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 an absorption solvent in an absorption tower; supplying a first (meth)acrylic acid solution discharged from a bottom of the absorption tower to a high-boiling by-product separation tower and supplying an upper discharge stream of the high-boiling by-product separation tower to the crystallization apparatus; supplying a second (meth)acrylic acid solution discharged from a side of the absorption tower to the crystallization apparatus; obtaining (meth)acrylic acid crystallized in the crystallization apparatus; and circulating a mother liquor recovered from the crystallization apparatus to the absorption tower.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0109412 filed on August 30, 2022 and Korean Patent Application No. 10-2023-0106990 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 a (meth)acrylic acid solution. Subsequent processes for recovering the (meth)acrylic acid contained in the (meth)acrylic acid solution typically involve extraction, distillation, and purification. To improve the recovery efficiency of (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 the by-product from the (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] Therefore, there is an urgent need to introduce a technology that can reduce the amount of energy used when obtaining high-purity (meth)acrylic acid from a (meth)acrylic acid solution and separating (meth)acrylic acid and by-products by distillation. Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a method for recovering (meth)acrylic acid, which can further reduce energy consumption in the purification process and simplify subsequent processes, in order to solve the problems mentioned in the Background of the Invention. [Means for solving the problem]

[0008] 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 an absorption solvent in an absorption tower; supplying a first (meth)acrylic acid solution discharged from a bottom of the absorption tower to a high-boiling by-product separation tower and supplying an upper discharge stream of the high-boiling by-product separation tower to the crystallization apparatus; supplying a second (meth)acrylic acid solution discharged from a side of the absorption tower to the crystallization apparatus; obtaining (meth)acrylic acid crystallized in the crystallization apparatus; and circulating a mother liquor recovered from the crystallization apparatus to the absorption tower. [Effects of the Invention]

[0009] The method for producing (meth)acrylic acid according to the present invention can significantly reduce the amount of energy used and can continuously recover high-purity (meth)acrylic acid with higher production efficiency than conventional recovery methods. [Brief explanation of the drawings]

[0010] [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 comparative example of a method for producing (meth)acrylic acid. DETAILED DESCRIPTION OF THE INVENTION

[0011] The terms and words used in the description and claims of the present invention should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0012] In the present invention, the term "stream" can refer to the flow of fluid within a process, or the fluid itself flowing in a pipe. Specifically, the term "stream" can simultaneously refer to the fluid itself flowing in a pipe connecting each device and the flow of the fluid. Furthermore, the fluid can refer to gas or liquid, and does not exclude cases where the fluid contains solid components.

[0013] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0014] 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 an absorption solvent in an absorption tower; supplying a first (meth)acrylic acid solution discharged from the bottom of the absorption tower to a high-boiling by-product separation tower and supplying an upper discharge stream of the high-boiling by-product separation tower to the crystallization apparatus; supplying a second (meth)acrylic acid solution discharged from the side of the absorption tower to the crystallization apparatus; obtaining (meth)acrylic acid crystallized in the crystallization apparatus; and circulating a mother liquor recovered from the crystallization apparatus to the absorption tower.

[0015] Referring to FIG. 1, each step that can be included in an embodiment of the present invention will be described.

[0016] 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 an absorbing solvent in an absorption tower 100. Here, the mixed gas containing (meth)acrylic acid is a general term for the gas phase components discharged from a reactor 10 that 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 gas, carbon monoxide, carbon dioxide, absorbing solvent 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.

[0017] Specifically, the mixed gas containing (meth)acrylic acid can be produced as follows.

[0018] 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.

[0019] 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.

[0020] The recycle gas may originate from the upper portion of the absorber 100 (described later). That is, the mixed gas is contacted with an absorption solvent in the absorber 100, and non-condensable gases not dissolved in the absorption solvent may be discharged as an upper discharge stream 110 from the absorber 100. The non-condensable gases may include impurities such as acetic acid, inert gases, unreacted raw material compounds, and a small amount of (meth)acrylic acid not dissolved in the absorption solvent. Meanwhile, a portion 3 of the upper discharge stream 110 from the absorber may be supplied to a cooling tower 20, and the remainder 120 may be supplied to a waste gas incinerator and disposed of. The content of (meth)acrylic acid in the upper discharge stream 110 from the absorber may be 0.03 mol% to 0.5 mol%.

[0021] The cooling tower 20 is provided with an absorption solvent supply line 5 at its top, and an absorption solvent can be supplied into the cooling tower 20 from the absorption solvent supply line 5. In the cooling tower 20, the absorption solvent can come into contact with the non-condensable gas contained in a portion 3 of the upper discharge stream 110 of the absorber. Components contained in the non-condensable gas, such as acetic acid and (meth)acrylic acid that were not dissolved in the absorption solvent in the absorber 100, are dissolved in the absorption solvent, which can be discharged as a lower discharge stream from the cooling tower 20.

[0022] Thereafter, the bottom discharge stream of the cooling tower 20 can be re-supplied to the absorber 100, and the bottom discharge stream of the cooling tower 20 can be supplied to the absorber 100 as a mixed stream with a separately supplied absorption solvent stream 6.

[0023] That is, the absorption solvent may be supplied to the absorber 100 by one or more of supplying the absorption solvent via an absorption solvent supply line 5 provided at the top of the cooling tower 20 and directly supplying the absorption solvent to the absorber 100. The direct supply 6 to the absorber 100 may be a mixed stream with the lower discharge stream of the cooling tower 20 and then supplied to the absorber 100. Meanwhile, the amount of the absorption solvent supplied to the absorber 100 may be determined within a range in which the content of (meth)acrylic acid in the lower part of the absorber 100 can be maintained at 85% by weight or more.

[0024] The absorption solvent supplied to the cooling tower 20 and the absorption tower 100 may be the same. Specifically, the absorption solvent may include water such as tap water or deionized water, or may include circulating process water introduced from another process (e.g., aqueous phase recycled from the extraction process and / or distillation process). The absorption solvent may also include a trace amount of organic by-products (e.g., acetic acid) introduced from another process.

[0025] Meanwhile, in the cooling tower 20, most of the acetic acid contained in the non-condensable gas is dissolved in the absorbing solvent and removed by contact with the absorbing solvent, and the gas that is not dissolved in the absorbing solvent 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 performed in the reactor 10. The recycled gas can be mixed with the reaction gas and supplied to the reactor 10, or can be supplied to the reactor 10 through a line separate from the line 1 through which the reaction gas is supplied.

[0026] As described above, in the cooling tower 20, acetic acid and (meth)acrylic acid in the non-condensable gas supplied from the absorber 100 can be dissolved in an absorption solvent and recycled to the absorber 100. This allows as much acetic acid in the system as possible to be discharged as the top discharge stream 110 of the absorber, thereby obtaining high-purity (meth)acrylic acid and minimizing the loss of (meth)acrylic acid.

[0027] Furthermore, by lowering the temperature inside the cooling tower 20, the content of the absorbing solvent in the recycle gas circulated from the cooling tower 20 to the reactor 10 can be reduced. That is, when the absorbing solvent is water, by reducing the moisture (water) content in the recycle gas, the moisture content in the stream supplied from the reactor 10 to the absorber 100 can be reduced, and thus the moisture content in the absorber 100 can be reduced. The absorbing solvent (water) discharged from the reactor may contain dissolved various by-products that are unsuitable for introduction into a crystallizer. If the absorbing solvent (water) is present in an excessive amount in the absorber 100, it is difficult to obtain a highly concentrated (meth)acrylic acid solution. Therefore, by reducing the content of the absorbing solvent (water) in the recycle gas, it becomes possible to immediately introduce the side discharge stream of the absorber 100 into a crystallizer, as will be described later.

[0028] When the absorption solvent is water, the water content in the recycle gas can be 1% to 10% by weight, specifically 3% to 5% by weight.

[0029] 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 required 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 may be controlled by a heat exchanger provided at the bottom of the cooling tower 20. Specifically, the temperature may be controlled by circulating a portion of the bottom stream of the cooling tower 20 through the heat exchanger and the cooling tower 20. On the other hand, the top of the cooling tower 20 may be operated under atmospheric pressure operating conditions.

[0030] Thereafter, a step can be carried out in which the mixed gas containing the (meth)acrylic acid is supplied to the absorption tower 100 via the reactor discharge line 2 and brought into contact with an absorption solvent in the absorption tower 100 to obtain a (meth)acrylic acid solution. Specifically, a mixed gas containing (meth)acrylic acid, organic by-products, and absorption solvent vapor produced by the synthesis reaction of (meth)acrylic acid is brought into contact with the absorption solvent in the absorption tower 100 to obtain a (meth)acrylic acid solution, specifically, a first and a second (meth)acrylic acid solution.

[0031] 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.

[0032] In addition, 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 the absorption solvent, specifically, the absorption solvent containing water, may be supplied to the upper part of the absorption tower 100.

[0033] 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.

[0034] Meanwhile, according to one embodiment of the present invention, through the absorption process performed in the absorption tower 100, a first (meth)acrylic acid solution can be obtained and discharged from the bottom of the absorption tower 100, and a second (meth)acrylic acid solution can be obtained and discharged from the side of the absorption tower 100.

[0035] The (meth)acrylic acid content in the first and second (meth)acrylic acid solutions discharged from the absorption tower 100 may be 85% by weight to 99% by weight, specifically 85% by weight to 95% by weight. This is a higher level than the (meth)acrylic acid content in (meth)acrylic acid solutions discharged from existing absorption towers. In particular, by setting the (meth)acrylic acid content in the second (meth)acrylic acid solution to 85% by weight or more, the second (meth)acrylic acid solution can be directly supplied to the crystallization apparatus 300 without undergoing a separate purification or separation process for the second (meth)acrylic acid solution. This allows for overall process energy savings and high-purity (meth)acrylic acid to be obtained from the crystallization apparatus 300.

[0036] A second (meth)acrylic acid solution having such a high (meth)acrylic acid content can be obtained by, for example, optimally controlling the operating conditions of the cooling tower 20 and the absorption tower 100 according to the substance components and their contents in the system, thereby minimizing the absorption solvent (water) content in the absorption tower 100. That is, a second (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, minimizing the input and use amounts of the absorption solvent supplied to the cooling tower 20 and the absorption tower 100, and further, for example, by setting the number of discharge stages of the second (meth)acrylic acid solution discharged from the absorption tower 100.

[0037] Specifically, the first (meth)acrylic acid solution may be discharged from the bottom of the absorption tower 100, and the second (meth)acrylic acid solution may be discharged from the side at a height of 80% to 99% downward from the top of the absorption tower 100, specifically, at a height of 80% to 90%. In particular, when the second (meth)acrylic acid solution is discharged from the side at a height of 80% to 99% downward from the top of the absorption tower 100, the contents of the absorption solvent (water) and high-boiling by-products in the discharged second (meth)acrylic acid solution may be minimized. As a result, the second (meth)acrylic acid solution containing a high concentration of (meth)acrylic acid may be directly supplied to the crystallization apparatus 300. Specifically, when the second (meth)acrylic acid solution is discharged from a position higher than 80% downward from the top of the absorber 100, the content of the absorbing solvent discharged through the side of the absorber increases, which may prevent sufficient absorption at a position lower than the side of the absorber, and may increase the amount of (meth)acrylic acid lost to the top of the absorber. On the other hand, when the second (meth)acrylic acid solution is discharged from a position lower than 99% downward from the top of the absorber 100, the content of high-boiling by-products increases, which may also make the second (meth)acrylic acid solution unsuitable for supply to the crystallization apparatus 300.

[0038] Meanwhile, the content of (meth)acrylic acid in the second (meth)acrylic acid solution may be higher than the content of (meth)acrylic acid in the first (meth)acrylic acid solution. That is, since relatively heavy high-boiling by-products are concentrated in the bottom portion of the absorber 100, the content of (meth)acrylic acid in the second (meth)acrylic acid solution associated with the side portion of the absorber 100 where almost no high-boiling by-products are present may be higher than the content of (meth)acrylic acid in the first (meth)acrylic acid solution.

[0039] Meanwhile, the mixed gas comes into contact with the absorption solvent in the absorption tower 100, and non-condensable gases that are not dissolved in the absorption solvent can be discharged as the upper discharge stream 110 of the absorption tower 100. As described above, a portion 3 of the upper discharge stream 110 of the absorption tower can be supplied to the cooling tower 20, and the remainder 120 can be supplied to a waste gas incinerator and disposed of.

[0040] The first (meth)acrylic acid solution can be supplied along first (meth)acrylic acid solution stream 150 to high-boiling by-product separation column 200, and the second (meth)acrylic acid solution can be supplied along second (meth)acrylic acid solution stream 160 to crystallization unit 300.

[0041] According to one embodiment of the present invention, the first (meth)acrylic acid solution supplied to the high-boiling by-product separation column 200 can be distilled 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 from the high-boiling by-product separation column 200 can be discharged as an upper discharge stream from the high-boiling by-product separation column and supplied to the crystallization column 300, and the lower fraction from the high-boiling by-product separation column 200 can be discharged as a lower discharge stream 220 from the high-boiling by-product separation column and disposed of or recycled through another purification process. Removing the high-boiling by-products upstream of the crystallization column 300 can prevent the accumulation of high-boiling by-products within the system, and the mother liquor discharged from the crystallization column 300, described below, can be directly circulated to the absorption column 100.

[0042] As the high-boiling by-products are removed from the first (meth)acrylic acid solution, the (meth)acrylic acid in the first (meth)acrylic acid solution becomes more concentrated, and therefore the content of (meth)acrylic acid in the top discharge stream of the high-boiling by-product separation column 200 may be 85% by weight to 99% by weight, or 90% by weight to 99% by weight, or specifically 90% by weight to 95% by weight.

[0043] Meanwhile, according to one embodiment of the present invention, the side discharge stream 160 of the absorption tower 100 containing the second (meth)acrylic acid solution and the top discharge stream 210 of the high boiling point by-product separation tower 200 may be supplied to a crystallization apparatus 300.

[0044] The (meth)acrylic acid contained in the (meth)acrylic acid solution supplied to the crystallization apparatus 300 can be recrystallized through a crystallization process to obtain high-purity crystallized (meth)acrylic acid. This crystallization process can be carried out under normal conditions.

[0045] 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 stage or two or more stages. As a non-limiting example, the (meth)acrylic acid can be provided as high-purity (meth)acrylic acid by dynamic crystallization.

[0046] Specifically, to dynamically crystallize (meth)acrylic acid before crystallization, the (meth)acrylic acid solution can be first made to flow in the form of a falling film on the inner wall of a tube. The temperature of the tube can be 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 can then be raised to near the freezing point of (meth)acrylic acid to sweat approximately 5 wt. % of (meth)acrylic acid. The sweated mother liquor can then be removed from the tube, and the crystals formed on the inner wall of the tube can be recovered to obtain high-purity crystallized (meth)acrylic acid. The mother liquor may refer to the remaining solution after removing the crystallized (meth)acrylic acid from the (meth)acrylic acid solution introduced into the crystallization apparatus 300. The mother liquor can include acetic acid, an absorbing solvent, and a low-boiling substance.

[0047] The separation of the mother liquor and the crystallized (meth)acrylic acid can be carried out using a solid-liquid separation device such as a belt filter or a centrifuge.

[0048] According to one embodiment of the present invention, the mother liquor may be discharged from the crystallizer and circulated to the absorber 100 along a mother liquor circulation line 310. The mother liquor may be directly supplied to the absorber 100 without undergoing a separate purification or separation process. That is, the ratio of the flow rate of the mother liquor recovered from the crystallizer 300 when introduced into the absorber to the flow rate of the mother liquor when discharged from the crystallizer may be 0.99 to 1.01, and more specifically, the flow rate ratio may be 1. Meanwhile, by not performing a separate process on the mother liquor, such as a distillation process, the process is simplified. Furthermore, since it is not necessary to distill the absorption solvent, specifically water, contained in the mother liquor, energy costs can be significantly reduced.

[0049] 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.

[0050] 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.

[0051] Specifically, in reactor 10, a gas phase oxidation reaction of a reactant containing air (oxygen), a raw material compound (propylene), and a recycled gas 4 was carried out in the presence of a catalyst to obtain a mixed gas 2 containing (meth)acrylic acid (7.0 mol%), water (11.8 mol%), a high boiling point substance (0.09 mol%), and an inert gas (80.6 mol%).

[0052] Next, the mixed gas 2 was fed to the 22nd stage of the absorption tower 100 from the top at a temperature of 164°C. The pressure at the top of the absorption tower 100 was 1.1 bar, and the temperature at the bottom of the absorption tower 100 was 96.4°C. The absorption solvent (water) fed to the absorption tower 100 was supplied via stream 6 directly fed to the absorption tower and the bottom discharge stream of the cooling tower 20. The absorption solvent was fed to the top of the absorption tower 100 at a flow rate of 6.6 wt% of the flow rate of the mixed gas 2.

[0053] On the other hand, mother liquor 310 circulated from a crystallization apparatus described later was introduced into the absorption tower 100 at a mass flow rate 1.3 times the flow rate of the absorption solvent introduced into the absorption tower 100, at a position 15 stages from the top of the absorption tower 100. The ratio of the mass flow rate of the mother liquor recovered from the crystallization apparatus 300 when introduced into the absorption tower 100 to the flow rate of the mother liquor discharged from the crystallization apparatus 300 was 1.

[0054] The absorption process performed in the absorber 100 produced an absorber top discharge stream 110 containing non-condensable gases, a first (meth)acrylic acid solution stream 150 containing the first (meth)acrylic acid solution, and a second (meth)acrylic acid solution stream 160 containing the second (meth)acrylic acid solution. The (meth)acrylic acid content in the absorber top discharge stream 110 was 0.146 mol %.

[0055] A portion 3 of the upper discharge stream from the absorber was supplied to a cooling tower 20, and the remainder 120 was discharged to the outside of the system. In the cooling tower 20, the non-condensable gas contained in the portion 3 of the upper discharge stream from the absorber came into contact with an absorption solvent supplied through an absorption solvent supply line 5 to obtain a lower discharge stream from the cooling tower 20 containing the absorption solvent and components dissolved in the absorption solvent (acetic acid and (meth)acrylic acid not dissolved in the absorption solvent in the absorption tower). The gas not dissolved in the absorption solvent (recycled gas) was supplied to the reactor 10 via a recycle gas transfer line 4. A portion of the lower discharge stream from the cooling tower 20 was supplied to the absorption tower 100, and the remainder was circulated to the cooling tower 20. The water content in the recycle gas 4 was 4.4 wt%.

[0056] Meanwhile, the first (meth)acrylic acid solution 150 discharged from the bottom of the absorption tower 100 contained (meth)acrylic acid (85.9 wt%), acetic acid (1.3 wt%), water (4.2 wt%), furfural (3.2 wt%), and maleic acid (5.0 wt%), and the second (meth)acrylic acid solution 160 discharged from the side of the absorption tower at a height of 86% from the top contained (meth)acrylic acid (88.8 wt%), acetic acid (2.3 wt%), water (5.3 wt%), furfural (3.1 wt%), and maleic acid (0.06 wt%). Here, the second (meth)acrylic acid solution stream 160 was obtained at a flow rate 7.3 times the mass flow rate of the first (meth)acrylic acid solution stream 150.

[0057] On the other hand, the mass flow rate of the absorbing solvent contained in the first and second (meth)acrylic acid solutions was 30 wt % of the flow rate of the absorbing solvent introduced into the absorption tower 100 .

[0058] The first (meth)acrylic acid solution stream 150 was supplied to a high-boiling by-product separation column 200, and high-boiling by-products were separated via a bottom discharge stream 220 of the high-boiling by-product separation column. A mixed stream was formed with a top discharge stream 210 of the high-boiling by-product separation column containing (meth)acrylic acid and a second (meth)acrylic acid solution stream 160, and the mixed stream was then supplied to a crystallization apparatus 300. The (meth)acrylic acid content in the top discharge stream 210 of the high-boiling by-product separation column was 92.8 wt%. Meanwhile, the mixed stream of the top discharge stream 210 of the high-boiling by-product separation column and the second (meth)acrylic acid solution stream 160 contained the high-boiling by-products furfural (2.8 wt%) and maleic acid (0.06 wt%).

[0059] In the crystallization apparatus 300, a mixed stream of the top discharge stream 210 from the high-boiling by-product separation column and the second (meth)acrylic acid solution stream 160 was crystallized, and (meth)acrylic acid was finally obtained from a (meth)acrylic acid recovery stream 320 containing (meth)acrylic acid, and the mother liquor was supplied to the absorption column 100 via a mother liquor circulation line 310. The content of (meth)acrylic acid contained in the (meth)acrylic acid recovery stream 320 was 99.5 wt % or more.

[0060] Here, 36.4 kcal / kg AA of energy was consumed in the high-boiling by-product separation column 200, and 99.5 wt% or more of (meth)acrylic acid was obtained from the crystallization apparatus. Meanwhile, the amount of (meth)acrylic acid lost through the upper discharge stream 110 of the absorption column was 0.146 mol%.

[0061] Example 2 In Example 2, (meth)acrylic acid was produced in the same process flow as in Example 1, except that the second (meth)acrylic acid solution discharged downward from the top of the absorption tower 100 at a height of 77% was supplied to a crystallization apparatus.

[0062] Here, the second (meth)acrylic acid solution contains (meth)acrylic acid (88.8 wt%), acetic acid (2.2 wt%), water (5.4 wt%), furfural (3.2 wt%), and maleic acid (0.04 wt%).

[0063] As a result, the content of (meth)acrylic acid in the (meth)acrylic acid recovery stream 320 was 99.5 wt % or more, and thus (meth)acrylic acid was obtained. On the other hand, the content of (meth)acrylic acid contained in the top discharge stream 110 of the absorption tower was 0.25 mol %.

[0064] As described above, when the discharge height of the side discharge stream from the absorber was controlled to be higher than that of Example 1, the loss of (meth)acrylic acid discharged as the top discharge stream from the absorber was 0.25 mol %, which was an increase compared to the loss of (meth)acrylic acid in Example 1.

[0065] (Comparative Example) (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.

[0066] Specifically, in Comparative Example 1, the (meth)acrylic acid solution was not obtained from the side and bottom of the absorption tower 100, but was obtained only from the bottom of the absorption tower and charged into the crystallization apparatus 300 to obtain (meth)acrylic acid 320. The mother liquor 310 after crystallization was charged into the high-boiling by-product separation tower 200 to obtain a bottom discharge stream 220 from the high-boiling by-product separation tower containing high-boiling by-products and an upper discharge stream 210 from the high-boiling by-product separation tower containing the mother liquor from which the high-boiling by-products had been removed. The upper discharge stream 210 from the high-boiling by-product separation tower was recycled to the absorption tower 100. Except for this, (meth)acrylic acid was produced in the same manner as in Example 1.

[0067] The (meth)acrylic acid solution 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%). This was fed into crystallization apparatus 300, and it was confirmed that the content of (meth)acrylic acid in (meth)acrylic acid recovery stream 320 was 99.5 wt% or more.

[0068] The energy used to remove high-boiling by-products from the mother liquor after crystallization in the high-boiling by-product separation column 200 was 154.5 kcal / kg AA, which indicates that more than four times the energy consumed in the high-boiling by-product separation column 200 in Example 1 was consumed. Meanwhile, the content of (meth)acrylic acid (amount of acrylic acid loss) in the top discharge stream 110 of the absorption column was 0.144 mol%.

Claims

1. contacting a mixed gas containing (meth)acrylic acid and high-boiling by-products with an absorption solvent in an absorption tower; The first (meth)acrylic acid solution discharged from the bottom of the absorption tower is supplied to a high-boiling by-product separation tower, and the top discharge stream of the high-boiling by-product separation tower is supplied to a crystallization device; supplying the second (meth)acrylic acid solution discharged from the side of the absorption tower to the crystallization device; obtaining (meth)acrylic acid crystallized in the crystallization apparatus, and circulating a mother liquor recovered from the crystallization apparatus to the absorption tower.

2. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the content of (meth)acrylic acid in the second (meth)acrylic acid solution is higher than the content of (meth)acrylic acid in the first (meth)acrylic acid solution.

3. The method for producing (meth)acrylic acid according to claim 1, wherein the contents of (meth)acrylic acid in the first (meth)acrylic acid solution and the second (meth)acrylic acid solution are both 85% by weight to 99% by weight.

4. 2. The method for producing (meth)acrylic acid according to claim 1, wherein a ratio of a flow rate of the recovered mother liquor when introduced into the absorption tower to a flow rate of the recovered mother liquor when discharged from the crystallization apparatus is 0.99 to 1.

01.

5. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the content of (meth)acrylic acid in the top discharge stream of the high-boiling by-product separation column is 90% by weight to 99% by weight.

6. The first (meth)acrylic acid solution is discharged from the bottom end of the absorption tower, 2. The method for producing (meth)acrylic acid according to claim 1, wherein the second (meth)acrylic acid solution is discharged from a side portion of the absorption tower at a height of 80% to 99% downward from the top of the absorption tower.

7. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the content of (meth)acrylic acid in the top discharge stream of the absorption tower is 0.03 mol % to 0.5 mol %.

8. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the flow rates of the absorption solvents contained in the first (meth)acrylic acid solution and the second (meth)acrylic acid solution are 30% by weight to 50% by weight relative to the flow rate of the absorption solvent introduced into the absorption tower.

9. 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 circulated to the reactor as a top discharge stream from a cooling tower after a part of the top discharge stream from the absorption tower is supplied to the cooling tower and cooled.

10. the absorption solvent is water; The method for producing (meth)acrylic acid according to claim 9, wherein the water content in the recycled gas is 1% by weight to 10% by weight.

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