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 a mother liquor separated from the purified (meth)acrylic acid; supplying a portion of the mother liquor to an extraction tower and supplying the remainder to a water separation tower; contacting an extractant with the mother liquor in the extraction tower and then supplying an upper outlet stream from the extraction tower to the water separation tower; separating the 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 in the water separation tower; 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. 10-2022-0109483 filed on August 30, 2022 and Korean Patent Application No. 10-2023-0107030 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 water 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 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 producing (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 (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 a mother liquor separated from the purified (meth)acrylic acid; supplying a portion of the mother liquor to an extraction tower and supplying the remainder to a water separation tower; contacting an extractant with the mother liquor in the extraction tower, and then supplying the top discharge stream from the extraction tower to the water separation tower; separating the top discharge stream from the water separation tower containing water and a bottom discharge stream from the water separation tower containing (meth)acrylic acid and high-boiling by-products in the water separation tower; and supplying the bottom discharge stream from the water separation tower to a high-boiling by-product separation tower and supplying the top discharge 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 distilled using extraction, thereby reducing energy consumption and reducing the loss of (meth)acrylic acid through the efficient removal of high-boiling by-products.

[0011] In addition, an extraction tower, a water separation tower and a layer separation device are provided after the absorption tower, so that acetic acid, which is a by-product, can be separated and removed, and the loss of (meth)acrylic acid from the top of the absorption tower can be reduced compared to the case where 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 illustrating 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] A method for producing (meth)acrylic acid according to one embodiment of the present invention includes 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 a mother liquor separated from the purified (meth)acrylic acid, supplying a portion of the mother liquor to an extraction tower and supplying the remainder to a water separation tower, contacting an extraction solvent with the mother liquor in the extraction tower and then supplying the top discharge stream from the extraction tower to the water separation tower, separating the top discharge stream from the water separation tower into a top discharge stream from the water separation tower containing water and a bottom discharge stream from the water separation tower containing (meth)acrylic acid and high-boiling by-products, and supplying the bottom discharge stream from the water separation tower to a high-boiling by-product separation tower and supplying the top discharge 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 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 can be reduced to the same level as that in the absorber 100. The water discharged from the reactor may contain dissolved various by-products that are inappropriate for introduction into a crystallization apparatus. If excessive water is present 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 a crystallization apparatus without a separate water distillation step, 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 (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 a step of supplying the (meth)acrylic acid aqueous solution to a crystallizer 300 and crystallizing the solution to obtain purified (meth)acrylic acid and a mother liquor separated from the purified (meth)acrylic acid.

[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 highly purified crystallized (meth)acrylic acid. In this specification, the (meth)acrylic acid crystallized in the crystallization apparatus may be referred to as purified (meth)acrylic acid. This crystallization process may 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. Therefore, the mother liquor may contain (meth)acrylic acid, water, acetic acid, and high-boiling by-products. The (meth)acrylic acid here is the residual (meth)acrylic acid that has not been crystallized in the crystallization apparatus 300, and can be separated in the high-boiling by-product separation column 600 described below and recycled to the crystallization apparatus 300.

[0051] The separation of the crystallized (meth)acrylic acid from the mother liquor can be carried out using a high-liquid separation device, for example, a belt filter, a centrifuge, etc. The purified (meth)acrylic acid can be recovered as a (meth)acrylic acid recovery stream 320, and the mother liquor is discharged from the crystallization device 300 via a mother liquor recovery line 310. A portion of the discharged mother liquor can be supplied to an extraction column 400, and the remainder can be supplied to a water separation column 500.

[0052] Specifically, the mother liquor recovery line 310 branches into a first crystallizer discharge line 330 and a second crystallizer discharge line 340. The first crystallizer discharge line 330 may be connected to an extraction tower 400, and the second crystallizer discharge line 340 may be connected to a water separation tower 500. The mother liquor is discharged from the crystallization unit 300 via the mother liquor recovery line 310, and then separated and supplied to the extraction tower 400 and the water separation tower 500, respectively.

[0053] Meanwhile, the mother liquor discharged from the crystallization apparatus 300 may contain 50% by weight to 80% by weight, specifically 60% by weight to 70% by weight of (meth)acrylic acid, and 20% by weight to 50% by weight, specifically 30% by weight to 40% by weight of water.

[0054] According to the present invention, by installing the extraction tower 400 before the water separation tower 500, it is possible to significantly reduce the treatment load of the aqueous (meth)acrylic acid solution in the water separation tower 500 and the energy consumption. Furthermore, in the method according to the present invention, the aqueous (meth)acrylic acid solution obtained from the absorption tower 100 is supplied separately to the extraction tower 400 and the water separation tower 500, thereby reducing the overall equipment load, and by reducing the amount of water that must be distilled in the water separation tower 500 through extraction, it is possible to save energy consumption.

[0055] The ratio of the mother liquor supplied to the extraction tower 400 and the water separation tower 500 can be determined taking into consideration the volume ratio between the extraction tower 400 and the water separation tower 500, the processing capacity, and the effect of increasing the energy efficiency of the entire process. Taking these conditions into consideration, the flow rate of the mother liquor supplied to the extraction tower 400 relative to the total flow rate of the mother liquor discharged through the mother liquor recovery line 310 can be 20 wt % to 60 wt %, specifically 30 wt % to 50 wt %, which is advantageous in terms of achieving the above-mentioned effects. The remainder of the flow rate supplied to the extraction tower 400 can be supplied to the water separation tower 500, as described above.

[0056] Meanwhile, the greater the amount of mother liquor supplied to extraction tower 400, the more the processing efficiency of water separation tower 500 can be improved, and the more energy efficiency of the entire process can be improved. However, if more mother liquor than necessary is supplied to extraction tower 400, a larger capacity extraction tower 400 is required, which can deteriorate the operating conditions of the downstream water separation tower 500 and increase the loss of (meth)acrylic acid, thereby potentially reducing process efficiency. Therefore, it is advantageous to adjust the mother liquor supply rate within the above-mentioned range. Furthermore, the greater the amount of mother liquor supplied to water separation tower 500, the more water must be removed by azeotropic distillation in water separation tower 500, which can reduce the effect of reducing energy consumption according to the present invention. Therefore, it is advantageous to adjust the mother liquor supply rate within the above-mentioned range.

[0057] According to one embodiment of the present invention, an extraction process step may be included in which an extraction solvent is contacted with the mother liquor in the extraction tower 400 to obtain an extract and a raffinate, and the extract stream 410 containing the extract is supplied to the water separation tower 500.

[0058] Extraction tower 400 receives a portion of the mother liquor discharged from crystallization apparatus 300, removes most of the water contained in the mother liquor without using a large amount of energy, and supplies the mother liquor to water separation tower 500, thereby reducing the energy required for azeotropic distillation in water separation tower 500, which will be described later. In this regard, it is preferable to use a liquid-liquid contact method for extraction in extraction tower 400 in order to improve the energy efficiency of the entire process.

[0059] The extraction solvent can be a hydrocarbon solvent that can form an azeotrope with water and organic by-products (such as acetic acid) but cannot form an azeotrope with (meth)acrylic acid, but can sufficiently extract (meth)acrylic acid. It is advantageous for the extraction process that the solvent has a boiling point of 10 to 120° C. Specifically, the extraction solvent can be benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butyl acetate, isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, or 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.

[0060] On the other hand, it is advantageous from the viewpoint of the process that the temperature of the mother liquor in the extraction step is 10 to 70° C. Also, it is advantageous from the viewpoint of the process that the weight ratio of the extraction solvent to the mother liquor in the extraction step is 1:1 to 1:5, preferably 1:1.2 to 1:2.5.

[0061] Additionally, a liquid-liquid contact type extraction device may be used as the extraction tower 400. Non-limiting examples of the extraction device include a Karr type reciprocating plate column, a rotary-disk contactor, a Scheibel column, a Kuhni column, a spray extraction tower, a packed extraction tower, a pulsed packed column, a mixer-settler bank, a mixer and centrifugal countercurrent extractor, and the like.

[0062] In this manner, a significant portion of the water in the mother liquor supplied to the extraction tower 400 via the first discharge line 330 of the crystallizer is removed, and an extract in which (meth)acrylic acid is extracted with the extraction solvent is obtained. The extract can be supplied to the water separation tower 500 as an extract stream 410. Specifically, the extract contains (meth)acrylic acid, acetic acid, the extraction solvent, and high-boiling by-products.

[0063] Furthermore, water contained in the mother liquor from the extraction process can be recovered as raffinate. The recovered raffinate is discharged as raffinate stream 420 and can be introduced into layer separation apparatus 550, which will be described later. In this way, by recovering water from the extraction process, the operational burden of the distillation process, which will be described later, can be reduced, thereby significantly reducing energy consumption.

[0064] According to one embodiment of the present invention, the stream supplied to the water separation tower 500 may include the mother liquor supplied along the second crystallizer discharge line 340 and the extract supplied along the extract stream 410.

[0065] The flow rate of water in the stream supplied to the water separation tower 500 may be 20% by weight to 50% by weight, specifically 25% by weight to 40% by weight, based on the flow rate of water introduced into the absorption tower 100.

[0066] The distillation step in the water separation column 500 for the stream supplied to the water separation column 500 can be a step of separating an upper fraction containing water and acetic acid from a lower fraction containing (meth)acrylic acid and high-boiling by-products by azeotropic distillation.

[0067] According to the present invention, distillation in the water separation column 500 is carried out in the presence of a hydrophobic azeotropic solvent, which makes it possible to simultaneously recover the hydrophobic azeotropic solvent, water, and organic by-products (such as acetic acid), which is advantageous from a process standpoint.

[0068] 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.

[0069] 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.

[0070] The hydrophobic azeotropic solvent may be the same as or different from the extraction solvent used in extraction tower 400. However, taking into consideration production efficiency in a continuous process, it is preferable that the hydrophobic azeotropic solvent be the same as the extraction solvent. When the same compound is used as the hydrophobic azeotropic solvent and the extraction solvent, at least a portion of the hydrophobic azeotropic solvent distilled and recovered from water separation tower 500 can be supplied to the lower part of extraction tower 400 and used as part of the extraction solvent.

[0071] When the hydrophobic azeotropic solvent is introduced into the water separation tower 500, the azeotropy 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 500. 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 500.

[0072] The thus recovered upper fraction of the water separation tower can be supplied to the layer separation apparatus 550 via the upper discharge stream 510 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 600 via the lower discharge stream 520 of the water separation tower.

[0073] Here, layer separator 550 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 layer separator 550 and a relatively heavy liquid into a lower portion of layer separator 550. Specifically, upper discharge stream 510 of the water separation tower supplied to layer separator 550 may be separated into an organic layer containing the hydrophobic azeotropic solvent and an aqueous layer containing water and acetic acid.

[0074] In addition, at least a portion of the organic layer separated in the layer separation apparatus 550 can be supplied to the top of the water separation tower 500 and reused as a hydrophobic azeotropic solvent, and the remainder can be supplied to the extraction tower 400 and reused as an extraction solvent.

[0075] Meanwhile, at least a portion of the aqueous layer separated in the layer separation device 550 can be supplied to the upper part of the absorption tower 100 to be used as an absorption solvent, and the remainder can be discharged as wastewater.

[0076] 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 500. According to the present invention, the concentration of acetic acid contained in the aqueous layer may be 1 to 30% by weight, preferably 2 to 20% by weight, and more preferably 3 to 10% by weight.

[0077] 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 500 and the layer separation device 550. 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 minimizing the loss of (meth)acrylic acid. Furthermore, process flexibility can be ensured compared to attempts to discharge the entire amount of acetic acid in the system to the top of the absorber.

[0078] From this perspective, 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 discharged in the aqueous layer of the layer separator 550.

[0079] Meanwhile, a method for producing (meth)acrylic acid according to one embodiment of the present invention may include the steps of supplying a bottom discharge stream from the water separation tower 500 to a high-boiling by-product separation tower 600, and supplying an upper discharge stream from the high-boiling by-product separation tower 600 containing the (meth)acrylic acid to the crystallization apparatus 300.

[0080] The high-boiling by-product separation column 600 can separate the bottom discharge stream from the water separation column 500 into a bottom fraction containing high-boiling by-products by distillation and an upper fraction containing a high content of (meth)acrylic acid by removing the high-boiling by-products. The upper fraction can be supplied to the crystallization apparatus 300 via the top discharge stream 610 from the high-boiling by-product separation column, and the content of the (meth)acrylic acid in the top discharge stream 510 from the high-boiling by-product separation column can be 90% by weight to 99% by weight, specifically 95% by weight to 99% by weight.

[0081] 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 has been removed through the extraction tower 400 and the water separation tower 500, the water content in the top discharge stream 610 of the high boiling by-product separation tower is controlled to be low, thereby realizing a concentrated stream with a high concentration of (meth)acrylic acid that can be immediately introduced into the crystallization apparatus 300. By introducing the top discharge stream 610 of the high boiling by-product separation tower into the crystallization apparatus 300, the loss of (meth)acrylic acid can be minimized.

[0082] 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.

[0083] 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.

[0084] 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%).

[0085] 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 the layer separation device 550 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% relative to the flow rate of the mixed gas 2. Based on the flow rate of acetic acid introduced into the absorption tower 100, the mass flow rate ratio of acetic acid discharged to the outside of the system via the upper discharge stream 110 of the absorption tower was 40.8 wt%. The pressure at the upper part of the absorption tower 100 was 1.1 bar, and the temperature at the lower part of the absorption tower 100 was 84.1°C.

[0086] In the absorber 100, non-condensable gases containing components not dissolved in water were 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. In the cooling tower 20, the non-condensable gases contained in the absorber top discharge stream portion 3 were dissolved in water. Here, the water was supplied via a water supply line 5. In the cooling tower 20, the gases not dissolved in water were supplied to the reactor 10 via a recycle gas transfer line 4, and a portion 6 of the cooling tower bottom discharge stream containing water and the components dissolved in water (acetic acid and (meth)acrylic acid not dissolved in water in the absorber) was supplied to the top of the absorber 100.

[0087] Meanwhile, the above-mentioned (meth)acrylic acid aqueous solution was supplied to a degassing tower 150 as a bottom discharge stream 120 of the absorber and degassed, and the low boiling point by-products were supplied to an absorption tower 100 as an upper discharge stream of the degassing tower, and the (meth)acrylic acid aqueous solution from which the low boiling point by-products had been degassed was supplied to a crystallization apparatus 300 as a bottom discharge stream 160 of the degassing tower. Here, the top discharge stream of the degassing tower was supplied to the absorption tower 100 at a flow rate of 25 wt% of the mass flow rate of water introduced into the absorption tower 100. Meanwhile, the composition of the bottom discharge stream 160 of the degassing tower included (meth)acrylic acid (89.5 wt%), acetic acid (1.8 wt%), water (7 wt%), furfural (0.8 wt%), and maleic acid (0.8 wt%).

[0088] The bottom discharge stream 160 from the degassing tower is mixed with the top discharge stream 610 from the high-boiling by-product separation tower described later and supplied to the crystallization apparatus 300, and the mixed stream contains (meth)acrylic acid (90.9 wt%), acetic acid (1.6 wt%), water (5.9 wt%), furfural (0.8 wt%) and maleic acid (0.7 wt%).

[0089] A (meth)acrylic acid recovery stream 320 containing (meth)acrylic acid was obtained by the crystallization process performed in the crystallization apparatus 300, and the (meth)acrylic acid was thus obtained. The content of (meth)acrylic acid in the (meth)acrylic acid recovery stream 320 was 99.5 wt % or more.

[0090] Furthermore, a mother liquor was obtained from the crystallization apparatus 300, which was separated from the (meth)acrylic acid. Here, the mother liquor contained (meth)acrylic acid (64 wt%), water (23.7 wt%), acetic acid (6.5 wt%), and high-boiling by-products (6.0 wt%).

[0091] The mother liquor discharged through mother liquor recovery line 310 was branched, and 40 wt % of the total weight of the mother liquor was supplied to extraction tower 400 through first discharge line 330 of the crystallizer, and the remaining 60 wt % of the mother liquor was supplied to water separation tower 500 through second discharge line 340 of the crystallizer. Meanwhile, the mother liquor from second discharge line 340 of the crystallizer was mixed with extract stream 410, which will be described later, and supplied to water separation tower 500.

[0092] In the extraction column 400, an extraction process was performed in the presence of an extraction solvent (toluene), yielding a raffinate stream 420 containing water and an extract stream 410 containing toluene and (meth)acrylic acid. Here, the toluene supplied to the bottom of the extraction column 400 was supplied at a mass flow rate 4.5 times the flow rate of water in the mother liquor supplied to the extraction column 400. The raffinate stream 420 was supplied to a phase separation apparatus 550, which will be described later, and the extract stream 410 was supplied to a water separation column 500.

[0093] In the water separation tower 500, an azeotropic distillation was carried out in the presence of a hydrophobic azeotropic solvent (toluene) to obtain a water separation tower top discharge stream 510 containing toluene, water, and acetic acid, and a water separation tower bottom discharge stream 520 containing (meth)acrylic acid and high-boiling by-products. The toluene supplied to the water separation tower 500 was supplied at a mass flow rate twice that of the toluene supplied to the extraction tower 400.

[0094] The top discharge stream 510 from the water separation tower was fed to a layer separation apparatus 550, where it was separated into 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 fed to an extraction tower 400 and a water separation tower 500.

[0095] Meanwhile, the above-mentioned bottom discharge stream 520 from the water separation tower was supplied to high-boiling by-product separation tower 600 to obtain top discharge stream 610 from the high-boiling by-product separation tower containing (meth)acrylic acid and bottom discharge stream 620 from the high-boiling by-product separation tower containing high-boiling by-products. As described above, the top discharge stream 610 from the high-boiling by-product separation tower was mixed with bottom discharge stream 160 from the degassing tower and supplied to crystallization apparatus 300. Here, the content of (meth)acrylic acid in the top discharge stream 610 from the high-boiling by-product separation tower was 98.6 wt %.

[0096] As a result, the energy consumed in the water separation tower 500 was 89.1 kcal / kg AA, and the energy consumed in the high boiling point by-product separation tower 600 was 35.9 kcal / kg AA, for a total of 125 kcal / kg AA of energy consumed.

[0097] On the other hand, the amount of (meth)acrylic acid lost through the upper discharge stream 110 of the absorption tower was 0.92 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 coming from the layer separation apparatus 250 was 0.13 wt % relative to the amount of (meth)acrylic acid produced, resulting in a total loss of 1.05 wt % of (meth)acrylic acid.

[0098] (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.

[0099] Specifically, in Comparative Example 1, a (meth)acrylic acid solution was obtained from the bottom of the absorption tower 100, and the (meth)acrylic acid solution was passed through a degassing tower 150 and introduced into a crystallization apparatus 300 to obtain (meth)acrylic acid 320. 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 2.

[0100] Mother liquor 310 obtained after crystallization in crystallizer 300 was fed to high-boiling by-product separation column 600, yielding a bottom discharge stream 620 from the high-boiling by-product separation column containing high-boiling by-products and an top discharge stream 610 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 610 from the high-boiling by-product separation column was recycled to absorption column 100. Except for this, (meth)acrylic acid was produced in the same manner as in Example 1.

[0101] The degassing tower bottom discharge stream 160 fed to the crystallization apparatus 300 contains (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%). As a result, 99.5 wt% or more of (meth)acrylic acid was obtained from the (meth)acrylic acid recovery stream 320 of the crystallization apparatus 300.

[0102] The energy used to remove high-boiling by-products from the mother liquor after crystallization in the high-boiling by-product separation column 600 was 154.5 kcal / kg AA. On the other hand, the amount of (meth)acrylic acid lost via the top discharge stream 110 of the absorption column was 1.56 wt % based on the amount of (meth)acrylic acid produced.

[0103] In Comparative Example 1, the mother liquor 310 was supplied to the high-boiling by-product separation column 600, and compared to Example 1, the total energy consumption increased and the loss of (meth)acrylic acid also increased by about 1.5 times.

[0104] (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.

[0105] Specifically, in Comparative Example 1, the bottom discharge stream 160 from the degassing tower, which had the same composition as in Example 1, was not supplied to the crystallization apparatus, but the bottom discharge stream 160 from the degassing tower was branched, and 40 wt % of the total weight of the bottom discharge stream 160 from the degassing tower was supplied to the extraction tower 400, and the remaining 60 wt % was supplied to the water separation tower 500.

[0106] However, it was confirmed that the content of (meth)acrylic acid in the lower discharge stream of the branched degassing tower, which was supplied to the extraction tower 400, was so high that the extraction process could not be carried out even when an extraction solvent was supplied to the extraction tower 400, and no phase separation occurred. Furthermore, it was ultimately impossible to obtain (meth)acrylic acid.

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 and crystallizing the solution to obtain purified (meth)acrylic acid and a mother liquor separated from the purified (meth)acrylic acid; feeding a portion of the mother liquor to an extraction column and a remainder to a water separation column; contacting an extraction solvent with the mother liquor in the extraction tower to obtain a raffinate and an extract, and supplying the extract to the water separation tower; Separating the water separation tower into a water separation tower top discharge stream containing water and a water separation tower bottom discharge 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 raffinate comprises water, and a raffinate stream comprising the raffinate is fed to the layer separation device.

7. 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.

8. 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.

9. 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.

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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