Acrylic acid manufacturing method

Abstract

The present invention provides a method for producing acrylic acid, comprising the steps of: supplying an aqueous lactic acid solution to a reactor and carrying out a dehydration reaction to obtain a reaction product containing lactic acid, water, a light gas component and acrylic acid; supplying the reaction product to a first cooling tower to separate it into a bottom fraction containing acrylic acid and lactic acid and an upper fraction containing acrylic acid, water and a light gas component; supplying the upper fraction of the first cooling tower to a second cooling tower to obtain a bottom fraction containing acrylic acid and water; supplying the bottom fraction of the second cooling tower to an extraction tower to obtain an extract containing acrylic acid and an extraction solvent; supplying the bottom fraction of the first cooling tower and the extract to an azeotropic distillation tower to obtain a bottom fraction containing acrylic acid and lactic acid; and supplying the bottom fraction of the azeotropic distillation tower to an acrylic acid recovery tower to obtain acrylic acid.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0115926, 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 losses of lactic acid and acrylic acid and effectively removing by-products when producing acrylic acid by dehydration 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, and to provide a method for effectively separating lactic acid and acrylic acid from a reaction product produced in the production of acrylic acid by the dehydration reaction of lactic acid, thereby minimizing the loss of lactic acid and acrylic 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, comprising the steps of: supplying an aqueous lactic acid solution to a reactor and subjecting it to a dehydration reaction to obtain a reaction product containing lactic acid, water, light gas components, and acrylic acid; supplying the reaction product to a first cooling tower and separating it into a bottom fraction containing acrylic acid and lactic acid and an top fraction containing acrylic acid, water, and light gas components; supplying the top fraction of the first cooling tower to a second cooling tower to obtain a bottom fraction containing acrylic acid and water; supplying the bottom fraction of the second cooling tower to an extraction tower to obtain an extract containing acrylic acid and an extraction solvent; supplying the bottom fraction of the first cooling tower and the extract to an azeotropic distillation tower to obtain a bottom fraction containing acrylic acid and lactic acid; and supplying the bottom fraction of the azeotropic distillation tower to an acrylic acid recovery tower to obtain acrylic acid. [Effects of the Invention]

[0008] According to the method for producing acrylic acid of the present invention, two cooling towers are used before the distillation of the reaction product, thereby reducing the energy cost required for purifying acrylic acid and enabling the production of highly pure acrylic acid.

[0009] In addition, the loss of lactic acid in the first cooling tower can be prevented by condensing and separating the maximum amount of lactic acid contained in the reaction product in the first cooling tower. In particular, by first separating the lactic acid and acrylic acid condensed in the first cooling tower and supplying them to an azeotropic distillation tower for acrylic acid purification, not only can the loss of acrylic acid be reduced but also high-purity acrylic acid can be obtained. [Brief explanation of the drawings]

[0010] [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

[0011] 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.

[0012] 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.

[0013] 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.

[0014] Furthermore, unless otherwise specified, in the present invention, the operating temperature of a cooling tower may mean the operating temperature at the lower part of the cooling tower, and the operating pressure of a cooling tower may mean the operating pressure at the upper part of the cooling tower.

[0015] Hereinafter, each step that can be included in an embodiment of the present invention will be described with reference to FIG.

[0016] A method for producing acrylic acid according to one embodiment of the present invention includes the steps of: supplying an aqueous lactic acid solution to a reactor and subjecting it to a dehydration reaction to obtain a reaction product containing lactic acid, water, light gas components, and acrylic acid; supplying the reaction product to a first cooling tower to separate it into a bottom fraction containing acrylic acid and lactic acid and an top fraction containing acrylic acid, water, and light gas components; supplying the top fraction of the first cooling tower to a second cooling tower to obtain a bottom fraction containing acrylic acid and water; supplying the bottom fraction of the second cooling tower to an extraction tower to obtain an extract containing acrylic acid and an extraction solvent; supplying the bottom fraction of the first cooling tower and the extract to an azeotropic distillation tower to obtain a bottom fraction containing acrylic acid and lactic acid; and supplying the bottom fraction of the azeotropic distillation tower to an acrylic acid recovery tower to obtain acrylic acid.

[0017] 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 reaction product containing lactic acid, water, a light gas component, and acrylic acid.

[0018] 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.

[0019] 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 gas-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 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.

[0020] In order to solve the problems of the related art, 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 during which 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 minimizes the loss of acrylic acid that may occur during the recovery of unreacted lactic acid.

[0021] That is, the entire amount of lactic acid is condensed and separated by the supercooling operation of the first cooling tower, and in this case, acrylic acid that can be condensed together with lactic acid is efficiently separated and purified, thereby providing a method for recovering or obtaining high-purity lactic acid and acrylic acid, respectively, without loss of lactic acid and acrylic acid.

[0022] According to one embodiment of the present invention, a reaction product containing acrylic acid can be produced by first supplying an aqueous lactic acid solution to a reactor and carrying out 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 in 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. When lactic acid is present at a high concentration, it can form oligomers such as dimers and trimers through an equilibrium reaction, and can be used in the form of an aqueous solution with a concentration within the above range.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The reaction product produced by the dehydration reaction of lactic acid may contain water (HO), light gas components, and lactic acid in addition to the target product, acrylic acid. Here, the lactic acid may be unreacted lactic acid from the dehydration reaction of lactic acid.

[0027] The method for producing acrylic acid by the dehydration of lactic acid can secure competitiveness as a raw material compared to the conventional method of air-oxidizing propylene and can eliminate environmental pollution issues, but the conversion rate of lactic acid is low and various by-products are produced, resulting in a low yield of acrylic acid. Therefore, the development of a process to improve economic efficiency is necessary. In contrast, the present invention provides a method that not only can obtain high-purity acrylic acid without loss of acrylic acid, but also increases the recovery rate of unreacted lactic acid and reduces overall equipment and energy costs, thereby improving economic efficiency.

[0028] The method for producing acrylic acid according to one embodiment of the present invention may include a step of supplying the reaction product to a first cooling tower 10 and separating the reaction product into a lower fraction containing acrylic acid and lactic acid and an upper fraction containing acrylic acid, water, and light gas components.

[0029] Specifically, the reactor discharge stream 1 containing the reaction products is a gas phase stream, and the reactor discharge stream 1 may be supplied to the first cooling tower 10 and cooled. That is, among the gas phase reaction products supplied to the first cooling tower 10, lactic acid having a relatively high boiling point may be condensed by being cooled to form a liquid phase condensate.

[0030] That is, by separating unreacted lactic acid contained in the reaction product in advance by cooling, deformation of lactic acid due to exposure to high temperatures, e.g., oligomerization, 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.

[0031] Here, in order to separate lactic acid without loss, it is important to control the operating conditions of the first cooling tower 10. That is, if the operating conditions of the first cooling tower 10 are such that lactic acid is excessively cooled, for example, if the cooling temperature is excessively lowered at the same pressure, all of the lactic acid can be recovered, but some acrylic acid may also be condensed along with the lactic acid, resulting in a loss of acrylic acid at the bottom of the first cooling tower. Conversely, if the operating conditions of the first cooling tower 10 are such that lactic acid is only slightly cooled, for example, if the cooling temperature is excessively increased at the same pressure, condensation of acrylic acid can be prevented, preventing a loss of acrylic acid, but some lactic acid may not be condensed, resulting in a loss of lactic acid at the top of the first cooling tower 10.

[0032] In the present invention, first cooling tower 10 is operated under conditions for excessive cooling of lactic acid so that as much lactic acid contained in the reaction product as possible is condensed, thereby separating lactic acid and acrylic acid as a lower fraction of first cooling tower 10. This prevents the loss of lactic acid to the upper part of first cooling tower 10 due to non-condensation of lactic acid. Meanwhile, acrylic acid contained in the lower fraction of first cooling tower 10 is recovered in azeotropic distillation tower 200 and acrylic acid recovery tower 400, which will be described later, thereby preventing the loss of acrylic acid. Therefore, the loss of acrylic acid and lactic acid can be minimized and high-purity acrylic acid and lactic acid can be obtained and recovered, thereby improving product quality and economic efficiency.

[0033] For this purpose, the operating temperature of the first cooling tower 10 may be 110°C or more and 140°C or less, more specifically, 120°C or more and 140°C or less. Within this temperature range, the entire amount of lactic acid can be condensed, minimizing the loss of lactic acid. In addition, acrylic acid can be condensed to such an extent that it can be separated with high purity in the acrylic acid recovery tower described below.

[0034] The operating pressure of the first cooling tower 10 is 1 kg / cm 2 More than 1.5kg / cm 2 or more than 2kg / 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.

[0035] 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.

[0036] In this respect, the upper fraction discharged from the first cooling tower 10 may not contain lactic acid, or even if it does, the content of lactic acid may be 2 wt % or less, specifically 1 wt % or less.

[0037] Meanwhile, the content of acrylic acid contained in the upper fraction discharged from the first cooling tower 10 may be 80 wt% or less, or 60 wt% or less, or 40 wt% or less, or 10 wt% or more, or 20 wt% or more, or 30 wt% or more, based on the acrylic acid introduced into the first cooling tower 10.

[0038] In addition, it is preferable that as much of the lactic acid contained in the reaction product as possible be condensed and separated in the first cooling tower 10. Specifically, the ratio of the mass flow rate of the lactic acid contained in the lower fraction discharged from the first cooling tower 10 to the mass flow rate of the lactic acid contained in the reaction product may be 95% by weight to 99% by weight. That is, almost all of the lactic acid contained in the reaction product may be condensed and separated in the first cooling tower 10. Therefore, in the present invention, the overcooling condition of lactic acid may refer to a cooling condition under which the ratio of the mass flow rate of the lactic acid contained in the lower fraction discharged from the first cooling tower 10 to the mass flow rate of the lactic acid contained in the reaction product satisfies the above range. Meanwhile, the separated lactic acid, together with acrylic acid, may be distilled and separated from water in the azeotropic distillation tower 200 described below, and then separated into lactic acid and acrylic acid in the acrylic acid recovery tower 400.

[0039] Since the first cooling tower 10 operates under the condition of excessively cooling lactic acid, the upper fraction of the first cooling tower 10 can contain acrylic acid, water, and light gas components. Here, the light gas components are components with a boiling point lower than that of water, and specifically, can contain carbon monoxide, carbon dioxide, and acetaldehyde in addition to diluent gases.

[0040] The upper fraction of the first cooling tower 10 can then be supplied to the second cooling tower 20 as the upper discharge stream 12 of the first cooling tower. Meanwhile, the lower fraction of the first cooling tower 10 containing acrylic acid and lactic acid is discharged as the lower discharge stream 11 of the first cooling tower, which can be supplied to the azeotropic distillation tower 200.

[0041] The upper discharge stream 12 of the first cooling tower 10 supplied to the second cooling tower 20 can be further cooled to be separated into a lower fraction containing acrylic acid and water and an upper fraction containing light gas components.

[0042] 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 1 kg / cm 2 More than 1.5kg / cm 2 or more than 2kg / 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 above-described ranges of operating temperature and operating pressure, the composition of the light gas components separated as the top discharge stream 22 of the second cooling tower 20 can be controlled, thereby minimizing the loss of acrylic acid and removing the light gas components including diluent gas and acetaldehyde from the system.

[0043] 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.

[0044] Meanwhile, the bottom fraction of the second cooling tower 20 may be discharged through a second cooling tower bottom discharge stream 21 and supplied to an extraction tower 100. The second cooling tower bottom discharge stream 21 may contain acrylic acid that has not been condensed in the first cooling tower 10. An extraction process performed in the extraction tower 100 may result in obtaining an extract containing acrylic acid and an extraction solvent.

[0045] Specifically, the extraction tower 100 removes most of the water contained in the bottom discharge stream 21 of the second cooling tower without using much 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 regard, it is preferable that the extraction in the extraction tower 100 be performed by contacting the extraction solvent with the extraction tower feed stream through liquid-liquid contact, in order to improve the energy efficiency of the entire process.

[0046] 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.

[0047] 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.

[0048] In this manner, an extract containing the extraction solvent and acrylic acid is obtained, and the extract can be supplied to the azeotropic distillation column 200 as the top discharge stream 102 of the extraction column. Furthermore, water can be recovered from the extraction step as a raffinate, which can be discharged as the bottom discharge stream 101 of the extraction column. By recovering water in this manner in the extraction step, the operating load of the distillation step described below can be reduced, and energy consumption can be significantly reduced.

[0049] According to one embodiment of the present invention, the bottom discharge stream 11 from the first cooling tower containing acrylic acid and lactic acid can be supplied to an azeotropic distillation column 200. The ratio of the water content to the acrylic acid content contained in the bottom discharge stream 11 from the first cooling tower can be 2.5 to 4.0. If the bottom discharge stream 11 from the first cooling tower is supplied to, for example, an extraction column 100, the lactic acid may be discharged together with water during the extraction process, resulting in a loss of lactic acid, or a separate device and associated energy are required to separate the lactic acid discharged together with water. Therefore, in the present invention, the bottom discharge stream 11 from the first cooling tower is supplied to an azeotropic distillation column 200 together with the extract separated in the extraction column, thereby minimizing the loss of lactic acid and acrylic acid during the process of obtaining acrylic acid. In addition, since the first cooling tower 10 is operated under the condition of excessively cooling lactic acid, even if acrylic acid is discharged together with the total amount or excessively condensed lactic acid, the acrylic acid and lactic acid can be separated from each other in the acrylic acid recovery tower 400, thereby minimizing the loss of acrylic acid.

[0050] Meanwhile, according to one embodiment of the present invention, the bottom discharge stream 11 of the first cooling tower and the top discharge stream 102 of the extraction tower may be supplied to an azeotropic distillation column 200, where a distillation process may be performed on these streams. The distillation process in the azeotropic distillation column 200 on the stream supplied to the azeotropic distillation column 200 may be a process of separating an upper fraction containing water and an extraction solvent from a lower fraction containing acrylic acid and lactic acid by azeotropic distillation.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] When the azeotropic solvent is introduced into the azeotropic distillation column 200, azeotropic distillation of acrylic acid and water occurs. As a result, water 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. A lower fraction containing acrylic acid and lactic acid can be recovered from the lower part of the azeotropic distillation column 200.

[0055] 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.

[0056] 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.

[0057] Meanwhile, the bottom fraction of azeotropic distillation column 200 containing acrylic acid and lactic acid can be supplied to acrylic acid recovery column 400 as bottom discharge stream 201 of the azeotropic distillation column. By the distillation performed in acrylic acid recovery column 400, lactic acid can be separated into bottom discharge stream 401 of acrylic acid recovery column 400 and acrylic acid can be separated into top discharge stream 402. The lactic acid separated in the bottom of acrylic acid recovery column 400 can be circulated to the reactor and reused as a raw material for the dehydration reaction.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Specifically, a 30 wt % aqueous lactic acid solution and nitrogen (N2) as a diluent gas were supplied to a reactor, and a reaction product containing lactic acid, water, light gas components, and acrylic acid was produced by a dehydration reaction.

[0062] The reactor discharge stream containing the reaction product was supplied to a first cooling tower 10. In the first cooling tower 10, the reaction product was cooled and condensed, and separated into a first cooling tower lower discharge stream 11 containing acrylic acid and lactic acid, and a first cooling tower upper discharge stream 12 containing acrylic acid, water, and light gas components. Here, the lower operating temperature of the first cooling tower 10 was set to 120°C, and the upper operating pressure was set to 1.9 kg / cm. 2 was controlled.

[0063] Next, the bottom discharge stream 11 of the first cooling tower was introduced into an azeotropic distillation tower 200. Meanwhile, the top discharge stream 12 of the first cooling tower was supplied to a second cooling tower 20 to be cooled and condensed, thereby separating the bottom discharge stream 21 of the second cooling tower containing water and acrylic acid and the light gas component containing nitrogen into an top discharge stream 22 of the second cooling tower. Here, the bottom operating temperature of the second cooling tower 20 was set to 107°C, and the top operating pressure was set to 1.3 kg / cm. 2 was controlled.

[0064] Meanwhile, the bottom discharge stream 21 from the second cooling tower was supplied to the extraction tower 100, and 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 into the top discharge stream 102 from the extraction tower 100 and supplied to the azeotropic distillation tower 200, and the bottom discharge stream 101 from the extraction tower 100 containing water was discharged outside the system.

[0065] Furthermore, distillation was carried out in azeotropic distillation column 200, to which the bottom discharge stream from first cooling tower 10 and top discharge stream 102 from extraction column 100 were supplied, to obtain bottom discharge stream 201 containing lactic acid and acrylic acid, which was supplied to acrylic acid recovery column 400. Meanwhile, stream 202 containing water and extraction solvent was discharged to the top of azeotropic distillation column 200. Next, stream 202 containing water and extraction solvent was supplied to a layer separator to separate the water and extraction solvent, after which the water was discharged outside the system and the extraction solvent was divided and circulated between extraction column 100 and azeotropic distillation column 200.

[0066] Meanwhile, distillation was carried out in the acrylic acid recovery column 400, with lactic acid being collected at the bottom and acrylic acid being collected at the top.

[0067] The flow rate (kg / hr) and composition (wt%) of each component in each stream in Figure 1 are shown in Table 1 below.

[0068] [Table 1]

[0069] From Table 1 and FIG. 1, the mass flow rates of acrylic acid and lactic acid introduced into the first cooling tower 10 via stream 1a were compared with the mass flow rates of acrylic acid and lactic acid obtained at the upper and lower parts (streams 8a and 9a) of the acrylic acid recovery tower 400. As a result, it was confirmed that the recovery rate of lactic acid was 97% and the recovery rate of acrylic acid reached 99.2%.

[0070] 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.

[0071] Specifically, the same procedure as in Example 1 was carried out, except that a 40 wt % aqueous lactic acid solution was supplied to the reactor.

[0072] The flow rate (kg / hr) and composition (wt%) of each component in each stream in Figure 1 are shown in Table 2 below.

[0073] [Table 2]

[0074] From Table 2 and FIG. 1, the mass flow rates of acrylic acid and lactic acid introduced into the first cooling tower 10 via stream 1a were compared with the mass flow rates of acrylic acid and lactic acid obtained at the upper and lower parts (streams 8a and 9a) of the acrylic acid recovery tower 400. As a result, it was confirmed that the recovery rate of lactic acid was 97.6% and the recovery rate of acrylic acid reached 97.7%.

[0075] 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.

[0076] Comparative Example 1 is an example in which a single cooling tower 10 was used to separate light gas components, a part of the bottom discharge stream from the cooling tower 10 containing acrylic acid and lactic acid was supplied to the extraction tower 100, and the remainder was introduced into the azeotropic distillation tower 200, thereby realizing the same recovery rate of acrylic acid as in Example 1.

[0077] 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, water, light gas components, and acrylic acid was produced by a dehydration reaction.

[0078] 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, acrylic acid, and water was separated from the lower portion. Here, the lower operating temperature of the first cooling tower 10 was set to 108°C, and the upper operating pressure was set to 1.3 kg / cm. 2 was controlled.

[0079] Half of the mass flow rate of the bottom discharge stream from the cooling tower 10 was fed to the extraction tower 100 and the other half was fed to the azeotropic distillation tower 200 .

[0080] 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 into an upper discharge stream from the extraction column 100 and supplied to the azeotropic distillation column 200. Then, distillation was carried out in the azeotropic distillation column 200 to separate a lower discharge stream containing lactic acid and acrylic acid from an upper discharge stream containing water and the extraction solvent. Meanwhile, the lower discharge stream from the azeotropic distillation column 200 containing lactic acid and acrylic acid was supplied to the acrylic acid recovery column 400, and distillation was carried out in the acrylic acid recovery column 400 to obtain lactic acid at the bottom and acrylic acid at the top.

[0081] 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.

[0082] [Table 3]

[0083] From Table 3 and FIG. 2, it can be seen that the recovery rate of lactic acid is 58.5% by comparing the mass flow rate of lactic acid introduced via stream 1b (600 kg / hr) with the mass flow rate of lactic acid recovered via stream 7b (351 kg / hr).

[0084] 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.

[0085] 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 same recovery rate of acrylic acid as in Example 1 (97.7%) was achieved.

[0086] 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.

[0087] [Table 4]

[0088] From Table 4 and FIG. 2, it can be seen that the recovery rate of lactic acid is 61.5% by comparing the mass flow rate of lactic acid introduced through stream 1b (2000 kg / hr) with the mass flow rate of lactic acid recovered through stream 7b (1229 kg / hr).

Claims

1. Supplying an aqueous lactic acid solution to a reactor and subjecting it to a dehydration reaction to obtain a reaction product containing lactic acid, water, a light gas component, and acrylic acid; Supplying the reaction product to a first cooling tower to separate it into a bottom fraction containing acrylic acid and lactic acid and an top fraction containing acrylic acid, water and light gas components; feeding the top fraction of the first cooling tower to a second cooling tower to obtain a bottom fraction comprising acrylic acid and water; Supplying the lower fraction of the second cooling tower to an extraction tower to obtain an extract containing acrylic acid and an extraction solvent; Supplying the bottom fraction of the first cooling tower and the extract to an azeotropic distillation tower to obtain a bottom fraction containing acrylic acid and lactic acid; and supplying the bottom fraction of the azeotropic distillation column to an acrylic acid recovery column to obtain acrylic acid.

2. The operating temperature of the first cooling tower is 110°C to 140°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

3. 2. The method for producing acrylic acid according to claim 1, wherein the content of lactic acid contained in the upper fraction discharged from the first cooling tower is 2 wt% or less.

4. 2. The method for producing acrylic acid according to claim 1, wherein a ratio of a mass flow rate of lactic acid contained in the lower fraction discharged from the first cooling tower to a mass flow rate of lactic acid contained in the reaction product is 95% by weight to 99% by weight.

5. 2. The method for producing acrylic acid according to claim 1, wherein the ratio of the water content to the acrylic acid content contained in the lower fraction discharged from the first cooling tower is 2.5 to 4.

0.

6. 2. The method for producing acrylic acid according to claim 1, wherein a light gas component is separated in an upper portion of the second cooling tower.

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 2. The method for producing acrylic acid according to claim 1, wherein

8. 2. The method for producing acrylic acid according to claim 1, wherein lactic acid is separated in a lower portion of the acrylic acid recovery column and acrylic acid is separated in an upper portion thereof.

9. 9. The method for producing acrylic acid according to claim 8, wherein the lactic acid separated in the lower part of the acrylic acid recovery column is circulated to the reactor.

10. 2. The method for producing acrylic acid according to claim 1, wherein the upper fraction of the azeotropic distillation column is supplied to a layer separator to separate water and the extracting solvent, and the separated extracting solvent is recycled to one or more of the extraction column and the azeotropic distillation column.

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