Acrylic acid manufacturing method

Abstract

The present invention provides a method for producing acrylic acid, the method including the steps of: supplying an aqueous lactic acid solution to a reactor and performing a dehydration reaction to obtain a first reaction product containing lactic acid, lactic acid dimer, water and acrylic acid; supplying the first reaction product to a first cooling tower and separating it into a lower fraction of the first cooling tower containing lactic acid and lactic acid dimer and an upper fraction of the first cooling tower containing water and acrylic acid; supplying the lower fraction of the first cooling tower to a lactic acid conversion tank and converting the lactic acid dimer to lactic acid to obtain a second reaction product; separating lactic acid from the second reaction product to recover lactic acid; and separating acrylic acid from the upper fraction of the first cooling tower to obtain acrylic acid.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0115920, filed September 14, 2022, and all contents disclosed in the documents of that Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for producing acrylic acid, and more particularly to a method for reducing the loss of acrylic acid and effectively removing by-products when producing acrylic acid by the dehydration reaction of lactic acid. [Background technology]

[0003] Acrylic acid is used as a polymer raw material for fibers, adhesives, paints, fiber processing, leather, building materials, etc., and the demand for acrylic acid is expanding. Acrylic acid is also used as a raw material for water-absorbent resins, and is widely used industrially in absorbent articles such as disposable diapers and sanitary napkins, agricultural and horticultural water retention agents, and industrial water-stopping materials.

[0004] Conventional methods for producing acrylic acid generally involve air oxidation of propylene. This method involves converting propylene into acrolein through a gas-phase catalytic oxidation reaction, which is then subjected to a gas-phase catalytic oxidation reaction to produce acrylic acid, resulting in the production of acetic acid as a by-product. This by-product has the problem of being difficult to separate from acrylic acid. Furthermore, the method for producing acrylic acid using propylene uses propylene obtained by refining crude oil, a fossil resource, as a raw material, and in consideration of the recent rise in crude oil prices and issues such as global warming, this method has problems in terms of raw material costs and environmental pollution.

[0005] In response to this, research is being conducted into methods for producing acrylic acid from carbon-neutral biomass feedstocks. For example, there is a method for producing acrylic acid (AA) through the vapor-phase dehydration of lactic acid (LA). This method generally produces acrylic acid through intramolecular dehydration of lactic acid at high temperatures of 300°C or higher in the presence of a catalyst. The dehydration of lactic acid produces a reaction product containing acrylic acid, and depending on the conversion rate, the reaction product contains unreacted lactic acid. If the reaction product contains unreacted lactic acid, recovering it in a separation process can improve the economic efficiency of the process. However, lactic acid undergoes rapid oligomerization at high concentrations and high temperatures, making it difficult to recover. Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to solve the problems mentioned in the Background of the Invention above, and an object of the present invention is to provide a method for effectively separating unreacted lactic acid from a reaction product produced in the production of acrylic acid by a dehydration reaction of lactic acid, thereby reducing energy consumption, and for efficiently recovering unreacted lactic acid by converting a dimer of lactic acid produced by an oligomerization reaction of lactic acid into lactic acid. [Means for solving the problem]

[0007] According to one embodiment of the present invention for solving the above-mentioned problems, there is provided a method for producing acrylic acid, the method comprising the steps of: supplying an aqueous lactic acid solution to a reactor and performing a dehydration reaction to obtain a first reaction product containing lactic acid, lactic acid dimer, water, and acrylic acid; supplying the first reaction product to a first cooling tower and separating it into a lower fraction of the first cooling tower containing lactic acid and lactic acid dimer and an upper fraction of the first cooling tower containing water and acrylic acid; supplying the lower fraction of the first cooling tower to a lactic acid conversion tank and converting the lactic acid dimer to lactic acid to obtain a second reaction product; separating lactic acid from the second reaction product to recover the lactic acid; and separating acrylic acid from the upper fraction of the first cooling tower to obtain acrylic acid. [Effects of the Invention]

[0008] According to the method for producing acrylic acid of the present invention, by first separating unreacted lactic acid before distilling the reaction product containing acrylic acid, it is possible to reduce energy costs compared to the case where unreacted lactic acid is separated after distillation.

[0009] Furthermore, by converting the lactic acid dimer contained in the reaction product into lactic acid, the amount of lactic acid lost as the lactic acid dimer is minimized, thereby improving the recovery rate of unreacted lactic acid and improving the economic efficiency of the process.

[0010] Furthermore, by separately supplying the aqueous acrylic acid solution discharged from the cooling tower to the extraction tower and the azeotropic distillation tower, it is possible to reduce the amount of energy required for distilling water in the azeotropic distillation tower and to reduce the loss of acrylic acid, as well as to obtain high-purity acrylic acid. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a process flowchart of a method for producing acrylic acid according to one embodiment of the present invention. [Figure 2] 1 is a process flowchart of a comparative example of a method for producing acrylic acid compared with the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The terms and words used in the description and claims of the present invention should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are 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.

[0013] In the present invention, the term "stream" can refer to the flow of fluid within a process, or the fluid itself flowing in a pipe. Specifically, the term "stream" can simultaneously refer to the fluid itself flowing in a pipe connecting each device and the flow of the fluid. Furthermore, the fluid can refer to gas or liquid, and does not exclude cases where the fluid contains solid components.

[0014] Meanwhile, in the present invention, in an apparatus such as a cooling tower, extraction tower, or distillation tower, the "lower part" of the apparatus means a point 95% to 100% below the top of the apparatus, specifically the lowest end (bottom), unless otherwise specified. Similarly, the "upper part" of the apparatus means a point 0% to 5% below the top of the apparatus, specifically the highest part (top), unless otherwise specified.

[0015] Furthermore, unless otherwise specified, in the present invention, the operating temperature of a cooling tower may refer to the operating temperature at the lower part of the cooling tower, and the operating pressure of a cooling tower may refer to the operating pressure at the upper part of the cooling tower.

[0016] Hereinafter, each step that can be included in an embodiment of the present invention will be described with reference to FIG.

[0017] A method for producing acrylic acid according to one embodiment of the present invention may include the steps of: supplying an aqueous lactic acid solution to a reactor and performing a dehydration reaction to obtain a first reaction product containing lactic acid, lactic acid dimers, water, and acrylic acid; supplying the first reaction product to a first cooling tower and separating it into a lower fraction of the first cooling tower containing lactic acid and lactic acid dimers and an upper fraction of the first cooling tower containing water and acrylic acid; supplying the lower fraction of the first cooling tower to a lactic acid conversion tank and converting the lactic acid dimers to lactic acid to obtain a second reaction product; separating lactic acid from the second reaction product to recover the lactic acid; and separating acrylic acid from the upper fraction of the first cooling tower to obtain acrylic acid.

[0018] First, a method for producing acrylic acid according to one embodiment of the present invention may include a step of supplying an aqueous lactic acid solution to a reactor and subjecting it to a dehydration reaction to obtain a first reaction product containing lactic acid, a lactic acid dimer, water, and acrylic acid.

[0019] Specifically, a conventional method for producing acrylic acid generally involves air oxidation of propylene, which involves converting propylene into acrolein through a gas-phase catalytic oxidation reaction, and then subjecting this to a gas-phase catalytic oxidation reaction to produce acrylic acid, resulting in the generation of acetic acid as a by-product, which is problematic in that it is difficult to separate from acrylic acid. Furthermore, the method for producing acrylic acid using propylene uses propylene obtained by refining crude oil, a fossil resource, as a raw material, and in consideration of the recent rise in crude oil prices and issues such as global warming, this method has problems in terms of raw material costs and environmental pollution.

[0020] To address the problems inherent in conventional acrylic acid production methods, research has been conducted into methods for producing acrylic acid from carbon-neutral biomass feedstocks. For example, there is a method for producing acrylic acid (AA) through the vapor-phase dehydration of lactic acid (LA). This method generally involves the intramolecular dehydration of lactic acid at high temperatures in the presence of a catalyst. The dehydration of lactic acid produces a reaction product containing acrylic acid, and depending on the conversion rate, unreacted lactic acid may be present in the reaction product. If unreacted lactic acid is present in the reaction product, recovering it through a separation process can improve the economic efficiency of the process. However, lactic acid undergoes rapid oligomerization at high concentrations and high temperatures, making it difficult to recover. Furthermore, the need for a separate distillation column or other equipment to recover lactic acid increases overall process costs due to the significant energy required for operation.

[0021] In contrast, in order to solve the above-mentioned conventional problems, the present invention provides a method for separating lactic acid from a reaction product containing acrylic acid produced by the dehydration reaction of lactic acid prior to the distillation step, thereby shortening the time that high-concentration lactic acid is exposed to high temperatures and preventing oligomerization of lactic acid. This not only improves the recovery rate of unreacted lactic acid, but also reduces the cost of equipment such as a separate distillation apparatus for separating lactic acid in a subsequent step, as well as the operating cost for operating the apparatus.

[0022] In addition, the present invention provides a method for further improving the recovery rate of unreacted lactic acid by converting lactic acid dimers, which may be produced by the oligomerization reaction of lactic acid during the dehydration reaction, back into lactic acid.

[0023] According to one embodiment of the present invention, a first reaction product containing acrylic acid can be produced by first supplying an aqueous lactic acid solution to a reactor and subjecting it to a dehydration reaction. The dehydration reaction can be carried out as a gas-phase reaction in the presence of a catalyst. For example, the lactic acid concentration of the aqueous lactic acid solution can be 10 wt% or more, 20 wt% or more, or 30 wt% or more, and 40 wt% or less, 50 wt% or less, 60 wt% or less, or 70 wt% or less. Since excessive lactic acid oligomers can be produced through an equilibrium reaction between lactic acid and lactic acid dimers when present at a high concentration, the lactic acid can be used in the form of an aqueous solution having a concentration within the above range.

[0024] The reactor may include a reactor capable of performing a conventional dehydration reaction of lactic acid, and the reactor may include a reaction tube filled with a catalyst, and lactic acid may be dehydrated by a gas-phase catalytic reaction while a reaction gas containing volatile components of a raw material lactic acid aqueous solution is passed through the reaction tube to produce acrylic acid. In addition to lactic acid, the reaction gas may further include one or more diluent gases selected from water vapor, nitrogen, and air for adjusting the concentration.

[0025] The reactor may be operated under typical lactic acid dehydration reaction conditions, and the operating temperature of the reactor may refer to the set temperature of a heat medium or the like used to control the temperature of the reactor.

[0026] The catalyst used in the dehydration reaction of lactic acid may include, for example, one or more catalysts selected from the group consisting of sulfate catalysts, phosphate catalysts, and nitrate catalysts. Specific examples of the sulfates include Na2SO4, K2SO4, CaSO4, and Al2(SO4)3; the phosphates include Na3PO4, Na2HPO4, NaH2PO4, K3PO4, K2HPO4, KH2PO4, CaHPO4, Ca3(PO4)2, AlPO4, CaH2P2O7, and Ca2P2O7; and the nitrates include NaNO3, KNO3, and Ca(NO3)2. The catalyst may also be supported on a support. The support may include, for example, one or more catalysts selected from the group consisting of diatomaceous earth, alumina, silica, titanium dioxide, carbide, and zeolite.

[0027] The first reaction product produced by the dehydration of lactic acid may include lactic acid, lactic acid dimer, and water (HO) in addition to the target product, acrylic acid. It may also include light gas components and heavy by-products. The lactic acid may be unreacted lactic acid, and the lactic acid dimer may be a by-product produced by oligomerization of the unreacted lactic acid during the dehydration reaction. Meanwhile, the heavy by-product refers to by-products other than the lactic acid dimer that have a higher boiling point than acrylic acid and lactic acid, such as 3,4-dimethyl-2,5-furandione (CHO).

[0028] The method for producing acrylic acid by dehydration of lactic acid can secure competitiveness as a raw material and eliminate environmental pollution issues compared to the conventional method of air-oxidizing propylene, but the conversion rate of lactic acid is low and various by-products are generated, resulting in a low yield of acrylic acid. Therefore, process development to improve economic efficiency is necessary. In contrast, the present invention provides a method that not only increases the recovery rate of unreacted lactic acid but also reduces overall equipment costs and energy costs, thereby improving economic efficiency.

[0029] A method for producing acrylic acid according to one embodiment of the present invention may include the step of supplying the first reaction product to a first cooling tower and separating the first reaction product into a lower fraction of the first cooling tower containing lactic acid and lactic acid dimer and an upper fraction of the first cooling tower containing water and acrylic acid.

[0030] Specifically, reactor discharge stream 1 containing the first reaction product is a gas phase stream, and may be supplied to first cooling tower 10 for cooling. That is, among the first reaction products supplied to first cooling tower 10, lactic acid, lactic acid dimer, and heavy by-products, which have relatively high boiling points, are condensed by cooling to form liquid condensates, which may be separated as a lower fraction of first cooling tower 10. Meanwhile, among the reaction products, acrylic acid, water, and light gas components, which have relatively low boiling points, are in the gas phase and may be separated as an upper fraction of first cooling tower 10. Here, the light gas components are components with a boiling point lower than that of water, and specifically may include carbon monoxide, carbon dioxide, and acetaldehyde in addition to diluent gases.

[0031] By preliminarily separating the lactic acid contained in the first reaction product by cooling, deformation, e.g., oligomerization, of lactic acid due to exposure to high temperatures can be prevented, thereby increasing the recovery rate of lactic acid, and the recovered lactic acid can be efficiently reused as a raw material for the dehydration reaction for producing acrylic acid. Furthermore, there is no need to install a separate distillation apparatus for separating and recovering lactic acid in a subsequent process, thereby reducing the energy cost for operating the distillation apparatus. Furthermore, by separating unreacted lactic acid before the azeotropic distillation process described below, the amount of energy used for azeotropic distillation can be reduced.

[0032] For this reason, the operating temperature of the first cooling tower 10 can be 100°C or higher, 110°C or higher, or 120°C or higher, and 180°C or lower, 170°C or lower, or 160°C or lower. If the temperature is below 100°C, components other than unreacted lactic acid may be excessively condensed, reducing the purity of the recovered lactic acid and resulting in a loss of the desired product, acrylic acid. On the other hand, if the temperature exceeds 180°C, unreacted lactic acid cannot be sufficiently condensed. This means that unreacted lactic acid is discharged to the top of the first cooling tower 10, reducing the recovery rate of lactic acid and making it difficult to obtain high-purity acrylic acid.

[0033] The operating pressure of the first cooling tower 10 is 1 kg / cm 2 More than 1.5kg / cm 2 or more than 1.8 kg / cm 2 or more, and 20 kg / cm 2 Below, 10kg / cm 2 or less than 5kg / cm 2 When the pressure is high, the volume flow rate can be reduced to reduce the equipment cost of the cooling tower, but the operating temperature of the cooling tower becomes high, which may cause the production of dimers of lactic acid and acrylic acid, and it is therefore necessary to set an appropriate operating pressure at which the dimers are not produced.

[0034] By controlling the operating conditions of the first cooling tower 10 within the operating temperature and operating pressure ranges, the compositions of the lower discharge stream and the upper discharge stream of the first cooling tower 10 can be controlled, and thus the composition of the aqueous acrylic acid solution stream discharged from the lower part of the second cooling tower 20 can be easily controlled.

[0035] In this regard, the upper fraction discharged from the first cooling tower may not contain unreacted lactic acid, or even if it does, the content of unreacted lactic acid may be 5 wt % or less, specifically 3 wt % or less.

[0036] Meanwhile, the ratio of the flow rate of water in the stream discharged to the lower part of the first cooling tower to the flow rate (kg / hr) of water contained in the reaction product introduced into the first cooling tower 10 may be 15 wt% or less, and the ratio of the flow rate of acrylic acid in the stream discharged to the lower part of the first cooling tower to the flow rate (kg / hr) of acrylic acid contained in the reaction product introduced into the first cooling tower 10 may be 15 wt% or less.

[0037] Meanwhile, the upper fraction of the first cooling tower 10 containing water and acrylic acid, specifically the upper fraction of the first cooling tower 10 containing water, acrylic acid, and light gas components, can be discharged as the upper discharge stream 12 of the first cooling tower and introduced into an acrylic acid purification process. The acrylic acid purification process is a process of separating acrylic acid from other components to obtain high-purity acrylic acid at a high concentration. Meanwhile, the lower fraction of the first cooling tower 10 containing lactic acid and lactic acid dimer, specifically the lower fraction of the first cooling tower 10 containing lactic acid, lactic acid dimer, and heavy by-products, can be discharged as the lower discharge stream 11 of the first cooling tower and supplied to a lactic acid conversion tank 300. An equilibrium reaction in which lactic acid dimer is converted to lactic acid takes place in the lactic acid conversion tank 300, thereby minimizing the loss of lactic acid as lactic acid dimer.

[0038] Meanwhile, according to one embodiment of the present invention, the upper discharge stream 12 from the first cooling tower may be supplied to a second cooling tower 20 before being introduced into a purification process for acrylic acid, thereby performing a process of removing light gas components contained in the upper discharge stream 12 from the first cooling tower. Specifically, the upper discharge stream 12 from the first cooling tower may be supplied to the second cooling tower 20 and further cooled, thereby being separated into a bottom fraction containing water and acrylic acid and an upper fraction containing light gas components.

[0039] The operating temperature of the second cooling tower 20 can be 60°C or more, 80°C or more, or 100°C or more, and 140°C or less, 130°C or less, or 120°C or less, and the operating pressure can be 0.8 kg / cm 2 More than 1.0kg / cm 2or more than 1.3 kg / cm 2 or more, and 20 kg / cm 2 Below, 10kg / cm 2 or less than 5kg / cm 2 By controlling the operating conditions of the second cooling tower 20 within the operating temperature and operating pressure ranges, the composition of the light gas components separated as the upper discharge stream 24 of the second cooling tower 20 can be controlled to minimize the loss of acrylic acid, and the light gas components including diluent gas and acetaldehyde can be removed to the outside of the system, thereby controlling the composition of the aqueous acrylic acid stream 21 containing acrylic acid and water discharged from the bottom of the second cooling tower 20.

[0040] In the past, cooling towers have been used in the production of acrylic acid, but these were used to cool the gaseous reaction product so that it would be suitable for introduction into the purification step of acrylic acid, and not for the purpose of separating substances. This is because when substances are separated by cooling, it is difficult to recover substances of the desired purity. However, the present invention controls the cooling rate of the cooling tower to adjust the amount of components cooled, thereby simultaneously achieving the effect of separating substances in addition to the original purpose of cooling the reaction product.

[0041] Next, the aqueous acrylic acid solution stream, specifically the top discharge stream from the first cooling tower 10 containing the water and acrylic acid, or the bottom discharge stream 21 from the second cooling tower 20 when the top discharge stream from the first cooling tower 10 is further cooled in the second cooling tower 20, can be introduced into a purification step for obtaining acrylic acid. The purification step is a step for obtaining high-purity acrylic acid from water and some impurities in the aqueous acrylic acid solution, and not only must the obtained acrylic acid be recovered with high purity, but also, from an economical perspective, it is necessary to be able to reduce the amount of energy used in the step.

[0042] For example, the purification step can be carried out by an extraction step in which the aqueous acrylic acid solution is separated into an extract containing acrylic acid and the extractant and a raffinate containing water in an extraction column using an extraction solvent. Although the extraction step has the advantage of reducing energy consumption compared to the distillation step, it may be difficult to obtain high-purity acrylic acid because the extract contains some by-products that must be removed together with water.

[0043] On the other hand, as another example of the purification step, the purification step may be carried out by an azeotropic distillation step. In this case, assuming the use of an azeotropic solvent, the separation efficiency of water and acrylic acid is higher than that of a simple extraction step, and therefore there is an advantage that high-purity acrylic acid can be obtained, but since this involves the distillation of water which has a high specific heat, excessive energy consumption is required, and there is a possibility that it is not so preferable from the viewpoint of economy.

[0044] Therefore, according to one embodiment of the present invention, a portion of the aqueous acrylic acid solution stream obtained by the cooling process performed by the first cooling tower or the first and second cooling towers is supplied to extraction tower 100 as first aqueous acrylic acid solution stream 22, and the remainder is supplied to azeotropic distillation tower 200 as second aqueous acrylic acid solution stream 23, thereby performing the purification process in a manner in which the extraction process and the azeotropic distillation process are carried out in parallel. That is, by dividing aqueous acrylic acid solution stream 21 and supplying it to extraction tower 100 and azeotropic distillation tower 200, energy consumption in the subsequent processes can be reduced, and by-products that may be partially contained in aqueous acrylic acid solution stream 21 can be efficiently separated.

[0045] Specifically, the ratio of the flow rate of the first aqueous acrylic acid stream 22 supplied to the extraction tower to the total flow rate of the aqueous acrylic acid stream 21 before branching, i.e., the first and second aqueous acrylic acid streams after branching, can be 30% by weight to 70% by weight, and more specifically, 40% by weight to 50% by weight. When the flow rate ratio is 30% by weight or more, the flow rate introduced into the azeotropic distillation tower 200 is reduced, thereby reducing the amount of energy required for distilling water, which has a high specific heat, in the azeotropic distillation tower 200. On the other hand, when the flow rate ratio is 70% by weight or less, by-products can be efficiently separated in the upper part of the azeotropic distillation tower 200, preventing the accumulation of the by-products in the system and obtaining high-purity acrylic acid. The amount of extractant required for removing water in the extraction tower 100 can be reduced. The flow rate of the extractant introduced into the azeotropic distillation tower 200 is reduced, thereby reducing the amount of energy required for distillation, and by-products can be efficiently separated to obtain high-purity acrylic acid.

[0046] Meanwhile, the extraction tower 100 removes most of the water contained in the first aqueous acrylic acid solution stream 22 without using a large amount of energy and supplies the removed water to the azeotropic distillation tower 200, which will be described later, thereby reducing the energy used for azeotropic distillation in the azeotropic distillation tower 200. In this respect, it is preferable that the extraction in the extraction tower 100 is carried out by contacting the extraction solvent with the extraction tower feed stream through a liquid-liquid contact method, in terms of improving the energy efficiency of the entire process.

[0047] Here, the extraction solvent may be a hydrocarbon solvent that can form an azeotrope with water but not with acrylic acid, but can sufficiently extract acrylic acid, and is advantageous in the extraction process for having a boiling point of 10 to 120° C. Specifically, the extraction solvent may be benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butyl acetate, isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methyl isobutyl ketone, or the like. The solvent may be one or more selected from the group consisting of methyl ketone, 2-methyl-1-heptene, 6-methyl-1-heptene, 4-methyl-1-heptene, 2-ethyl-1-hexene, ethylcyclopentane, 2-methyl-1-hexene, 2,3-dimethylpentane, 5-methyl-1-hexene, and isopropyl-butyl-ether.

[0048] Additionally, a liquid-liquid contact type extraction device may be used as the extraction tower 100. Non-limiting examples of the extraction device include a Karr-type reciprocating plate column, a rotary-disk contactor, a Scheibel column, a Kuhni column, a spray extraction tower, a packed extraction tower, a pulsed packed column, a mixer-settler bank, a mixer and a centrifugal countercurrent extractor, etc.

[0049] In this manner, a substantial amount of water is removed from the aqueous acrylic acid stream supplied to the extraction column 100, and an extract containing the extractant and acrylic acid is obtained. The extract can be supplied to the azeotropic distillation column 200 as the top discharge stream 103 of the extraction column.

[0050] In addition, water contained in the aqueous acrylic acid stream from the extraction process can be recovered as a raffinate. Conventionally, the raffinate has generally been discharged as wastewater. However, in the present invention, after the raffinate is discharged from the extraction tower, a portion 101 is introduced into the lactic acid conversion tank 300, where the water contained in the raffinate functions to adjust the reaction equilibrium so that the equilibrium reaction of lactic acid dimer to lactic acid is promoted. The remaining portion 102 can be discharged to the outside of the system as wastewater. This also has the effect of reducing the amount of wastewater discharged compared to conventional methods in which the entire raffinate is discharged to the outside of the system. Furthermore, by recovering water in the extraction process, the operational burden of the distillation process described below can be reduced, significantly reducing energy consumption.

[0051] Then, according to one embodiment of the present invention, the second aqueous acrylic acid solution stream 23 and the top discharge stream 102 of the extraction tower are supplied to an azeotropic distillation tower 200, where a distillation process for these streams can be carried out. The distillation process for the stream supplied to the azeotropic distillation tower 200 in the azeotropic distillation tower 200 can be a process of separating an upper fraction containing water and the extraction solvent from a lower fraction containing acrylic acid by azeotropic distillation.

[0052] According to the present invention, it is advantageous in terms of process that the distillation in the azeotropic distillation column 200 is carried out in the presence of an azeotropic solvent. Here, the azeotropic solvent is a hydrophobic solvent that can form an azeotrope with water but not with acrylic acid, and any hydrocarbon solvent that satisfies the above physical properties can be used without limitation. In addition, the azeotropic solvent may have a boiling point lower than that of acrylic acid, preferably 10 to 120°C.

[0053] According to the present invention, the azeotropic solvents satisfying the above physical properties include benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butyl acetate, isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, and methyl isobutyl ketone. The solvent may be one or more selected from the group consisting of methyl ketone, 2-methyl-1-heptene, 6-methyl-1-heptene, 4-methyl-1-heptene, 2-ethyl-1-hexene, ethylcyclopentane, 2-methyl-1-hexene, 2,3-dimethylpentane, 5-methyl-1-hexene, and isopropyl-butyl-ether.

[0054] The azeotropic solvent may be the same as or different from the extraction solvent used in extraction tower 100. However, in consideration of production efficiency in a continuous process, it is preferable that the azeotropic solvent is the same as the extraction solvent. When the same compound is used as the azeotropic solvent and the extraction solvent, at least a portion of the azeotropic solvent distilled and recovered in azeotropic distillation tower 200 can be supplied to extraction tower 100 and used as part of the extraction solvent.

[0055] When the azeotropic solvent is introduced into the azeotropic distillation column 200, azeotropic distillation of acrylic acid and water occurs. As a result, the water supplied to the azeotropic distillation column 200 and the azeotropic solvent used in the azeotropic distillation are azeotropically distilled together, and can be recovered as an upper fraction of the azeotropic distillation column 200. And, a lower fraction 201 containing acrylic acid can be recovered from the lower part of the azeotropic distillation column 200.

[0056] The recovered top fraction of the azeotropic distillation column can be supplied to a layer separator via the azeotropic distillation column top discharge stream 202. A layer separator is a liquid-liquid layer separator that separates immiscible fluids using gravity or centrifugal force due to differences in density, and can separate relatively light liquids into the upper portion of the layer separator and relatively heavy liquids into the lower portion of the layer separator. Specifically, the azeotropic distillation column top discharge stream 202 supplied to the layer separator can be separated into an organic layer containing the azeotropic solvent and an aqueous layer containing water.

[0057] In addition, the organic layer separated in the layer separator is discharged as a layer separator discharge stream, and the layer separator discharge stream containing the azeotropic solvent or extraction solvent can be recycled to one or more of an extraction column and an azeotropic distillation column and reused as the azeotropic solvent or extraction solvent.

[0058] Meanwhile, the method for producing acrylic acid according to one embodiment of the present invention may include the step of supplying the lower fraction of the first cooling tower to a lactic acid conversion tank and converting the lactic acid dimer into lactic acid to obtain a second reaction product.

[0059] Specifically, the lower fraction of the first cooling tower containing lactic acid and lactic acid dimers can be discharged as the lower discharge stream 11 of the first cooling tower and supplied to the lactic acid conversion tank 300, where the lactic acid dimers can be converted to lactic acid using a reverse reaction of the equilibrium reaction between lactic acid and lactic acid dimers, as shown in Reaction Scheme 1 below.

[0060] [ka]

[0061] Referring to Reaction Scheme 1 above, an equilibrium reaction can occur in the lactic acid conversion tank 300. This equilibrium reaction involves both a forward reaction in which lactic acid is converted into lactic acid dimers and water, and a reverse reaction in which lactic acid dimers react with water to convert lactic acid. By supplying additional water to the lactic acid conversion tank 300, the concentration of the reverse reaction reactants can be increased, thereby accelerating the reverse reaction. Therefore, the lactic acid dimers contained in the lower discharge stream 11 of the first cooling tower can be converted to lactic acid to the maximum extent possible. This prevents unreacted lactic acid from being lost in the form of lactic acid dimers, thereby increasing the recovery rate of lactic acid.

[0062] Meanwhile, the water supplied to the lactic acid conversion tank 300 may be water separated in the above-mentioned acrylic acid purification process. The acrylic acid purification process involves a process of separating acrylic acid from an aqueous acrylic acid solution containing acrylic acid and water, and therefore, for example, water-containing streams may be separated and discharged from the extraction column 100 and the azeotropic distillation column 200 in the acrylic acid purification process. These water-containing streams may be supplied to the lactic acid conversion tank 300 and used in the equilibrium reaction.

[0063] According to one embodiment of the present invention, a raffinate containing water is discharged from the bottom of the extraction tower 100 during the extraction process, and a portion thereof, stream 101, can be supplied to the lactic acid conversion tank 300. Meanwhile, the raffinate contains 95% or more by weight of water, and the water contained in the raffinate is supplied to the lactic acid conversion tank 300, thereby accelerating the reaction of lactic acid dimers to lactic acid in the lactic acid conversion tank 300.

[0064] Meanwhile, the flow rate of the raffinate discharged from the bottom of the extraction tower 100 and supplied to the lactic acid conversion tank 300 can be determined based on the relationship between the contents of lactic acid and lactic acid dimers and the water content in the lactic acid conversion tank 300. That is, if the water content in the lactic acid conversion tank 300 is excessively low, the reaction of lactic acid dimers to lactic acid does not proceed smoothly, resulting in an increased amount of lactic acid lost in the form of lactic acid dimers. Furthermore, if the water content in the lactic acid conversion tank 300 is excessively high, lactic acid can be sufficiently converted from lactic acid dimers, but the amount of energy required to separate lactic acid and water in the lactic acid purification tower 400 increases. In this regard, the water content in the lactic acid conversion tank 300 is preferably maintained at 60 to 70 wt% based on the total weight of the components in the lactic acid conversion tank. Furthermore, the bottom discharge stream of the extraction tower 100 can be supplied to the lactic acid conversion tank 300 at a flow rate that allows the water content to be maintained within the above range.

[0065] Due to the conversion of the lactic acid dimer to lactic acid, the content of lactic acid contained in the second reaction product becomes higher than the content of lactic acid contained in the stream supplied to the lactic acid conversion tank 300, for example, the lower discharge stream 11 of the first cooling tower. Specifically, the mass flow rate of lactic acid contained in the second reaction product discharged from the lactic acid conversion tank 300 may be increased by 5 wt % to 20 wt % relative to the mass flow rate of lactic acid contained in the lower discharge stream 11 of the first cooling tower.

[0066] Meanwhile, according to one embodiment of the present invention, the second reaction product discharged from the lactic acid conversion tank 300 may be supplied to the lactic acid purification tower 400 as a lactic acid conversion tank discharge stream 301.

[0067] Lactic acid and water contained in the second reaction product are separated in the lactic acid purification tower 400 and can be recycled to the reactor 402 and reused as raw materials for the dehydration reaction of lactic acid performed in the reactor 402. Meanwhile, the remaining components other than lactic acid and water, for example, lactic acid dimer and heavy by-product components, can be discharged from the bottom of the lactic acid purification tower 400 and discharged to the outside of the system 401.

[0068] The method for producing acrylic acid according to the present invention has been described and illustrated in the drawings. However, the description and the illustrations in the drawings only describe and illustrate essential components for understanding the present invention. In addition to the steps and apparatuses described and illustrated in the drawings, other steps and apparatuses not described or illustrated can be appropriately applied and used to carry out the method for producing acrylic acid according to the present invention.

[0069] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention. The scope of the present invention is not limited to these examples alone.

[0070] Example Example 1 The acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, according to the process flow chart shown in FIG.

[0071] Specifically, a 30 wt % aqueous lactic acid solution and nitrogen (N2) as a diluent gas were supplied to a reactor, and a first reaction product containing lactic acid, lactic acid dimer, water, and acrylic acid was produced by a dehydration reaction.

[0072] The reactor discharge stream containing the first reaction product was supplied to a first cooling tower 10. In the first cooling tower 10, the reactor discharge stream was cooled and condensed, and separated into a first cooling tower lower discharge stream 11 containing lactic acid and lactic acid dimers, and a first cooling tower upper discharge stream 12 containing light gas components, water, and acrylic acid. Here, the lower operating temperature of the first cooling tower 10 was set to 125°C, and the upper operating pressure was set to 1.9 kg / cm. 2 was controlled.

[0073] Next, the lower discharge stream 11 of the first cooling tower was introduced into the lactic acid conversion tank 300. Meanwhile, the upper discharge stream 12 of the first cooling tower was supplied to the second cooling tower 20 for cooling and condensation, thereby separating the lower discharge stream 21 of the second cooling tower containing water and acrylic acid, and the light gas component containing nitrogen into the upper discharge stream 24 of the second cooling tower. Here, the lower operating temperature of the second cooling tower 20 was set to 107°C, and the upper operating pressure was set to 1.3 kg / cm. 2 was controlled.

[0074] A portion of bottom discharge stream 21 from the second cooling tower was supplied to extraction tower 100 as first aqueous acrylic acid solution stream 22, and the remainder was supplied to azeotropic distillation tower 200 as second aqueous acrylic acid solution stream 23, with the mass flow rate ratio of first aqueous acrylic acid solution stream 22 supplied to extraction tower 100 to the flow rate of bottom discharge stream 21 from the second cooling tower being maintained at 50% by weight.

[0075] Meanwhile, in the extraction column 100, acrylic acid was dissolved using toluene as an extraction solvent, and then the extract containing acrylic acid and the extraction solvent was separated as an upper discharge stream 103 from the extraction column 100 and supplied to the azeotropic distillation column 200. A portion of a lower discharge stream 101 from the extraction column 100 containing water was supplied to the lactic acid conversion tank 300.

[0076] Further, distillation was carried out in an azeotropic distillation column 200 to which the second aqueous acrylic acid solution stream 23 and the top discharge stream 103 of the extraction column 100 were supplied, with acrylic acid being obtained at the bottom and a stream containing water and the extraction solvent being discharged at the top. Next, the stream containing water and the extraction solvent was supplied to a layer separator to separate the water and the extraction solvent, after which the water was discharged outside the system and the extraction solvent was divided and circulated between the extraction column 100 and the azeotropic distillation column 200.

[0077] Meanwhile, a second reaction product was obtained by converting a portion of the lactic acid dimer into lactic acid through an oligomerization reaction of lactic acid and its reverse reaction in the lactic acid conversion tank 300. The obtained second reaction product was supplied to a lactic acid purification column 400 and distilled, and unreacted lactic acid was recovered from an upper portion 402 of the lactic acid purification column 400.

[0078] The flow rate (kg / hr) and composition (wt%) of each component in each stream in Figure 1 are shown in Table 1 below.

[0079] [Table 1]

[0080] 1, it can be seen that the recovery rate of lactic acid is 85% based on the mass flow rate of lactic acid recovered as stream 11a (510 kg / hr) relative to the mass flow rate of lactic acid introduced through stream 1a (600 kg / hr). Furthermore, when comparing the streams before and after being introduced into lactic acid conversion tank 300, it can be seen that lactic acid increases by 5.1% due to the reverse reaction of the lactic acid oligomerization reaction that occurs in the lactic acid conversion tank.

[0081] Example 2 The acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, according to the process flow chart shown in FIG.

[0082] Specifically, the same method as in Example 1 was used, except that a 40 wt % aqueous lactic acid solution was supplied to the reactor and the temperature at the bottom of the first cooling tower 10 was controlled to 133°C.

[0083] The flow rate (kg / hr) and composition (wt%) of each component in each stream in Figure 1 are shown in Table 2 below.

[0084] [Table 2]

[0085] 1, it can be seen that the recovery rate of lactic acid is 89.1% based on the mass flow rate of lactic acid introduced via stream 1a (2000 kg / hr) and the mass flow rate of lactic acid recovered as stream 11a (1782 kg / hr). Furthermore, when comparing the streams before and after being introduced into lactic acid conversion tank 300, it can be seen that lactic acid increases by 15% due to the reverse reaction of the lactic acid oligomerization reaction that occurs in the lactic acid conversion tank.

[0086] Comparative Example Comparative Example 1 The acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, according to the process flow chart shown in FIG.

[0087] Comparative Example 1 is a case in which one cooling tower is used to separate light gas components, and another distillation tower is used downstream of the extraction tower and the azeotropic distillation tower in order to realize the content of acrylic acid in the stream from which acrylic acid is recovered to 96 wt %, as in Example 1.

[0088] In Comparative Example 1, a reaction product was produced using the same aqueous lactic acid solution as in Example 1. Specifically, a 30 wt % aqueous lactic acid solution and nitrogen (N) as a diluent gas were supplied to a reactor, and a reaction product containing lactic acid, a lactic acid dimer, water, and acrylic acid was produced by a dehydration reaction.

[0089] The reaction product was supplied to a cooling tower 10, where light gas components such as nitrogen were separated from the upper portion, and a stream containing lactic acid, lactic acid dimer, acrylic acid, and water was separated from the lower portion. Here, the operating temperature at the bottom of the cooling tower 10 was set to 108°C, and the operating pressure at the top was set to 1.3 kg / cm. 2 was controlled.

[0090] Next, a part of the bottom discharge stream from the cooling tower 10 was supplied to an extraction tower 100, and the remainder was supplied to an azeotropic distillation tower 200, while the ratio of the mass flow rate of the aqueous acrylic acid solution stream supplied to the extraction tower 100 to the flow rate of the bottom discharge stream from the cooling tower was maintained at 50% by weight.

[0091] Meanwhile, in the extraction tower 100, acrylic acid was dissolved using toluene as an extraction solvent, and then the extract containing acrylic acid and the extraction solvent was separated as a top discharge stream from the extraction tower 100 and supplied to the azeotropic distillation tower 200. Then, distillation was carried out in the azeotropic distillation tower 200 to separate a bottom discharge stream containing lactic acid, lactic acid dimer, and acrylic acid from a top discharge stream containing water and the extraction solvent.

[0092] The bottom discharge stream of the extraction tower and the bottom discharge stream of the azeotropic distillation tower both contained lactic acid and lactic acid dimer, and it was necessary to introduce first and second lactic acid separation towers 150 and 250 to separate the lactic acid contained therein.

[0093] Specifically, the first lactic acid separation tower 150 separates lactic acid, lactic acid dimer, and water contained in the bottom discharge stream of the extraction tower 100 by distillation, and the second lactic acid separation tower 250 separates lactic acid, lactic acid dimer, and acrylic acid contained in the bottom discharge stream of the azeotropic distillation tower 200 by distillation.

[0094] Meanwhile, acrylic acid was obtained from the upper part of the second lactic acid separation column 250, and the lower discharge stream of the second lactic acid separation column 250 was supplied to the heavy component separation column 500 and distilled, and lactic acid was separated at the upper part of the heavy component separation column 500, and lactic acid dimer and heavy components were separated at the lower part.

[0095] The flow rate (kg / hr) and composition (wt%) of each component in each stream in Comparative Example 1 (FIG. 2) are shown in Table 3 below.

[0096] [Table 3]

[0097] From Table 3 and FIG. 2, it can be seen that the recovery rate of lactic acid is 61.5%, based on the mass flow rate of lactic acid recovered as streams 8b and 6b (236 + 133 kg / hr) relative to the mass flow rate of lactic acid introduced via stream 1b (600 kg / hr).

[0098] Comparative Example 2 The acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, according to the process flow chart shown in FIG.

[0099] Specifically, the same method as in Comparative Example 1 was used, except that a 40 wt % aqueous lactic acid solution was supplied to the reactor and the temperature at the bottom of the cooling tower 10 was controlled to 109°C.

[0100] In Comparative Example 2, in comparison with Example 2 in which a 40 wt % aqueous lactic acid solution was supplied to the reactor, another distillation column was used downstream of the extraction column and the azeotropic distillation column in order to realize the content of acrylic acid in the stream from which acrylic acid is recovered to 90 wt %, as in Example 2.

[0101] The flow rate (kg / hr) and composition (wt%) of each component in each stream in Comparative Example 2 (FIG. 2) are shown in Table 4 below.

[0102] [Table 4]

[0103] From Table 4 and FIG. 2, it can be seen that the recovery rate of lactic acid is 62.2%, based on the mass flow rate of lactic acid recovered as streams 8b and 6b (695 + 549 kg / hr) relative to the mass flow rate of lactic acid introduced via stream 1b (2000 kg / hr).

Claims

1. Supplying an aqueous lactic acid solution to a reactor and subjecting it to a dehydration reaction to obtain a first reaction product containing lactic acid, a lactic acid dimer, water, and acrylic acid; Supplying the first reaction product to a first cooling tower and separating it into a lower fraction of the first cooling tower containing lactic acid and lactic acid dimers and an upper fraction of the first cooling tower containing water and acrylic acid; Supplying the lower fraction of the first cooling tower to a lactic acid conversion tank to convert the lactic acid dimer into lactic acid to obtain a second reaction product; Separating lactic acid from the second reaction product to recover lactic acid; and separating acrylic acid from the upper fraction of the first cooling tower to obtain acrylic acid; The method for producing acrylic acid, wherein water is further supplied to the lactic acid conversion tank to convert the lactic acid dimer into lactic acid.

2. 2. The method for producing acrylic acid according to claim 1, further comprising the steps of supplying the second reaction product to a lactic acid purification column and recovering lactic acid from an upper portion of the lactic acid purification column.

3. the lower fraction of the first cooling tower is supplied to the lactic acid conversion tank as a lower discharge stream of the first cooling tower; 2. The method for producing acrylic acid according to claim 1, wherein the mass flow rate of the lactic acid contained in the second reaction product discharged from the lactic acid conversion tank is increased by 5 wt % to 20 wt % relative to the mass flow rate of the lactic acid contained in the lower discharge stream of the first cooling tower.

4. The operating temperature of the first cooling tower is 100°C to 180°C, and the operating pressure is 1 kg / cm ２ ~20 kg / cm ２ 2. The method for producing acrylic acid according to claim 1, wherein

5. The step of separating acrylic acid from the upper fraction of the first cooling tower to obtain acrylic acid includes: Supplying the top fraction of the first cooling tower to an extraction tower, and separating it in the extraction tower into an extract containing acrylic acid and an extractant and a raffinate containing water; Separating acrylic acid from the extract to obtain acrylic acid; and feeding the raffinate to a lactic acid conversion tank.

6. The step of separating acrylic acid from the upper fraction of the first cooling tower to obtain acrylic acid includes: supplying an upper fraction of the first cooling tower to a second cooling tower and separating a lower fraction of the second cooling tower comprising acrylic acid and water; supplying a portion of the bottom fraction of the second cooling tower as a first aqueous acrylic acid stream to an extraction tower and a remainder as a second aqueous acrylic acid stream to an azeotropic distillation tower; feeding the aqueous raffinate obtained from the extraction column to a lactic acid conversion tank; A step of supplying an extract containing acrylic acid and an extraction solvent obtained from the extraction column to an azeotropic distillation column; and obtaining acrylic acid from the lower fraction of the azeotropic distillation column.

7. The operating temperature of the second cooling tower is 60°C to 140°C, and the operating pressure is 1 kg / cm ２ ~20 kg / cm ２ The method for producing acrylic acid according to claim 6, wherein

8. 7. The method for producing acrylic acid according to claim 6, wherein a ratio of a flow rate of the first aqueous acrylic acid stream supplied to the extraction column to a total flow rate of the first aqueous acrylic acid stream and the second aqueous acrylic acid stream is 30% by weight to 70% by weight.

9. 7. The method for producing acrylic acid according to claim 6, wherein the upper fraction of the azeotropic distillation column is supplied to a layer separator to separate water and the extractant, and the separated extractant is recycled to one or more of the extraction column and the azeotropic distillation column.

10. 2. The method for producing acrylic acid according to claim 1, wherein the oligomerization reaction of the lactic acid and its reverse reaction are carried out in the lactic acid conversion tank.

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