Preparation method of acrylic acid

Abstract

The invention provides a method for preparing acrylic acid, the method comprises a multi-stage crystallization process performed by more than two crystallization units connected in series, each crystallization unit comprises a crystallizer and a solid-liquid separator, and the first-stage crystallization unit of the more than two crystallization units comprises a crystallizer with the crystallization temperature of-20 to-10 DEG C.

Description

Technical Field

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0126965, filed on September 22, 2023, the entire contents of which are incorporated into this specification by reference. Technical Field

[0004] The present invention relates to a method for preparing acrylic acid, and more particularly, to a method for preparing high-purity acrylic acid according to a continuous crystallization process. Background Art

[0005] Acrylic acid is usually prepared by a method of subjecting compounds such as propane, propylene and acrolein to a gas phase oxidation reaction in the presence of a catalyst. For example, in the presence of a suitable catalyst in a reactor, propane, propylene, etc. are converted into acrylic acid via acrolein by a gas phase oxidation reaction, and at the rear end of the reactor, a mixed gas containing acrylic acid, unreacted propane or propylene, acrolein, an inert gas, carbon dioxide, water vapor and various organic byproducts (acetic acid, low boiling point byproducts, high boiling point byproducts, etc.) produced by the reaction is obtained.

[0006] The mixed gas containing acrylic acid is contacted with an absorption solvent such as water in an absorption tower and recovered as an acrylic acid solution. In addition, as a subsequent process for obtaining acrylic acid contained in the acrylic acid solution, processes such as extraction, distillation and purification are generally involved.

[0007] However, since the specific heat of the absorption solvent such as water used in the absorption tower is high, very high energy consumption is required to separate the by-products from the acrylic acid solution containing the absorption solvent through a process such as distillation. In addition, through a process such as high-temperature distillation, a polymer of acrylic acid as a reactive monomer is generated, and there is a problem that regular cleaning is required.

[0008] Meanwhile, although a crystallization process is involved to obtain acrylic acid contained in the acrylic acid solution, since the melting point of acetic acid as an organic by-product is similar to that of acrylic acid, when a large amount of acetic acid is introduced into the crystallization process, acrylic acid of a desired purity cannot be obtained only through a single-stage crystallization process, and it is difficult to obtain acrylic acid at a desired level.

[0009] Therefore, there is an urgent need to introduce a technology that can obtain high-purity acrylic acid from an acrylic acid solution while increasing the final yield of acrylic acid. Summary of the invention

[0010] Technical issues

[0011] In order to solve the problems mentioned in the background art, an object of the present invention is to provide a method for preparing acrylic acid, which can improve the final yield of acrylic acid and finally obtain high-purity acrylic acid when obtaining acrylic acid contained in an acrylic acid solution.

[0012] Technical Solution

[0013] In a general aspect, a method for preparing acrylic acid includes a multi-stage crystallization process performed by two or more crystallization units connected in series, each crystallization unit including a crystallizer and a solid-liquid separator, wherein, in the crystallizers of each stage, acrylic acid contained in an acrylic acid solution introduced into the crystallizers of each stage is crystallized to obtain a suspension containing acrylic acid crystals, and the suspension is supplied to the solid-liquid separators of each stage; in the solid-liquid separators of each stage, the suspension is separated into a solid and a liquid to obtain a concentrated acrylic acid solution and a mother liquor; the mother liquor is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor is separated into a first mother liquor stream and a second mother liquor stream. The invention relates to a method for preparing a crystallization unit comprising a first crystallization unit and a second crystallization unit comprising a first crystallization unit and a second crystallization unit comprising a second crystallization unit. The method comprises the steps of: circulating a first crystallization unit stream to a crystallizer or a mother liquor treatment process, the crystallizer being located at a front stage of a stage including a solid-liquid separator for separating the mother liquor, and circulating a second mother liquor stream to a crystallizer, the crystallizer being located at a stage including a solid-liquid separator for separating the mother liquor; introducing a concentrated acrylic acid solution into a crystallizer, the crystallizer being located at a rear stage of a stage including a solid-liquid separator for separating the concentrated acrylic acid solution; obtaining purified acrylic acid from the solid-liquid separator of the last crystallization unit of the two or more crystallization units; and a first crystallization unit of the two or more crystallization units comprises a crystallizer having a crystallization temperature of -20 to -10°C.

[0014] Beneficial Effects

[0015] According to the method for preparing acrylic acid of the present invention, acrylic acid contained in an acrylic acid solution is crystallized through a multi-stage crystallization process performed by crystallization units connected in multiple stages, so that high-purity acrylic acid can be obtained and the final yield of acrylic acid can be improved.

[0016] In particular, the crystallization temperature in the crystallizer of the first-stage crystallization unit among the two or more crystallization units is controlled to -20 to -10°C so that the amount of acrylic acid crystallized in the crystallizer of the first-stage crystallization unit can be the highest. In this way, the amount of mother liquor separated in the solid-liquid separator of the first-stage crystallization unit can be reduced, and when a part of the mother liquor separated from the first-stage crystallization unit is recycled to the mother liquor treatment process, the amount of mother liquor to be treated in the mother liquor treatment process is small, which is preferred in terms of energy or economic feasibility. In addition, as the amount of crystallized acrylic acid increases, the final yield of purified acrylic acid can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a flow chart illustrating a multi-stage crystallization process in a method for preparing acrylic acid according to one embodiment of the present invention.

[0018] Figures 2 to 4 is a flow chart showing a multi-stage crystallization process in a method for preparing acrylic acid according to a comparative example. DETAILED DESCRIPTION

[0019] The terms and words used in the specification and claims of the present invention should not be restrictively understood as having conventional or dictionary meanings, but should be understood as having meanings and concepts consistent with the technical concept of the present invention based on the principle that inventors can appropriately define the concepts of the terms in order to best describe their own inventions.

[0020] Hereinafter, the present invention will be described in more detail.

[0021] The term "flow" in the present invention may refer to the flow of a fluid in a process, or may refer to the fluid itself flowing through a moving pipeline (pipeline). Specifically, "flow" may refer to both the fluid itself flowing through a pipeline connecting various devices to each other, and the flow of the fluid. In addition, the fluid may refer to one or more of a gas, a liquid, and a solid.

[0022] A method for preparing acrylic acid according to an embodiment of the present invention may include a multi-stage crystallization process performed by two or more crystallization units connected in series, each crystallization unit including a crystallizer and a solid-liquid separator, wherein, in the crystallizers of each stage, acrylic acid contained in the acrylic acid solution introduced into the crystallizers of each stage is crystallized to obtain a suspension containing acrylic acid crystals, and the suspension is supplied to the solid-liquid separators of each stage; in the solid-liquid separators of each stage, the suspension is separated into solid and liquid to obtain a concentrated acrylic acid solution and a mother liquor; the mother liquor is divided into a first mother liquor stream and a second mother liquor stream, the first mother liquor stream is circulated to the crystallizer or the mother liquor treatment process, the crystallizer being located at the front stage of the stage including the solid-liquid separator for separating the mother liquor, and the second mother liquor stream is circulated to the crystallizer being located at the rear stage of the stage including the solid-liquid separator for separating the mother liquor; the concentrated acrylic acid solution is introduced into the crystallizer, the crystallizer being located at the rear stage of the stage including the solid-liquid separator for separating the concentrated acrylic acid solution; purified acrylic acid is obtained from the solid-liquid separator of the last stage of the two or more crystallization units; and the two or more crystallization units include a crystallizer having a crystallization temperature of -20 to -10°C.

[0023] The method for preparing acrylic acid according to one embodiment of the present invention may include a multi-stage crystallization process performed by two or more crystallization units connected in series, each of which includes a crystallizer and a solid-liquid separator.

[0024] Specifically, in the multi-stage crystallization process, the two or more crystallization units may include a multi-stage crystallizer connected in multiple stages, and the crystallization process performed in each crystallization unit at each stage may be performed continuously. Each crystallization unit at each stage may include a crystallizer and a solid-liquid separator.

[0025] The crystallizer may be a device that crystallizes a specific substance into a solid by utilizing the solubility of the substance in a liquid mixture according to a temperature difference, and the solid-liquid separator may be a device that separates a solid-liquid mixture supplied to the solid-liquid separator into a solid phase and a liquid phase.

[0026] Meanwhile, when the crystallization of the acrylic acid solution is performed through a single-stage crystallization process, since the content of impurities in the acrylic acid solution is high, acrylic acid crystals having a desired purity cannot be obtained through only the single-stage crystallization process.

[0027] However, when the crystallization process is performed in multiple stages as in the present invention, the acrylic acid solution is concentrated and crystallized in the multiple stages, so that the final yield of acrylic acid can be met and the purity of acrylic acid can be improved.

[0028] In the method for preparing acrylic acid according to one embodiment of the present invention, in the crystallizers of each stage, acrylic acid contained in the acrylic acid solution introduced into the crystallizers of each stage may be crystallized to obtain a suspension containing acrylic acid crystals, and the suspension may be supplied to the solid-liquid separators of each stage.

[0029] Specifically, the acrylic acid solution introduced into the crystallizer of the first-stage crystallization unit in the crystallizers of each stage may be a crude acrylic acid aqueous solution containing crude acrylic acid. In this case, the crude acrylic acid may be acrylic acid before crystallization. Meanwhile, the first-stage crystallization unit may be a crystallization unit located at the first stage among the two or more crystallization units, and may be located at a stage including a crystallizer into which the crude acrylic acid aqueous solution is introduced.

[0030] A crude aqueous acrylic acid solution can be prepared as follows.

[0031] First, reactants containing oxygen-containing gas and raw material compounds can be supplied to a reactor equipped with a catalyst, and a gas phase oxidation reaction can be carried out in the reactor in the presence of the catalyst to obtain a mixed gas containing acrylic acid. In this case, the acrylic acid can be crude acrylic acid, and the oxygen-containing gas can be air.

[0032] The raw material compound may be one or more compounds selected from the group consisting of propane, propylene, butane, isobutylene, tert-butylene, and acrolein. Specifically, the raw material compound may include propylene.

[0033] Therefore, the mixed gas containing acrylic acid of the present invention can be a reaction product produced by a gas phase oxidation reaction of reactants containing air and raw material compounds in a reactor. Specifically, the mixed gas can contain acrylic acid, unreacted raw material compounds, acrolein, inert gases, carbon monoxide, carbon dioxide and various organic by-products (acetic acid, low boiling point by-products, high boiling point by-products, etc.). Here, "low boiling point by-products (light fractions)" or "high boiling point by-products (heavy fractions)" refer to the types of by-products that may be produced in the process of preparing the desired acrylic acid, and can be compounds with a molecular weight less than or greater than acrylic acid.

[0034] The acrylic acid solution introduced into the crystallizer of the first-stage crystallization unit can be obtained by contacting a mixed gas containing acrylic acid with an absorption solvent.

[0035] Specifically, the acrylic acid solution can be obtained by an absorption process in which a mixed gas containing acrylic acid is contacted with water as an absorption solvent. In this case, considering the efficiency of the absorption process, the mixed gas can be supplied to the lower part of the absorption tower where the absorption process is performed, and the absorption solvent, specifically, water, can be supplied to the upper part of the absorption tower.

[0036] Therefore, the acrylic acid solution obtained through the absorption process, that is, the crude acrylic acid aqueous solution may be introduced into the crystallizer of the first-stage crystallization unit, and the crystallization process may be performed.

[0037] According to the present invention, the content of acrylic acid contained in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit may be 80 to 95% by weight, specifically, 82 to 90% by weight. Depending on the content of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first stage crystallization unit, the temperature at which acrylic acid is crystallized in the crystallizers of each stage and the amount of acrylic acid crystals generated according to the temperature may vary.

[0038] More specifically, when the content of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first-stage crystallization unit is less than 80% by weight, due to the low content of acrylic acid in the acrylic acid solution, when the acrylic acid solution is supplied to the crystallizer, the amount of acrylic acid crystals obtained by crystallization will also be small, and the process performed in the present invention to meet the desired level of acrylic acid purity and yield will become complicated. Meanwhile, when the content of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first-stage crystallization unit exceeds 95% by weight, an additional purification process will be required to obtain such acrylic acid solution, which will be undesirable from the perspective of economic feasibility such as the process facility cost and equipment cost for performing the purification process. In addition, when the purification process is performed, energy consumption will increase excessively.

[0039] Meanwhile, as described above, the crude acrylic acid aqueous solution obtained as described above can be introduced as an acrylic acid solution into the crystallizer of the first stage crystallization unit. Meanwhile, the concentrated acrylic acid solution separated in the solid-liquid separator described below, specifically, the solid-liquid separator of the previous stage, can be introduced as an acrylic acid solution into each crystallizer of the crystallization unit after the first stage crystallization unit, that is, each crystallizer of the crystallization unit starting from the second stage.

[0040] Here, the crystallization unit after the first-stage crystallization unit may refer to any crystallization unit after the first-stage crystallization unit in two or more crystallization units. For example, when the crystallization unit is included in a total of four stages, the crystallization unit after the first-stage crystallization unit may be a second-stage crystallization unit, a third-stage crystallization unit, and a fourth-stage crystallization unit.

[0041] Therefore, the content of acrylic acid contained in the concentrated acrylic acid solution introduced into the crystallizer of each crystallization unit increases as the crystallization unit is located at a later stage of the crystallization unit after the first-stage crystallization unit.

[0042] Meanwhile, acrylic acid contained in the acrylic acid solution is crystallized by the crystallization process performed in the crystallizers of each stage, thereby obtaining a suspension containing acrylic acid crystals. Thereafter, the suspension obtained in the crystallizers of each stage may be supplied to a solid-liquid separator located at the stage including the crystallizer in which the suspension is obtained.

[0043] According to one embodiment of the present invention, the ratio of the mass of acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizers of each stage may be 10 to 40% by weight, specifically, 20 to 35% by weight. The ratio of the mass of acrylic acid crystals contained in the suspension to the total mass of the suspension discharged from the crystallizers of each stage may have the same meaning as the ratio of the mass flow rate of crystallized acrylic acid contained in the suspension to the mass flow rate of the suspension supplied to the solid-liquid separators of each stage.

[0044] More specifically, when the ratio of the mass of acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizers of each stage, that is, the acrylic acid crystal concentration (acrylic acid crystal content) in the suspension is less than 10% by weight, since a relatively small amount of acrylic acid is crystallized in the crystallizers of each stage, the total number of times and the production volume of the multi-stage crystallization process may be increased in order to meet the desired level of acrylic acid production. When the acrylic acid crystal concentration in the suspension exceeds 40% by weight, the content of acrylic acid crystals as solids in the suspension increases, which may make it difficult to mix the suspension in the crystallizers of each stage. Therefore, it may also be difficult to move the suspension to the solid-liquid separator, which may make it difficult to perform the crystallization process.

[0045] According to the method for preparing acrylic acid in one embodiment of the present invention, the suspension can be separated into solid and liquid in the solid-liquid separators of each stage to obtain a concentrated acrylic acid solution and a mother liquor. Specifically, in the solid-liquid separators of each stage, the suspension obtained in the crystallizers of each stage can be separated into solid and liquid to obtain solid acrylic acid crystals and a liquid mother liquor. The mother liquor can be a residue obtained by separating acrylic acid crystals from the suspension, and can contain uncrystallized acrylic acid, water, and acetic acid.

[0046] In addition, in the solid-liquid separators of each stage, the suspension can be separated into solid and liquid to obtain acrylic acid crystals and the acrylic acid crystals can be melted to obtain concentrated acrylic acid. That is, the concentrated acrylic acid solution can be obtained by melting the acrylic acid crystals by heating. For example, the molten acrylic acid crystals can be introduced into the crystallizer of the subsequent stage as the concentrated acrylic acid solution.

[0047] More specifically, melting may be a physical process of transition from a solid phase to a liquid phase, and even when melting of acrylic acid crystals is performed, the number of moles of acrylic acid contained in the acrylic acid crystals does not change. In this case, a separate heat supply device, for example, a heat exchanger, may be additionally provided to melt the acrylic acid crystals. The concentrated acrylic acid solution may contain acrylic acid, and further, may contain impurities (water, acetic acid, etc.) contained in the acrylic acid crystals and trace amounts of mother liquor that are not separated in the solid-liquid separators of each stage and remain in the acrylic acid crystals.

[0048] It is preferred to melt the acrylic acid crystals separated in the solid-liquid separators of the two or more crystallization units so as to introduce the acrylic acid crystals into the crystallizer of the crystallization unit located at the rear stage of the stage including the solid-liquid separator for separating the acrylic acid crystals, or to obtain the acrylic acid crystals as a product. That is, since the acrylic acid crystals are in a solid phase, the melting of the acrylic acid crystals can be performed for the movement of the acrylic acid crystals in the multi-stage crystallization process.

[0049] According to the method for preparing acrylic acid according to one embodiment of the present invention, the mother liquor can be divided into a first mother liquor stream and a second mother liquor stream, the first mother liquor stream can be circulated to a crystallizer or a mother liquor treatment process, the crystallizer being located at a front stage of a stage including a solid-liquid separator for separating the mother liquor, and the second mother liquor stream can be circulated to a crystallizer being located at a stage including a solid-liquid separator for separating the mother liquor.

[0050] Specifically, the mother liquid is the mother liquid separated from the solid-liquid separators of each stage, and can be divided into a first mother liquid stream and a second mother liquid stream.

[0051] Afterwards, the first mother liquor stream may be circulated to a mother liquor treatment process or a crystallizer located at a preceding stage of a stage including a solid-liquid separator from which the first mother liquor stream is obtained. Specifically, the first mother liquor stream separated from the mother liquor obtained from the solid-liquid separator of the first-stage crystallization unit may be circulated to the mother liquor treatment process. Meanwhile, the first mother liquor stream separated from the mother liquor obtained from the solid-liquid separator of a crystallization unit after the first-stage crystallization unit may be circulated to a crystallizer located at a preceding stage of a stage including a solid-liquid separator from which the mother liquor is obtained.

[0052] According to the present invention, the mother liquor treatment process may include one or more of a purge and an acrylic acid purification process. Specifically, the mother liquor treatment process may be a process for treating a first mother liquor stream in the mother liquor separated in the solid-liquid separator of the first stage crystallization unit.

[0053] More specifically, when the content of acrylic acid in the first mother liquid stream separated from the solid-liquid separator of the first-stage crystallization unit is relatively low, purging can be performed, and purging can be a process of discharging and discarding the first mother liquid stream separated from the solid-liquid separator of the first-stage crystallization unit to the outside of the system.

[0054] Meanwhile, when the content of acrylic acid in the first mother liquid stream separated from the solid-liquid separator of the first-stage crystallization unit is relatively high, an acrylic acid purification process may be performed, and the acrylic acid purification process may be a process of distilling the first mother liquid stream separated from the solid-liquid separator of the first-stage crystallization unit and separating acrylic acid.

[0055] At the same time, the second mother liquor stream may be recycled to a crystallizer located at a stage including a solid-liquid separator from which the second mother liquor stream is separated.

[0056] According to one embodiment of the present invention, the mass flow ratio of the first mother liquor stream and the second mother liquor stream may be 0.5:9.5 to 9.5:0.5, specifically, 1:9 to 9:1. The mass flow ratio of the first mother liquor stream and the second mother liquor stream may refer to the mass flow ratio of the first mother liquor stream and the second mother liquor stream separated from the solid-liquid separators of each stage. When the mass flow ratio of the first mother liquor stream and the second mother liquor stream is controlled within the above range, the acrylic acid crystal concentration in the above suspension may be controlled to be 10 to 40% by weight. In this way, the fluidity of the suspension can be maximized, and the fluidity of the stream can be flexible when a multi-stage crystallization process is performed.

[0057] According to the method for preparing acrylic acid according to one embodiment of the present invention, the concentrated acrylic acid solution may be introduced into a crystallizer located at a subsequent stage of a stage including a solid-liquid separator for separating the concentrated acrylic acid solution.

[0058] Specifically, the concentrated acrylic acid solution is obtained by melting acrylic acid crystals separated in the solid-liquid separators of each stage. The concentrated acrylic acid solution can be introduced into a crystallizer located at the rear stage of the stage including the solid-liquid separator for separating the concentrated acrylic acid solution. Therefore, as described above, the concentrated acrylic acid solution can be introduced as an acrylic acid solution into the crystallizer of the crystallization unit after the first stage crystallization unit.

[0059] For example, when the crystallization units are included in three stages in total, the concentrated acrylic acid solution separated in the solid-liquid separator of the second-stage crystallization unit may be introduced into the crystallizer of the third-stage crystallization unit.

[0060] According to the method for preparing acrylic acid in one embodiment of the present invention, purified acrylic acid can be obtained from the solid-liquid separator of the last crystallization unit among two or more crystallization units.

[0061] As described above, acrylic acid crystals separated in the solid-liquid separators of each stage may be melted to obtain a concentrated acrylic acid solution, and the concentrated acrylic acid solution may be introduced into a crystallizer located at a subsequent stage of the stage including the solid-liquid separator from which the concentrated acrylic acid solution is obtained.

[0062] However, since there is no crystallization unit located at the rear stage of the final crystallization unit and acrylic acid needs to be finally obtained, the acrylic acid crystals separated in the solid-liquid separator of the final crystallization unit may be melted to obtain purified acrylic acid, which is the product of the present invention. The final crystallization unit may refer to a crystallization unit located at the final stage of two or more crystallization units connected in multiple stages.

[0063] According to the method for preparing acrylic acid of the present invention, the first-stage crystallization unit among the two or more crystallization units may include a crystallization unit having a crystallization temperature of -20 to -10°C. In this case, the crystallization temperature may refer to an operating temperature of a crystallizer for crystallizing an acrylic acid solution introduced into the crystallizers of each stage into acrylic acid crystals. When the crystallization temperature in the crystallizer included in the first-stage crystallization unit is within the above range, the yield of acrylic acid in the crystallizer of the first-stage crystallization unit may be the highest. In this case, the yield of acrylic acid may refer to the mass of acrylic acid crystallized in the crystallizers of each stage relative to the mass of acrylic acid contained in the acrylic acid solution introduced into the crystallizers of each stage.

[0064] In this way, the amount of mother liquor separated in the solid-liquid separator of the first-stage crystallization unit can be reduced, and when a part of a small amount of mother liquor is recycled to the mother liquor treatment process, it is preferred from the viewpoint of economic feasibility or energy consumption. For example, when a large amount of mother liquor is purged, the loss cost of acrylic acid contained in the mother liquor is too high, and when a large amount of mother liquor is recycled to the acrylic acid purification process, the energy used to purify the large amount of mother liquor in the acrylic acid purification process will increase significantly. Therefore, it is preferred to reduce the amount of mother liquor recycled to the mother liquor treatment process.

[0065] In addition, the acrylic acid crystals separated in the solid-liquid separator of the first-stage crystallization unit are melted, the melted acrylic acid crystals are introduced into the crystallizer of the crystallization unit at the rear stage of the first-stage crystallization unit, and a multi-stage crystallization process is performed, so that the final yield of acrylic acid can be met and purified acrylic acid with high purity can be obtained. In this case, the final yield of acrylic acid may refer to the ratio of the mass of acrylic acid contained in the concentrated acrylic acid solution separated in the solid-liquid separator of the last-stage crystallization unit to the mass of acrylic acid in the acrylic acid solution introduced into the crystallizer of the first-stage crystallization unit.

[0066] In the following, reference will be made to Figure 1 Processes are described that may be included in embodiments of the present invention.

[0067] According to one embodiment of the present invention, two or more crystallization units are included in a total of two stages, the crystallization temperature in the crystallizer (a) of the first stage crystallization unit may be -20 to -10° C., and the crystallization temperature in the crystallizer (a) of the second stage crystallization unit may be 0 to 12° C. Specifically, the crystallization temperature in the crystallizer (a) of the first stage crystallization unit may be -14 to -9° C., and the crystallization temperature in the crystallizer (a) of the second stage crystallization unit may be 4 to 9° C.

[0068] More specifically, as the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit decreases, the yield of acrylic acid in the crystallizer (a) of the first-stage crystallization unit can be maximized, but since crystals of acrylic acid and water are simultaneously produced at a temperature lower than the eutectic point of acrylic acid and water, it is preferred that the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit is a temperature higher than the eutectic point. Therefore, when the content of acrylic acid contained in the acrylic acid solution is 80 to 95% by weight, the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit may be a temperature close to the eutectic point of acrylic acid and water contained in the acrylic acid solution introduced into the crystallizer of the above-mentioned first-stage crystallization unit, but higher than the eutectic point.

[0069] In addition, when the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit is within the above range, the yield of acrylic acid in the crystallizer (a) of the first-stage crystallization unit can be the highest. This is because as the crystallization temperature approaches the eutectic point, the mass of the solid produced in the crystallizer increases compared to the liquid. Therefore, in the crystallizer (a) of the first-stage crystallization unit, a large amount of acrylic acid crystals are produced, and the acrylic acid crystals are melted and subjected to a multi-stage crystallization process by the crystallization units after the first-stage crystallization unit, so that the final yield of purified acrylic acid can be improved.

[0070] Meanwhile, when the crystallization temperature in the crystallizer (a) of the second stage crystallization unit is within the above range, the first and second mother liquid streams separated from the solid-liquid separator (b) of the second stage crystallization unit are supplied to the crystallizers (a) of the first and second stage crystallization units, respectively, to control the acrylic acid crystal concentration in the suspension discharged from the crystallizers (a) of the first and second stage crystallization units to be 10 to 40% by weight. In addition, in terms of refrigerant (utility) use of the crystallization process and the purity of acrylic acid, it is preferred that the crystallization temperature in the crystallizer of the second stage crystallization unit be controlled within the above range.

[0071] According to one embodiment of the present invention, the mass flow ratio of the first mother liquid stream separated from the solid-liquid separator (b) of the first stage crystallization unit and the second mother liquid stream can be 0.5:9.5 to 1:1, and the mass flow ratio of the first mother liquid stream separated from the solid-liquid separator (b) of the second stage crystallization unit can be 1:1 to 9:1. In this case, the concentration of acrylic acid crystals in the suspension discharged from the crystallizer (a) of each stage can be controlled to be 10 to 40% by weight. In this way, when a multi-stage crystallization process is performed, the flow of the stream in the crystallization unit or between the crystallization units can be continuously performed. In this case, the stream can contain, for example, a suspension.

[0072] The range of the mass flow ratio of the first mother liquor stream separated from the solid-liquid separator (b) of the first stage crystallization unit and the mass flow ratio of the first mother liquor stream separated from the solid-liquid separator (b) of the second stage crystallization unit can be determined according to the crystallization temperature in the crystallizer (a) of each stage and the content of acrylic acid crystals contained in the suspension discharged from the crystallizer (a) of each stage. Therefore, the mass flow ratio in each of the first and second stage crystallization units can be a mass flow ratio controlled when the crystallization temperature in the crystallizer (a) of the first stage crystallization unit is -20 to -10°C and the crystallization temperature in the crystallizer (a) of the second stage crystallization unit is 0 to 12°C.

[0073] According to one embodiment, the first stage crystallization unit may include an auxiliary crystallizer disposed at the front stage of the crystallizer. Specifically, the auxiliary crystallizer is a device separated from the crystallizer, and the auxiliary crystallizer and the crystallizer may be connected to each other. For example, an acrylic acid solution, that is, a crude acrylic acid aqueous solution, may be supplied to the auxiliary crystallizer, and the suspension obtained in the auxiliary crystallizer may be supplied to a crystallizer subsequently connected to the auxiliary crystallizer.

[0074] When the first-stage crystallization unit further includes an auxiliary crystallizer, a temperature gradient may be formed through the auxiliary crystallizer and the crystallizer, and a crystallization process may be performed in the first-stage crystallization unit.

[0075] Specifically, the crystallization temperature in the auxiliary crystallizer may be -5 to 5° C. More specifically, when the crystallization temperature in the auxiliary crystallizer is within the above range, there is not much difference between the temperature of the crude acrylic acid aqueous solution supplied to the auxiliary crystallizer and the crystallization temperature in the auxiliary crystallizer. This is preferred in terms of the purity of the produced acrylic acid crystals.

[0076] Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are provided to illustrate the present invention. It will be apparent to those skilled in the art that various modifications and changes may be made without departing from the scope and concept of the present invention, and protection scope of the present invention is not limited thereto.

[0077] Example

[0078] Example 1

[0079] according to Figure 1 The acrylic acid production process was simulated using the flow chart shown in , using Aspen Plus simulator available from Aspen Technology, Inc. As a crystallizer model, a model was used that reflects the distribution coefficient values ​​of water and acetic acid from the solid-liquid equilibrium (SLE) data of acrylic acid and water, acrylic acid and acetic acid, and water and acetic acid, and the crystallization experimental results of acrylic acid, water, and acetic acid.

[0080] Specifically, an acrylic acid solution containing acrylic acid (85 wt%), acetic acid (3 wt%) and water (12 wt%) was prepared and introduced into a multi-stage crystallization process performed by crystallization units connected in two stages in total.

[0081] Specifically, the acrylic acid solution was supplied to the crystallizer (a) of the first stage crystallization unit, and the crystallization process was performed. In this way, a suspension containing acrylic acid crystals was obtained. At this time, the crystallization temperature in the crystallizer (a) of the first stage crystallization unit was -13°C. The ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the first stage crystallization unit was 30% by weight.

[0082] Thereafter, the obtained suspension is supplied from the crystallizer (a) of the first stage crystallization unit to the solid-liquid separator (b) of the first stage crystallization unit. In the solid-liquid separator (b) of the first stage crystallization unit, the suspension obtained in the crystallizer (a) of the first stage crystallization unit is separated into acrylic acid crystals and mother liquor. At this time, in the solid-liquid separator (b) of the first stage crystallization unit, solid-liquid separation of the suspension is performed by filtration.

[0083] The mother liquor separated in the solid-liquid separator (b) of the first-stage crystallization unit is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream and the second mother liquor stream are circulated to the mother liquor treatment process and the crystallizer (a) of the first-stage crystallization unit, respectively. At this time, the mass flow ratio of the first mother liquor stream and the second mother liquor stream separated from the solid-liquid separator (b) of the first-stage crystallization unit is 1.2:8.8.

[0084] At the same time, acrylic acid crystals separated in the solid-liquid separator (b) of the first stage crystallization unit are melted to obtain a concentrated acrylic acid solution. The concentrated acrylic acid solution from the solid-liquid separator (b) of the first stage crystallization unit is supplied to the crystallizer (a) of the second stage crystallization unit.

[0085] A suspension containing acrylic acid crystals was obtained by the crystallization process performed in the crystallizer (a) of the second stage crystallization unit. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was 8° C. The ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second stage crystallization unit was 30% by weight.

[0086] Thereafter, the obtained suspension is supplied from the crystallizer (a) of the second stage crystallization unit to the solid-liquid separator (b) of the second stage crystallization unit. In the solid-liquid separator (b) of the second stage crystallization unit, the suspension obtained in the crystallizer (a) of the second stage crystallization unit is separated into acrylic acid crystals and mother liquor. At this time, in the solid-liquid separator (b) of the second stage crystallization unit, solid-liquid separation of the suspension is performed by filtration.

[0087] The mother liquor separated in the solid-liquid separator (b) of the second-stage crystallization unit is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream and the second mother liquor stream are respectively circulated to the crystallizer (a) of the first-stage crystallization unit and the second-stage crystallization unit. At this time, the mass flow ratio of the first mother liquor stream and the second mother liquor stream separated from the solid-liquid separator (b) of the second-stage crystallization unit is 6.7:3.3.

[0088] At the same time, acrylic acid crystals separated in the solid-liquid separator (b) of the second-stage crystallization unit are melted to obtain a concentrated acrylic acid solution as purified acrylic acid.

[0089] As a result, the purified acrylic acid contained acrylic acid (99.0 wt%), acetic acid (0.61 wt%) and water (0.37 wt%). In addition, the ratio of the mass of acrylic acid contained in the acrylic acid crystals separated in the solid-liquid separator (b) of the second stage crystallization unit to the mass of acrylic acid contained in the acrylic acid solution supplied to the crystallizer (a) of the first stage crystallization unit, that is, the final yield of acrylic acid was 69.8%.

[0090] Example 2

[0091] Compared with Example 1, in Example 2, the crystallization temperature in the crystallizer (a) of the second-stage crystallization unit is -2°C, the mass flow ratio of the first mother liquor flow separated from the solid-liquid separator of the first-stage crystallization unit to the second mother liquor flow is 2.4:7.6, and the mass flow ratio of the first mother liquor flow separated from the solid-liquid separator (b) of the second-stage crystallization unit to the second mother liquor flow is 0.5:9.5.

[0092] As a result, acrylic acid (97.5 wt%), acetic acid (1.2 wt%), and water (1.3 wt%) were contained in the purified acrylic acid, and the final yield of acrylic acid was 72.5%.

[0093] Comparative Example

[0094] Comparative Example 1

[0095] according to Figure 2 The process flow chart shown was simulated using Aspen Plus simulator available from Aspen Technology, Inc. to simulate the acrylic acid preparation process.

[0096] In Comparative Example 1, the mother liquor separated in each solid-liquid separator (b) of the first-stage crystallization unit and the second-stage crystallization unit was not separated, and the mother liquor was supplied to the mother liquor treatment process and the crystallizer (a) of the first-stage crystallization unit, respectively.

[0097] Specifically, an acrylic acid solution prepared in the same composition as in Example 1 was introduced into the crystallizer (a) of the first-stage crystallization unit to obtain a suspension containing acrylic acid crystals. The acrylic acid solution had the same composition as in Example 1. The crystallization temperature in the crystallizer (a) of the first-stage crystallization unit was -0.2°C. The obtained suspension was supplied from the crystallizer (a) of the first-stage crystallization unit to the solid-liquid separator (b) of the first-stage crystallization unit. At this time, the ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second-stage crystallization unit was 30% by weight.

[0098] In the solid-liquid separator (b) of the first-stage crystallization unit, the suspension obtained in the crystallizer (a) of the first-stage crystallization unit is separated into acrylic acid crystals and a mother liquor. At this time, in the solid-liquid separator (b) of the first-stage crystallization unit, solid-liquid separation of the suspension is performed by filtration. The acrylic acid crystals separated in the solid-liquid separator (b) of the first-stage crystallization unit are melted to obtain a concentrated acrylic acid solution. The concentrated acrylic acid solution from the solid-liquid separator (b) of the first-stage crystallization unit is supplied to the crystallizer (a) of the second-stage crystallization unit, and the mother liquor separated in the solid-liquid separator (b) of the first-stage crystallization unit is introduced into a mother liquor treatment process.

[0099] In the crystallizer (a) of the second stage crystallization unit, the concentrated acrylic acid solution from the solid-liquid separator (b) of the first stage crystallization unit was crystallized to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was 11.1°C.

[0100] The obtained suspension is supplied from the crystallizer (a) of the second stage crystallization unit to the solid-liquid separator (b) of the second stage crystallization unit. In the solid-liquid separator (b) of the second stage crystallization unit, the suspension obtained in the crystallizer (a) of the second stage crystallization unit is separated into acrylic acid crystals and mother liquor. At this time, in the solid-liquid separator (b) of the second stage crystallization unit, solid-liquid separation of the suspension is performed by filtration. The separated mother liquor is supplied from the solid-liquid separator (b) of the second stage crystallization unit to the crystallizer (a) of the first stage crystallization unit. The acrylic acid crystals separated in the solid-liquid separator (b) of the second stage crystallization unit are melted to obtain a concentrated acrylic acid solution as purified acrylic acid.

[0101] As a result, acrylic acid (99.6 wt%), acetic acid (0.29 wt%), and water (0.15 wt%) were contained in the purified acrylic acid, and the final yield of acrylic acid was 13.8%.

[0102] Compared with Example 1, Comparative Example 1 is a case where the mother liquid separated in the solid-liquid separators of the first and second stage crystallization units is not separated, and it is confirmed that the final yield of acrylic acid is the lowest.

[0103] Comparative Example 2

[0104] Compared with Comparative Example 1, in Comparative Example 2, the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit was -4.5°C, and the ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the first-stage crystallization unit was 50% by weight.

[0105] As a result, mixing was not performed in the crystallizer (a) of the first-stage crystallization unit, and therefore, the crystallization process did not proceed, and acrylic acid was not obtained.

[0106] Comparative Example 3

[0107] according to Figure 3 The process flow chart shown was simulated using Aspen Plus simulator available from Aspen Technology, Inc. to simulate the acrylic acid preparation process.

[0108] Specifically, an acrylic acid solution having the same composition as that of Example 1 was introduced into the crystallizer (a) of the first-stage crystallization unit. In the crystallizer (a) of the first-stage crystallization unit, the acrylic acid solution was crystallized to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit was -2.6°C. The ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the first-stage crystallization unit was 30% by weight.

[0109] The obtained suspension is supplied from the crystallizer (a) of the first stage crystallization unit to the solid-liquid separator (b) of the first stage crystallization unit. In the solid-liquid separator (b) of the first stage crystallization unit, the suspension obtained in the crystallizer (a) of the first stage crystallization unit is separated into acrylic acid crystals and mother liquor. At this time, in the solid-liquid separator (b) of the first stage crystallization unit, the solid-liquid separation of the suspension is performed by filtration. At the same time, the acrylic acid crystals separated in the solid-liquid separator (b) of the first stage crystallization unit are melted to obtain a concentrated acrylic acid solution.

[0110] The separated mother liquor was supplied from the solid-liquid separator (b) of the first stage crystallization unit to the crystallizer (a) of the second stage crystallization unit and crystallized to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was -7.7° C. The ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second stage crystallization unit was 30% by weight.

[0111] The obtained suspension is supplied from the crystallizer (a) of the second stage crystallization unit to the solid-liquid separator (b) of the second stage crystallization unit, and acrylic acid crystals and mother liquor are separated. At this time, in the solid-liquid separator (b) of the second stage crystallization unit, solid-liquid separation of the suspension is performed by filtration. The mother liquor separated in the solid-liquid separator (b) of the second stage crystallization unit is discharged.

[0112] At the same time, acrylic acid crystals separated in the solid-liquid separator (b) of the second-stage crystallization unit are melted to obtain a concentrated acrylic acid solution, a mixed stream is formed from the concentrated acrylic acid solution separated in the solid-liquid separator (b) of the second-stage crystallization unit and the concentrated acrylic acid solution separated in the solid-liquid separator (b) of the first-stage crystallization unit, and the mixed stream is obtained as purified acrylic acid.

[0113] The purified acrylic acid contained acrylic acid (97.1 wt%), acetic acid (1.1 wt%) and water (1.7 wt%), and the final yield of acrylic acid was 59.6%.

[0114] As a result, in Comparative Example 3, it could be confirmed that the purity of purified acrylic acid and the final yield of acrylic acid were decreased compared with Examples.

[0115] Comparative Example 4

[0116] according to Figure 4 The process flow chart shown was simulated using Aspen Plus simulator available from Aspen Technology, Inc. to simulate the acrylic acid preparation process.

[0117] Specifically, an acrylic acid solution having the same composition as that of Example 1 was introduced into the crystallizer (a) of the first-stage crystallization unit. In the crystallizer (a) of the first-stage crystallization unit, the acrylic acid solution was crystallized to obtain a suspension containing acrylic acid crystals. At this time, the crystallization temperature in the crystallizer (a) of the first-stage crystallization unit was -3.0°C. The ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the first-stage crystallization unit was 30% by weight.

[0118] The obtained suspension is supplied from the crystallizer (a) of the first stage crystallization unit to the solid-liquid separator (b) of the first stage crystallization unit. In the solid-liquid separator (b) of the first stage crystallization unit, the suspension obtained in the crystallizer (a) of the first stage crystallization unit is separated into acrylic acid crystals and mother liquor. At this time, in the solid-liquid separator (b) of the first stage crystallization unit, the solid-liquid separation of the suspension is performed by filtration. At the same time, the acrylic acid crystals separated in the solid-liquid separator (b) of the first stage crystallization unit are melted to obtain a concentrated acrylic acid solution.

[0119] The mother liquor separated in the solid-liquid separator (b) of the first-stage crystallization unit is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream and the second mother liquor stream are circulated to the crystallizer (a) of the first-stage crystallization unit and the crystallizer (a) of the second-stage crystallization unit, respectively. At this time, the mass flow ratio of the first mother liquor stream separated from the solid-liquid separator (b) of the first-stage crystallization unit to the second mother liquor stream is 0.9:9.1.

[0120] A suspension containing acrylic acid crystals was obtained by the crystallization process performed in the crystallizer (a) of the second stage crystallization unit. At this time, the crystallization temperature in the crystallizer (a) of the second stage crystallization unit was -13° C. The ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from the crystallizer (a) of the second stage crystallization unit was 30% by weight.

[0121] After that, the obtained suspension is supplied from the crystallizer (a) of the second stage crystallization unit to the solid-liquid separator (b) of the second stage crystallization unit. In the solid-liquid separator (b) of the second stage crystallization unit, the suspension obtained in the crystallizer (a) of the second stage crystallization unit is separated into acrylic acid crystals and mother liquor. At this time, in the solid-liquid separator (b) of the second stage crystallization unit, the solid-liquid separation of the suspension is performed by filtration. At the same time, the acrylic acid crystals separated in the solid-liquid separator (b) of the second stage crystallization unit are melted to obtain a concentrated acrylic acid solution.

[0122] The mother liquor separated in the solid-liquid separator (b) of the second-stage crystallization unit is divided into a first mother liquor stream and a second mother liquor stream, and the first mother liquor stream and the second mother liquor stream are respectively supplied to the crystallizer (a) of the second-stage crystallization unit and the outside of the system. At this time, the mass flow ratio of the first mother liquor stream and the second mother liquor stream separated from the solid-liquid separator (b) of the second-stage crystallization unit is 1:1.

[0123] Meanwhile, a mixed stream is formed from the concentrated acrylic acid solution separated in the solid-liquid separator (b) of the second stage crystallization unit and the concentrated acrylic acid solution separated in the solid-liquid separator (b) of the first stage crystallization unit, and the mixed stream is obtained as purified acrylic acid.

[0124] The purified acrylic acid contained acrylic acid (96.6 wt%), acetic acid (1.3 wt%) and water (2.1 wt%), and the final yield of acrylic acid was 73.6%.

[0125] As a result, in Comparative Example 4, it could be confirmed that the purity of the purified acrylic acid, that is, the content of acrylic acid contained in the purified acrylic acid was the lowest.

[0126] Comparative Example 5

[0127] Compared with Example 1, in Comparative Example 5, the crystallization temperature in the crystallizer of the first-stage crystallization unit is -5°C, the mass flow ratio of the first mother liquor flow separated from the solid-liquid separator of the first-stage crystallization unit to the second mother liquor flow is 4.4:5.6, and the mass flow ratio of the first mother liquor flow separated from the solid-liquid separator of the second-stage crystallization unit is 2.5:7.5.

[0128] As a result, the purified acrylic acid contained acrylic acid (99.0 wt%), acetic acid (0.57 wt%) and water (0.38 wt%), and the final yield of acrylic acid was 45.8%.

[0129] Compared with Example 1, Comparative Example 5 is a case where the crystallization temperature in the crystallizer of the first stage crystallization unit is higher, and it can be confirmed that the purity of acrylic acid in the purified acrylic acid is the same as that in Example 1, but the final yield of acrylic acid is significantly reduced.

[0130] [Explanation of Reference Numerals]

[0131] (a) Crystallizer

[0132] (b) Solid-liquid separator

Claims

1. A method for preparing acrylic acid, the method comprising a multi-stage crystallization process performed by two or more crystallization units connected in series, each crystallization unit comprising a crystallizer and a solid-liquid separator, the method comprising: In the crystallizers of each stage, acrylic acid contained in the acrylic acid solution introduced into the crystallizers of each stage is crystallized to obtain a suspension containing acrylic acid crystals, and the suspension is supplied to the solid-liquid separators of each stage, In the solid-liquid separators at each stage, the suspension is separated into solid and liquid to obtain a concentrated acrylic acid solution and a mother liquor. dividing the mother liquor into a first mother liquor stream and a second mother liquor stream, recycling the first mother liquor stream to a crystallizer or a mother liquor treatment process, the crystallizer being located at a stage preceding a stage including a solid-liquid separator for separating the mother liquor, and recycling the second mother liquor stream to a crystallizer being located at a stage including a solid-liquid separator for separating the mother liquor, introducing the concentrated acrylic acid solution into a crystallizer located at a subsequent stage of a stage including a solid-liquid separator for separating the concentrated acrylic acid solution, and Purified acrylic acid is obtained from the solid-liquid separator of the last crystallization unit among the two or more crystallization units, Wherein, the first-stage crystallization unit among the two or more crystallization units comprises a crystallizer with a crystallization temperature of -20 to -10°C.

2. The method according to claim 1, wherein: The content of acrylic acid contained in the acrylic acid solution introduced into the crystallizer of the first-stage crystallization unit is 80 to 95% by weight.

3. The method according to claim 1, wherein: The ratio of the mass of the acrylic acid crystals contained in the suspension to the mass of the suspension discharged from each stage of the crystallizer is 10 to 40% by weight.

4. The method according to claim 1, wherein: The mass flow ratio of the first mother liquid stream to the second mother liquid stream is 0.5:9.5 to 9.5:0.

5.

5. The method according to claim 1, wherein: The two or more crystallization units are comprised in two stages in total, The crystallization temperature in the crystallizer of the first stage crystallization unit is -20 to -10°C. The crystallization temperature in the crystallizer of the second stage crystallization unit is 0 to 12°C.

6. The method according to claim 5, wherein: The mass flow ratio of the first mother liquid stream separated from the solid-liquid separator of the first stage crystallization unit to the second mother liquid stream is 0.5:9.5 to 1:1, The mass flow ratio of the first mother liquid stream and the second mother liquid stream separated from the solid-liquid separator of the second-stage crystallization unit is 1:1 to 9:

1.

7. The method according to claim 1, wherein: The first-stage crystallization unit includes an auxiliary crystallizer disposed at a front stage of the crystallizer.

8. The method according to claim 7, wherein: The crystallization temperature in the auxiliary crystallizer is -5 to 5°C.

9. The method according to claim 1, wherein: The acrylic acid solution introduced into the crystallizer of the first-stage crystallization unit is obtained by contacting a mixed gas containing acrylic acid with an absorption solvent.

10. The method according to claim 9, wherein: The mixed gas containing acrylic acid is a reaction product obtained by subjecting reactants containing an oxygen-containing gas and a raw material compound to a gas-phase oxidation reaction.

11. The method according to claim 10, wherein: The raw material compound is one or more compounds selected from propane, propylene, butane, isobutylene, tert-butylene and (meth)acrolein.

12. The method according to claim 1, wherein: The concentrated acrylic acid solution is obtained in the solid-liquid separators at each stage, comprising: Obtaining acrylic acid crystals by separating the suspension into solid and liquid in the solid-liquid separators at each stage; and The concentrated acrylic acid solution is obtained by melting the acrylic acid crystals.

13. The method according to claim 1, wherein: The mother liquor treatment process includes one or more of a purging and an acrylic acid purification process.

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