Method for producing high-purity (meth)acrylic acid

Abstract

The present invention provides a method for producing (meth)acrylic acid, comprising the steps of: contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain an aqueous (meth)acrylic acid solution; supplying the aqueous (meth)acrylic acid solution to a crystallization apparatus and crystallizing it to obtain purified (meth)acrylic acid; and supplying a mother liquor separated from the purified (meth)acrylic acid to a water separation tower; separating the water in the water separation tower into an upper outlet stream from the water separation tower containing water and a lower outlet stream from the water separation tower containing (meth)acrylic acid and high-boiling by-products; and supplying the lower outlet stream from the water separation tower to a high-boiling by-product separation tower and supplying the upper outlet stream from the high-boiling by-product separation tower containing (meth)acrylic acid to the crystallization apparatus.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0109449 filed on August 30, 2022 and Korean Patent Application No. 10-2023-0107015 filed on August 16, 2023, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a method for producing high-purity (meth)acrylic acid. [Background technology]

[0003] (Meth)acrylic acid is generally produced by a method of subjecting compounds such as propane, propylene, (meth)acrolein, etc. to a gas-phase oxidation reaction in the presence of a catalyst. For example, in a reactor, in the presence of a suitable catalyst, propane, propylene, etc. are converted to (meth)acrylic acid via (meth)acrolein by a gas-phase oxidation reaction, and a mixed gas containing (meth)acrylic acid, unreacted propane or propylene, (meth)acrolein, inert gas, carbon dioxide, water vapor, and various organic by-products of the reaction (acetic acid, low-boiling by-products, high-boiling by-products, etc.) is obtained in the downstream of the reactor.

[0004] The (meth)acrylic acid-containing mixed gas is contacted with an absorption solvent such as water in an absorption tower to recover an aqueous (meth)acrylic acid solution. Subsequent processes for recovering the (meth)acrylic acid contained in the aqueous (meth)acrylic acid solution typically involve extraction, distillation, and purification. To improve the recovery efficiency of such (meth)acrylic acid, various methods for adjusting process conditions or process sequences have been proposed.

[0005] However, since the specific heat of the absorption solvent such as water used in the absorption tower is high, a considerable amount of energy is required to separate by-products from the aqueous (meth)acrylic acid solution containing the absorption solvent by a process such as distillation. On the other hand, when the subsequent process is simplified and simplified to reduce the amount of energy used, it is possible to reduce the amount of energy used, but it is difficult to obtain high-purity (meth)acrylic acid.

[0006] Furthermore, acetic acid and high-boiling by-products, which are the main by-products in the (meth)acrylic acid production process, are separated and removed to prevent their accumulation in the system, but this process causes a loss of the desired product, (meth)acrylic acid.

[0007] Therefore, there is an urgent need to introduce a technology that can minimize the loss of high-purity (meth)acrylic acid from the aqueous (meth)acrylic acid solution and reduce the amount of energy used when separating (meth)acrylic acid and by-products throughout the entire process. Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a method for recovering (meth)acrylic acid, which can ensure a high recovery rate of (meth)acrylic acid and can further reduce the amount of energy used in the purification process, in order to solve the problems mentioned in the Background of the Invention above. [Means for solving the problem]

[0009] According to one embodiment of the present invention for solving the above-mentioned problems, there is provided a method for producing (meth)acrylic acid, comprising the steps of: contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain an aqueous solution of (meth)acrylic acid; supplying the aqueous solution of (meth)acrylic acid to a crystallization apparatus and crystallizing it to obtain purified (meth)acrylic acid; and supplying a mother liquor separated from the purified (meth)acrylic acid to a water separation tower; separating the water in the water separation tower into an upper outlet stream from the water separation tower containing water and a lower outlet stream from the water separation tower containing (meth)acrylic acid and high-boiling by-products; and supplying the lower outlet stream from the water separation tower to a high-boiling by-product separation tower and supplying the upper outlet stream from the high-boiling by-product separation tower containing (meth)acrylic acid to the crystallization apparatus. [Effects of the Invention]

[0010] According to the method for producing (meth)acrylic acid according to the present invention, the amount of water in the system is minimized in the process after the absorption tower, and the aqueous (meth)acrylic acid solution discharged from the absorption tower is supplied to a crystallizer to obtain high-purity (meth)acrylic acid. In the subsequent process, the crystallization mother liquor is subjected to azeotropic distillation, thereby reducing energy consumption, and the loss of (meth)acrylic acid can be reduced by efficiently removing acetic acid and high-boiling by-products.

[0011] For this reason, a water separation tower and a layer separation device are provided after the absorption tower to separate and remove the by-product acetic acid, and the loss of (meth)acrylic acid from the top of the absorption tower can be reduced compared to when all of the acetic acid from the top of the absorption tower is discharged.

[0012] Furthermore, high-boiling by-products are separated from the water separation tower and thereafter to prevent accumulation of high-boiling by-products in the system, thereby making it possible to obtain purified (meth)acrylic acid with high purity, and the overhead discharge stream of the high-boiling by-products can be supplied again to crystallization, thereby further reducing loss of (meth)acrylic acid. [Brief explanation of the drawings]

[0013] [Figure 1]1 is a process flow chart showing a method for producing (meth)acrylic acid according to one embodiment of the present invention. [Figure 2] 1 is a process flow chart showing a method for producing (meth)acrylic acid according to a comparative example of the present invention. [Figure 3] 1 is a process flow chart showing a method for producing (meth)acrylic acid according to a comparative example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] 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.

[0015] 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.

[0016] Meanwhile, in the present invention, in apparatuses such as an absorption tower, a degassing tower, a distillation tower or column, and a crystallization apparatus, the "lower part" of the apparatus means, unless otherwise specified, a point 95% to 100% below the top of the apparatus, specifically the lowest end (bottom). Similarly, the "upper part" of the apparatus means, unless otherwise specified, a point 0% to 5% below the top of the apparatus, specifically the highest part (top).

[0017] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0018] According to the present invention, there is provided a method for producing (meth)acrylic acid, comprising the steps of: contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain an aqueous (meth)acrylic acid solution; supplying the aqueous (meth)acrylic acid solution to a crystallization apparatus and crystallizing it to obtain purified (meth)acrylic acid; and supplying a mother liquor separated from the purified (meth)acrylic acid to a water separation tower; separating the water in the water separation tower into an upper outlet stream from the water separation tower containing water and a lower outlet stream from the water separation tower containing (meth)acrylic acid and high-boiling by-products; and supplying the lower outlet stream from the water separation tower to a high-boiling by-product separation tower and supplying the upper outlet stream from the high-boiling by-product separation tower containing (meth)acrylic acid to the crystallization apparatus.

[0019] Hereinafter, each step that can be included in an embodiment of the present invention will be described with reference to FIG.

[0020] First, a method for producing (meth)acrylic acid according to one embodiment of the present invention may include contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain an aqueous (meth)acrylic acid solution. Here, the mixed gas containing (meth)acrylic acid is a general term for the gas phase components discharged from reactor 10, which produces (meth)acrylic acid by a gas-phase oxidation reaction. Specifically, the mixed gas may contain (meth)acrylic acid, unreacted raw material compounds, (meth)acrolein, inert gases, carbon monoxide, carbon dioxide, water vapor, and various organic by-products (e.g., acetic acid, low-boiling by-products, high-boiling by-products, etc.). Here, "light ends" or "heavies" refer to a type of by-product that may be generated during the production and recovery process of the target (meth)acrylic acid, and may be a compound with a molecular weight smaller or larger than that of (meth)acrylic acid.

[0021] Specifically, the mixed gas containing (meth)acrylic acid can be produced as follows.

[0022] First, a reaction gas containing an oxygen-containing gas and a raw material compound is supplied to a reactor 10 equipped with a catalyst via a reaction gas supply line 1, and a gas phase oxidation reaction is carried out in the reactor 10 in the presence of the catalyst to obtain a mixed gas containing the (meth)acrylic acid.

[0023] Here, the oxygen-containing gas may be air. The raw material compound may be one or more compounds selected from the group consisting of propane, propylene, butane, i-butylene, t-butylene, and (meth)acrolein, and specifically, the raw material compound may include propylene. Meanwhile, the reaction gas supplied to the reactor 10 may further include a recycled gas recovered from the top of the absorption tower 100 and recycled. Therefore, the mixed gas containing (meth)acrylic acid may be a reaction product of a gas-phase oxidation reaction of reactants including air, the raw material compound, and the recycled gas in the reactor 10.

[0024] The recycle gas may originate from the upper portion of the absorber 100, which will be described later. That is, the mixed gas comes into contact with water, which is an absorption solvent, in the absorber 100, and non-condensable gases not dissolved in the water may be discharged as an upper discharge stream 110 of the absorber 100. The non-condensable gases may include impurities such as acetic acid, inert gases, unreacted raw material compounds, and a minimum content of (meth)acrylic acid.

[0025] That is, when acetic acid is discharged from the top of the absorber 100, the content of (meth)acrylic acid discharged from the top of the absorber 100 tends to increase as the amount of acetic acid discharged increases. This means a loss of (meth)acrylic acid. As will be described later, according to the present invention, the water separation tower and layer separation device subsequent to the absorber can further separate and remove acetic acid from the system, and it is not necessary to forcibly discharge acetic acid from the system as the top discharge stream 110 of the absorber. Specifically, only an amount of acetic acid sufficient to minimize the content of (meth)acrylic acid in the top discharge stream 110 of the absorber can be discharged as the top discharge stream 110. This minimizes the content of (meth)acrylic acid lost when discharged from the top of the absorber 100.

[0026] Alternatively, a portion 3 of the absorber top discharge stream 110 may be fed to a cooling tower 20, and the remainder may be fed to a waste gas incinerator for disposal.

[0027] The cooling tower 20 is provided with a water supply line 5 at its top, and water used as an absorption solvent in the absorption tower can be supplied to the cooling tower 20 from the water supply line 5. In the cooling tower 20, the water can come into contact with non-condensable gases contained in a portion 3 of the upper discharge stream 110 of the absorption tower. As described above, the non-condensable gases can include acetic acid and a minimum amount of (meth)acrylic acid, and these components can be dissolved in the water, which can be discharged as a lower discharge stream from the cooling tower 20 in the form of an aqueous solution.

[0028] A portion 6 of the bottom discharge stream of the cooling tower 20 can then be fed to the absorber 100, and the remainder can be cooled via a heat exchanger and then recycled to the cooling tower.

[0029] That is, the water required in the absorption tower 100 can be supplied through a water supply line 5 provided at the top of the cooling tower 20. The water can specifically include tap water, deionized water, etc., and can also include circulating process water introduced from other processes (e.g., aqueous phase recycled from the extraction process and / or distillation process). The absorption solvent can also contain a trace amount of organic by-products (e.g., acetic acid) introduced from other processes.

[0030] Meanwhile, most of the acetic acid contained in the non-condensable gases due to contact with water in the cooling tower 20 is dissolved in water and removed, and the gas that does not dissolve in water is discharged as a recycled gas through a recycled gas transfer line 4 provided at the top of the cooling tower 20. The recycled gas can be supplied to the reactor 10 so that it can be used in the gas-phase oxidation reaction for producing (meth)acrylic acid, which is carried out in the reactor. The recycled gas can be mixed with the reaction gas and supplied to the reactor, and can be supplied to the reactor through a line 4 separate from the line 1 through which the reaction gas is supplied.

[0031] Furthermore, by lowering the temperature inside the cooling tower 20, the water content in the recycle gas circulated from the cooling tower 20 to the reactor can be reduced. That is, by reducing the moisture (water) content in the recycle gas, the water content in the stream supplied from the reactor 10 to the absorber 100 can be reduced, and thus the water content in the absorber 100 can be reduced. The water discharged from the reactor may contain dissolved various by-products that are inappropriate for introduction into the crystallization apparatus, and if there is an excess amount of water in the absorber 100, it is difficult to obtain a highly concentrated aqueous (meth)acrylic acid solution. By reducing the water content in the recycle gas, it becomes possible to introduce the discharge stream from the absorber 100 into the crystallization apparatus without a separate water distillation process, as will be described later.

[0032] Specifically, when the absorption solvent is water, the moisture content in the recycle gas may be 1 wt% to 10 wt%, specifically 3 wt% to 5 wt%. If the moisture content in the recycle gas is less than 1 wt%, operating costs, particularly costs related to the installation and operation of a cooler, may increase. On the other hand, if the moisture content in the recycle gas exceeds 10 wt%, the moisture content supplied to the absorption tower 100 via the reactor 10 increases, making it impossible to obtain high-purity (meth)acrylic acid. Furthermore, it may be difficult to easily obtain high-purity (meth)acrylic acid through a crystallizer without a water distillation process for the aqueous (meth)acrylic acid solution discharged from the absorption tower. Furthermore, the increased amount of moisture (water) in subsequent processes may increase energy consumption when separating and distilling it.

[0033] For this purpose, the temperature at the top of the cooling tower 20 may be 35°C to 55°C, specifically 35°C to 45°C. If the temperature at the top of the cooling tower 20 is less than 35°C, an excessive amount of refrigerant may be used to reduce the moisture content in the recirculated gas, or a lower-temperature refrigerant may be required, which may not be very beneficial in terms of efficient energy use. On the other hand, if the temperature at the top of the cooling tower 20 exceeds 55°C, the content of the absorption solvent (moisture) contained in the recirculated gas transfer line 4 may increase excessively, making it difficult to obtain a highly concentrated aqueous (meth)acrylic acid solution discharged from the absorption tower 100. The temperature at the top of the cooling tower 20 is controlled by a heat exchanger provided at the bottom of the cooling tower 20. Specifically, this may be achieved by circulating a portion of the bottom stream of the cooling tower 20 through the heat exchanger and the cooling tower 20. Meanwhile, the top of the cooling tower 20 may be operated under atmospheric pressure operating conditions.

[0034] Thereafter, a step can be carried out in which the mixed gas containing the (meth)acrylic acid is supplied to an absorption tower 100 via a reactor discharge line 2 and brought into contact with water in the absorption tower 100 to obtain an aqueous (meth)acrylic acid solution. Specifically, a mixed gas containing (meth)acrylic acid, organic by-products, and water vapor produced by a synthesis reaction of (meth)acrylic acid is brought into contact with water, which is an absorption solvent, in the absorption tower 100 to obtain an aqueous (meth)acrylic acid solution.

[0035] The type of the absorber 100 may be determined taking into consideration the contact efficiency between the mixed gas and the absorbing solvent, and may be, for example, a packed column type absorber or a multistage tray type absorber. The packed column type absorber may have a filler such as a lashing ring, a pall ring, a saddle, gauze, or a structured packing applied thereto.

[0036] In consideration of the efficiency of the absorption process, the mixed gas 2 may be supplied to the lower part of the absorption tower 100, and water as an absorption solvent may be supplied to the upper part of the absorption tower 100.

[0037] Meanwhile, the absorption tower 100 may be operated under an internal pressure of 1 to 1.5 bar or 1 to 1.3 bar and an internal temperature of 50 to 120°C or 50 to 100°C, taking into consideration the condensation conditions of (meth)acrylic acid and the water content due to saturated water vapor pressure.

[0038] Meanwhile, according to one embodiment of the present invention, the (meth)acrylic acid aqueous solution is obtained through an absorption process performed in the absorber 100, and the (meth)acrylic acid aqueous solution may be discharged as a lower discharge stream 120 of the absorber 100.

[0039] Meanwhile, the top discharge stream of the absorber 100 may contain non-condensable gases that are not dissolved in water, which is the absorption solvent in the absorber 100, as described above. The non-condensable gases may include acetic acid, inert gases, unreacted raw material compounds, and a minimum amount of (meth)acrylic acid.

[0040] In the past, discharging as much acetic acid as possible as the top discharge stream from the absorber 100 prevented acetic acid from concentrating in the system and simplified subsequent processes after the absorber. However, when the amount of acetic acid discharged from the top of the absorber 100 increased beyond a certain level, the content of (meth)acrylic acid discharged from the top of the absorber 100 also increased, resulting in a problem of increased loss of (meth)acrylic acid in the absorber. Therefore, the present invention minimizes the content of (meth)acrylic acid lost in the absorber by controlling the amount of acetic acid contained in the top discharge stream from the absorber 100. That is, the content of acetic acid in the top discharge stream from the absorber can be controlled so as to minimize the content of (meth)acrylic acid lost to the top of the absorber. In addition, acetic acid can be further separated and removed using a water separation tower and layer separation device after the absorber, which will be described later, thereby solving the problem of acetic acid accumulating in the system and acting as an impurity.

[0041] In this regard, the flow rate ratio of acetic acid discharged from the top of the absorber based on the flow rate of acetic acid introduced into the absorber may be 20 wt% to 80 wt%, specifically 30 wt% to 60 wt%, while the content of (meth)acrylic acid contained in the top discharge stream of the absorber may be 0.1 wt% to 0.5 wt%, specifically 0.2 wt% to 0.3 wt%.

[0042] Meanwhile, a method for producing (meth)acrylic acid according to one embodiment of the present invention may include the steps of supplying the aqueous (meth)acrylic acid solution to a crystallizer 300, crystallizing the solution to obtain purified (meth)acrylic acid, and supplying a mother liquor separated from the purified (meth)acrylic acid to a water separation tower.

[0043] Specifically, the (meth)acrylic acid aqueous solution can be supplied as a bottom discharge stream from the absorber 100 to the crystallizer 300 via the absorber discharge line 120 .

[0044] Meanwhile, the (meth)acrylic acid aqueous solution can be directly supplied to the crystallization apparatus 300. Specifically, before the (meth)acrylic acid aqueous solution is introduced into the crystallization apparatus, the (meth)acrylic acid aqueous solution can be supplied to the degassing tower 150 to remove low-boiling by-products including acrolein, and then supplied to the crystallization apparatus 300.

[0045] The acrolein may be used as a raw material for producing (meth)acrylic acid, or may be generated as a product during a gas-phase oxidation reaction for producing (meth)acrylic acid. To obtain high-purity purified (meth)acrylic acid in the crystallizer 300, it is preferable to remove and separate low-boiling by-products such as acrolein before crystallization. The gas phase fraction containing the low-boiling by-products from the degassing tower 150 can be recycled to the absorption tower 100, and the aqueous (meth)acrylic acid solution from which the low-boiling by-products have been degassed can be introduced into the crystallizer 300 as the bottom discharge stream 160 of the degassing tower 150.

[0046] In this case, the content of (meth)acrylic acid in the lower discharge stream 160 of the degassing tower may be 85 wt% to 99 wt%, specifically 85 wt% to 95 wt%. This is a higher level than the content of (meth)acrylic acid in the aqueous (meth)acrylic acid solution discharged from an existing absorption tower. In particular, by setting the content of (meth)acrylic acid in the aqueous (meth)acrylic acid solution to 85 wt% or more, the aqueous (meth)acrylic acid solution can be directly supplied to the crystallization apparatus 300 without undergoing a separate purification or separation process, thereby enabling overall process energy savings and enabling high-purity (meth)acrylic acid to be obtained in the crystallization apparatus 300.

[0047] An aqueous (meth)acrylic acid solution having such a high (meth)acrylic acid content can be achieved by, for example, optimally controlling the operating conditions of the cooling tower 20 and the absorption tower 100 according to the material components and their contents in the system, thereby minimizing the water content in the absorption tower 100. That is, an aqueous (meth)acrylic acid solution having a high (meth)acrylic acid concentration can be realized by minimizing the absorption solvent component in the recycle gas circulated from the cooling tower 20 to the reactor 10 and minimizing the input and consumption amounts of water supplied to the cooling tower 20 and the absorption tower 100.

[0048] Meanwhile, the (meth)acrylic acid contained in the (meth)acrylic acid aqueous solution supplied to the crystallization apparatus 300 can be recrystallized through a crystallization process to obtain high-purity crystallized (meth)acrylic acid. In this specification, the high-purity crystallized (meth)acrylic acid obtained through recrystallization may be referred to as purified (meth)acrylic acid. This crystallization process can be carried out under conventional conditions.

[0049] In the present invention, the crystallization method for obtaining a product by crystallization can be suspension crystallization or layer crystallization without limitation, and can be either continuous or batchwise, and can be carried out in one or more stages. As a non-limiting example, the (meth)acrylic acid can be provided as purified (meth)acrylic acid by dynamic crystallization.

[0050] Specifically, to dynamically crystallize the (meth)acrylic acid before crystallization, the (meth)acrylic acid aqueous solution is first flowed onto the inner wall of a tube in the form of a falling film. The temperature of the tube is then adjusted to below the freezing point of (meth)acrylic acid to form crystals on the inner wall of the tube. The temperature of the tube is then raised to near the freezing point of (meth)acrylic acid to sweat approximately 5 wt. % of the (meth)acrylic acid. The sweated mother liquor is then removed from the tube, and the crystals formed on the inner wall of the tube are collected to obtain high-purity purified (meth)acrylic acid. The mother liquor may refer to the remaining solution from which purified (meth)acrylic acid has been removed from the (meth)acrylic acid aqueous solution introduced into the crystallization apparatus 300.

[0051] The separation of the mother liquor and the crystallized (meth)acrylic acid can be carried out using a high-liquid separation device, such as a belt filter, a centrifuge, etc. The purified (meth)acrylic acid can be recovered as a (meth)acrylic acid recovery stream 310, and the mother liquor can be supplied to the water separation tower 400 via a mother liquor recovery line 320.

[0052] The mother liquor supplied to the water separation tower 400 via the mother liquor recovery line 320 contains (meth)acrylic acid, water, acetic acid, and high-boiling by-products. Here, the (meth)acrylic acid contained in the mother liquor is the residual (meth)acrylic acid that has not been crystallized in the crystallization apparatus 300, and can be separated in a high-boiling by-product separation tower 500 (described later) and recycled to the crystallization apparatus 300.

[0053] The mother liquor may contain 50 to 90% by weight, specifically 60 to 80% by weight, of (meth)acrylic acid, and 10 to 50% by weight, specifically 20 to 40% by weight of water.

[0054] Furthermore, the flow rate ratio of water in the mother liquor introduced into the water separation tower 400 can be 30% by weight to 50% by weight, specifically 35% by weight to 45% by weight, based on the flow rate of water introduced into the absorption tower.

[0055] The distillation step in the water separation tower 400 for the mother liquor supplied via the mother liquor recovery line 320 can be a step of azeotropically distilling the mother liquor to separate it into an upper fraction containing water and acetic acid and a lower fraction containing (meth)acrylic acid and high-boiling-point by-products.

[0056] According to the present invention, the distillation in the water separation column 400 is carried out in the presence of a hydrophobic azeotropic solvent, which is advantageous from a process standpoint because it allows the hydrophobic azeotropic solvent, water, and organic by-products (such as acetic acid) to be recovered simultaneously.

[0057] Here, the hydrophobic azeotropic solvent can form an azeotrope with water and acetic acid but not with (meth)acrylic acid, and any hydrocarbon solvent that satisfies the above physical properties can be used without limitation. In addition, the hydrophobic azeotropic solvent can have a boiling point lower than that of (meth)acrylic acid, preferably 10 to 120°C.

[0058] According to the present invention, the hydrophobic 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.

[0059] Meanwhile, the water separation tower 400 may be equipped with a packed column or a multi-stage column containing the above-mentioned packing material, preferably a sieve tray column or a dual flow tray column.

[0060] When the hydrophobic azeotropic solvent is introduced into the water separation tower 400, the azeotrope between (meth)acrylic acid and water is broken. Accordingly, the water and acetic acid in the mother liquor and the hydrophobic azeotropic solvent used in the azeotropic distillation form an azeotrope together, and can be recovered as an upper fraction of the water separation tower 400. In addition, a lower fraction containing (meth)acrylic acid and high-boiling by-products can be recovered from the lower part of the water separation tower 400.

[0061] The thus recovered upper fraction of the water separation tower can be supplied to the layer separation apparatus 450 via the upper discharge stream 410 of the water separation tower, and the lower fraction of the water separation tower can be supplied to the high-boiling by-product separation tower 500 via the lower discharge stream 420 of the water separation tower.

[0062] Here, the layer separator 450 is a liquid-liquid layer separator that separates immiscible fluids using gravity or centrifugal force due to differences in density, and a relatively light liquid may be separated into an upper portion of the layer separator 450 and a relatively heavy liquid into a lower portion of the layer separator 450. Specifically, the upper discharge stream 410 of the water separation tower supplied to the layer separator 450 may be separated into an organic layer containing the hydrophobic azeotropic solvent and an aqueous layer containing water and acetic acid.

[0063] The organic layer separated in the layer separator 450 can be supplied to the top of the water separator 400 and reused as a hydrophobic azeotropic solvent. At least a portion of the aqueous layer separated in the layer separator 450 can be supplied to the top of the absorber 100 and used as an absorbing solvent, and the remainder can be discharged as wastewater.

[0064] Here, the aqueous layer may contain acetic acid, and the concentration of acetic acid contained in the aqueous layer may vary depending on the type of hydrophobic azeotropic solvent and the reflux ratio of the column installed in the water separation tower 400. According to the present invention, the concentration of acetic acid contained in the aqueous layer may be 1 to 30 wt%, preferably 2 to 20 wt%, and more preferably 3 to 10 wt%.

[0065] That is, according to one embodiment of the present invention, acetic acid is discharged through the top discharge stream of the absorber 100, and at the same time, it can be discharged by azeotropic distillation performed through the water separation tower 400 and the layer separation device 450. Therefore, compared to a process in which acetic acid is removed only from the top of the absorber, acetic acid accumulated in the system can be removed more efficiently, thereby obtaining highly purified (meth)acrylic acid. Furthermore, compared to an attempt to discharge the entire amount of acetic acid in the system to the top of the absorber, process flexibility can be ensured, which has the advantage of minimizing the amount of (meth)acrylic acid lost from the top of the absorber.

[0066] More specifically, the total flow rate of acetic acid introduced into the absorber 100 may be equal to the sum of the flow rate of acetic acid in the top discharge stream of the absorber 100 and the flow rate of acetic acid in the stream branched off from the aqueous layer of the layer separator 450 and discharged.

[0067] Meanwhile, a method for producing (meth)acrylic acid according to one embodiment of the present invention may include a step of supplying a bottom discharge stream from the water separation tower 400 to a high-boiling by-product separation tower 500, and supplying an upper discharge stream from the high-boiling by-product separation tower 500 containing the (meth)acrylic acid to the crystallization apparatus 300.

[0068] The high-boiling by-product separation tower 500 distills the bottom discharge stream from the water separation tower 400 to separate it into a bottom fraction containing high-boiling by-products, and an upper fraction containing a high content of (meth)acrylic acid after the high-boiling by-products have been removed. The upper fraction can be supplied to the crystallization apparatus 300 via the high-boiling by-product separation tower top discharge stream 510, and the (meth)acrylic acid content in the high-boiling by-product separation tower top discharge stream 510 can be 90% to 99% by weight, specifically 95% to 99% by weight. That is, since the amount of water contained in each stream has already been reduced in the processes after the absorption tower 100, and a considerable amount of water is removed through the water separation tower 400, the water content in the high-boiling by-product separation tower top discharge stream 510 can be controlled to a low level, thereby producing a concentrated stream of (meth)acrylic acid that can be immediately introduced into the crystallization apparatus 300. Here, the upper discharge stream 510 of the high boiling by-product separation column may be introduced into the crystallization apparatus 300 by mixing it with the lower discharge stream 160 of the degassing column. By introducing the upper discharge stream 510 of the high boiling by-product separation column into the crystallization apparatus 300, the loss of (meth)acrylic acid can be reduced to the maximum.

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

[0070] Example 1 The (meth)acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, following the process flow illustrated in FIG.

[0071] Specifically, a reaction gas containing air and a raw material compound (propylene) was supplied to a reactor 10 equipped with a catalyst via a reaction gas supply line 1, and a recycle gas derived from a cooling tower 20 was supplied to the reactor 10 via a recycle gas transfer line 4. A gas-phase oxidation reaction carried out in the reactor 10 produced a mixed gas 2 containing (meth)acrylic acid (7.0 mol%), water (11.8 mol%), high boiling point substances (0.09 mol%), and inert gases (80.6 mol%).

[0072] The mixed gas 2 was introduced into the absorption tower 100 from the top to the 22nd stage at a temperature of 164°C. In the absorption tower 100, the mixed gas was contacted with an absorption solvent (water) to obtain an aqueous (meth)acrylic acid solution. The water introduced into the absorption tower 100 was supplied via the lower discharge stream 6 of the cooling tower and a water layer from a layer separation device 450 described below, and the water was supplied to the upper part of the absorption tower 100 at a mass flow rate of 5.8 wt% with respect to the flow rate of the mixed gas 2. The pressure at the upper part of the absorption tower 100 was 1.1 atmospheres, and the temperature at the lower part of the absorption tower 100 was 84°C.

[0073] In the absorber 100, non-condensable gas containing components not dissolved in water was separated as an absorber top discharge stream 110, a portion 3 of the absorber top discharge stream was supplied to a cooling tower 20, and the remainder was discharged to the outside of the system. Based on the flow rate of acetic acid introduced into the absorber 100, the mass flow ratio of acetic acid discharged to the outside of the system via the absorber top discharge stream was 39.6 wt%.

[0074] In the cooling tower 20, non-condensable gases contained in a portion 3 of the upper discharge stream from the absorber were dissolved in water. Here, the water was supplied through a water supply line 5. The gases not dissolved in water in the cooling tower 20 were supplied to the reactor 10 through a recycle gas transfer line 4, and a portion of the lower discharge stream 6 from the cooling tower containing water and the components dissolved in the water (acetic acid and the residual (meth)acrylic acid not dissolved in water in the absorber) was supplied to an absorber 100.

[0075] Meanwhile, the (meth)acrylic acid aqueous solution was supplied to a degassing tower 150 as a bottom discharge stream 120 from the absorption tower and degassed, and the low-boiling by-products were supplied to an absorption tower 100 as an upper discharge stream from the degassing tower. The (meth)acrylic acid aqueous solution from which the low-boiling by-products had been degassed was supplied to a crystallization apparatus 300 as a bottom discharge stream 160 from the degassing tower. The top discharge stream from the degassing tower was supplied to the absorption tower 100 at a flow rate of 25% by weight based on the absorption solvent (water) fed to the absorption tower 100. The composition of the bottom discharge stream 160 from the degassing tower included (meth)acrylic acid (89.5% by weight), acetic acid (1.8% by weight), water (7% by weight), furfural (0.8% by weight), and maleic acid (0.8% by weight).

[0076] The bottom discharge stream 160 from the degassing tower is mixed with the top discharge stream 510 from the high-boiling by-product separation tower described below and supplied to the crystallization apparatus 300, and the mixed stream contains (meth)acrylic acid (90.9 wt%), acetic acid (1.6 wt%), water (6.0 wt%), furfural (0.8 wt%) and maleic acid (0.7 wt%).

[0077] A (meth)acrylic acid recovery stream 310 containing (meth)acrylic acid was obtained by the crystallization process performed in the crystallization apparatus 300. The content of (meth)acrylic acid in the (meth)acrylic acid recovery stream 310 was 99.5 wt % or more, and finally, 99.5 wt % or more of (meth)acrylic acid was obtained from the crystallization apparatus.

[0078] The mother liquor 320 separated from (meth)acrylic acid in the crystallizer was supplied to a water separation tower 400. The mother liquor contained (meth)acrylic acid (64 wt%), water (23.7 wt%), acetic acid (6.3 wt%), and high-boiling point by-products (6.0 wt%), and the flow rate ratio of the water contained in the mother liquor based on the mass flow rate of water introduced into the absorption tower 100 was 39 wt%.

[0079] In the water separation tower 400, the mother liquor was azeotropically distilled in the presence of a hydrophobic azeotropic solvent (toluene) to obtain a water separation tower top effluent stream 410 containing acetic acid, the hydrophobic azeotropic solvent, and water, and a water separation tower bottom effluent stream 420 containing (meth)acrylic acid and high-boiling by-products. The hydrophobic azeotropic solvent (toluene) was supplied to the water separation tower 400 at a mass flow rate 1.7 times the flow rate of the mother liquor 320. The amount of acetic acid in the water separation tower top effluent stream 410 relative to the amount of acetic acid in the mother liquor 320 supplied to the water separation tower was 97.8 wt %, and the amount of acetic acid in the water separation tower bottom effluent stream 420 relative to the amount of acetic acid in the mother liquor 320 was 2.2 wt %. The concentration of acetic acid in the water separation tower bottom effluent stream 420 was 0.2 wt %.

[0080] The top effluent stream 410 from the water separation tower was fed to a layer separation apparatus 450 to obtain an organic layer containing the hydrophobic azeotropic solvent and an aqueous layer containing water and acetic acid. The organic layer was fed to a water separation tower 400, a portion of the aqueous layer was fed to an absorption tower 100, and the remainder was discharged to the outside of the system as wastewater.

[0081] Meanwhile, the bottom discharge stream 420 from the water separation tower was supplied to a high-boiling by-product separation tower 500 and distilled to obtain a bottom discharge stream 520 from the high-boiling by-product separation tower containing high-boiling by-products and an upper discharge stream 510 from the high-boiling by-product separation tower containing (meth)acrylic acid. The upper discharge stream 510 from the high-boiling by-product separation tower was supplied to the crystallization apparatus 300, and the content of the (meth)acrylic acid in the upper discharge stream 510 from the high-boiling by-product separation tower was 98.8 wt %.

[0082] As a result, the energy consumed in the water separation column 400 and the high boiling point by-product separation column 500 by this process was 117.2 kcal / kg AA and 35 kcal / kg AA, respectively, for a total of 152.2 kcal / kg AA.

[0083] On the other hand, the amount of (meth)acrylic acid lost through the upper discharge stream 110 of the absorption tower was 0.94 wt % relative to the amount of (meth)acrylic acid produced (the amount of (meth)acrylic acid obtained from the crystallization apparatus), and the amount of (meth)acrylic acid lost through the wastewater derived from the layer separation apparatus 450 was 0.23 wt % relative to the amount of (meth)acrylic acid produced, resulting in a total loss of 1.17 wt % of (meth)acrylic acid.

[0084] (Comparative Example 1) The (meth)acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, following the process flow illustrated in FIG.

[0085] Specifically, in Comparative Example 1, an aqueous (meth)acrylic acid solution was obtained from the bottom of the absorption tower, and the aqueous (meth)acrylic acid solution was passed through a degassing tower 150 and introduced into a crystallization apparatus 300 to obtain (meth)acrylic acid 310. Here, the water introduced into the absorption tower 100 was a mixture of stream 6 directly supplied to the absorption tower and a portion of the lower discharge stream of the cooling tower, and the water was supplied to the upper part of the absorption tower at a mass flow rate of 6.6 wt % with respect to the flow rate of the mixed gas.

[0086] The degassing tower bottom discharge stream 160 introduced into the crystallization apparatus 300 contained (meth)acrylic acid (90.5 wt%), acetic acid (1.8 wt%), water (5.9 wt%), furfural (0.7 wt%), and maleic acid (0.7 wt%). The crystallization process performed in the crystallization apparatus 300 produced a (meth)acrylic acid recovery stream 310 containing (meth)acrylic acid and a mother liquor recovery stream 320 containing a mother liquor. The (meth)acrylic acid content in the (meth)acrylic acid recovery stream 310 was 99.5 wt% or more, and ultimately, 99.5 wt% or more of (meth)acrylic acid was obtained from the crystallization apparatus.

[0087] The mother liquor recovery stream 320 was fed into a high-boiling by-product separation column 500 to obtain a bottom discharge stream 520 from the high-boiling by-product separation column containing high-boiling by-products and an top discharge stream 510 from the high-boiling by-product separation column containing the mother liquor from which the high-boiling by-products had been removed. The top discharge stream 510 from the high-boiling by-product separation column was supplied to an absorption column 100 at a position 15 plates from the top. Except for this, (meth)acrylic acid was produced in the same manner as in Example 1.

[0088] As a result, the energy used to remove high-boiling by-products from the mother liquor after crystallization in the high-boiling by-product separation tower 500 was 154.5 kcal / kg AA. Meanwhile, the amount of (meth)acrylic acid lost through the upper discharge stream 110 of the absorption tower was 1.56 wt% based on the amount of (meth)acrylic acid produced. It was confirmed that the amount of energy used in Comparative Example 1 was slightly higher than that in Example 1, but the amount of lost (meth)acrylic acid increased by approximately 1.3 times or more.

[0089] (Comparative Example 2) The (meth)acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, following the process flow illustrated in FIG.

[0090] In Comparative Example 2, the process for obtaining the degassing tower bottom discharge stream 160 was carried out in the same manner as in Example 1. The degassing tower bottom discharge stream 160 contained (meth)acrylic acid (89.5 wt%), acetic acid (1.8 wt%), water (7 wt%), furfural (0.8 wt%), and maleic acid (0.8 wt%), as in Example 1. The degassing tower bottom discharge stream 160 was then supplied to a water separation tower 400, and a hydrophobic azeotropic solvent (toluene) was supplied to the top of the water separation tower 400 at a mass flow rate 7.2 times the flow rate of the water in the degassing tower bottom discharge stream 160. Azeotropic distillation performed in the water separation tower 400 produced a water separation tower top discharge stream 410 containing acetic acid, the absorption solvent (water), and toluene, and a water separation tower bottom discharge stream 420 containing (meth)acrylic acid and high-boiling by-products.

[0091] Meanwhile, the amount of acetic acid in the bottom discharge stream 420 of the water separation tower relative to the amount of acetic acid in the bottom discharge stream 160 of the degassing tower was 46 wt %, and the amount of acetic acid in the top discharge stream 410 of the water separation tower relative to the amount of acetic acid in the bottom discharge stream 160 of the degassing tower was 54 wt %. Also, the concentration of acetic acid in the bottom discharge stream 420 of the water separation tower was 1.5 wt %.

[0092] The top discharge stream 410 from the water separation tower was fed to a layer separation apparatus 450 to obtain an aqueous layer containing water and acetic acid and an organic layer containing toluene. A portion of the aqueous layer was fed to an absorption tower 100, and the remainder was discharged to the outside of the system as wastewater. Meanwhile, the organic layer was circulated to the water separation tower 400.

[0093] Meanwhile, bottom discharge stream 420 from the water separation tower was supplied to high-boiling by-product separation tower 500 to obtain bottom discharge stream 520 from the high-boiling by-product separation tower containing high-boiling by-products and top discharge stream 510 from the high-boiling by-product separation tower containing (meth)acrylic acid. Top discharge stream 510 from the high-boiling by-product separation tower was supplied to a crystallizer to obtain 99.5 wt % or more of (meth)acrylic acid from (meth)acrylic acid recovery stream 310.

[0094] For this reason, the energy consumed in the water separation tower 400 was 140.4 kcal / kg AA, and the energy consumed in the high boiling point by-product separation tower 500 was 187.2 kcal / kg AA, for a total of 327.7 kcal / kg AA.

[0095] In Comparative Example 3, the bottom discharge stream 160 of the degassing tower was supplied to the water separation tower 400, and it was confirmed that the total energy consumption was 327.7 kcal / kg AA, the highest.

Claims

1. a step of contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain an aqueous solution of (meth)acrylic acid; supplying the aqueous (meth)acrylic acid solution to a crystallizer, crystallizing the solution to obtain purified (meth)acrylic acid, and supplying a mother liquor separated from the purified (meth)acrylic acid to a water separation tower; Separating the water separation tower into a water separation tower top effluent stream containing water and a water separation tower bottom effluent stream containing (meth)acrylic acid and high-boiling by-products in the water separation tower; supplying a bottom discharge stream from the water separation tower to a high-boiling by-product separation tower, and supplying an top discharge stream from the high-boiling by-product separation tower containing the (meth)acrylic acid to the crystallization apparatus.

2. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the aqueous (meth)acrylic acid solution is supplied to a degassing column, and a bottom discharge stream from the degassing column from which low-boiling by-products have been removed is supplied to the crystallization apparatus.

3. The method for producing (meth)acrylic acid according to claim 2, wherein the content of (meth)acrylic acid in the bottom discharge stream of the degassing tower is 85% by weight to 99% by weight.

4. The method for producing (meth)acrylic acid according to claim 1 , wherein the mother liquor contains (meth)acrylic acid, water, acetic acid, and high-boiling by-products.

5. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the top discharge stream of the water separation tower is fed to a layer separation device, a part of the aqueous phase containing water and acetic acid is recycled to the absorption tower, and the remainder is discharged as wastewater.

6. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the content of the (meth)acrylic acid in the top discharge stream of the high-boiling by-product separation column is 95% by weight to 99% by weight.

7. The method for producing (meth)acrylic acid according to claim 1, wherein a flow rate ratio of the acetic acid discharged from the top of the absorption tower based on a flow rate of the acetic acid introduced into the absorption tower is 30% by weight to 60% by weight.

8. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the mother liquor contains 50% by weight to 80% by weight of (meth)acrylic acid and 20% by weight to 50% by weight of water.

9. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the flow rate ratio of the water contained in the mother liquor is 35% by weight to 45% by weight based on the flow rate of the water introduced into the absorption tower.

10. the mixed gas containing (meth)acrylic acid is a reaction product obtained by a gas-phase oxidation reaction of reactants containing air, a raw material compound, and a recycled gas in a reactor, 2. The method for producing (meth)acrylic acid according to claim 1, wherein the recycle gas is a part of the top discharge stream from the absorption tower that is supplied to a cooling tower and cooled, and then the recycle gas is discharged as the top discharge stream from the cooling tower and circulated to the reactor.

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