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 an extraction tower and contacting the aqueous (meth)acrylic acid solution with an extraction solvent to extract it and obtain an extract containing the (meth)acrylic acid and the extraction solvent; supplying the extract to a solvent purification tower and separating it in the solvent purification tower into a bottom discharge stream from the solvent purification tower containing (meth)acrylic acid and an upper discharge stream from the solvent purification tower containing the extraction solvent; supplying the bottom discharge stream from the solvent purification tower to a crystallization apparatus to obtain crystallized (meth)acrylic acid in the crystallization apparatus; and, after the crystallization, supplying a mother liquor to a high-boiling by-product separation tower and circulating the upper discharge stream from the high-boiling by-product separation tower from which the high-boiling by-products have been removed to the solvent purification tower.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0109527 filed on August 30, 2022 and Korean Patent Application No. 10-2023-0107080 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 further reduce the amount of energy used in the purification process, in order to solve the problems mentioned in the Background of the Invention. [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 an extraction tower and contacting the aqueous (meth)acrylic acid solution with an extraction solvent to extract the aqueous (meth)acrylic acid solution and obtaining an extract containing the (meth)acrylic acid and the extraction solvent; supplying the extract solution to a solvent purification tower and separating it in the solvent purification tower into a bottom discharge stream from the solvent purification tower containing (meth)acrylic acid and an upper discharge stream from the solvent purification tower containing the extraction solvent; supplying the bottom discharge stream from the solvent purification tower to a crystallization apparatus to obtain crystallized (meth)acrylic acid in the crystallization apparatus; and, after the crystallization, supplying a mother liquor to a high-boiling by-product separation tower and circulating the top discharge stream from the high-boiling by-product separation tower from which the high-boiling by-products have been removed to the solvent purification tower. [Effects of the Invention]

[0010] According to the method for producing (meth)acrylic acid according to the present invention, the entire aqueous (meth)acrylic acid solution discharged from the absorption tower is subjected to an extraction process before distillation to remove water contained in the aqueous (meth)acrylic acid solution, and in the subsequent solvent purification process, the distillation is performed so that the extraction solvent is contained in the bottom discharge stream of the solvent purification tower containing (meth)acrylic acid, thereby reducing the amount of energy required. Furthermore, high-purity (meth)acrylic acid can be obtained by a crystallization process of the bottom discharge stream of the solvent purification tower.

[0011] Furthermore, since the mother liquor from which most of the (meth)acrylic acid has been removed by the crystallization process is distilled to remove high-boiling by-products, it is possible to prevent the accumulation of high-boiling by-products in the system and also to reduce the amount of energy consumption by reducing the amount of high-boiling by-products that must be distilled for removal. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a process flow chart showing a method for producing (meth)acrylic acid according to one embodiment of the present invention. [Figure 2] 1 is a process flow chart showing a method for producing (meth)acrylic acid according to a comparative example of the present invention. [Figure 3] 1 is a process flow chart showing a method for producing (meth)acrylic acid according to a comparative example of the present invention. [Figure 4] 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

[0013] 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.

[0014] 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.

[0015] 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).

[0016] The present invention will now be described in more detail to facilitate understanding of the present invention.

[0017] 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 an extraction tower and contacting the aqueous (meth)acrylic acid solution with an extraction solvent to extract it and obtain an extract containing the (meth)acrylic acid and the extraction solvent; supplying the extract to a solvent purification tower and separating it in the solvent purification tower into a bottom discharge stream from the solvent purification tower containing (meth)acrylic acid and an upper discharge stream from the solvent purification tower containing the extraction solvent; supplying the bottom discharge stream from the solvent purification tower to a crystallization apparatus to obtain crystallized (meth)acrylic acid in the crystallization apparatus; and, after the crystallization, supplying a mother liquor to a high-boiling by-product separation tower and circulating the top discharge stream from the high-boiling by-product separation tower from which the high-boiling by-products have been removed to the solvent purification tower.

[0018] Hereinafter, each step that can be included in an embodiment of the present invention will be described with reference to FIG.

[0019] First, a method for producing (meth)acrylic acid according to one embodiment of the present invention may include a step of contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain an aqueous (meth)acrylic acid solution.

[0020] 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 gas, carbon monoxide, carbon dioxide, water vapor, and various organic by-products (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 produced in 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. 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 acetic acid in the system can be further separated and removed using a solvent purification tower and a layer separation device subsequent to the absorption tower. Therefore, it is not necessary to forcibly discharge the acetic acid in 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 absorber 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 absorber's upper discharge stream 110. 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 bottom discharge stream from the cooling tower 20 in the form of an aqueous solution. Thereafter, the bottom discharge stream 6 from the cooling tower 20 can be supplied to the absorber 100.

[0028] Water required for 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 include tap water, deionized water, and other water, and can also include recycled 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 trace amounts of organic by-products (e.g., acetic acid) introduced from other processes.

[0029] 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.

[0030] Thereafter, a step for obtaining an aqueous (meth)acrylic acid solution can be carried out by supplying the mixed gas containing the (meth)acrylic acid to an absorption tower 100 via a reactor discharge line 2 and bringing it into contact with water in the absorption tower 100. 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 as an absorption solvent in the absorption tower 100, thereby obtaining an aqueous (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 rashing ring, a pall ring, a saddle, gauze, or a structured packing applied thereto.

[0032] 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.

[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 100°C or 50 to 90°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, 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.

[0035] 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.

[0036] However, when the amount of acetic acid discharged to the top of the absorber 100 increases beyond a certain level, the content of (meth)acrylic acid discharged to the top of the absorber 100 also increases, resulting in an increase in the amount of (meth)acrylic acid lost in the absorber. Therefore, the present invention minimizes the amount of (meth)acrylic acid lost in the absorber by controlling the amount of acetic acid contained in the top discharge stream of the absorber 100. That is, the content of acetic acid in the top discharge stream of the absorber can be controlled so as to minimize the amount of (meth)acrylic acid lost to the top of the absorber. In addition, the solvent purification tower and layer separation device subsequent to the absorber, which will be described later, can further separate and remove acetic acid, thereby solving the problem of acetic acid accumulating in the system and acting as an impurity.

[0037] In this regard, the flow rate ratio of acetic acid discharged from the upper part 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%. Meanwhile, the content of (meth)acrylic acid contained in the upper discharge stream of the absorber may be 0.1 wt% to 0.5 wt%, specifically 0.2 wt% to 0.3 wt%. Meanwhile, the (meth)acrylic acid aqueous solution may be discharged via absorber discharge line 120 and supplied to extraction tower 300. The absorber discharge line 120 may be provided at the lower part of absorber 100.

[0038] According to one embodiment of the present invention, the (meth)acrylic acid aqueous solution may be directly supplied to the extraction tower 300 or may be supplied to the extraction tower 300 via a degassing tower 150. Specifically, the (meth)acrylic acid aqueous solution may be supplied to the degassing tower 150, and the degassing tower discharge stream 160 from which low-boiling by-products, including acrolein, have been removed may be supplied to the extraction tower. Acrolein may be used as a raw material for producing (meth)acrylic acid or may be generated as a by-product during the gas-phase oxidation reaction for producing (meth)acrylic acid. The gas-phase fraction containing the low-boiling by-products from the degassing tower 150 may be circulated to the absorption tower 100, and the (meth)acrylic acid aqueous solution from which the low-boiling by-products have been removed may be discharged from the bottom of the degassing tower 150 and introduced into a process for obtaining purified (meth)acrylic acid.

[0039] A method for producing (meth)acrylic acid according to one embodiment of the present invention can include the steps of supplying the aqueous (meth)acrylic acid solution, specifically, the aqueous (meth)acrylic acid solution degassed through a degassing tower, to an extraction tower, and contacting the aqueous (meth)acrylic acid solution with an extraction solvent to extract it, thereby obtaining an extract containing the (meth)acrylic acid and the extraction solvent.

[0040] The extraction process performed in the extraction tower 300 of the present invention can remove most of the water contained in the aqueous (meth)acrylic acid solution without using a large amount of energy and supply the solution to the solvent purification tower 400. In this regard, it is preferable to use a liquid-liquid contact method for the extraction in the extraction tower 300 in order to improve the energy efficiency of the entire process. Furthermore, in the present invention, in the solvent purification process subsequent to the extraction tower, distillation is performed so that the extraction solvent is contained in the bottom discharge stream 420 of the solvent purification tower containing (meth)acrylic acid, thereby reducing the amount of energy required for the distillation process.

[0041] 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.

[0042] On the other hand, in the extraction step, it is advantageous from the viewpoint of the process that the temperature of the aqueous (meth)acrylic acid solution is 10 to 70° C. Also, in the extraction step, it is advantageous from the viewpoint of the process that the weight ratio of the aqueous (meth)acrylic acid solution to the extraction solvent is 1:1 to 1:5, preferably 1:1.2 to 1:2.5.

[0043] Additionally, a liquid-liquid contact type extractor may be used as the extraction tower 300. Non-limiting examples of the extractor include a Karr 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.

[0044] In this manner, water is removed from the aqueous (meth)acrylic acid solution discharged from the absorption tower 100, and an extract in which (meth)acrylic acid is extracted with the extraction solvent is obtained. The extract can be supplied to the solvent purification tower 400 as an extract stream 310. Specifically, the extract can contain acetic acid, (meth)acrylic acid, the extraction solvent, and high-boiling by-products.

[0045] Additionally, water contained in the aqueous (meth)acrylic acid solution from the extraction process can be recovered as a raffinate, which can be discharged as a raffinate stream 320 and introduced into a layer separation apparatus 450, which will be described later.

[0046] Next, the method for producing (meth)acrylic acid of the present invention can include a step of supplying the extract to a solvent purification column and separating the extract in the solvent purification column into a bottom discharge stream of the solvent purification column containing (meth)acrylic acid and an top discharge stream of the solvent purification column containing the extraction solvent.

[0047] Meanwhile, the content of (meth)acrylic acid contained in the bottom discharge stream 420 of the solvent purification tower may be 85 wt% to 98 wt%, specifically 90 wt% to 95 wt%, so that purified (meth)acrylic acid with high purity can be obtained from the bottom discharge stream 420 of the solvent purification tower through a crystallization process.

[0048] Furthermore, the bottom discharge stream 420 of the solvent purification tower may contain an extractant, and the content of the extractant may be 1 to 10 wt %, specifically 5 to 10 wt %. When the content of the extractant contained in the bottom discharge stream 420 of the solvent purification tower is 1 wt % or more, the amount of energy consumed in the solvent purification tower 400 can be reduced. When the content is 10 wt % or less, high-purity purified (meth)acrylic acid can be obtained through the crystallization process performed in the crystallization apparatus 500, and the energy required to recycle the extractant and (meth)acrylic acid in the high-boiling by-product separation tower 600 can be reduced.

[0049] Meanwhile, the bottom discharge stream 420 from the solvent purification tower contains the above-mentioned (meth)acrylic acid and extractant in the above-mentioned amounts, and may contain other components such as high-boiling by-products as the remaining amount. This extractant content differs from that of the prior art, in which the extractant is entirely purified through a solvent purification tower, and also differs from the extractant content when an attempt is made to distill off all of the extractant but some remains.

[0050] That is, in the present invention, the (meth)acrylic acid aqueous solution discharged from absorption tower 100 or the (meth)acrylic acid aqueous solution that has passed through degassing tower 150 can all be supplied to extraction tower 300 to remove water contained in the (meth)acrylic acid aqueous solution, and the subsequent solvent purification process can be performed by distilling the extractant so that it is contained in the bottom discharge stream of the solvent purification tower containing (meth)acrylic acid, thereby reducing the amount of energy used in the distillation process. When all or as much of the extractant is removed from the top of solvent purification tower 400, the amount of (meth)acrylic acid lost along with the extractant can increase, making it necessary to increase the reflux flow rate at the top of solvent purification tower 400. However, when bottom discharge stream 420 of the solvent purification tower contains a certain amount of extractant, as in the present invention, the reflux flow rate at the top of solvent purification tower 400 can be reduced while minimizing the loss of (meth)acrylic acid, thereby reducing the amount of energy used in solvent purification tower 400. In other words, by not distilling all of the extractive solvent in the solvent purification column 400, the amount of energy used in the solvent purification column can be reduced compared to when the entire extractive solvent is distilled. In this way, even if only a portion of the extractive solvent is distilled in the solvent purification column, the remaining extractive solvent can be separated in the crystallization step 500 described below.

[0051] For this reason, the operating temperature in the solvent purification column is 30°C to 120°C, and specifically, can be 40°C to 100°C.

[0052] Meanwhile, the top discharge stream 410 of the solvent purification tower 400 and the water-containing raffinate from the above extraction step, ie, the bottom discharge stream 320 of the extraction tower, can be introduced into a layer separation device 450 .

[0053] Here, the layer separator 450 is a liquid-liquid layer separator that separates immiscible fluids using gravity or centrifugal force based on the difference in density, and the relatively light liquid can be separated into the upper part of the layer separator 450 and the relatively heavy liquid can be separated into the lower part of the layer separator 450. Specifically, the stream supplied to the layer separator 450 can be separated into an organic layer 460 containing the extraction solvent and an aqueous layer 470 containing water and acetic acid.

[0054] In addition, at least a portion of the organic layer separated in the layer separation device 450 can be supplied to the upper part of the solvent purification column 400 and reused as a reflux liquid, and the remainder can be supplied to the extraction column 300 and reused as an extraction solvent.

[0055] According to one embodiment of the present invention, the ratio of the flow rate of the extraction solvent in the portion of the organic layer supplied to the solvent purification tower to the flow rate of the extraction solvent in the top discharge stream 410 of the solvent purification tower may be 0.3 to 0.6. When the ratio of the flow rate of the extraction solvent in the portion of the organic layer supplied to the solvent purification tower to the flow rate of the extraction solvent in the top discharge stream of the solvent purification tower is controlled within this range, the reflux flow rate at the top of the solvent purification tower is small, thereby reducing the amount of energy used in the solvent purification tower 400.

[0056] Meanwhile, at least a portion of the aqueous layer separated in the layer separator 450 can be supplied to the upper portion of the absorber 100 to be used as an absorbing solvent, and the remainder can be discharged as wastewater.

[0057] That is, according to one embodiment of the present invention, acetic acid can be discharged through the top discharge stream of the absorber 100, and can also be discharged through the solvent purification tower 400 and the layer separation device 450. Therefore, compared to a process in which acetic acid is removed only from the top of the absorber, acetic acid accumulated in the system can be removed more efficiently, thereby 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.

[0058] The method for producing (meth)acrylic acid according to one embodiment of the present invention may include supplying the bottom discharge stream 420 of the solvent purification tower to a crystallization apparatus 500 and obtaining crystallized (meth)acrylic acid in the crystallization apparatus 500.

[0059] In this specification, the (meth)acrylic acid crystallized in the crystallizer may be referred to as “purified (meth)acrylic acid.” Such a crystallization process may be carried out under ordinary conditions.

[0060] In the present invention, the crystallization method for obtaining the 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.

[0061] Specifically, to dynamically crystallize (meth)acrylic acid prior to crystallization, the bottom discharge stream from the solvent purification tower can be first flowed in the form of a falling film onto the inner wall of a tube. The temperature of the tube can then be adjusted 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 purified (meth)acrylic acid. The mother liquor may refer to the remaining solution after removing the purified (meth)acrylic acid from the bottom discharge stream from the solvent purification tower introduced into the crystallization apparatus 500. Therefore, the mother liquor may contain trace amounts of (meth)acrylic acid, the extraction solvent, and high-boiling by-products. The (meth)acrylic acid here may be the residual (meth)acrylic acid that has not been crystallized in the crystallization apparatus 500, which is separated in the high-boiling by-product separation column 600 (described later), and recycled to the solvent purification column 400.

[0062] The separation of the mother liquor and the crystallized (meth)acrylic acid can be carried out using a solid-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 510, and the mother liquor can be discharged from the crystallization device 500 via a mother liquor recovery line 520 and supplied to a high-boiling by-product separation column 600.

[0063] That is, the high-boiling by-product separation column 600 can separate the mother liquor into a lower fraction containing high-boiling by-products by distillation and an upper fraction of high-boiling by-products from which the high-boiling by-products have been removed.

[0064] The upper fraction of the high-boiling by-product separation column can contain 30 to 60% by weight of the extractant, 40 to 70% by weight of the (meth)acrylic acid, and the remainder of the by-products. That is, the upper fraction contains mostly the extractant and (meth)acrylic acid, which can be recycled and further recovered.

[0065] According to one embodiment of the present invention, the upper fraction of the high boiling by-product separation column 600 may be discharged through an upper discharge stream 610 of the high boiling by-product separation column and supplied to the solvent purification column 400. This allows for recycling of the extraction solvent and minimizes loss of (meth)acrylic acid.

[0066] 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.

[0067] 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.

[0068] 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 (6.6 mol%), water (16.4 mol%), high boiling point substances (0.09 mol%), and inert gases (76.3 mol%).

[0069] The mixed gas 2 was introduced into the absorption tower 100 from the top to the 11th 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 bottom discharge stream 6 of the cooling tower and a water layer from a layer separation device described below, and the water was supplied to the absorption tower 100 at a flow rate of 10.6 wt% with respect to the mass flow rate of the mixed gas 2. Here, 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 73.3°C.

[0070] Meanwhile, non-condensable gases containing components not dissolved in water were separated in the absorber 100 as an absorber top discharge stream 110, a portion 3 of the absorber top discharge stream 110 was supplied to a cooling tower 20, and the remainder was discharged outside the system.

[0071] In the cooling tower 20, non-condensable gases contained in a portion 3 of the upper discharge stream from the absorber were dissolved in water. Here, the water was supplied through a water supply line 5. The gases not dissolved in water in the cooling tower 20 were supplied to the reactor 10 through a recycle gas transfer line 4, and the lower discharge stream 6 from the cooling tower containing water and the components dissolved in the water (acetic acid and (meth)acrylic acid not dissolved in water in the absorber) was supplied to the top of the absorber 100.

[0072] Meanwhile, the (meth)acrylic acid aqueous solution was supplied to the degassing tower 150 as the bottom discharge stream 120 of the absorber and degassed, and the low-boiling by-products were supplied to the absorption tower 100 as the top discharge stream of the degassing tower. The (meth)acrylic acid aqueous solution from which the low-boiling by-products had been degassed was supplied to the extraction tower 300 as the 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 13.6 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 (64.3 wt%), acetic acid (2.7 wt%), water (32.2 wt%), furfural (0.5 wt%), and maleic acid (0.6 wt%). Here, the flow rate of the bottom discharge stream 160 of the degassing tower was 2.3 times the mass flow rate of water supplied to the absorption tower 100.

[0073] In the extraction tower 300, an extraction process was carried out in the presence of an extraction solvent (toluene), yielding a raffinate stream 320 containing water and an extract stream 310 containing toluene and (meth)acrylic acid. The extraction solvent (toluene) fed to the bottom of the extraction tower 300 was supplied at a flow rate four times the mass flow rate of water in the bottom effluent stream 160 of the degassing tower fed to the extraction tower 300. The raffinate stream 320 was supplied to a phase separation apparatus 450, which will be described later, and the extract stream 310 was supplied to a solvent purification tower 400.

[0074] In the solvent purification column 400, distillation yielded an upper effluent stream 410 containing toluene, water, and acetic acid, and a lower effluent stream 420 containing toluene, (meth)acrylic acid, and high-boiling by-products. The toluene supplied to the upper part of the solvent purification column 400 was supplied at a flow rate 0.66 times the mass flow rate of the toluene supplied to the extraction column 300. Meanwhile, the lower effluent stream 420 contained (meth)acrylic acid (92.2 wt%), acetic acid (1.2 wt%), toluene (5.1 wt%), furfural (0.7 wt%), and maleic acid (0.5 wt%).

[0075] The top discharge stream 410 from the solvent purification column was supplied to a layer separation apparatus 450 and separated into an aqueous layer 470 containing water and acetic acid and an organic layer 460 containing toluene. The concentration of (meth)acrylic acid in the aqueous layer 470 was 1.56% by weight, and a portion of the aqueous layer was supplied to the absorption column 100, while the remainder was discharged to the outside of the system as wastewater. Meanwhile, a portion of the organic layer was supplied to the solvent purification column 400, and the remainder was supplied to the extraction column 300. The mass flow ratio of toluene in the portion of the organic layer 460 supplied to the solvent purification column 400 to the mass flow rate of toluene in the top discharge stream 410 from the solvent purification column was 0.4.

[0076] Meanwhile, the bottom discharge stream 420 from the solvent purification column was supplied to a crystallizer 500 and crystallized, and (meth)acrylic acid was finally obtained from a (meth)acrylic acid-containing (meth)acrylic acid recovery stream 510, and the mother liquor was supplied to a high-boiling by-product separation column 600 via a mother liquor recovery line 520. The (meth)acrylic acid content of the (meth)acrylic acid contained in the (meth)acrylic acid recovery stream 510 was 99.5 wt% or more.

[0077] The mother liquor was distilled in the high-boiling by-product separation column 600 to obtain a high-boiling by-product separation column bottom effluent stream 620 containing high-boiling by-products and a high-boiling by-product separation column top effluent stream 610 containing (meth)acrylic acid (54.2 wt %), toluene (37.3 wt %), and the remaining by-products. The high-boiling by-product separation column top effluent stream 610 was supplied to the solvent purification column 400.

[0078] As a result, the energy consumed in the solvent purification column 400 was 426.4 kcal / kg AA, the energy consumed in the high-boiling by-product separation column 600 was 36.8 kcal / kg AA, and the energy consumed in the crystallization apparatus 500 was 144.5 kcal / kg AA, for a total of 607.7 kcal / kg AA.

[0079] Example 2 In Example 2, unlike Example 1, toluene was supplied to the upper part of the solvent purification tower 400 at a flow rate 0.67 times the mass flow rate of toluene supplied to the extraction tower 300, and the bottom discharge stream 420 from the solvent purification tower contained (meth)acrylic acid (87.3 wt%), acetic acid (1.3 wt%), toluene (10.1 wt%), furfural (0.6 wt%), and maleic acid (0.7 wt%), and the content of the extraction solvent (toluene) in the bottom discharge stream 420 from the solvent purification tower was controlled to 10.1 wt%.

[0080] As a result, 99.5 wt % or more of (meth)acrylic acid was obtained from the (meth)acrylic acid recovery stream 510 of the crystallizer.

[0081] In addition, the energy consumed in the solvent purification column 400 was 431.4 kcal / kg AA, the energy consumed in the high-boiling by-product separation column 600 was 78.2 kcal / kg AA, and the energy consumed in the crystallization apparatus 500 was 144.5 kcal / kg AA, for a total of 654.1 kcal / kg AA.

[0082] (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.

[0083] Specifically, in Comparative Example 1, a mixed gas 2 obtained by the same steps as in Example 1 was introduced into an absorption tower 100 under the same conditions (operating conditions and the flow rate of water introduced into the absorption tower), and the mixed gas was contacted with water in the absorption tower 100 to obtain an aqueous (meth)acrylic acid solution. The aqueous (meth)acrylic acid solution was supplied to a degassing tower 150 to obtain an upper discharge stream from the degassing tower containing low-boiling by-products and a lower discharge stream from the degassing tower 160 containing the aqueous (meth)acrylic acid solution from which the low-boiling by-products had been removed. Here, the upper discharge stream from the degassing tower had a flow rate of 13.6 wt% of the mass flow rate of water introduced into the absorption tower, and the lower discharge stream from the degassing tower 160 had a flow rate 2.3 times the mass flow rate of water introduced into the absorption tower. The bottom discharge stream 160 from the degassing tower contained (meth)acrylic acid (64.3 wt%), acetic acid (2.7 wt%), water (31.9 wt%), furfural (0.5 wt%) and maleic acid (0.6 wt%), and the bottom discharge stream 160 from the degassing tower was supplied to a water separation tower 700.

[0084] Azeotropic distillation in the presence of an azeotropic solvent (toluene) in the water separation tower 700 produced an upper discharge stream 710 from the water separation tower containing toluene, water, and acetic acid, and a lower discharge stream 720 from the water separation tower containing (meth)acrylic acid and high-boiling by-products. The lower discharge stream 720 from the water separation tower contained (meth)acrylic acid (98.2 wt%), acetic acid (0.08 wt%), toluene (0.0 wt%), furfural (0.81 wt%), and maleic acid (0.93 wt%). The azeotropic solvent was supplied to the upper part of the water separation tower 700 at a flow rate 2.1 times the mass flow rate of the lower discharge stream 160 from the degassing tower.

[0085] The top discharge stream 710 from the water separation tower was fed to a layer separation apparatus 450, where it was separated into an aqueous layer 470 containing water and acetic acid and an organic layer 460 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 460 was recycled to the water separation tower 700.

[0086] Meanwhile, bottom discharge stream 720 from the water separation tower was supplied to high-boiling by-product separation tower 600 to obtain bottom discharge stream 620 from the high-boiling by-product separation tower containing high-boiling by-products and top discharge stream 610 from the high-boiling by-product separation tower containing (meth)acrylic acid. The content of (meth)acrylic acid in top discharge stream 610 from the high-boiling by-product separation tower was 99.5 wt% or more, and 99.5 wt% or more of (meth)acrylic acid was obtained through top discharge stream 610 from the high-boiling by-product separation tower.

[0087] As a result, the energy consumed in the water separation tower 700 was 683.6 kcal / kg AA, and the energy consumed in the high boiling point by-product separation tower 600 was 179.5 kcal / kg AA, for a total of 863.1 kcal / kg AA.

[0088] (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.

[0089] In Comparative Example 2, the bottom discharge stream 160 of the degassing tower, having the same composition as in Comparative Example 1, was branched off at 35 wt % and 65 wt % of the total weight of the bottom discharge stream 160 of the degassing tower, and supplied to the extraction tower 300 and the water separation tower 700, respectively.

[0090] In the extraction tower 300, an extraction process was performed in the presence of an extraction solvent (toluene), yielding a raffinate stream 320 containing water and an extract stream 310 containing toluene and (meth)acrylic acid. The extract solvent was branched off from the top of the extraction tower 300 and supplied to the bottom of the extraction tower 300 at a flow rate 4.1 times the mass flow rate of water in the bottom discharge stream from the degassing tower. The raffinate stream 320 was supplied to a layer separation apparatus 450, and the extract stream 310 was mixed with the bottom discharge stream from the degassing tower, which was branched off and supplied to the water separation tower 700, and then supplied to the water separation tower 700.

[0091] Azeotropic distillation in the presence of an azeotropic solvent (toluene) in the water separation tower 700 produced an upper discharge stream 710 from the water separation tower containing toluene, water, and acetic acid, and a lower discharge stream 720 from the water separation tower containing (meth)acrylic acid and high-boiling by-products. The lower discharge stream 720 from the water separation tower contained (meth)acrylic acid (98.2 wt%), acetic acid (0.1 wt%), toluene (0.0 wt%), furfural (0.81 wt%), and maleic acid (0.93 wt%). The azeotropic solvent was supplied to the top of the water separation tower 700 at a flow rate 2.1 times the mass flow rate of the extraction solvent supplied to the extraction tower.

[0092] The top discharge stream 710 from the water separation tower was fed to a layer separation apparatus 450 to obtain an aqueous layer 470 containing water and acetic acid and an organic layer 460 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 460 was fed to a water separation tower 700 and an extraction tower 300.

[0093] Meanwhile, bottom discharge stream 720 from the water separation tower was supplied to high-boiling by-product separation tower 600 to obtain bottom discharge stream 620 from the high-boiling by-product separation tower containing high-boiling by-products and top discharge stream 610 from the high-boiling by-product separation tower containing (meth)acrylic acid. The content of (meth)acrylic acid in top discharge stream 610 from the high-boiling by-product separation tower was 99.5 wt% or more, and 99.5 wt% or more of (meth)acrylic acid was obtained through top discharge stream 610 from the high-boiling by-product separation tower.

[0094] As a result, the energy consumed in the water separation tower 700 was 474.5 kcal / kg AA, and the energy consumed in the high boiling point by-product separation tower 600 was 179.5 kcal / kg AA, for a total of 654 kcal / kg AA.

[0095] (Comparative Example 3) The (meth)acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, following the process flow illustrated in FIG.

[0096] In Comparative Example 3, mixed gas 2 obtained by the same steps as in Example 1 was introduced into absorption tower 100 under the same conditions (operating conditions and flow rate of water introduced into the absorption tower) as in Example 1, and the mixed gas was contacted with water in absorption tower 100 to obtain an aqueous solution of (meth)acrylic acid. The aqueous solution of (meth)acrylic acid was supplied to degassing tower 150, and an upper discharge stream from the degassing tower containing low-boiling by-products and a lower discharge stream from the degassing tower containing the aqueous solution of (meth)acrylic acid from which the low-boiling by-products had been removed were obtained.

[0097] The bottom effluent stream 160 from the degassing tower was fed to an extraction tower 300. In the extraction tower 300, an extraction step was carried out in the presence of an extraction solvent (toluene), resulting in a raffinate stream 320 containing water and an extract stream 310 containing toluene and (meth)acrylic acid.

[0098] The raffinate stream 320 was fed to a phase separator 450, described below, and the extract stream 310 was fed to a solvent purification column 400.

[0099] In the solvent purification column 400, a solvent purification column top discharge stream 410 containing toluene, water, and acetic acid and a solvent purification column bottom discharge stream 420 containing (meth)acrylic acid and high-boiling by-products were obtained by distillation. Here, the toluene supplied to the solvent purification column 400 was supplied to the top of the solvent purification column 400 at a flow rate 1.75 times the mass flow rate of the toluene supplied to the extraction column 300. Meanwhile, the solvent purification column bottom discharge stream 420 contained (meth)acrylic acid (92.2 wt%), acetic acid (0.1 wt%), toluene (0.01 wt%), furfural (0.8 wt%), and maleic acid (0.9 wt%).

[0100] The top discharge stream 410 from the solvent purification tower was supplied to a layer separation device 450 and separated into an aqueous layer containing water and acetic acid and an organic layer containing toluene. The concentration of (meth)acrylic acid in the aqueous layer was 1.54 wt %, and a portion of the aqueous layer was supplied to an absorption tower 100, while the remainder was discharged to the outside of the system as wastewater. Meanwhile, the organic layer was supplied to an extraction tower 300 and a solvent purification tower 400.

[0101] Meanwhile, the bottom discharge stream 420 from the solvent purification column was supplied to a high-boiling by-product separation column 600 to obtain a bottom discharge stream 620 from the high-boiling by-product separation column containing high-boiling by-products and an upper discharge stream 610 from the high-boiling by-product separation column containing (meth)acrylic acid. The content of (meth)acrylic acid in the upper discharge stream 610 from the high-boiling by-product separation column was 99.5 wt% or more, and thus, finally, 99.5 wt% or more of (meth)acrylic acid was obtained.

[0102] As a result, the energy consumed in the solvent purification column 400 was 658.2 kcal / kg AA, and the energy consumed in the high boiling point by-product separation column 600 was 179.5 kcal / kg AA, for a total of 837.7 kcal / kg AA.

[0103] In Comparative Example 3, in contrast to Example 1, the extraction solvent (toluene) was distilled in the solvent purification tower so that a relatively small amount of the extraction solvent was contained in the bottom discharge stream of the solvent purification tower. Unlike Comparative Examples 1 and 2, without providing a crystallization apparatus, it was possible to obtain 99.5 wt% or more of (meth)acrylic acid through the high-boiling by-product separation tower. However, it was confirmed that the total energy used in the process of Comparative Example 3 was significantly increased compared to the Examples.

Claims

1. A step 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 an extraction tower, contacting the aqueous (meth)acrylic acid solution with an extraction solvent to extract the aqueous (meth)acrylic acid solution, and obtaining an extract containing the (meth)acrylic acid and the extraction solvent; feeding the extract to a solvent purification column, and separating the extract in the solvent purification column into a solvent purification column bottom effluent stream containing (meth)acrylic acid and a solvent purification column top effluent stream containing the extractant; The bottom discharge stream of the solvent purification tower is supplied to a crystallization apparatus, and (meth)acrylic acid is obtained crystallized in the crystallization apparatus; and feeding, after the crystallization, the mother liquor to a high-boiling by-product separation column, and circulating the top discharge stream from the high-boiling by-product separation column from which the high-boiling by-products have been removed to the solvent purification column.

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 tower, and a bottom discharge stream from the degassing tower from which low-boiling by-products have been removed is supplied to the extraction tower.

3. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the content of (meth)acrylic acid contained in the bottom discharge stream of the solvent purification column is 90 to 95% by weight.

4. the bottoms effluent stream of the solvent purification column comprises the extractant; 2. The method for producing (meth)acrylic acid according to claim 1, wherein the content of the extraction solvent contained in the bottom discharge stream of the solvent purification column is 1 to 10 wt %.

5. feeding the water-containing raffinate produced by the extraction and the overhead effluent stream from the solvent purification column to a layer separation device to separate the organic layer containing the extraction solvent and the aqueous layer containing water and acetic acid; 2. The method for producing (meth)acrylic acid according to claim 1, wherein a part of the aqueous layer 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 top discharge stream of the high-boiling by-product separation column contains 30 to 60% by weight of the extraction solvent, 40 to 70% by weight of the (meth)acrylic acid, and the balance being by-products.

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

8. 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.

9. 6. The method for producing (meth)acrylic acid according to claim 5, wherein a part of the organic layer containing the extraction solvent is supplied to a solvent purification column, and the remainder is supplied to an extraction column.

10. The method for producing (meth)acrylic acid according to claim 9, wherein the ratio of the flow rate of the extraction solvent in the portion of the organic layer supplied to the solvent purification column to the flow rate of the extraction solvent in the top discharge stream of the solvent purification column is 0.3 to 0.

6.

11. The method for producing (meth)acrylic acid according to claim 1, wherein the extraction solvent comprises one or more of benzene, toluene, xylene, n-heptane, cycloheptane, and cycloheptene.

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