition, the temperature of the side discharge stream discharged from the fifth column 500 may be 40°C to 80°C or 40°C to 60°C, and the temperature of the side stream supplied again to the fifth column 500 after heat exchange may be 80°C to 100°C or 85°C to 95°C. This allows the temperature profile for each height of the fifth column 500 to be appropriately controlled. This allows the thermal energy required for the fifth column 500, which has conventionally been supplied only by the second reboiler 520, to be replaced, specifically, by more than half as much as possible.

[0136] Meanwhile, according to one embodiment of the present invention, the operating pressure at the top of the fifth column 500 is 15 kg / cm 2 g~20kg / cm 2 g, or 16 kg / cm 2 g~19kg / cm 2The fifth column 500 may be operated under high pressure conditions of 1000°C to 180°C. The operating temperature at the bottom of the fifth column 500 may be 140°C to 180°C, or 150°C to 180°C. Within the operating temperature and pressure range of the fifth column 500, the separation efficiency of the fifth column 500 is improved, and all of the isopropyl alcohol, water, and by-products can be recovered from the bottom of the fifth column 500. Furthermore, the condenser provided at the top of the fifth column 500 can use inexpensive cooling water as a cooling heat source.

[0137] Meanwhile, when the reaction product and the side discharge stream of the fifth column 500 are heat-exchanged through the first reboiler 510 of the fifth column according to one embodiment of the present invention, a gradual temperature profile can be achieved for each height of the fifth column 500, resulting in an increase in the section where the temperature changes for each height of the fifth column 500, i.e., the distillation zone where distillation and purification can occur. That is, the stream introduced into the fifth column 500 contains not only light components such as propylene and inert gases, but also heavy components such as isopropyl alcohol and water. That is, because the stream introduced into the fifth column 500 contains components with large boiling point differences, the temperature profile within the fifth column 500 generally changes abruptly in a certain section. In this case, depending on the height of the column, there may be a region (so-called dead zone) where the temperature change is small and component separation is difficult. However, by heat exchange using the first heat exchanger 510 of the fifth column of the present invention, a gradual temperature profile can be realized in the fifth column 500, i.e., an appropriate temperature gradient can be realized depending on the height of the column, thereby converting the region where component separation is difficult into a region where component separation by stripping is possible, thereby increasing the component separation efficiency of the fifth column 500.

[0138] In addition, in the past, when the fifth column 500 was operated with only one lower reboiler as shown in FIG. 5 , a high-temperature (e.g., 160°C or higher) high-grade heat source (e.g., steam) was required for the lower reboiler. However, when the first reboiler 510 of the fifth column 500 is provided in the fifth column 500 as in one embodiment of the present invention, the first reboiler 510 of the fifth column 500 can be operated using low-grade waste heat of about 120°C. In addition, the amount of high-grade heat source required for the second reboiler 520 of the fifth column 500 can be reduced compared to the past, thereby reducing the amount of thermal energy used.

[0139] Meanwhile, the fifth column 500 may further include a second reboiler 520 connected to a lower portion of the fifth column 500 in addition to the first reboiler 510. The thermal energy supplied to the fifth column by the first reboiler 510 of the fifth column may be 50% to 90% of the total thermal energy supplied to the fifth column 500 by the first reboiler 510 of the fifth column and the second reboiler 520 of the fifth column.

[0140] The top discharge stream of the fifth column 500 includes propylene, light gas components, and heavy gas components, and the top discharge stream of the fifth column 500 can be supplied to a sixth column 600 via a condenser.

[0141] In the sixth column 600, a portion of the side discharge stream containing propylene from the sixth column is recycled to the reactor, and the remainder is purged and discharged to the outside of the system. The gas phase components including inert gases in the top discharge stream from the sixth column 600 are purged to separate and remove some or all of the inert gases, thereby reducing the content of inert gases in the stream returned to the reactor and preventing the accumulation of inert gases in the process.

[0142] Meanwhile, as described above, the lower discharge stream of the sixth column 600 may be heat exchanged with the upper discharge stream of the second column 200 in the first sixth column reboiler 610 (heat exchanger D in FIG. 3) provided at the bottom of the sixth column 600. As a result, the thermal energy of the upper discharge stream of the second column 200 may be supplied to the sixth column 600. Furthermore, if the thermal energy of the upper discharge stream of the second column 200 alone is not enough to replace all of the reboiler energy required to operate the sixth column 600, an auxiliary reboiler 615 may be provided at the bottom of the sixth column 600, in addition to the first sixth column reboiler 610.

[0143] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention, and the scope of the present invention is not limited to these examples.

[0144] In the following Examples and Comparative Examples, the method of the present invention was simulated using Aspen Plus V12.1, a commercial process replication program.

[0145] Example 1 The isopropyl alcohol production process was carried out according to the process flow shown in FIG. 1 and FIGS.

[0146] Specifically, water and propylene were supplied to a reactor and reacted in a gas phase to produce a reaction product containing isopropyl alcohol, water, and propylene. The reaction product was passed through a heat exchanger 90 and branched into first, second, and third branch streams. The mass flow ratio of these first, second, and third branch streams was 1:0.33:0.57. The first branch stream 50 was heat exchanged with the bottom discharge stream of the fourth column 400 in the first reboiler 410 of the fourth column, and the second branch stream 60 was heat exchanged with the side discharge stream of the fifth column 500 in the first reboiler 510 of the fifth column. The heat-exchanged branch streams were combined with the third branch stream 70 and supplied to the top of the absorber 10.

[0147] In this case, the heat energy required for operating the fourth column could be entirely replaced by the heat energy supplied by the first branch stream, so there was no need to supply a separate heat source to the auxiliary reboiler 415 for operating the fourth column.

[0148] Meanwhile, the bottom discharge stream from the absorber 10 was supplied to the flash drum 20, and then the bottom discharge stream from the flash drum 20 was supplied to the first column 100 in the isopropyl alcohol purification section, which includes the first to fourth columns. The top discharge stream from the absorber 10 was compressed by a compressor, and then a portion of it was supplied to the fifth column 500 in the gas purification section, which includes the fifth and sixth columns.

[0149] The feed stream 30 supplied to the first column 100 contained 10.395 wt% isopropyl alcohol, 88.9 wt% water, 0.5 wt% diisopropyl ether (DIPE) as a first light by-product, 0.005 wt% acetone as a second light by-product, and 0.2 wt% n-propyl alcohol (NPA) and hexanol as heavy by-products.

[0150] Isopropyl alcohol was obtained by sequentially passing through the bottom draw stream of the first column 100, the first side draw stream of the second column 200, the bottom draw stream of the first zone of the third column 300, and the top draw stream of the fourth column 400. Diisopropyl ether (DIPE) was removed from the top of the first column 100, and acetone was removed from the top of the second column 200. Meanwhile, water was removed from the bottom draw stream of the second column 200 and the bottom of the second zone of the third column 300, respectively. The heavy by-products were removed from the second side draw stream of the second column 200 and the bottom draw stream of the fourth column 400, respectively.

[0151] Meanwhile, stream 40 fed to fifth column 500 contained propylene and gas components. The propylene was recovered by passing through the top effluent stream of fifth column 500 and the side effluent stream of sixth column 600 in sequence.

[0152] Here, the upper discharge stream of the second column 200 was heat exchanged with the lower discharge stream of the sixth column 600 in the first reboiler 610 of the sixth column. The heat-exchanged upper discharge stream of the second column was passed through a condenser 280 provided at the top of the second column 200 and branched into a stream that was refluxed to the second column 200 and a stream that was discharged to the outside of the system.

[0153] In this case, the heat energy required for the operation of the sixth column could be entirely replaced by the heat energy supplied by the upper discharge stream of the second column, so there was no need to supply a separate heat source to the auxiliary reboiler 615 for the operation of the sixth column.

[0154] Meanwhile, the upper discharge stream 330 of the third column 300 was branched at a mass flow ratio of 1:6 and supplied to the first reboiler 110 of the first column and the first reboiler 210 of the second column, respectively, to provide heat energy to the lower portions of the first and second columns. The operating pressure in the upper region of the third column 300 was 5.0 bar.g, and the temperature of the upper discharge stream 330 was 122°C. Meanwhile, the temperature of the lower discharge stream of the first column was 85°C, and the temperature of the lower discharge stream of the second column was 95°C. The temperature difference between the low-temperature medium and the high-temperature medium supplied to the first reboiler 110 of the first column and the first reboiler 210 of the second column was appropriate, allowing for efficient heat exchange.

[0155] At this time, the thermal energy of the upper discharge stream 330 of the third column alone was not enough to maintain the desired operating conditions of the first and second columns, so additional thermal energy was supplied to the first and second columns by auxiliary reboilers 115 and 215 installed at the bottom of the first and second columns, respectively.

[0156] Meanwhile, the bottom discharge stream from the first zone of the third column 300, which contained isopropyl alcohol and n-propyl alcohol, was supplied to the fourth column 400, and isopropyl alcohol was obtained from the top of the fourth column 400. The content of isopropyl alcohol in the top discharge stream from the fourth column was confirmed to be 99.8 wt%.

[0157] The energy consumed by the reboilers of each column is shown in Table 1. Specifically, the thermal energy supplied to the first reboiler 110 of the first column and the first reboiler 210 of the second column is supplied from the upper part of the third column, so the reboiler energy consumed in the first and second columns is shown in Table 1 as the thermal energy supplied by the auxiliary reboilers 115 and 215 provided at the lower part of the first and second columns, respectively. Meanwhile, the thermal energy supplied by the reboiler 310 connected to the lower part of the first region of the third column and the thermal energy supplied by the reboiler 315 connected to the lower part of the second region of the third column are shown in Table 1, respectively.

[0158] Comparative Example 1 An isopropyl alcohol production process was carried out according to the process diagram shown in Figure 5. The flow rate and composition of the stream introduced into the C1 column of the isopropyl alcohol purification section were the same as those of the stream introduced into the first column in Example 1, and the flow rate and composition of the stream introduced into the C7 column of the gas purification section were the same as those of the stream introduced into the fifth column in Example 1. Isopropyl alcohol in Comparative Example 1 was obtained from the top of the C6 column. The thermal energy required to operate each column to obtain an isopropyl alcohol content of 99.8 wt%, the same as in Example 1, in the C6 column top discharge stream was measured and listed in Table 1.

[0159] Specifically, the bottom discharge stream of the C1 column, which had the same composition as in Example 1, was obtained and introduced into the C2 column.

[0160] The C2 column in Comparative Example 1 was a column without a separating wall. The C2 column separated the four effluent streams by distillation in the same manner as in Example 1: a top effluent stream from the C2 column containing acetone, a first side effluent stream from the C2 column containing an azeotropic mixture of isopropyl alcohol and water, a second side effluent stream from the C2 column containing n-propyl alcohol (NPA) and hexanol, and a bottom effluent stream from the C2 column containing water.

[0161] In this case, the second side draw stream from the C2 column contained a large amount of isopropyl alcohol and was discharged without effectively separating the heavy by-products and water, so a C3 column was required to further purify the isopropyl alcohol in the second side draw stream from the C2 column and separate the heavy by-products and water. Specifically, the second side draw stream from the C2 column was introduced into the C3 column, and a stream containing isopropyl alcohol was separated from the top of the C3 column and fed back to the C2 column.

[0162] The energy required to operate the C1 to C3 columns was supplied by a reboiler installed at the bottom of the C1 to C3 columns.

[0163] The first side discharge stream from the C2 column, containing an azeotropic mixture of isopropyl alcohol and water, was passed through a conventional C4 column (azeotropic distillation column) without a separating wall, a C5 column (azeotropic agent recovery column), and a C6 column (isopropyl alcohol recovery column), and isopropyl alcohol was recovered from the top of the C6 column. Specifically, isopropyl alcohol was obtained by sequentially passing through the bottom discharge stream from the C4 column and the top discharge stream from the C6 column. Each of the C4 column, C6 column, and C6 column was equipped with a condenser at the top and a reboiler at the bottom.

[0164] On the other hand, the stream supplied to the C7 column in the gas purification section of Comparative Example 1 contained propylene and gas components. The propylene was recovered by passing through the top discharge stream of the C7 column and the side discharge stream of the C8 column in that order.

[0165] As a result, the content of isopropyl alcohol obtained in Comparative Example 1 was confirmed to be 99.8 wt %, the same as in Example 1.

[0166] At this time, the energy (thermal energy) used in the reboilers provided at the bottom of each column (columns C1 to C8) in Comparative Example 1 is shown in Table 1.

[0167] [Table 1]

[0168] As can be seen from the above results, high levels of isopropyl alcohol purity and yield were maintained in Example 1. In particular, when dividing wall distillation columns having a specific structure were used as the second and third columns and the heat of the top discharge stream of the third column was used as the energy source required to operate the first and second columns, it was found that the energy efficiency of the entire process from the first to fourth columns was maximized.

[0169] Furthermore, by replacing all or part of the heat energy required to operate the fifth and fourth columns with the heat energy of the reaction product before it is supplied to the absorption tower, and by replacing all or part of the heat energy required to operate the sixth column with the heat energy of the top discharge stream of the second column, the energy required for the entire process from reaction to purification and recovery of unreacted substances for the production of isopropyl alcohol can be efficiently managed. [Explanation of symbols]

[0170] 100 Column 1 200 Column 2 300 Column 3 300 Column 3 400 Column 4 500 Column 5 600 Column 6

Claims

1. reacting propylene monomer and water to provide a reaction product comprising propylene and isopropyl alcohol; cooling the reaction product and supplying the cooled reaction product to an absorber; A method for producing isopropyl alcohol, comprising: supplying a bottom discharge stream from the absorption tower containing isopropyl alcohol to an isopropyl alcohol purification section including first to fourth columns, and supplying an top discharge stream from the absorption tower containing propylene to a gas purification section including fifth and sixth columns, The isopropyl alcohol contained in the bottom discharge stream of the absorption tower supplied to the isopropyl alcohol purification section is obtained by sequentially passing through a bottom discharge stream of a first column, a first side discharge stream of a second column, a bottom discharge stream of a first region of a third column, and an top discharge stream of a fourth column; the propylene contained in the top discharge stream of the absorber supplied to the gas purification section is obtained by passing through the top discharge stream of the fifth column and the side discharge stream of the sixth column in this order; all or a portion of the reaction product is cooled by heat exchange with one or more of the bottom effluent stream of the fourth column and the side effluent stream of the fifth column; the upper effluent stream of the second column is heat exchanged with the lower effluent stream of the sixth column; 1. A method for producing isopropyl alcohol, wherein the top effluent stream of the third column is heat exchanged with one or more of the bottom effluent stream of the first column and the bottom effluent stream of the second column.

2. the absorber bottoms effluent stream comprises isopropyl alcohol, water, a first light by-product, a second light by-product, and a heavy by-product; separating the first light by-product from the top effluent stream of the first column; 2. The method for producing isopropyl alcohol of claim 1, wherein the bottoms effluent stream from the first column containing the isopropyl alcohol, water, a second light by-product, and a heavy by-product is fed to a second column.

3. the first light by-product comprises diisopropyl ether (DIPE); 3. The method for producing isopropyl alcohol of claim 2, wherein the second light by-product comprises acetone.

4. the second column includes a separation wall spaced from the bottom and extending along the length of the column; The second column is divided by the separation wall into a top region, a bottom region, a supply region, and a discharge region; a first side draw stream and a second side draw stream of the second column are discharged from the discharge region; 2. The method for producing isopropyl alcohol according to claim 1, wherein the first side discharge stream is discharged from a discharge region above the second side discharge stream.

5. the first side draw stream of the second column comprises a mixture of isopropyl alcohol and water; a second side draw stream of the second column comprising heavy by-products; 5. The method for producing isopropyl alcohol of claim 4, wherein the heavy by-products include n-propyl alcohol (NPA) and hexanol.

6. the bottoms effluent stream of the second column comprises water; 2. The method for producing isopropyl alcohol according to claim 1, wherein a branch stream obtained by branching a portion of the bottom discharge stream from the second column is circulated to an upper portion of the first column and an upper portion of the absorption tower.

7. the bottom effluent stream of the absorber is fed to a first column; The mass flow rate of the stream in which a portion of the lower discharge stream of the second column is branched and circulated to the upper part of the first column is 0.4 to 1.2 relative to the mass flow rate of the lower discharge stream of the absorption tower supplied to the first column. The method for producing isopropyl alcohol according to claim 6.

8. the third column includes a separation wall connected to the bottom and extending along the length of the column; The method for producing isopropyl alcohol according to claim 1, wherein the separation wall divides the mixture into a first region, a second region opposite the first region, and an upper region located above an upper end of the separation wall.

9. 2. The method for producing isopropyl alcohol of claim 1, wherein the top effluent stream of the third column is heat exchanged with the bottom effluent stream of the first column and the bottom effluent stream of the second column by a first reboiler of the first column and a first reboiler of the second column.

10. the top discharge stream of the third column is split to form a split stream that is fed to a first reboiler of the first column and a split stream that is fed to a first reboiler of the second column; 10. The method for producing isopropyl alcohol according to claim 9, wherein the ratio of the mass flow rate of the branch stream supplied to the first reboiler to the mass flow rate of the branch stream supplied to the second reboiler is 1:5 to 1:

7.

11. the first zone bottom effluent stream of the third column is fed to a fourth column; 2. The method for producing isopropyl alcohol according to claim 1, wherein isopropyl alcohol is obtained from the top of the fourth column and heavy by-products are separated from the bottom of the fourth column.

12. Cooling the reaction product includes:

2. The method for producing isopropyl alcohol according to claim 1, further comprising: a first cooling step in which all or a portion of the reaction product stream is cooled by heat exchange with one or more of the bottom draw stream of the fourth column and the side draw stream of the fifth column; and a second cooling step in which the first cooled reaction product stream is cooled by heat exchange with a refrigerant.

13. The fifth column includes a first reboiler for the fifth column provided on a side of the fifth column and a second reboiler for the fifth column provided in a lower portion of the fifth column; 13. The method for producing isopropyl alcohol of claim 12, wherein the heat exchange between all or a portion of the reaction product stream and the side draw stream of the fifth column occurs in a first reboiler of the fifth column.

14. the reaction product stream is branched into a first branch stream, a second branch stream, and a third branch stream; the first cooling is performed by heat exchange between the first branch stream and the bottom discharge stream of the fourth column, and by heat exchange between the second branch stream and the side discharge stream of the fifth column; the first cooled first and second branch streams and the first uncooled third branch stream are combined to form a combined stream; The method for producing isopropyl alcohol according to claim 12, wherein the second cooling is performed by heat exchange between the combined stream and a refrigerant.

15. The mass flow rate of the first branch stream, the mass flow rate of the second branch stream, and the mass flow rate of the third branch stream are 1:0.2 to 0.4:0.4 to 0.

7. The method for producing isopropyl alcohol according to claim 14.

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