Method for preparing isopropanol

Abstract

There is provided a process for preparing isopropanol, comprising: supplying a feed comprising isopropanol, water, a first light by-product, a second light by-product, and a heavy by-product to a first column and separating the first light by-product; and supplying the lower discharge stream of the first column to a second column, and separating the stream into an upper discharge stream of the second column comprising a second light by-product, a first side discharge stream of the second column comprising a mixture of isopropanol and water, a second side discharge stream of the second column comprising a heavy by-product, and a lower discharge stream of the second column comprising water, respectively.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority of Korean Patent Application No. 10-2023-0158482, filed on November 15, 2023, and Korean Patent Application No. 10-2024-0147860, filed on October 25, 2024, which are hereby incorporated by reference in their entirety as a part of this specification.

[0003] The present invention relates to a method for purifying isopropyl alcohol, and more particularly, to a method for reducing energy usage and process costs in purifying isopropyl alcohol from a reaction product of an isopropyl alcohol production process. Background Art

[0004] Isopropyl alcohol (IPA) is considered an excellent solvent in various industries and for a variety of uses due to its ability to dissolve a wide variety of materials, rapid evaporation, and relatively low toxicity. Isopropyl alcohol is an essential material in various manufacturing industries, healthcare, and direct consumer applications.

[0005] In the method for preparing isopropyl alcohol, for example, propylene and water are used as raw material components. Here, propylene and water react to produce isopropyl alcohol. In addition to isopropyl alcohol, unreacted propylene monomer and unreacted water, the reaction product of the isopropyl alcohol preparation method also includes various types of impurities or by-products, such as diisopropyl ether (DIPE), acetone, n-propyl alcohol (NPA) and hexanol.

[0006] In order to obtain isopropyl alcohol from the reaction product, a process for purifying the isopropyl alcohol must be involved. Therefore, an efficient isopropyl alcohol purification process is needed to obtain high-purity isopropyl alcohol, and an improved design is also needed in terms of economic feasibility to reduce energy use and also reduce operating costs and equipment costs. Summary of the Invention

[0007] Technical issues

[0008] In order to solve the problems mentioned in the background art, an object of the present invention is to provide a method for preparing isopropyl alcohol, which can prepare high-purity isopropyl alcohol while reducing energy usage and improving operating costs / equipment costs.

[0009] However, the objects to be solved in the present application are not limited to the above objects, and those skilled in the art can clearly understand other objects not mentioned from the following description.

[0010] Technical Solution

[0011] In one general aspect, a method for preparing isopropyl alcohol comprises: supplying a feed comprising isopropyl alcohol, water, a first light by-product, a second light by-product, and a heavy by-product to a first tower provided with a first reboiler; separating the first light by-product from an upper discharge stream of the first tower; supplying a lower discharge stream of the first tower comprising isopropyl alcohol, water, the second light by-product, and the heavy by-product to a second tower provided with a second reboiler, and separating the stream into an upper discharge stream of the second tower comprising the second light by-product, a first side discharge stream of the second tower comprising a mixture of isopropyl alcohol and water, and a second discharge stream of the second tower comprising the heavy by-product. The invention relates to a method for preparing an azeotropic distillation product according to the present invention; supplying the first side effluent stream of the second column containing a mixture of isopropyl alcohol and water to a third tower which is partitioned into a first region, a second region and an upper region by a dividing wall and provided with a layer separator in the upper region, and performing azeotropic distillation in the presence of an entrainer; and obtaining isopropyl alcohol from the lower effluent stream of the first region of the third tower, wherein the upper effluent stream of the third tower is heat-exchanged with one or more of the lower effluent stream of the first tower and the lower effluent stream of the second tower through one or more of the first reboiler and the second reboiler.

[0012] Beneficial effects

[0013] According to the method for producing isopropyl alcohol of the present invention, by using at least two dividing wall distillation columns when separating isopropyl alcohol from a feed containing isopropyl alcohol, water, and by-products, a method for producing isopropyl alcohol of high purity isopropyl alcohol is provided by using fewer columns than previously required.

[0014] That is, according to the present invention, by reducing the number of distillation columns, by operating a smaller number of distillation columns than previously required, reboiler energy is reduced (energy saving), and reductions in installation cost and operation cost of the apparatus can be achieved.

[0015] Furthermore, by using the high-temperature and high-pressure stream as the upper exhaust stream of the dividing wall distillation column as a heat source for the reboiler of other distillation columns before being introduced into a condenser or a layer separator provided at the upper portion of the dividing wall distillation column, it is possible to provide a method for producing isopropyl alcohol with improved energy efficiency of the overall process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a process flow chart of a method for preparing isopropyl alcohol according to an exemplary embodiment of the present invention.

[0017] Figure 2 1 is a process flow chart of a method for preparing isopropyl alcohol according to a comparative example. DETAILED DESCRIPTION

[0018] Based on the principle that inventors are able to appropriately define the concepts of terms in order to describe their own inventions in the best way, the terms and words used in the description and claims of the present invention should not be restrictively interpreted as having common meanings or dictionary meanings, but should be interpreted as having meanings and concepts that satisfy the technical concept of the present invention.

[0019] Regarding the description of the drawings, like reference numerals may be used for similar or related components.

[0020] Unless otherwise clearly indicated in the relevant context, a singular form of a noun corresponding to an item may include one or more items.

[0021] In the present disclosure, each of the phrases 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" may include any one of the items listed with the corresponding phrase of the phrase or all possible combinations of them.

[0022] The term "and / or" includes a combination of a plurality of described related components or any one of the plurality of described related components.

[0023] Terms such as “first” or “second” or “1st” or “2nd” may be used simply to distinguish a corresponding component from another corresponding component, and the corresponding components are not limited in other aspects (for example, importance or order).

[0024] In addition, terms such as "front surface", "rear surface", "upper surface", "lower surface", "side surface", "left side", "right side", "upper part" and "lower part" used in this application are defined based on the drawings, and the shape and position of each component are not limited by these terms.

[0025] The terms “including” or “having” are intended to specify the existence of stated features, steps, operations, components, parts or their combinations, but do not preclude the existence or addition of one or more other features, numbers, steps, operations, components, parts or their combinations.

[0026] When describing that a component is “connected,” “coupled,” “supported,” or “in contact with” another component, it includes not only the case where the components are directly connected, coupled, supported, or in contact, but also the case where they are indirectly connected, coupled, supported, or in contact through a third component.

[0027] When a component is described as being "on" another component, it includes not only a case where the component is in contact with another component but also a case where other components exist between the two components.

[0028] The term "stream" as used in this application may refer to the flow of fluid in a process, or may refer to the fluid itself flowing in a pipeline. Specifically, "stream" may refer to both the fluid itself flowing in the pipeline connecting each device and the flow of fluid. In addition, a fluid may include any one or more components of a gas, a liquid, and a solid.

[0029] Unless otherwise specified, the term "upper portion" used in this specification refers to a point at a height of 0% to 10% from the top of the device, specifically, the top (tower top). In addition, the term "lower portion" refers to a point at a height of 90% to 100% from the top of the device, specifically, the bottom (tower bottom).

[0030] In addition, the "pressure" mentioned in this specification refers to the gauge pressure measured under atmospheric pressure conditions.

[0031] Meanwhile, unless otherwise specifically stated in this specification, the operating pressure of a column refers to the pressure in the upper portion of the column, and the operating temperature of a column refers to the temperature in the lower portion of the column.

[0032] An exemplary embodiment of the present invention relates to a method for preparing isopropyl alcohol (IPA), and hereinafter, the method for preparing isopropyl alcohol of the present invention will be described in detail with reference to the accompanying drawings.

[0033] Figure 1 is a process flow chart of a method for preparing isopropyl alcohol according to an exemplary embodiment of the present invention.

[0034] The method for preparing isopropyl alcohol according to the present invention includes supplying a feed 10 including isopropyl alcohol, water, a first light by-product, a second light by-product, and a heavy by-product to a first column 100 .

[0035] Feed 10 may be a reaction product comprising isopropyl alcohol produced by the reaction of propylene monomer and water carried out in the reaction section. Specifically, feed 10 may be a residue recovered after separation of a gas component comprising (unreacted) propylene and an inert gas contained in the reaction product.

[0036] The propylene that is supplied to reactive part is only partially used in the reaction.Therefore, except the isopropyl alcohol produced by the reaction of propylene monomer and water, reaction product can also include unreacted propylene and unreacted water.For example, reaction product can include the unreacted propylene monomer of 65 % by weight to 85 % by weight, the isopropyl alcohol of 4 % by weight to 8 % by weight and the water of 5 % by weight to 30 % by weight.In addition, reaction product can include two or more types of light by-products and heavy by-products as by-products.Particularly, light by-products can include diisopropyl ether (DIPE) and acetone, and heavy by-products can include n-propyl alcohol (NPA) and hexanol.Therefore, need a kind of method of separating unreacted raw materials and purifying isopropyl alcohol from various by-products from reaction product.

[0037] There are various methods for recovering (unreacted) propylene from the reaction products in order to prepare the feed 10 of the present invention. Hereinafter, among the various methods for recovering (unreacted) propylene from the reaction products, a method for recovering high-purity (unreacted) propylene for recycling to the reaction section where the gas phase reaction is performed is exemplified.

[0038] According to an exemplary embodiment of the present invention, recovery of propylene from the reaction product may be performed through a gas purification section provided with two or more of an absorption tower, a flash tank, and a gas purification tower.

[0039] Specifically, the reaction product is supplied to the lower portion of an absorption tower, and water is added to the upper portion of the absorption tower to separate propylene. Here, the water can be water supplied from the lower effluent stream of the second tower described later. In the absorption tower, the gaseous isopropyl alcohol contained in the reaction product is absorbed in the water and obtained as a lower liquid stream, and the gaseous stream containing propylene can be separated into the upper portion of the absorption tower. The propylene contained in the gaseous stream can be recycled to the reaction section.

[0040] Simultaneously, in the lower liquid stream of absorption tower, except Virahol and water, can also be included in the low-boiling-point gas component that has not yet separated in absorption tower on a small amount such as the inert gas that comprises propylene.Therefore, the liquid stream that comprises the Virahol that separates from absorption tower can be supplied to flash tank to further reclaim propylene.For example, liquid stream can be supplied to one or more flash tanks that operate under reduced pressure to reclaim the low-boiling-point gas component that comprises propylene that is included in the liquid stream as gas, then gas is supplied to gas purification tower to further reclaim the propylene that may remain in the liquid stream that comprises Virahol.

[0041] Through this process, a gaseous upper stream containing propylene and a liquid lower stream containing isopropyl alcohol, water, etc. can be separated in an absorption tower, a flash tank, and a gas purification tower.

[0042] At the same time, in addition to isopropyl alcohol and water, the liquid lower stream separated in the absorption tower, the flash tank, and the gas purification tower may also contain a first light by-product including diisopropyl ether (DIPE), a second light by-product including acetone, and a heavy by-product including n-propyl alcohol (NPA) and hexanol. Therefore, the liquid lower stream separated in one or more of the absorption tower, the flash tank, and the gas purification tower for recovering propylene can be the feed 10 of the present invention supplied to the first tower 100.

[0043] The feed 10 may be introduced at a height point 30% to 50% downward from the top of the first column 100 .

[0044] According to an exemplary embodiment of the present invention, the first light by-product included in the feed 10 may be first separated and removed through the layer separator 120 connected to the first tower 100 and the upper portion of the first tower 100 .

[0045] Specifically, the upper discharge stream 160 of the first column including isopropyl alcohol, water, the first light by-product, and optionally the second light by-product, and the lower discharge stream 150 of the first column including isopropyl alcohol, water, the second light by-product, and the heavy by-product can be discharged from the upper and lower parts of the first column 100, respectively, by distillation in the first column 100.

[0046] After being discharged from first tower 100, upper discharge stream 160 of the first tower can be supplied to condenser 110 for cooling and liquefaction. The liquefied upper discharge stream of the first tower can be supplied to layer separator 120 for liquid-liquid separation. Through liquid-liquid separation, the aqueous phase stream containing isopropyl alcohol, water, and optionally a second light by-product is refluxed to the first tower, and the oil phase stream 170 containing the first light by-product can be discharged from the system. When the content of the first light by-product contained in feed 10 is 100 wt%, the amount of the first light by-product discharged from the system can be 97 wt% or more, 99 wt% or more, or specifically 100 wt%.

[0047] In order to easily separate the first light by-product by distillation in the first tower 100 and liquid-liquid separation in the layer separator 120 provided at the upper portion of the first tower, at least the first light by-product should be an oily component insoluble in water. That is, the first tower 100 is operated under an operating condition in which the heavy by-product is not evaporated, and the first light by-product can be effectively separated by substantially separating water and isopropyl alcohol dissolved in the water from the first light by-product in the layer separator 120.

[0048] According to an exemplary embodiment of the present invention, the first light by-product can be diisopropyl ether (DIPE) that is insoluble in water, and the second light by-product can be acetone that is soluble in water. Since the boiling point of acetone is lower than that of diisopropyl ether, the upper discharge stream 160 of the first tower can include water, isopropyl alcohol, acetone and diisopropyl ether (DIPE). The isopropyl alcohol contained in the upper discharge stream 160 of the first tower is separated from the first light by-product (oil phase) by the liquid-liquid separation carried out in the layer separator 120, and the water, isopropyl alcohol and acetone contained in the aqueous phase are refluxed to the first tower 100 again. Therefore, the amount of isopropyl alcohol lost in the upper part of the first tower 100 can be minimized by the layer separator 120 provided on the upper part of the first tower 100.

[0049] At the same time, almost all of the first light by-products contained in the feed 10 can be discharged from the system. To this end, the operating conditions of the first tower 100 can be controlled so that almost all of the first light by-products contained in the feed 10 are contained in the upper discharge stream 160 of the first tower 100.

[0050] Specifically, the operating temperature of the first tower 100 may be 75° C. or higher, 80° C. or higher, and 95° C. or lower, or 90° C. or lower. The operating temperature may refer to the temperature of the lower portion of the first tower 100. Meanwhile, the operating pressure of the first tower 100 may be 1 kg / cm 2 ·g or less or 0.5kg / cm 2 g or less. The operating pressure may refer to the pressure at the top of first tower 100. When first tower 100 is operated at the operating temperature and pressure described above, the first light by-product can be separated as much as possible into upper exhaust stream 160 of the first tower. This prevents the first light by-product from flowing into lower exhaust stream 150 of the first tower and ultimately remaining as an impurity in the produced isopropyl alcohol. Furthermore, when the operating temperature and pressure of first tower 100 are as described above, energy can be efficiently utilized through heat exchange with the upper exhaust stream of the third tower, which will be described later.

[0051] Meanwhile, in order to efficiently recover isopropyl alcohol contained in the upper discharge stream 160 of the first tower and reflux it to the first tower again by liquid-liquid separation performed in the layer separator 120, water should be supplied to the upper portion of the first tower. The water supplied to the upper portion of the first tower is supplied to the first tower separately from the water contained in the feed 10. The water supplied to the upper portion of the first tower may be water contained in the stream 20 which is a part of the lower discharge stream 250 of the second tower that is branched and circulated.

[0052] At the same time, according to an exemplary embodiment of the present invention, it is necessary to control the mass flow rate of the branch stream 20 of the lower discharge stream 250 of the second tower recycled to the upper part of the first tower from the perspective of the amount of isopropyl alcohol lost from the layer separator 120 and the energy use in the first tower 100. Specifically, the mass flow rate of the branch stream 20 of the lower discharge stream 250 of the second tower relative to the mass flow rate of the feed 10 supplied to the first tower 100 can be 0.4 to 1.2, 0.4 to 1.0 or 0.5 to 0.8. When the flow rate of water supplied to the upper part of the first tower is greater than 1.2, the energy use required in the first tower is excessively increased. However, when the flow rate of water supplied to the upper part of the first tower is less than 0.4, it is difficult to supply enough water to the layer separator 120, so that the loss of isopropyl alcohol to the oil phase or the amount of loss may be excessively increased.

[0053] Meanwhile, in the layer separator 120 provided at the upper portion of the first tower 100, isopropyl alcohol should be contained in the aqueous phase and refluxed together with water into the first tower 100. When isopropyl alcohol is contained in the oil phase, loss of isopropyl alcohol may occur in the layer separator 120, and in order to prevent such loss of isopropyl alcohol, a sufficient amount of water should be ensured 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 tower 100.

[0054] According to an exemplary embodiment of the present invention, the water introduced into the first tower 100 may be water contained in the feed 10 and water contained in the stream 20, which is a part of the lower discharge stream 250 of the second tower that is branched and recycled. In order to minimize the loss of isopropyl alcohol in the layer separator 120, the sum of the mass flow rate of the water contained in the feed 10 and the mass flow rate of the water contained in the stream 20, which is a part of the lower discharge stream 250 of the second tower that is branched and recycled, is preferably 12 to 15 times (mass flow rate ratio of isopropyl alcohol to water) relative to the mass flow rate of the isopropyl alcohol contained in the feed 10. In this case, a sufficient amount of water can be supplied to the layer separator 120, thereby preventing the loss of isopropyl alcohol in the layer separator 120 into the oil phase, and at the same time, optimizing the energy usage required for the operation of the first tower 100.

[0055] Specifically, the branch stream 20 as a part of the lower discharge stream of the second tower containing water that is branched may be a branch stream that is a part of the stream branched after the stream immediately refluxed to the reboiler 230 after being discharged to the lower part of the second tower.

[0056] That is, when the mass flow rate ratio between isopropyl alcohol and water supplied to the first column is less than 12, it is difficult to ensure a sufficient amount of water in the layer separator 120, so isopropyl alcohol is lost to the oil phase, and it is difficult to achieve a desired recovery rate of isopropyl alcohol. In addition, in this case, a portion of the first light by-product, which should be contained in the oil phase in the layer separator 120 and removed, may be contained in the water phase and introduced into the second column 200. When the first light by-product is introduced into the second column 200, it is contained 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 in the second column.

[0057] In addition, when the ratio of the mass flow rate of isopropyl alcohol to water supplied to the first tower is greater than 15, the loss of isopropyl alcohol in the layer separator 120 can be prevented, but the amount of water circulating in the first tower 100 and the second tower 200 is excessively increased, thereby increasing energy usage of the two towers.

[0058] Furthermore, in terms of minimizing the amount of isopropyl alcohol lost in the layer separator 120 and reducing energy usage in the first and second towers, the mass flow rate of water contained in the stream 20 as a part of the lower discharge stream 250 of the second tower that is branched and recycled may be 58% to 90% based on the mass flow rate of water contained in the feed 10.

[0059] Meanwhile, a first reboiler 130 for supplying heat energy required for the operation of the first tower is provided in the lower portion of the first tower 100. A reflux stream of the lower exhaust stream 150 of the first tower may be introduced into the first reboiler 130, heat-exchanged with a high-temperature heat source, and then reintroduced into the lower portion of the first tower 100. The heat energy required for the operation of the first tower 100 may be supplied to the first tower 100 through the first reboiler 130.

[0060] According to an exemplary embodiment of the present invention, the heat source of the first reboiler 130, that is, the heat source for heat exchange with the reflux stream of the lower exhaust stream 150 of the first tower, as described below, may be the upper exhaust stream 330 of the third tower 300. Specifically, before all or a portion of the upper exhaust stream 330 of the third tower is introduced into the condenser 380 or the layer separator 340 provided at the upper portion of the third tower 300, the stream may be heat exchanged with the reflux stream of the lower exhaust stream 150 of the first tower in the first reboiler 130. Therefore, the heat energy of the upper exhaust stream of the third tower 300 may be supplied to the first tower 100.

[0061] Meanwhile, according to an exemplary embodiment of the present invention, when the reboiler energy required for the operation of the first tower 100 is not entirely replaced by only the thermal energy of the upper exhaust stream 330 of the third tower 300, an auxiliary reboiler 135 separated from the first reboiler 130 may be provided at the lower portion of the first tower 100.

[0062] According to an exemplary embodiment of the present invention, the lower exhaust stream 150 of the first column is introduced into the second column 200, and the second light by-product, the mixture of isopropyl alcohol and water, the heavy by-product, and water may be separated according to boiling points.

[0063] Specifically, the lower discharge stream 150 of the first column including isopropyl alcohol, water, the second light by-products, and the heavy by-products is supplied to the second column 200 provided with the second reboiler 230, and processes of separating the upper discharge stream 260 of the second column including the second light by-products, the first side discharge stream 290 of the second column including the mixture of isopropyl alcohol and water, the second side discharge stream 280 of the second column including the heavy by-products, and the lower discharge stream 250 of the second column including water may be respectively performed.

[0064] The second light by-product is a by-product with a lower boiling point than other separated components. The second light by-product can be a compound with a boiling point of 50 ℃ to 70 ℃, specifically, acetone. Acetone can be a by-product produced during the gas phase reaction for preparing isopropyl alcohol, and can be a by-product produced by the oxidation of isopropyl alcohol in a subsequent process after the gas phase reaction. The upper discharge stream 260 of the second tower can include more than 60 weight %, more than 70 weight % or more than 90 weight %, and a mixture of the second light by-product and the isopropyl alcohol of a residual amount with water of less than 100 weight %. After discharging from the second tower, the upper discharge stream 260 of the second tower is refluxed to the second tower by a condenser again, and the remainder 270 can be discharged from the system.

[0065] Meanwhile, the mixture of isopropyl alcohol and water may be an azeotrope of isopropyl alcohol and water. That is, water having a boiling point of about 100° C. and isopropyl alcohol having 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 and lower than the boiling point of the heavy by-product.

[0066] Therefore, a portion of the water introduced into the second column forms an azeotrope with the isopropyl alcohol and is discharged to the first side discharge stream 290 of the second column, and the remaining water is discharged as the lower discharge stream 250 of the second column.

[0067] A second reboiler 230 for supplying heat energy required for the operation of the second tower 200 is provided at the lower portion of the second tower 200. A reflux stream of the lower exhaust stream of the second tower can be introduced into the second reboiler 230, heat-exchanged with a high-temperature heat source, and then reintroduced into the lower portion of the second tower 200. The heat energy required for the operation of the second tower 200 can be supplied to the second tower 200 through the second reboiler 230.

[0068] According to an exemplary embodiment of the present invention, the heat source of the second reboiler 230, that is, the heat source for heat exchange with the reflux stream of the lower exhaust stream of the second tower, as described below, may be the upper exhaust stream 330 of the third tower 300. Specifically, before all or a portion of the upper exhaust stream 330 of the third tower is introduced into the condenser 380 or the layer separator 340 provided at the upper portion of the third tower 300, the stream may be heat exchanged with the reflux stream of the lower exhaust stream 250 of the second tower in the second reboiler 230. Therefore, the heat energy of the upper exhaust stream of the third tower 300 may be supplied to the first tower 100.

[0069] According to an exemplary embodiment of the present invention, when the reboiler energy required for the operation of the second tower 200 is not entirely replaced by the heat energy of the upper exhaust stream 330 of the third tower 300, an auxiliary reboiler 235 separated from the second reboiler 230 may be provided at the lower portion of the second tower 200.

[0070] Meanwhile, the branch stream 20 as a part of the lower discharge stream 250 of the second tower containing water, specifically, the stream 250 branched from the stream discharged to the lower portion of the second tower 200 and not supplied to the reboiler 230, can be recycled to the upper portion of the first tower. The water recycled from the second tower 200 can be used to supplement a sufficient amount of water so that the phase separation between the water phase and the oil phase performed in the layer separator 120 provided at the upper portion of the first tower 100 is well performed.

[0071] Meanwhile, the heavy by-products may include n-propyl alcohol (NPA) and hexanol, and the heavy by-products may be discharged into the second side discharge stream 280 of the second column.

[0072] The second tower 200 according to an exemplary embodiment of the present invention includes a partition wall spaced apart from the bottom of the tower and disposed along the length direction of the tower, and the second tower may be a distillation tower divided into a top region 201, a bottom region 202, a supply region 203, and a discharge region 204 by the partition wall.

[0073] Reference Figure 1 The interior of the second tower 200 is divided by a partition wall and an imaginary dotted line. Specifically, the top region 201 is located above the upper end of the partition wall, and the upper exhaust stream 260 of the second tower is discharged therefrom. The bottom region 202 is located below the lower end of the partition wall, and the lower exhaust stream 250 of the second tower is discharged therefrom. At the same time, the lower exhaust stream 150 of the first tower can be supplied to the supply region 203.

[0074] The first side effluent stream 290 of the second tower and the second side effluent stream 280 of the second tower can be discharged from the discharge area 204 in the area separated by the dividing wall. Specifically, the first side effluent stream 290 can be discharged from the discharge area above the second side effluent stream 280.

[0075] That is, according to an exemplary embodiment of the present invention, a composition (lower discharge stream of the first column) including at least four components such as isopropyl alcohol, water, a second light by-product, and a heavy by-product is separated by one column (second column) provided with a dividing wall and discharged to the upper portion, the first side portion, the second side portion, and the lower portion, thereby reducing the number of distillation columns previously required for separating these components.

[0076] Specifically, refer to Figure 2 , using a distillation column without a dividing wall as the second column C2, it is impossible to Figure 2 The separated materials are discharged from the upper part, the lower part, the first side part and the second side part of the second column C2 in the reactor. However, since the side discharge stream from which the heavy by-products are separated contains a large amount of isopropyl alcohol and water, further purification of the side discharge stream is required to increase the yield of isopropyl alcohol. That is, a process is required to introduce the side discharge stream 280 into the third column C3 to further recover the stream containing isopropyl alcohol in the upper part and supply it to the second column C2 again. That is, referring to Figure 2 According to the present invention, since the same role previously performed by the second tower C2 and the third tower C3 can be performed by one distillation tower provided with a dividing wall, the number of towers can be reduced and the energy usage (e.g., steam usage) required for tower operation can be reduced, and also since the second tower provided with a dividing wall is used, pre-separation occurs in the supply area 203 and final purification is performed in the discharge area 204, it is possible to obtain a greater energy usage reduction effect than simply combining two towers and operating them.

[0077] Meanwhile, the upper end of the partition wall is located at a height point of 3% to 30% downward from the top of the second tower, and the lower end of the partition wall may be located at a height point of 70% to 95% downward from the top of the second tower.

[0078] Furthermore, the first side bleed stream 290 may be discharged from a height point 5% to 33% below the top of the second tower, and the second side bleed stream 280 may be discharged from a height point 40% to 80% below the top of the second tower.

[0079] By the location of the dividing wall and the discharge points of the first and second side bleed streams, energy usage can be reduced compared to previous energy usage when two columns are used while obtaining four streams discharged from the second column of the desired purity.

[0080] The operating temperature and operating pressure of the top region 201 and the bottom region 202 of the second column 200 also need to be controlled according to the purity of the components to be separated, such as isopropyl alcohol, and the energy required to separate the components.

[0081] Specifically, the operating temperature of the top region 201 of the second tower 200 may be below 90° C., below 85° C., or below 80° C., and the operating pressure of the top region 201 may be 2 kg / cm 2 ·g or less, 1kg / cm 2 ·g or less or 0.05kg / cm 2 Specifically, the operating temperature of the bottom region 202 of the second tower 200 may be 85° C. or 88° C. or more and 105° C. or 103° C. or less. Meanwhile, the operating pressure of the bottom region 202 may be 1.0 kg / cm 2 ·g or less or 0.5kg / cm 2 ·g or less.

[0082] When the operating temperature and the operating pressure of the second tower 200 are as described above, it is possible to efficiently utilize energy through heat exchange with an upper exhaust stream of a third tower described later.

[0083] A method for preparing isopropyl alcohol according to an exemplary embodiment may include supplying a first side effluent stream 290 of a second column including a mixture of isopropyl alcohol and water to a third column 300 divided into a first region 301, a second region 302, and an upper region 303 by a partition wall 305 and provided with a layer separator 340 on the upper region, and performing azeotropic distillation in the presence of an entrainer.

[0084] Specifically, first side effluent stream 290 of second column 200 may comprise a mixture of isopropyl alcohol and water, specifically, an azeotrope of isopropyl alcohol and water. More specifically, first side effluent stream 290 of second column 200 may comprise 80 wt% to 90 wt% of isopropyl alcohol and 10 wt% to 20 wt% of water.

[0085] Meanwhile, the third distillation tower 300 according to an exemplary embodiment of the present invention is a dividing wall type distillation tower and may include a first region 301, a second region 302, and an upper region 303 divided by a dividing wall 305. The dividing wall 305 is connected (bonded) to the bottom of the third distillation tower 300 and extends upward in the length direction of the third distillation tower 300 and is provided. Here, the first region 301 and the second region 302 are regions divided by the dividing wall 305 therebetween so that they face each other, and the second region 302 is a region opposite to the first region 301. Meanwhile, the upper region 303 is a region located above the upper end of the dividing wall and is located Figure 1 The area above the imaginary boundary line marked with a dotted line in the third tower 300.

[0086] Meanwhile, azeotropic distillation can be performed in the presence of an entrainer in third distillation column 300. A portion of the isopropyl alcohol and a portion of the water contained in first side bleed stream 290 of second column 200 can form an azeotrope. Water, with a boiling point of approximately 100°C, and isopropyl alcohol, with a boiling point of approximately 82.3°C, form an azeotrope at an azeotropic temperature of approximately 81°C. Since these components cannot be completely separated in this azeotrope by conventional distillation, the isopropyl alcohol and water can be separated at high purity after removing the azeotropic relationship between the isopropyl alcohol and water, typically using an entrainer. The entrainer of the present invention that performs this function can be one or more selected from cyclohexane, benzene, toluene, and isopropyl acetate.

[0087] The entrainer is a material that is further added separately from the feed components for azeotropic distillation, but since the entrainer is an impurity to isopropyl alcohol etc., it should be separated by a separate distillation column etc., and from the economical viewpoint, the separated entrainer can be recycled.

[0088] That is, reference to the prior art Figure 2 Conventionally, to separate isopropyl alcohol and water from a feed containing an azeotrope of isopropyl alcohol and water and byproducts, azeotropic distillation is performed in a conventional azeotropic column C4 without a dividing wall in the presence of an entrainer. The upper discharge stream containing water and the entrainer is then phase-separated from a layer separator, and the oil phase containing the entrainer is then recirculated to the azeotropic distillation column C4. However, since the aqueous phase contains a large amount of entrainer in addition to water, the aqueous phase is introduced into an entrainer recovery column C5 to separate the entrainer and water by distillation. The recovered entrainer is then reintroduced into the azeotropic distillation column C4, and the water is discharged to the outside of the system. Here, to separate the entrainer and water by distillation in the entrainer recovery column C5, a large amount of energy must be supplied via a reboiler located at the bottom of the entrainer recovery column C5.

[0089] At the same time, according to the conventional art, the heat energy required for the operation of azeotropic distillation column C4 is supplied via a reboiler provided at the bottom. When the upper effluent stream of azeotropic distillation column C4 contains water and an entrainer, the lower effluent stream of azeotropic distillation column C4 contains isopropyl alcohol and by-products. The lower effluent stream of azeotropic distillation column C4 is supplied to isopropyl alcohol recovery column C6 to obtain isopropyl alcohol in the upper portion of isopropyl alcohol recovery column C6, and the by-products are separated into the lower portion of isopropyl alcohol recovery column C6.

[0090] However, with reference to the method for preparing isopropyl alcohol according to an exemplary embodiment of the present invention Figure 1While a dividing wall is provided in the third distillation column 300 performing azeotropic distillation, the reflux point for the aqueous and oil phases in the layer separator 340 is optimized to produce high-purity isopropyl alcohol. The conventional entrainer recovery column C5 for separating the entrainer and water is omitted. Consequently, the heat energy supplied to the reboiler for operating the conventional entrainer recovery column C5 can be reduced, and the cooling energy required for operating the condenser installed above the entrainer recovery column C5 can also be reduced. Furthermore, even 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, the energy consumption required for distillation column operation can be reduced by not operating the entrainer recovery column C5.

[0091] To this end, according to one exemplary embodiment of the present invention, a reboiler 315 connected to the lower portion of the first region is provided in the first region 301 disposed in the lower portion of the third distillation column 300, and a reboiler 325 connected to the lower portion of the second region may be provided in the second region 302. Here, the lower portion refers to a point at a height that is 90% to 100% downward from the top (top) of the third distillation column 300. Heat energy may be supplied to the first region 301 and the second region 302 through the reboiler 315 and the reboiler 325, respectively, and the heat energy supplied to each of the reboiler 315 and the reboiler 325 may be adjusted to adjust the operating conditions of the first region 301 and the second region 302.

[0092] According to an exemplary embodiment of the present invention, the heat energy supplied by the reboiler 315 connected to the lower portion of the first section may be 1.5 to 3 times, more specifically, 1.8 to 2.5 times, the heat energy supplied by the reboiler 325 connected to the lower portion of the second section. Therefore, isopropyl alcohol having a desired purity can be separated into the lower exhaust stream of the first section, and pure water can be separated into the lower exhaust stream of the second section of the third distillation column.

[0093] The temperature of the lower portion of first region 301 may be 135°C or 137°C or higher and 150°C or 148°C or lower. Furthermore, the temperature of the lower portion of second region 302 may be 155°C or 158°C or higher and 170°C or 168°C or lower. The respective lower portion temperatures in the first and second regions refer to operating temperatures at points 90% to 100% of the height downward from the top (or upper portion) of column 100. By controlling the temperatures of the lower portions of the first and second regions, the energy required for distillation in third distillation column 300 can be reduced, isopropyl alcohol of desired purity can be obtained from the lower portion of the first region, and pure water can be separated from the lower portion of the second region.

[0094] Meanwhile, the first region lower effluent stream 310 discharged from the first region of the third distillation column 300 may contain isopropyl alcohol and heavy by-products. Here, the heavy by-products may include n-propyl alcohol (NPA). A portion of the first region lower effluent stream 310 may be heat-exchanged in a reboiler 315 connected to the lower portion of the first region and then refluxed to the first region, and the remainder of the first region lower effluent stream 310 may be supplied to the fourth column 400.

[0095] Meanwhile, the second region lower exhaust stream 320 discharged from the second region 302 may contain water. A portion of the second region lower exhaust stream 320 may be heat-exchanged in a reboiler 325 connected to the lower portion of the second region and then refluxed to the second region, and the remainder of the second region lower exhaust stream 320 may be discharged from the system.

[0096] As described above, the region above the upper end of the dividing wall in the third distillation column 300 may form the upper region 303 .

[0097] The partition wall 305 extends from the bottom of the column, but the upper end of the partition wall may be located at a height point of 10% to 45%, specifically, 15% to 30%, downward from the top of the third distillation column 300. Thus, the separation efficiency of the third distillation column 300 can be maximized to obtain isopropyl alcohol having a desired purity from the lower portion of the first region and to separate pure water from the lower portion of the second region.

[0098] An upper discharge stream 330 comprising water and entrainer may be discharged from the upper portion of the upper zone.

[0099] According to an exemplary embodiment, the upper exhaust stream 330 of the third tower may be heat exchanged with one or more of the lower exhaust stream of the first tower and the lower exhaust stream of the second tower in one or more of the first reboiler 130 of the first tower 100 and the second reboiler 230 of the second tower 200. Thus, heat of the upper exhaust stream 330 of the third tower is supplied to one or more of the first tower and the second tower, thereby reducing the thermal energy required for the operation of one or more of the first tower and the second tower.

[0100] That is, refer to Figure 1, the heat exchanger A provided at the upper portion of the third tower may be one or more of the first reboiler 130 of the first tower and the second reboiler 230 of the second tower. After being discharged from the third tower 300, the upper discharge stream 330 of the third tower is transferred to one or more of the first reboiler 130 and the second reboiler 230, and the retained heat energy may be supplied to one or more of the first tower 100 and the second tower 200. Here, the upper discharge stream 330 of the third tower may be heat-exchanged with the first reboiler 130 or the second reboiler 230, or heat-exchanged in both the first reboiler 130 and the second reboiler 230. When the upper discharge stream 330 of the third tower is heat-exchanged in the first reboiler 130 and the second reboiler 230, the upper discharge stream 330 of the third tower is branched into two streams, and each branch stream may be heat-exchanged in each of the first reboiler 130 and the second reboiler 230. Also in this case, in Figure 1 , the heat exchanger A may refer to both the first reboiler 130 and the second reboiler 230. After the upper discharge stream 330 of the third column is heat-exchanged with one or more of the first reboiler 130 and the second reboiler 230, the heat-exchanged upper discharge stream 330 of the third column may be transferred to the condenser 380 provided at the upper portion 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 130 and the second reboiler 230, each branched stream after heat exchange may be merged and transferred to the condenser 380.

[0101] The operating pressure of the upper portion of the third tower 300 may be 4.9 bar.g to 5.1 bar.g. When the operating pressure of the upper portion of the third tower is higher than 4.9 bar.g, the temperature of the upper exhaust stream 330 of the third tower may be at least 10° higher than the temperature of the lower portions of the first and second towers. Thus, the temperature difference between the first reboiler 130 of the first tower 100 and the second reboiler 230 of the second tower 200 for heat exchange may be maintained.

[0102] In particular, when the operating pressure of the upper portion of the third tower 300 is higher than 5.1 bar.g, a high temperature of the upper exhaust stream 330 of the third tower can be achieved, and thus there is no problem in supplying heat to the first tower 100 and the second tower 200, but the separation performance performed in the third tower 300 is reduced. In this case, since additional energy must be supplied to the third tower 300 to separate the components with the desired purity, this is not preferable from the perspective of reducing energy use. Conversely, when the operating pressure of the upper portion of the third tower 300 is less than 4.9 bar.g, it is difficult to maintain the temperature of the upper exhaust stream 330 of the third tower at a high temperature, and therefore it is difficult to ensure a sufficient temperature difference to allow heat exchange in the first reboiler 130 and the second reboiler 230.

[0103] Meanwhile, the operating temperature of the upper portion of the third tower 300, specifically, the operating temperature of the upper region of the third tower 300 may be 120° C. or higher, specifically, 122° C. or higher. In this case, since an appropriate temperature difference (e.g., a temperature difference of at least 10° C. or higher) required for heat exchange with the lower portion of the first tower 100 and the lower portion of the second tower 200 can be ensured, efficient energy supply to the first tower 100 and the second tower 200 through the upper exhaust stream 330 of the third tower can be allowed.

[0104] Furthermore, the upper discharge stream 330 of the third tower can undergo heat exchange with the lower discharge streams of the first tower and the second tower via the first reboiler 130 and the second reboiler 230. Specifically, when the upper discharge stream 330 of the third tower undergoes heat exchange with both the first reboiler 130 and the second reboiler 230, the upper discharge stream 330 of the third tower can branch to form a branch stream supplied to the first reboiler 130 and a branch stream supplied to the second reboiler 230. Here, the ratio between the mass flow rate of the branch stream supplied to the first reboiler and the mass flow rate of the branch stream supplied to the second reboiler can be 1:5 to 1:7. Because this ratio maximizes the logarithmic mean temperature difference (LMTD) between the low-temperature medium (the lower discharge streams of the first and second towers) and the high-temperature medium (the upper discharge stream of the third tower) undergoing heat exchange in the first and second reboilers 130 and 230, the first and second reboilers 130 and 230 can be efficiently designed and operated. In addition, the sizes of the auxiliary reboiler 135 of the first column and the auxiliary reboiler 235 of the second column described above may be minimized.

[0105] The upper exhaust stream 330 of the third tower 300 may be heat exchanged with one or more of the lower exhaust streams of the first tower 100 and the lower exhaust streams of the second tower 200 in one or more of the first reboiler 130 of the first tower 100 and the second reboiler 230 of the second tower 200, and then cooled so that all or part of it may be condensed into a liquid phase. The condensed upper exhaust stream 330 of the third tower may be introduced into a condenser 380 provided at the upper portion of the third tower and further condensed to a desired condensation condition.

[0106] The discharge stream of the condenser 380 may be introduced into the layer separator 340 provided at the upper portion of the third column after further condensation. The layer separator 340 is a device for separating fluids by density difference, and an aqueous phase containing water and an oil phase containing an azeotropic agent may be separated by the layer separator 340. The oil phase stream 350 containing the azeotropic agent may be refluxed to the upper region 303, and the aqueous phase stream 360 containing water may be refluxed to the second region 302.

[0107] That is, since the upper effluent stream 330 is separated into an oil phase and an aqueous phase by the layer separator 340 and then the separated oil phase and aqueous phase are refluxed to the third distillation column 300 again, the mass flow rate of the upper effluent stream 330 of the third distillation column can be equal to the sum of the mass flow rates of the aqueous phase stream 360 and the oil phase stream 350 refluxed to the third distillation column 300 through the layer separator 340. That is, substantially no components are supplied to other distillation columns or discharged from the system from the upper effluent stream 330 of the third distillation column 300. That is, after being discharged from the third distillation column 300, the upper effluent stream 330 of the third distillation column 300 is supplied to one or more of the first reboiler 130 and the second reboiler 230, supplied to the condenser 380, passed through the layer separator 340, and then completely refluxed to the third distillation column 300.

[0108] The entrainer contained in the oil phase stream 350 is reused for the azeotropic distillation performed in the third distillation column 300. Furthermore, both the phase-separated oil phase and aqueous phase are refluxed to the third distillation column 300, but the reflux point is optimized, thereby separating the lower effluent stream 310 of the first zone and the lower effluent stream 320 of the second zone with high purity. At the same time, the entrainer 370 inevitably consumed as the process proceeds can be supplied to the layer separator 340 and replenished.

[0109] The reflux point of the aqueous phase to the second region may be 10% to 50% from the bottom of the column, specifically 25% to 40% from the dividing wall. Thus, the energy required for distillation is maximized while pure water can be separated from the lower portion of the second region.

[0110] More specifically, by setting the position of the upper end of partition wall 305 and the position of the reflux point of the aqueous phase to the second region as described above, it is possible to simultaneously ensure sufficient azeotropic distillation for separating isopropyl alcohol and water using an entrainer and a distillation region for purifying isopropyl alcohol in third distillation column 300. Furthermore, upper region 303 in the upper partition wall shares the first and second regions, thereby reducing the energy required in condenser 380. Furthermore, the liquid reflux flow, which branches from the bottom of upper region 303 into first and second regions 301 and 302 and flows downward, is optimized and distributed between the first and second regions, minimizing the amount of heat required in the reboiler in each region.

[0111] Meanwhile, according to an exemplary embodiment of the present invention, the lower exhaust stream 310 of the first zone discharged from the first zone 301 can be supplied to the fourth tower 400 to recover isopropyl alcohol. The fourth tower 400 is operated by a reboiler 430 located at the lower portion, and isopropyl alcohol 410 is obtained at the upper portion of the fourth tower 400. Heavy by-products 420 can be separated to the lower portion of the fourth tower.

[0112] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are provided to illustrate the present invention, and it will be apparent to those skilled in the art that various modifications and variations may be made without departing from the scope and spirit of the present invention, and the scope of the present invention is not limited thereto.

[0113] In the following Examples and Comparative Examples, the process according to the present invention was simulated using the commercial process simulation program Aspen Plus V12.1.

[0114] Example 1

[0115] According to Figure 1 The process diagram shown is a process for preparing isopropyl alcohol.

[0116] Specifically, water and propylene are supplied to a reaction section and subjected to a gas phase reaction to produce a reaction product comprising isopropyl alcohol, water, and propylene. Feed 10 is prepared from the residue remaining after separating and recovering propylene from the reaction product. Feed 10 comprises 10.395 wt % of isopropyl alcohol, 88.9 wt % of water, 0.5 wt % of diisopropyl ether (DIPE) as a first light by-product, 0.005 wt % of acetone as a second light by-product, and 0.2 wt % of n-propyl alcohol (NPA) and hexanol as heavy by-products.

[0117] The feed 10 is supplied to the first tower, and a portion of the lower discharge stream of the second tower 200 is branched and introduced into the upper portion of the first tower 100, and the mass flow rate of the branched stream 20 as a portion of the lower discharge stream of the second tower 200 is 0.6 of the mass flow rate of the feed 10 supplied to the first tower 100.

[0118] A stream 160 containing isopropyl alcohol, water, diisopropyl ether, and acetone is discharged to the upper portion of the first column 10 and supplied to the condenser 110 and the layer separator 120, the aqueous phase containing isopropyl alcohol, water, and acetone is refluxed to the first column 100 again, and the oil phase containing diisopropyl ether is discharged from the system.

[0119] The lower effluent stream of the first column is introduced into a supply region 203 of a second column provided with a dividing wall to be separated by distillation into four effluent streams: an upper effluent stream 260 of the second column containing acetone, a first side effluent stream 290 of the second column containing an azeotrope of isopropyl alcohol and water, a second side effluent stream 280 of the second column containing n-propyl alcohol (NPA) and hexanol, and a lower effluent stream 250 of the second column containing water.

[0120] Meanwhile, a first reboiler 130 is provided at the lower portion of the first tower 100, and a second reboiler 230 is provided at the lower portion of the second tower 200. An upper exhaust stream 330 of a third tower described later is branched to form a branch stream supplied to the first reboiler 130 and a branch stream supplied to the second reboiler 230, and each branch stream is introduced into the first reboiler 130 and the second reboiler 230 at a mass flow ratio of 1:6, thereby supplying heat energy to the lower portions of the first tower and the second tower.

[0121] At this time, since the operating conditions of the first tower and the second tower cannot reach the desired level using only the thermal energy of the upper exhaust stream 330 of the third tower, additional thermal energy is supplied to the first tower and the second tower through the auxiliary reboiler 135 and the auxiliary reboiler 235 provided at the lower parts of the first tower and the second tower respectively.

[0122] Meanwhile, first side bleed stream 290 of the second column contained 85.78 wt% of isopropyl alcohol, 13.58 wt% of water, and 0.64 wt% of normal propyl alcohol (NPA) as a by-product. Since the ratio of the mass flow rate of isopropyl alcohol contained in first side bleed stream 290 of the second column to the mass flow rate of isopropyl alcohol contained in feed 10 was 99.4%, there was no need to perform additional distillation on second side bleed stream 280 of the second column in order to improve the recovery rate of isopropyl alcohol.

[0123] Subsequently, the first side discharge stream 290 of the second column including the azeotrope of isopropyl alcohol and water is supplied to the first region of the third column 300 and subjected to azeotropic distillation in the presence of cyclohexane as an azeotropic agent.

[0124] The upper exhaust stream 330 discharged from the upper region 303 of the third tower 300 is branched into a mass flow ratio of 1:6 and supplied to the first reboiler 130 and the second reboiler 230, respectively, thereby supplying heat energy to the lower portions of the first and second towers. At this time, the operating pressure of the upper region 303 of the third tower is 5.0 barg, and the temperature of the upper exhaust stream 330 is 122°C. Meanwhile, the temperature of the lower exhaust stream of the first tower supplied to the first reboiler 130 is 85°C, and the temperature of the lower exhaust stream of the second tower supplied to the second reboiler 230 is 95°C. Due to the appropriate temperature difference between the low-temperature medium and the high-temperature medium supplied to the first and second reboilers 130 and 230, efficient heat exchange is achieved.

[0125] After heat exchange in the first reboiler 130 and the second reboiler 230, the upper exhaust stream 330 of the third column passes through a condenser 380 and a layer separator 340 in sequence to separate into an oil phase and an aqueous phase. The oil phase stream 350 containing cyclohexane is refluxed to the upper region, and the aqueous phase stream 360 containing water is refluxed to the second region. Here, the reflux point of the aqueous phase to the second region is 30% of the height of the column bottom from the dividing wall.

[0126] Meanwhile, the lower effluent stream 310 of the first zone containing isopropyl alcohol and n-propyl alcohol was supplied to the fourth tower 400, and isopropyl alcohol was obtained at the upper portion of the fourth tower 400. It was confirmed that the isopropyl alcohol content in the upper effluent stream of the fourth tower was 99.8 wt%.

[0127] At this time, the energy consumed in the reboiler in each tower is shown in Table 1. Specifically, since the heat energy supplied to the first reboiler of the first tower and the second reboiler of the second tower is supplied from the upper portion of the third tower, Table 1 shows the reboiler energy consumed in the first and second towers, as well as the heat energy supplied by the auxiliary reboiler 135 and the auxiliary reboiler 235 provided at the lower portions of the first and second towers, respectively. Meanwhile, the heat energy supplied by the reboiler 315 connected to the lower portion of the first region of the third tower and the heat energy supplied by the reboiler 325 connected to the lower portion of the second region of the third tower are respectively shown in Table 1.

[0128] Comparative Example 1

[0129] according to Figure 2 The process diagram shown is a process for preparing isopropyl alcohol.

[0130] For the same feed 10 of Example 1, the lower discharge stream of the first column C1 having the same composition as that of Example 1 was obtained and introduced into the second column C2.

[0131] The second column C2 of Comparative Example 1 is a column without a dividing wall. As in Example 1, the stream is separated into four outlet streams by distillation: an upper outlet stream of the second column containing acetone, a first side outlet stream of the second column containing an azeotrope of isopropyl alcohol and water, a second side outlet stream of the second column containing n-propyl alcohol (NPA) and hexanol, and a lower outlet stream of the second column containing water.

[0132] In this case, the second side bleed stream of the second column contains a large amount of isopropyl alcohol, and since heavy by-products and water are discharged in an inefficiently separated state, a yield of 99% of isopropyl alcohol contained in the first side bleed stream of the second column cannot be achieved by operating the second column C2 alone. Therefore, the third column C3 is required for further purifying the isopropyl alcohol in the second side bleed stream of the second column and separating the heavy by-products and water.

[0133] Specifically, the second side exhaust stream of the second column is introduced into the third column C3, the stream containing isopropyl alcohol is separated into the upper part of the third column and supplied to the second column C3 again, water is separated into the lower part of the third column, and heavy by-products (n-propyl alcohol and hexanol) are separated into the side of the third column.

[0134] Energy required for the operations of the first to third columns is supplied through reboilers provided at lower portions of the first to third columns.

[0135] The first side discharge stream of the second column, containing the azeotrope of isopropyl alcohol and water, is passed through a conventional azeotropic column C4 without a dividing wall, an entrainer recovery column C5, and an isopropyl alcohol recovery column C6, and isopropyl alcohol is recovered from the upper portion of the isopropyl alcohol recovery column C6. Each of the three columns is provided with a condenser at the upper portion and a reboiler at the lower portion.

[0136] Specifically, the first side effluent stream from the second column, containing an azeotrope of isopropyl alcohol and water, is supplied to a conventional azeotropic distillation column C4, where azeotropic distillation is performed in the presence of cyclohexane. The upper effluent stream, containing water and an entrainer, is phase-separated in a layer separator, and the oil phase containing the entrainer is refluxed back to the azeotropic distillation column C4. The aqueous phase containing water is supplied to an entrainer recovery column C5. The lower effluent stream from the azeotropic distillation column C4, containing isopropyl alcohol and heavy byproducts, is supplied to an isopropyl alcohol recovery column C6, where isopropyl alcohol is recovered from the upper portion.

[0137] Meanwhile, in Comparative Example 1, the composition and flow rate of the lower effluent stream of the azeotropic distillation column C4 introduced into the isopropyl alcohol recovery column C6 were the same as those in Example 1, and the operating conditions and energy usage of the isopropyl alcohol recovery column C6 in Comparative Example 1 were also the same as those in Example 1. As a result, it was confirmed that the isopropyl alcohol content obtained in Comparative Example 1 was 99.8% by weight, the same as in Example 1.

[0138] At this time, the energy (heat energy) used in the reboiler provided at the lower portion of each column (C1 column to C6 column) in Comparative Example 1 is shown in Table 1.

[0139] [Table 1]

[0140]

[0141]

[0142] As confirmed above, high levels of isopropyl alcohol purity and yield were maintained in Example 1. In particular, it was found that when the second and third columns were used as dividing wall distillation columns having a specific structure and the heat of the upper exhaust stream of the third column was used as the energy source required for the operation of the first and second columns, the energy efficiency of the entire process from the first to fourth columns was maximized.

[0143] [Explanation of Reference Numerals]

[0144] 10: Feed

[0145] 100: First Tower

[0146] 200: Second Tower

[0147] 300: Third Tower

[0148] 400: Fourth Tower

Claims

1. A method for preparing isopropyl alcohol, comprising: supplying a feed comprising isopropyl alcohol, water, a first light by-product, a second light by-product, and a heavy by-product to a first column provided with a first reboiler; separating the first light by-product from the upper effluent stream of the first column; supplying a lower discharge stream of the first column containing isopropyl alcohol, water, a second light by-product, and a heavy by-product to a second column provided with a second reboiler, and separating the lower discharge stream of the first column into an upper discharge stream of the second column containing the second light by-product, a first side discharge stream of the second column containing a mixture of isopropyl alcohol and water, a second side discharge stream of the second column containing heavy by-products, and a lower discharge stream of the second column containing water; supplying the first side discharge stream of the second column containing a mixture of isopropyl alcohol and water to a third column partitioned into a first region, a second region, and an upper region by a dividing wall and provided with a layer separator at the upper portion, to perform azeotropic distillation in the presence of an entrainer; as well as isopropyl alcohol is obtained from the lower effluent stream of the first zone of the third column, The upper exhaust stream of the third tower is heat-exchanged with one or more of the lower exhaust stream of the first tower and the lower exhaust stream of the second tower through one or more of the first reboiler and the second reboiler.

2. The method for preparing isopropyl alcohol according to claim 1, wherein The upper exhaust stream of the third column is heat-exchanged with one or more of the lower exhaust stream of the first column and the lower exhaust stream of the second column, and then sequentially supplied to the condenser provided at the upper portion of the third column and the layer separator.

3. The method for preparing isopropyl alcohol according to claim 1, in, The second tower includes a partition wall spaced apart from the tower bottom and arranged along the length direction of the tower, The second column is divided into a top region, a bottom region, a supply region, and a discharge region by the dividing wall, the first side bleed stream and the second side bleed stream of the second column are discharged from the discharge zone, and The first side exhaust stream is discharged from a discharge area above the second side exhaust stream.

4. The method for preparing isopropyl alcohol according to claim 1, in, The third column includes a dividing wall connected to the column bottom and extending in the length direction of the column, and The partition wall divides the area into a first area, a second area opposite to the first area, and an upper area located above the upper end of the partition wall.

5. The method for preparing isopropyl alcohol according to claim 1, wherein The branched stream, which is a portion of the branched lower discharge stream of the second column containing water, is recycled to the upper portion of the first column.

6. The method for preparing isopropyl alcohol according to claim 5, wherein The mass flow rate of the branch stream recycled to the upper portion of the first column is 0.4 to 1.2 relative to the mass flow rate of the feed supplied to the first column.

7. The method for preparing isopropyl alcohol according to claim 1, wherein The upper exhaust stream of the third tower is heat-exchanged with the lower exhaust stream of the first tower and the lower exhaust stream of the second tower through the first reboiler and the second reboiler.

8. The method for preparing isopropyl alcohol according to claim 1, in, The upper exhaust stream of the third column is branched to form a branch stream supplied to the first reboiler and a branch stream supplied to the second reboiler, and A ratio of a mass flow rate of the branch stream supplied to the first reboiler to a mass flow rate of the branch stream supplied to the second reboiler is 1:5 to 1:

7.

9. The method for preparing isopropyl alcohol according to claim 1, wherein The upper effluent stream of the third column is pressurized to 4.9 bar·g to 5.1 bar·g and then heat-exchanged with one or more of the lower effluent stream of the first column and the lower effluent stream of the second column.

10. The method for preparing isopropyl alcohol according to claim 1, wherein An upper discharge stream containing water and an entrainer discharged from an upper portion of the upper region of the third column is supplied to the layer separator to separate an aqueous phase stream containing water and an oil phase stream containing the entrainer, the oil phase stream is refluxed to the upper region, and the aqueous phase stream is refluxed to the second region.

11. The method for preparing isopropyl alcohol according to claim 10, wherein The reflux point of the aqueous phase to the second region is a point at a height of 20% to 50% from the bottom of the column to the dividing wall.

12. The method for preparing isopropyl alcohol according to claim 10, wherein The mass flow rate of the upper discharge stream is equal to the sum of the mass flow rates of the water phase stream and the oil phase stream which are refluxed to the third distillation column through the layer separator.

13. The method for preparing isopropyl alcohol according to claim 1, in, supplying the lower effluent stream from the first zone of the third column to the fourth column, and Isopropyl alcohol is obtained in the upper portion of the fourth column, and the heavy by-products are separated into the lower portion of the fourth column.

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