How is isopropyl alcohol produced?

Abstract

The present invention relates to a method for producing IPA, and provides a purification method using multiple columns, comprising: a first column separating a feed stream containing IPA, NPA, water, and high-boiling organic compounds into an upper stream containing a mixture of IPA, NPA, and water and a lower stream containing water and high-boiling organic compounds; a second column separating the upper stream from the first column using an organic solvent to remove a lower stream containing IPA and NPA, and an upper stream in which the solvent forms a ternary azeotrope with water and IPA; a third column having a dividing wall structure, supplying a mixed stream of a branched stream of the lower stream from the first column and the lower stream from the second column to a first zone; and separating from the mixed stream an upper stream containing water from which high-boiling organic compounds have been removed, a side stream containing IPA from which NPA has been removed, and a lower stream containing the high-boiling organic compounds and NPA; and recovering the side stream containing IPA from a second zone.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0103273 filed on August 18, 2022 and Korean Patent Application No. 10-2023-0069395 filed on May 30, 2023, 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 producing isopropyl alcohol, and more particularly to a method for purifying isopropyl alcohol to a high purity from a reaction product. [Background technology]

[0003] Isopropyl alcohol (IPA) is used in a variety of applications, including as a cleaning agent in the electronics industry, such as in the manufacturing of semiconductors and liquid crystal displays (LCDs), as a raw material for industrial coatings and reagents, and as a solvent for paints and inks.

[0004] IPA can be produced by reacting propylene with water. For example, propylene monomer and water are reacted in a reactor to obtain a reaction product containing IPA, unreacted propylene monomer, unreacted water, n-propyl alcohol (NPA), and by-products such as low-boiling organics or high-boiling organics. The reaction product is then transferred to a gas purification section, where low-boiling substances (including unreacted propylene monomer) are discharged from the upper section. A stream containing IPA, NPA, and water is separated from the lower section, and the bottom stream (containing IPA, NPA, water, and high-boiling organics) is then transferred to an IPA purification section containing multiple columns to separate IPA. The unreacted propylene monomer and unreacted water can be recovered and reused in the IPA production process.

[0005] 1 and 2 are diagrams schematically illustrating the IPA purification process carried out in the prior art IPA production method.

[0006] Referring first to Figure 1, a feed stream containing IPA, NPA, water, and high-boiling organics was supplied to the first column of the purification section, a stream containing water and high-boiling organics was discharged from the bottom, and a stream containing an azeotrope of IPA, NPA, and water was separated from the top and transferred to the second column, while NPA was removed from the bottom of the third column connected to the side of the first column. The second column then used a solvent to break the azeotrope, separating the bottom stream containing IPA from the top stream containing the solvent and water. The solvent and water were then separated in the fourth column. In other words, in the IPA purification process shown in Figure 1, NPA was removed first, followed by separation of water.

[0007] The first and third columns contain a large amount of water, and since the azeotropic points of IPA and water at atmospheric pressure are 80.4°C and 87.7°C, respectively, azeotropes of water / IPA and water / NPA are formed. Therefore, even if NPA is removed from the bottom of the third column, NPA is contained in the stream transferred to the second column, and NPA remains when the final IPA is recovered, making it difficult to produce high-purity IPA.

[0008] To solve this problem, Korean Patent Publication No. 10-2020-0065579 attempts to produce high-purity IPA by first separating water before removing NPA in the IPA purification process.

[0009] Specifically, referring to Figure 2, the first column of the purification section separates the feed stream into an upper stream containing an azeotropic mixture of IPA, NPA, and water and a lower stream containing high-boiling organics and water. The upper stream is then transferred to the second column to separate the water first, and the stream containing IPA and NPA is then transferred to the third column to remove the NPA, thereby recovering IPA. That is, in the IPA purification process of Figure 2, because water is first separated from the azeotropic mixture of IPA, NPA, and water in the second column, no azeotrope is formed in the third column, and NPA is easily removed. As a result, the residual NPA in the final recovered IPA is lower than in the purification of Figure 1, but water that was not separated in the second column may still be present in the final recovered IPA.

[0010] Furthermore, in the conventional IPA purification process shown in FIGS. 1 and 2, the water discharged from the bottom of the first column contains high-boiling-point organic substances, which increases the chemical oxygen demand (COD) of the discharged water, and may require additional processes when treating process water or wastewater. Summary of the Invention [Problem to be solved by the invention]

[0011] In order to solve the problem of conventional methods in which water forms an azeotrope with IPA and NPA, respectively, making it impossible to effectively remove NPA and resulting in high COD of water treated as process water or wastewater, the present invention provides a production method in which the purification order is changed so that water is separated before NPA removal, and a dividing wall column (DWC) is used to separate IPA and NPA as well as water and high-boiling organic compounds, thereby recovering high-purity isopropyl alcohol. [Means for solving the problem]

[0012] According to one aspect of the present invention for solving the above problems, there is provided a method for producing isopropyl alcohol (IPA), comprising: (S1) performing gas purification from a reaction product of propylene monomer and water to obtain a feed stream containing IPA, NPA, water, and high-boiling organics; (S2) supplying the feed stream to a purification section including a plurality of columns to recover IPA; a first column of said purification section separating said feed stream into an overhead stream containing IPA, NPA and water and a bottom stream containing water and high boiling organics; In a second column of the purification section, an organic solvent is used to remove water from the top stream of the first column to separate a stream containing IPA and NPA into a bottom stream, and the solvent forms a ternary azeotrope with water and IPA, which is discharged into the top stream; The third column of the purification section includes first and second zones separated by a central separating wall, and a mixed stream of a branched stream of the bottom stream of the first column and the bottom stream of the second column is supplied to the first zone, and an upper stream containing water from which high-boiling-point organics have been removed, a side stream containing IPA from which NPA has been removed, and a bottom stream containing the high-boiling-point organics and NPA are separated from the mixed stream, and the side stream containing IPA is recovered from the second zone. [Effects of the Invention]

[0013] According to the present invention, in the production of IPA, in a purification step using multiple columns, water is first separated from a feed stream containing IPA, NPA, water, and high molecular weight organic compounds, and then a branched stream of the bottom stream from the first column (containing water and high boiling point organic compounds) and a mixed stream of the bottom stream from the second column (containing IPA and NPA) are supplied to a first zone of a dividing wall-type third column to separate the high boiling point organic compounds and NPA. High-purity IPA from which NPA has been removed is recovered on the side of the second zone of the third column, and is discharged into an upper stream containing water from which the high boiling point organic compounds have been removed.

[0014] The IPA recovered in the second zone of the dividing wall-type third column can account for 99.99% or more of the IPA contained in the feed.

[0015] In addition, the dividing wall-type third column separates the water contained in the branch stream of the lower stream of the first column from the high boiling point organic matter and then refluxes it. As a result, the water remaining in the lower stream of the first column merges with a part of the stream separated at the bottom of the fourth column, and the discharged water can be reused as process water or treated as wastewater with reduced chemical oxygen demand (COD). [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing a schematic diagram of an IPA purification process carried out in a conventional IPA manufacturing method. [Figure 2] 1 is a diagram showing a schematic diagram of an IPA purification process carried out in a conventional IPA manufacturing method. [Figure 3] 1 is a diagram illustrating a process of purifying IPA performed in a method for producing IPA according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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.

[0018] As used herein, the meaning of "comprise" or "contain" is to embody a particular property, region, constant, step, operation, element, or component, and does not exclude the addition of other particular properties, regions, constants, steps, operations, elements, or components.

[0019] The term "stream" as used herein may refer to the flow of fluid within a process or the fluid itself flowing in a pipe. Specifically, the stream may simultaneously refer to the fluid itself flowing in a pipe connecting each device and the flow of the fluid. The fluid may contain one or more components of gas, liquid, or solid.

[0020] Unless otherwise specified, the term "upper portion" used in this application means a point 0 to 20% below the top of the apparatus, specifically the top (top of the column), and the term "lower portion" means a point 80 to 100% below the top of the apparatus, specifically the bottom (bottom of the column).

[0021] As used herein, the term "side stream" may refer to a stream that is discharged from 25-80% height or 40-70% height downward from the top of the device, unless otherwise specified.

[0022] Furthermore, "pressure" as referred to in this application means gauge pressure measured relative to atmospheric pressure.

[0023] One embodiment of the present invention relates to a method for producing isopropyl alcohol (IPA), specifically including a step (S1) of obtaining a feedstream and a step (S2) of purifying IPA from the feedstream.

[0024] Hereinafter, a method for manufacturing IPA according to an embodiment of the present invention will be described in detail step by step.

[0025] In step (S1) of the method for producing IPA according to the present invention, a gas purification is carried out from the reaction product of propylene monomer and water to obtain a feed stream containing IPA, NPA, water and high-boiling organic substances.

[0026] Specifically, the feed stream can be obtained by reacting propylene monomer with water in a reactor to produce a reaction product containing IPA, unreacted propylene monomer, unreacted water, n-propyl alcohol (NPA) as a by-product, low-boiling-point organic substances, and high-boiling-point organic substances, and then performing gas purification to separate the unreacted propylene monomer and other low-boiling-point components from the reaction product.

[0027] In the reactor, propylene and water can be reacted in any one of a gas phase reaction, a gas / liquid phase reaction, and a liquid phase reaction, and the water can be obtained by reacting the propylene monomer with a molar ratio of 0.3 to 2 or 0.35 to 1.5. When the molar ratio is satisfied, the forward reaction of the equilibrium reaction is promoted and the reverse reaction is prevented, thereby increasing the yield of IPA.

[0028] Furthermore, the reactor can be operated under optimal conditions for efficiently producing IPA by the reaction of propylene monomer with water. For example, in the case of a gas phase reaction, the reactor can be operated at a pressure of 10 to 50 kg / cm2·g, 30 to 50 kg / cm2·g, or 35 to 45 kg / cm2·g and a temperature of 150 to 220°C, 160 to 220°C, or 180 to 215°C.

[0029] In addition to IPA, the reaction product may contain unreacted propylene monomer, unreacted water, and by-products such as n-propyl alcohol (NPA), isopropyl ether (DIPE), heavy high-boiling organics (e.g., hexanol), and low-boiling organics (e.g., acetone). Therefore, to obtain high-purity IPA, a process for recovering IPA by separating the unreacted materials and by-products contained in the reaction product is necessary. In addition, the water separated from the reaction product can be recovered and reused as process water or treated as wastewater. If heavy high-boiling organics are present, the chemical oxygen demand (COD) may increase, and therefore a process for reducing the COD may be required during wastewater treatment.

[0030] For this purpose, the reaction product is first subjected to gas purification before being supplied to the IPA purification unit. The gas purification is for removing low boiling point components including unreacted propylene monomer from the reaction product, and can be performed using an absorption tower, a gas purification unit, etc.

[0031] In step (S2) of the method for producing IPA according to the present invention, IPA is purified from a stream containing IPA, NPA, water, and heavy high-boiling organic compounds, and the purification of IPA can be performed in a purification section including multiple columns, as shown in FIG. 3.

[0032] 3, the feed stream obtained in step (S1) is supplied from the first column of the purification section and contains 5-10 wt% IPA, 0.1-3 wt% NPA, 85-94 wt% water, and 0.05-2 wt% high-boiling organic compounds.

[0033] The first column of the purification section corresponds to a distillation tower for separating a large amount of water contained in the feed and separating IPA and NPA at the top. The IPA and NPA each form an azeotropic mixture with water and are separated as top stream 1a, and high boiling point organics together with water are discharged as bottom stream 1b.

[0034] The top output stream 1a of the first column can contain a mixture of 30-70 wt% IPA, 20-50 wt% NPA, and 10-50 wt% water, and the bottom output stream 1b of the first column can contain 95-99 wt% water and 1-5 wt% high-boiling by-products.

[0035] The first column can be operated at a pressure of 0 to 3 kg / cm2·g or 0 to 2 kg / cm2·g and a temperature of 80 to 150°C or 90 to 140°C to increase the efficiency of separating the alcohol component and water from the reaction product.

[0036] The first column is intended to separate water from IPA and NPA, but because the formation of an azeotrope with water makes it difficult to completely remove the water, the top stream 1a from the first column is transferred to the second column to completely separate the water from the azeotrope.

[0037] The second column in the purification section is used to separate water from the stream containing IPA, NPA, and water, specifically, stream 1a containing the IPA / water azeotrope and the NPA / water azeotrope. By adding an organic solvent (e.g., cyclohexane, benzene, toluene, isopropyl acetate, etc.) as an azeotropic agent, the azeotrope between IPA or NPA and water is broken, thereby separating water. Thus, water is removed in the second column, and stream 2b containing IPA and NPA is separated at the bottom. The organic solvent forms a ternary azeotrope with water and IPA, which is discharged as upper stream 2a.

[0038] The top stream 2a of the second column may contain an azeotropic mixture of 65-85 wt% organic solvent, 4-15 wt% water, and 10-30 wt% IPA when cyclohexane is used as the azeotropic agent.

[0039] The second column can be operated at a pressure of 0 to 2 kg / cm2·g or 0 to 1 kg / cm2·g and a temperature of 50 to 110°C or 60 to 100°C to increase the efficiency of water separation by the organic solvent used as the azeotropic agent.

[0040] The bottom stream 2b from the second column may contain 70-98 wt% IPA and 2-30 wt% NPA, and may also contain traces of water that were not separated in the previous step. The stream 2b is transferred to a third column for recovery of IPA.

[0041] The third column corresponds to a dividing wall distillation column (DWC) having two zones separated by a central dividing wall, as illustrated in Figure 3, and bottom stream 2b from the second column is supplied to one of the zones (zone 1). Here, a branch stream 1b' of stream 1b separated at the bottom of the first column and containing water and high boiling point organics can be mixed with bottom stream 2b from the second column, and the combined streams can be supplied to zone 1 of the third column.

[0042] The third column separates high-boiling organics and NPA from the mixed stream as bottom stream 3b, thereby obtaining top stream 3a containing water from which the high-boiling organics have been removed and a side stream containing IPA from which NPA has been removed. The side stream containing IPA from which NPA has been removed is recovered in another zone (second zone) of the third column, thereby purifying 99.99 wt% or more of the IPA contained in the feed.

[0043] The top stream 3a from the third column is water from which high-boiling organics have been removed and which forms an azeotrope with IPA, and is discharged. This stream 3a is mixed with the top stream 1a from the first column containing the IPA / water and NPA / water azeotropes and then transferred to the second column, where water can be separated from the azeotrope. The separated water can be discharged to the bottom of the fourth column.

[0044] In this way, the water contained in a portion of the bottom stream of the first column is separated from the high boiling point organics in the third column and refluxed. Water 1b″ remaining in the bottom stream of the first column is combined with stream 4b separated at the bottom of the fourth column and discharged as water 1b″, which can be reused as process water or treated as wastewater with reduced chemical oxygen demand (COD).

[0045] In one embodiment of the present invention, the content of high-boiling-point organics discharged to the bottom stream of the third column may be proportional to the branch flow rate of the bottom stream of the first column supplied to the first region of the third column, but appropriate control is required in consideration of the economic aspects of energy consumption. For example, the branch stream 1b' of the bottom stream of the first column supplied to the first region of the third column may be branched at a flow rate of 0.5 to 5 wt % or 1 to 3 wt % of the total flow rate of the bottom stream of the first column. If the branch flow rate is less than 0.5 wt %, the removal rate of high-boiling-point organics is low, resulting in insufficient COD reduction effect, while if it exceeds 5 wt %, excessive energy consumption may occur in the third column.

[0046] The third column can be operated at a pressure of 0 to 2 kg / cm2·g or 0 to 1 kg / cm2·g and a temperature of 70 to 120°C or 80 to 110°C to increase the separation efficiency of high boiling point organics and NPAs from the mixed stream.

[0047] Meanwhile, the upper stream containing the solvent and water separated at the top of the second column may be transferred to the fourth column of the purification section to recover the organic solvent, where it may be separated into an upper stream 4a from which water has been removed and a lower stream 4b containing water, and the organic solvent contained in the upper stream 4a may be refluxed to the second column.

[0048] The fourth column is a solvent recovery column and can be operated at a pressure of 0-2 kg / cm2·g or 0-1 kg / cm2·g and a temperature of 70-120°C or 75°C-110°C to increase the separation efficiency of the organic solvent and water.

[0049] According to the present invention, in the production of IPA, in a purification step using multiple columns, water is first separated from a stream containing an azeotropic mixture of IPA / water and NPA / water, and then a branched stream of the bottom stream from the first column (containing water and high-boiling organics) and a mixed stream of the bottom stream from the second column (containing IPA and NPA) are supplied to a first zone of a dividing wall-type third column to separate the high-boiling organics and NPA. High-purity IPA from which NPA has been removed can be recovered from the side of the second zone of the third column, and an upper stream containing water from which the high-boiling organics have been removed can be discharged.

[0050] The IPA recovered in the second zone of the dividing wall-type third column can account for 99.99% by weight or more of the IPA contained in the feed.

[0051] In addition, the dividing wall-type third column separates the water contained in the branch stream of the lower stream of the first column from the high-boiling organic matter and then refluxes the separated water. The water remaining in the lower stream of the first column is combined with a portion of the separated stream at the bottom of the fourth column, and the discharged water can be reused as process water or treated as wastewater with reduced chemical oxygen demand (COD).

[0052] The present invention will be described in more detail with reference to the following 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.

[0053] Example 1 (Step 1) Obtaining the feed stream Propylene monomer and water were reacted in a gas phase at a 1:1 molar ratio to produce a reaction product containing isopropyl alcohol (IPA), unreacted propylene monomer, unreacted water, and by-product n-propyl alcohol (NPA), low-boiling organics, and high-boiling organics. A purification process was then performed to separate the unreacted propylene monomer, low-boiling components, and gas components from the reaction product to obtain a feedstream. The feedstream contained 7 wt% IPA, 0.2 wt% NPA, 92.7 wt% water, and 0.1 wt% high-boiling organics.

[0054] (Step 2) Purification of isopropyl alcohol (IPA) As shown in FIG. 3, the feed stream obtained in step 1 was supplied to a purification section including first to fourth columns to recover IPA.

[0055] First, the feed stream was supplied to the first column, which was operated at 0 kg / cm2·g, with an upper temperature of 90°C and a lower temperature of 140°C, to separate it into an upper stream 1a containing IPA, NPA, and water and a lower stream 1b containing water and high-boiling organic compounds.

[0056] The top stream 1a and an organic solvent (cyclohexane) as an azeotropic agent were fed to a second column, which was operated at 0 kg / cm2·g, 60°C at the top, and 100°C at the bottom to remove water from the stream 1a and separate stream 2b containing IPA and NPA at the bottom, while discharging the top stream formed by an azeotropic mixture of the organic solvent, water, and IPA.

[0057] Next, the bottom stream 2b from the second column and a branch stream 1b' from the bottom stream 1b from the first column were mixed and fed to the first zone of a third column having a dividing wall structure, where the flow rate of the branch stream 1b' was adjusted to 0.5 wt% of the total flow rate of the bottom stream from the first column.

[0058] The third column was operated at 0 kg / cm2·g, with an upper pressure of 80°C and a lower pressure of 110°C to separate high-boiling-point organics and NPA from the mixed stream as lower stream 3b, yielding upper stream 3a containing water from which the high-boiling-point organics had been removed, and a side stream containing IPA from which NPA had been removed. The side stream containing IPA from which NPA had been removed was recovered in the second zone of the third column, thereby purifying the IPA contained in the feed to a purity of 99.99% by weight or higher.

[0059] Meanwhile, the top stream from the second column (containing solvent and water) was transferred to a fourth column, which was operated at 0 kg / cm²·g, 75°C at the top, and 100°C at the bottom, separating the water-removed top stream 4a and the water-containing bottom stream 4b. The organic solvent contained in the top stream 4a was refluxed to the second column. Furthermore, the water 1b″ remaining in the bottom stream from the first column was combined with the stream 4b separated at the bottom of the fourth column and discharged (1b′″).

[0060] Example 2 IPA was recovered in the same manner as in Example 1, except that the flow rate of the lower branch stream 1b′ of the first column, which was supplied to the first zone of the third column, was adjusted to 5 wt % of the total flow rate of the lower stream of the first column.

[0061] Example 3 IPA was recovered in the same manner as in Example 1, except that the flow rate of the lower branch stream 1b′ of the first column, which was supplied to the first region of the third column, was adjusted to 10 wt % of the total flow rate of the lower stream of the first column.

[0062] Comparative Example 1 (Step 1) A feed stream was obtained in the same manner as in step 1 of Example 1.

[0063] (Step 2) The purification steps were carried out as shown in Figure 1.

[0064] Specifically, a feed stream was supplied to the first column, which separated an upper stream containing an azeotropic mixture of IPA, NPA, and water from a lower stream containing water and high-boiling organic compounds. The upper stream from the first column was transferred to the second column, while NPA was removed in the lower part of the third column connected to the side of the first column. Next, an organic solvent (cyclohexane) was used in the second column to break the azeotrope, separating the upper stream containing IPA from the solvent and water. The solvent and water were then separated in the fourth column.

[0065] Comparative Example 2 (Step 1) A feed stream was obtained in the same manner as in step 1 of Example 1.

[0066] (Step 2) The purification steps were carried out as shown in Figure 2.

[0067] Specifically, a feed stream was fed to the first column and separated into an upper stream containing an azeotropic mixture of IPA, NPA, and water, and a lower stream containing high-boiling organics and water. The upper stream from the first column was transferred to the second column to separate the water first, and the stream containing IPA and NPA was then transferred to the third column to remove NPA and recover IPA. Meanwhile, the fourth column separated the solvent and water used.

[0068] Table 1 below shows the recovery results of IPA through the purification steps of the Examples and Comparative Examples.

[0069] [Table 1]

[0070] In Comparative Example 1 shown in Table 1, NPA was first removed from the bottom of the third column connected to the side of the first column during IPA purification. However, water contained in the first and third columns formed an azeotrope with IPA and NPA, resulting in the presence of NPA in the stream transferred to the second column. As a result, 500 ppm of NPA and 250 ppm of water remained when the final IPA was recovered from the bottom of the second column. In addition, the water discharged from the bottom of the first column contained high-boiling-point organic substances, resulting in high chemical oxygen demand (COD), which may require additional processes during wastewater treatment.

[0071] In Comparative Example 2, during IPA purification, water was first separated from the azeotropic mixture of IPA, NPA, and water in the second column. Therefore, no azeotropic mixture was formed in the third column, and NPA was easily removed. As a result, the residual NPA in the final recovered IPA was low at 2 ppm. However, water that was not separated in the second column was present at a concentration of 50 ppm in the final recovered IPA. Furthermore, as in Comparative Example 1, the water discharged from the bottom of the first column contained high-boiling-point organic substances, resulting in high chemical oxygen demand (COD).

[0072] On the other hand, in Examples 1 to 3, a dividing wall-type third column was used to first separate water from a stream containing an azeotropic mixture of IPA / water and NPA / water, and then a mixed stream of a branched stream 1b' of the bottom stream from the first column (containing water and high-boiling organics) and a bottom stream 2b from the second column (containing IPA and NPA) were supplied to the first zone of the dividing wall-type third column to remove the high-boiling organics and NPA. As a result, high-purity IPA from which NPA had been removed was recovered, and the concentrations of residual NPA and residual water were low at 2 ppm and 10 ppm, respectively.

[0073] Furthermore, in Examples 1 to 3, the water contained in the lower branch stream 1b' of the first column was separated from the high boiling point organics and then refluxed, thereby reducing the COD of the water remaining in the lower stream of the first column. That is, the content of high boiling point organics discharged as the lower stream 3b of the third column was proportional to the branch flow rate of the lower stream of the first column supplied to the first region of the third column, and as a result, the COD of the water remaining in the lower stream of the first column was reduced.

[0074] On the other hand, in Example 3, the amount of steam used due to the branching is found to increase sharply as the branch flow rate of the lower branch stream 1b' from the first column increases to 10 wt%. Therefore, when branching the lower stream from the first column, it is preferable to adjust the branch flow rate within a predetermined range (e.g., 0.5 to 5 wt% of the total flow rate of the lower stream from the first column) in order to reduce the COD content of the wastewater and avoid excessive energy consumption.

Claims

1. A method for producing isopropyl alcohol (IPA), comprising the steps of: (S1) performing gas purification from a reaction product of propylene monomer and water to obtain a feed stream containing isopropyl alcohol (IPA), normal propyl alcohol (NPA), water, and high-boiling organic matter; (S2) supplying the feed stream to a purification section including a plurality of columns to recover the IPA; a first column of said purification section separating said feed stream into an overhead stream containing a mixture of said IPA, said NPA and said water and a bottom stream containing water and high boiling organics; In a second column of the purification section, an organic solvent is used to remove water from the top stream of the first column to separate a stream containing the IPA and the NPA into a bottom stream, and the organic solvent forms a ternary azeotrope with the water and the IPA, which is discharged into the top stream; a third column of the purification section comprising first and second zones separated by a central separating wall, a stream obtained by mixing a branch stream of the bottom stream of the first column and the bottom stream of the second column into the first zone, a top stream containing water from which high-boiling-point organics have been removed, a side stream containing IPA from which NPA has been removed, and a bottom stream containing the high-boiling-point organics and the NPA, and the side stream containing IPA are recovered from the second zone.

2. 2. The method of claim 1, wherein the top stream containing the ternary azeotrope of the organic solvent, the water, and the IPA separated from the top of the second column is transferred to a fourth column of a purification section to be separated into a water-removed top stream and a water-containing bottom stream, and the top stream is refluxed to the second column.

3. 10. The method of claim 1, wherein the feedstream comprises 5-10 wt. % IPA, 0.1-3 wt. % NPA, 85-94 wt. % water, and 0.05-2 wt. % high boiling organics.

4. 10. The method of claim 1, wherein the top stream of the first column comprises a mixture of 30-70 wt. % IPA, 20-50 wt. % NPA, and 10-50 wt. % water.

5. 2. The method of claim 1, wherein the branch flow rate of the bottom stream of the first column fed to the first region of the third column is adjusted to 0.5 to 5 wt % of the total flow rate of the bottom stream of the first column.

6. 2. The method of claim 1, wherein the content of the high boiling organics discharged in the bottom stream of the third column is proportional to the branch flow rate of the bottom stream of the first column fed to the first region of the third column.

7. 2. The method of claim 1, wherein the IPA recovered through the sidewall of the first region in the third column has a purity of 99.99% by weight or greater.

8. The method of claim 1 , wherein the high boiling point organic substance comprises hexanol.

9. 2. The method of claim 1, wherein the organic solvent used in the second column is selected from cyclohexane, benzene, toluene, and isopropyl acetate.

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