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 first and second aqueous (meth)acrylic acid solutions; discharging the first aqueous (meth)acrylic acid solution from a bottom of the absorption tower and supplying it to a crystallization apparatus, and discharging the second aqueous (meth)acrylic acid solution from a side of the absorption tower; supplying the second aqueous (meth)acrylic acid solution to a water separation tower to obtain a distillate containing (meth)acrylic acid and high-boiling by-products; supplying the distillate to a high-boiling by-product separation tower and supplying an upper discharge stream of the high-boiling by-product separation tower containing (meth)acrylic acid to the crystallization apparatus; obtaining purified (meth)acrylic acid in the crystallization apparatus, and circulating a portion of the mother liquor recovered in the crystallization apparatus to the absorption tower and the remainder to the water separation tower.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0109514 filed on August 30, 2022 and Korean Patent Application No. 10-2023-0107059 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 recovering (meth)acrylic acid, which can ensure high-purity (meth)acrylic acid at a high recovery rate and can further reduce the amount of energy used in the purification step, 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 first and second aqueous (meth)acrylic acid solutions; discharging the first aqueous (meth)acrylic acid solution from a bottom of the absorption tower and supplying it to a crystallization apparatus, and discharging the second aqueous (meth)acrylic acid solution from a side of the absorption tower; supplying the second aqueous (meth)acrylic acid solution to a water separation tower to obtain a distillate containing (meth)acrylic acid and high-boiling by-products; supplying the distillate to a high-boiling by-product separation tower and supplying an upper discharge stream of the high-boiling by-product separation tower containing (meth)acrylic acid to the crystallization tower; obtaining purified (meth)acrylic acid in the crystallization tower, and circulating a portion of the mother liquor recovered in the crystallization tower to the absorption tower and the remainder to the water separation tower. [Effects of the Invention]

[0010] According to the method for producing (meth)acrylic acid according to the present invention, the amount of water introduced into the absorption tower for purifying (meth)acrylic acid is minimized, and a part of the aqueous (meth)acrylic acid solution discharged from the absorption tower is directly supplied to the crystallization apparatus without undergoing a distillation process, thereby reducing the amount of energy consumed in the entire process.

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

[0012] Furthermore, after the water separation tower, high-boiling by-products are separated to prevent their accumulation in the system, and the overhead discharge stream of the high-boiling by-products is also supplied to the crystallization, thereby further reducing the loss of (meth)acrylic acid. [Brief explanation of the drawings]

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

[0014] The terms and words used in the description and claims of the present invention should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best describe their invention.

[0015] In the present invention, the term "stream" can refer to the flow of fluid within a process, or the fluid itself flowing in a pipe. Specifically, the term "stream" can simultaneously refer to the fluid itself flowing in a pipe connecting each device and the flow of the fluid. Furthermore, the fluid can refer to gas or liquid, and does not exclude cases where the fluid contains solid components.

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

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

[0018] A method for producing (meth)acrylic acid according to one embodiment of the present invention includes the steps of contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain first and second aqueous (meth)acrylic acid solutions; discharging the first aqueous (meth)acrylic acid solution from the bottom of the absorption tower and supplying it to a crystallization apparatus, and discharging the second aqueous (meth)acrylic acid solution from the side of the absorption tower; supplying the second aqueous (meth)acrylic acid solution to a water separation tower to obtain a distillate containing (meth)acrylic acid and high-boiling by-products; supplying the distillate to a high-boiling by-product separation tower and supplying an upper discharge stream of the high-boiling by-product separation tower containing (meth)acrylic acid to the crystallization apparatus; obtaining purified (meth)acrylic acid in the crystallization apparatus, and circulating a portion of the mother liquor recovered in the crystallization apparatus to the absorption tower and the remainder to the water separation tower.

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

[0020] First, a method for producing (meth)acrylic acid according to one embodiment of the present invention may include contacting a mixed gas containing (meth)acrylic acid with water in an absorption tower to obtain first and second aqueous (meth)acrylic acid solutions. 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 (e.g., acetic acid, low-boiling by-products, high-boiling by-products, etc.). Here, "light ends" or "heavies" refer to a type of by-product that may be generated during the production and recovery process of the target (meth)acrylic acid, and may be a compound with a molecular weight smaller or larger than that of (meth)acrylic acid.

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

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

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

[0024] The recycle gas may originate from the upper portion of the absorber 100 described below. That is, the mixed gas is contacted with water, which is an absorption solvent, in the absorber 100, and non-condensable gases not dissolved in the water may be discharged as the 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 minimal amount of (meth)acrylic acid. The recycle gas may 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.

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

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

[0027] The cooling tower 20 is provided with a water supply line 5 at its top, and water used as an absorption solvent in the 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 can be carried out in which the mixed gas containing (meth)acrylic acid, which is the product of the gas-phase oxidation reaction, is supplied to an absorption tower 100 via a reactor discharge line 2 and brought into contact with water, which is an absorption solvent, in the absorption tower 100 to obtain an aqueous (meth)acrylic acid solution. Specifically, the mixed gas can contain organic by-products such as (meth)acrylic acid, acetic acid, and acrolein, as well as water vapor.

[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 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, a first aqueous (meth)acrylic acid solution discharged from the bottom of the absorption tower 100 and a second aqueous (meth)acrylic acid solution discharged from the side of the absorption tower 100 can be obtained through an absorption process performed in the absorption tower 100.

[0035] The lower part of the absorption tower 100 to which the first aqueous (meth)acrylic acid solution is discharged may be a point 95% to 100% of the height downward from the top of the absorption tower 100, specifically, the tower bottom, which is the lowest part of the absorption tower. Meanwhile, the side part of the absorption tower 100 to which the second aqueous (meth)acrylic acid solution is discharged may be a side part 40% to 80% of the height downward from the top of the absorption tower 100. By setting the height (number of stages) at which the first and second aqueous (meth)acrylic acid solutions are discharged from the absorption tower, the contents of components contained in the first and second aqueous (meth)acrylic acid solutions, for example, the contents of water and (meth)acrylic acid, can be controlled.

[0036] The content of (meth)acrylic acid in the first aqueous (meth)acrylic acid solution may be 75% by weight to 95% by weight, specifically 80% by weight to 90% by weight. The content of water in the first aqueous (meth)acrylic acid solution may be 5% by weight to 20% by weight, specifically 10% by weight to 15% by weight. The first aqueous (meth)acrylic acid solution may contain the remaining amount of organic by-products in addition to the (meth)acrylic acid and water.

[0037] The content of (meth)acrylic acid in the first (meth)acrylic acid aqueous solution is higher than the content of (meth)acrylic acid in the (meth)acrylic acid aqueous solution discharged from an existing absorption tower. In particular, by making the content of (meth)acrylic acid in the first (meth)acrylic acid aqueous solution 75 wt % or more, the first (meth)acrylic acid aqueous solution can be directly supplied to crystallization apparatus 300 without undergoing a separate purification process or separation process for the first (meth)acrylic acid aqueous solution, thereby enabling overall process energy savings and enabling high-purity (meth)acrylic acid to be obtained in crystallization apparatus 300.

[0038] The content of (meth)acrylic acid in the second aqueous (meth)acrylic acid solution may be 30% by weight to 60% by weight, specifically 40% by weight to 55% by weight. The content of water in the second aqueous (meth)acrylic acid solution may be 40% by weight to 60% by weight. The second aqueous (meth)acrylic acid solution may contain a residual amount of organic by-products in addition to the (meth)acrylic acid and water. Therefore, the second aqueous (meth)acrylic acid solution may be discharged from a side portion of the absorption tower 100 at a height of 40% to 80% downward from the top of the absorption tower 100.

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

[0040] In the past, in order to obtain high-purity (meth)acrylic acid, it was common to discharge as much acetic acid as possible as the top discharge stream from the absorber. However, as the amount of acetic acid discharged to the top of the absorber 100 increases and exceeds a certain level, the content of (meth)acrylic acid discharged to the top of the absorber 100 also increases, resulting in a problem of an increase in the amount of (meth)acrylic acid lost in the absorber. Therefore, the present invention minimizes the content of (meth)acrylic acid lost in the absorber by controlling the amount of acetic acid contained in the top discharge stream from the absorber 100. That is, the content of acetic acid in the top discharge stream from the absorber can be controlled so as to minimize the content of (meth)acrylic acid lost to the top of the absorber. In addition, acetic acid can be further separated and removed by a water separation tower and a layer separation device downstream of the absorber, which will be described later, thereby solving the problem of acetic acid accumulating in the system and acting as an impurity.

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

[0042] Meanwhile, the first (meth)acrylic acid aqueous solution can be supplied to the crystallization apparatus 300 via the bottom discharge stream 130 of the absorption tower, and the second (meth)acrylic acid aqueous solution can be introduced into a process for obtaining a distillate containing (meth)acrylic acid and high-boiling by-products via the side discharge stream 120 of the absorption tower.

[0043] That is, by separately discharging the first and second (meth)acrylic acid aqueous solutions having different (meth)acrylic acid contents from the absorption tower 100, the amount of energy consumed in subsequent processes can be reduced. Specifically, since the first (meth)acrylic acid aqueous solution has a high (meth)acrylic acid content, it can be directly supplied to the crystallization apparatus 300 without undergoing a separate purification or separation process for the first (meth)acrylic acid aqueous solution, thereby reducing the overall process energy and obtaining high-purity (meth)acrylic acid in the crystallization apparatus 300. This is possible because the first (meth)acrylic acid aqueous solution has a high (meth)acrylic acid content, as described above.

[0044] In addition, the first aqueous (meth)acrylic acid solution also contains a predetermined amount of water. As will be described later, the mother liquor separated from the purified (meth)acrylic acid in the crystallization apparatus 300 is circulated to an absorption tower, so that the amount of water contained in the second aqueous (meth)acrylic acid solution is reduced by the amount of water contained in the mother liquor, thereby reducing the amount of energy used in the purification process for the second aqueous (meth)acrylic acid solution.

[0045] Specifically, the method for producing (meth)acrylic acid according to one embodiment of the present invention may include a step of supplying the first aqueous (meth)acrylic acid solution to a crystallization apparatus 300, crystallizing the solution, and obtaining purified (meth)acrylic acid and a mother liquor separated from the purified (meth)acrylic acid. In this specification, the (meth)acrylic acid crystallized in the crystallization apparatus may be referred to as purified (meth)acrylic acid.

[0046] The (meth)acrylic acid contained in the first aqueous (meth)acrylic acid solution supplied to the crystallization apparatus 300 can be recrystallized through a crystallization process to obtain purified (meth)acrylic acid with high purity. In addition to the first aqueous (meth)acrylic acid solution, a high-boiling by-product separation column top discharge stream, which is discharged from the top of the high-boiling by-product separation column 600 (described later) and contains a high content of (meth)acrylic acid, can also be introduced into the crystallization apparatus 300.

[0047] Such a crystallization step can be carried out under conventional conditions.

[0048] The crystallization method for obtaining the product by crystallization in the present invention is not limited to suspension crystallization or layer crystallization, and may be either continuous or batchwise, and may be carried out in one or more stages. As a non-limiting example, the (meth)acrylic acid may be provided as purified (meth)acrylic acid by dynamic crystallization.

[0049] Specifically, to dynamically crystallize the (meth)acrylic acid before crystallization, the (meth)acrylic acid aqueous solution is first flowed onto the inner wall of a tube in the form of a falling film. The temperature of the tube is then adjusted to below the freezing point of (meth)acrylic acid to form crystals on the inner wall of the tube. The temperature of the tube is then raised to near the freezing point of (meth)acrylic acid to sweat approximately 5 wt. % of the (meth)acrylic acid. The sweated mother liquor is then removed from the tube, and the crystals formed on the inner wall of the tube are collected to obtain high-purity purified (meth)acrylic acid. The mother liquor may refer to the remaining solution after the purified (meth)acrylic acid has been removed from the aqueous (meth)acrylic acid solution introduced into the crystallization apparatus 300. Therefore, the mother liquor may contain water, (meth)acrylic acid, acetic acid, and high-boiling by-products. The (meth)acrylic acid in this case may be the residual (meth)acrylic acid that was not crystallized in the crystallization apparatus 300.

[0050] The separation of the crystallized purified (meth)acrylic acid from the mother liquor can be carried out using a solid-liquid separation device, such as a belt filter, a centrifuge, etc. The purified (meth)acrylic acid can be recovered as a (meth)acrylic acid recovery stream 310, and the mother liquor can be discharged from the crystallization device 300 via a mother liquor discharge stream.

[0051] According to one embodiment of the present invention, a portion of the mother liquor discharged from the crystallization apparatus 300 may be circulated to the absorption tower 100 via a first mother liquor recovery line 320, and the remainder of the mother liquor may be circulated to the water separation tower 500 via a second mother liquor recovery line 330. Here, the water separation tower 500 is an apparatus for receiving all or a portion of the second aqueous (meth)acrylic acid solution and distilling the same to obtain a distillate containing (meth)acrylic acid and high-boiling by-products, as will be described later.

[0052] Meanwhile, the mother liquor discharged from the crystallization apparatus 300 may contain 50% by weight to 80% by weight, specifically 60% by weight to 75% by weight of (meth)acrylic acid. The mother liquor may also contain 20% by weight to 50% by weight, specifically 25% by weight to 40% by weight of water. The mother liquor discharged from the crystallization apparatus 300 may also contain residual organic by-products.

[0053] According to one embodiment of the present invention, the second aqueous (meth)acrylic acid solution can be introduced into a process for obtaining a distillate containing (meth)acrylic acid and high-boiling by-products.

[0054] Meanwhile, the process of obtaining the distillate containing (meth)acrylic acid and high-boiling by-products according to one embodiment of the present invention may include the steps of: supplying a portion of the second aqueous (meth)acrylic acid solution to extraction tower 400 as extraction tower feed stream 170, and supplying the remainder to water separation tower 500 as water separation tower feed stream 160; contacting the extraction tower feed stream with an extractant in extraction tower 400, and supplying an extract stream containing an extract to water separation tower 500; and separating the distillate containing (meth)acrylic acid and high-boiling by-products in water separation tower 500 into water separation tower top outlet stream 510 containing water and water separation tower bottom outlet stream 520.

[0055] That is, by separately supplying the second aqueous (meth)acrylic acid solution to the extraction tower 400 and the water separation tower 500, energy consumption in subsequent processes can be reduced and by-products such as acetic acid can be efficiently separated. Specifically, the flow rate ratio of the extraction tower feed stream 170 supplied to the extraction tower relative to the flow rate of the second aqueous (meth)acrylic acid solution can be 20 wt% to 60 wt%. When this flow rate ratio is 20 wt% or more, the flow rate introduced into the water separation tower 500 is reduced, thereby reducing the amount of energy required to distill water, which has a high specific heat capacity, in the water separation tower 500. On the other hand, when this flow rate ratio is 60 wt% or less, acetic acid, a by-product, can be efficiently separated in the upper part of the water separation tower 500, thereby minimizing the amount of acetic acid introduced into the high-boiling by-product separation tower 600. This reduces the content of acetic acid in the upper discharge stream of the high-boiling by-product separation tower 600, thereby enabling high-purity purified (meth)acrylic acid to be obtained in the crystallization apparatus 300.

[0056] Meanwhile, extraction tower 400 removes most of the water contained in extraction tower feed stream 170 without using a large amount of energy and supplies the removed water to water separation tower 500, thereby reducing the energy required for azeotropic distillation in water separation tower 500, which will be described later. In this regard, it is preferable that the extraction in extraction tower 400 be performed by contacting the extraction solvent with the extraction tower feed stream via liquid-liquid contact, in order to improve the energy efficiency of the entire process.

[0057] 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.

[0058] Additionally, a liquid-liquid contact type extraction device may be used as the extraction tower 400. Non-limiting examples of the extraction device include a Karr type reciprocating plate column, a rotary-disk contactor, a Scheibel column, a Kuhni column, a spray extraction tower, a packed extraction tower, a pulsed packed column, a mixer-settler bank, a mixer and centrifugal countercurrent extractor, and the like.

[0059] In this manner, a significant portion of the water in the extraction tower feed stream 170 supplied to the extraction tower 400 is removed, and an extract in which (meth)acrylic acid is extracted with the extraction solvent is obtained. The extract can be supplied to the water separation tower 500 as extract stream 410. Specifically, the extract can contain (meth)acrylic acid, acetic acid, the extraction solvent, and high-boiling by-products.

[0060] Additionally, water contained in the extraction tower feed stream 170 from the extraction process can be recovered as a raffinate. The recovered raffinate can be discharged as a raffinate stream 420 and introduced into a layer separation apparatus 550, which will be described later. In this way, by recovering water from the extraction process, the operational burden of the distillation process, which will be described later, can be reduced, thereby reducing energy consumption.

[0061] Then, according to one embodiment of the present invention, the water separation tower feed stream 160 and the extract stream 410 of the second aqueous (meth)acrylic acid solution are supplied to a water separation tower 500, where a distillation process may be performed on these streams.

[0062] The flow rate of water in the stream supplied to the water separation tower 500 may be 30% by weight to 70% by weight, specifically 40% by weight to 60% by weight, based on the flow rate of water introduced into the absorption tower. If the water flow rate ratio is less than 0% by weight, it may be difficult to separate acetic acid in the water separation tower 500. If the flow rate ratio exceeds 70% by weight, the amount of energy consumed for distilling water in the water separation tower 500 and the high-boiling by-product separation tower 600 may increase.

[0063] That is, by controlling the flow rate and content of water contained in the stream supplied to the water separation tower 500, by-products such as acetic acid can be efficiently removed in the water separation tower 500, and ultimately, highly purified (meth)acrylic acid can be obtained. This minimizes the amount of energy required for distilling water in the water separation tower 500 and the high-boiling by-product separation tower 600 described below, thereby reducing overall energy costs.

[0064] The distillation step in the water separation column 500 for the stream supplied to the water separation column 500 can be a step of separating an upper fraction containing water, a hydrophobic azeotropic solvent, and acetic acid from a lower fraction containing (meth)acrylic acid and high-boiling by-products by azeotropic distillation.

[0065] According to the present invention, distillation in the water separation column 500 is carried out in the presence of a hydrophobic azeotropic solvent, which makes it possible to simultaneously recover the hydrophobic azeotropic solvent, water, and organic by-products (such as acetic acid), which is advantageous from a process standpoint.

[0066] Here, the hydrophobic azeotropic solvent can form an azeotrope with water and acetic acid but not with (meth)acrylic acid, and any hydrocarbon solvent that satisfies the above physical properties can be used without limitation. In addition, the hydrophobic azeotropic solvent can have a boiling point lower than that of (meth)acrylic acid, preferably 10 to 120°C.

[0067] According to the present invention, the hydrophobic azeotropic solvents satisfying the above physical properties include benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butyl acetate, isobutyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, and methyl isobutyl ketone. The solvent may be one or more selected from the group consisting of methyl ketone, 2-methyl-1-heptene, 6-methyl-1-heptene, 4-methyl-1-heptene, 2-ethyl-1-hexene, ethylcyclopentane, 2-methyl-1-hexene, 2,3-dimethylpentane, 5-methyl-1-hexene, and isopropyl-butyl-ether.

[0068] The hydrophobic azeotropic solvent may be the same as or different from the extraction solvent used in extraction tower 400. However, in consideration of production efficiency in a continuous process, it is preferable that the hydrophobic azeotropic solvent be the same as the extraction solvent. When the same compound is used as the azeotropic solvent and the extraction solvent, at least a portion of the azeotropic solvent recovered by distillation in water separation tower 500 can be supplied to the lower part of extraction tower 400 and used as part of the extraction solvent.

[0069] When the hydrophobic azeotropic solvent is introduced into the water separation tower 500, the azeotropy between (meth)acrylic acid and water is broken. Accordingly, the water and acetic acid in the mother liquor and the hydrophobic azeotropic solvent used in the azeotropic distillation form an azeotrope together, and can be recovered as an upper fraction of the water separation tower 500. In addition, a lower fraction containing (meth)acrylic acid and high-boiling by-products can be recovered from the lower part of the water separation tower 500.

[0070] The thus recovered upper fraction of the water separation tower can be supplied to the layer separation apparatus 550 via the upper discharge stream 510 of the water separation tower, and the lower fraction of the water separation tower can be supplied to the high-boiling by-product separation tower 600 via the lower discharge stream 520 of the water separation tower.

[0071] Here, layer separator 550 is a liquid-liquid layer separator that separates immiscible fluids using gravity or centrifugal force due to differences in density, and a relatively light liquid may be separated into an upper portion of layer separator 550 and a relatively heavy liquid into a lower portion of layer separator 550. Specifically, upper discharge stream 510 of the water separation tower supplied to layer separator 550 may be separated into an organic layer containing the hydrophobic azeotropic solvent and an aqueous layer containing water and acetic acid.

[0072] The organic layer separated in the layer separator 550 is discharged as a layer separator discharge stream 560, and a portion of the layer separator discharge stream 560 is supplied to the top of the water separation tower 500 and reused as an azeotropic solvent, and the remainder is supplied to the extraction tower 400 and reused as an extraction solvent.

[0073] Meanwhile, a portion of the aqueous layer containing water and acetic acid from the layer separator 550 can be supplied to the upper portion of the absorber 100 and used as an absorption solvent, and the remainder can be discharged as wastewater.

[0074] Here, the aqueous layer may contain acetic acid, and the concentration of acetic acid contained in the aqueous layer may vary depending on the type of azeotropic solvent and the reflux ratio of the column installed in the water separation tower 500. According to the present invention, the concentration of acetic acid contained in the aqueous layer may be 1 to 30% by weight, preferably 2 to 20% by weight, and more preferably 3 to 10% by weight.

[0075] 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 by azeotropic distillation performed through the water separation tower 500 and the layer separation device 550. Therefore, compared to a process in which acetic acid is removed only from the top of the absorber, acetic acid accumulated in the system can be removed more efficiently, thereby obtaining purified (meth)acrylic acid with high purity. Furthermore, compared to attempts to discharge the entire amount of acetic acid in the system to the top of the absorber, process flexibility can be ensured, which has the advantage of minimizing the amount of (meth)acrylic acid lost from the top of the absorber.

[0076] From this perspective, the total flow rate of acetic acid introduced into the absorber 100 may be equal to the sum of the flow rate of acetic acid in the top discharge stream of the absorber 100 and the flow rate of acetic acid in the stream discharged in the aqueous layer of the layer separator 550.

[0077] Meanwhile, a method for producing (meth)acrylic acid according to one embodiment of the present invention may include the steps of supplying a bottom discharge stream from the water separation tower 500 to a high-boiling by-product separation tower 600, and supplying an upper discharge stream from the high-boiling by-product separation tower 600 containing the (meth)acrylic acid to the crystallization apparatus 300.

[0078] The high-boiling by-product separation column 600 can separate the bottom discharge stream from the water separation column 500 into a bottom fraction containing high-boiling by-products by distillation and an upper fraction containing a high content of (meth)acrylic acid by removing the high-boiling by-products. The upper fraction can be supplied to the crystallization apparatus 300 via the top discharge stream 610 from the high-boiling by-product separation column, and the content of the (meth)acrylic acid in the top discharge stream 510 from the high-boiling by-product separation column can be 90% by weight to 99% by weight, specifically 95% by weight to 99% by weight.

[0079] That is, since the amount of water contained in each stream has already been reduced in the processes after the absorption tower 100, and a considerable amount of water has been removed through the extraction tower 400 and the water separation tower 500, the water content in the top discharge stream 610 of the high boiling by-product separation tower is controlled to be low, thereby realizing a concentrated stream with a high concentration of (meth)acrylic acid that can be immediately introduced into the crystallization apparatus 300. By introducing the top discharge stream 610 of the high boiling by-product separation tower into the crystallization apparatus 300, the loss of (meth)acrylic acid can be minimized.

[0080] Meanwhile, the first aqueous (meth)acrylic acid solution discharged from the bottom of the absorption tower and the upper discharge stream of the high-boiling by-product separation tower may be supplied to the crystallization apparatus 300 as separate streams, or these streams may be supplied to the crystallization apparatus 300 as a mixed stream.

[0081] The (meth)acrylic acid content in the upper discharge stream from the high-boiling by-product separation tower may be higher than the (meth)acrylic acid content in the first aqueous (meth)acrylic acid solution, and when the first aqueous (meth)acrylic acid solution discharged from the bottom of the absorption tower and the upper discharge stream from the high-boiling by-product separation tower are supplied to the crystallization apparatus as a mixed stream, the (meth)acrylic acid content in the mixed stream may be 85 to 99 wt %. Therefore, the mixed stream can be directly introduced into the crystallization apparatus without a separate distillation process.

[0082] The present invention will be described in more detail below with reference to examples. However, the following examples are for illustrative purposes only, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and technical concept of the present invention. The scope of the present invention is not limited to these examples alone.

[0083] Example 1 The (meth)acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, following the process flow illustrated in FIG.

[0084] Specifically, a reaction gas containing air and a raw material compound (propylene) was supplied to a reactor 10 equipped with a catalyst via a reaction gas supply line 1, and a recycle gas derived from a cooling tower 20 was supplied to the reactor 10 via a recycle gas transfer line 4. A gas-phase oxidation reaction carried out in the reactor 10 produced a mixed gas 2 containing (meth)acrylic acid (6.6 mol%), water (16.4 mol%), high boiling point substances (0.09 mol%), and inert gases (76.3 mol%).

[0085] The mixed gas 2 was introduced into the 11th stage of the absorption tower 100 from the top at a temperature of 164°C. In the absorption tower 100, the mixed gas was contacted with an absorption solvent (water) to obtain a first aqueous (meth)acrylic acid solution and a second aqueous (meth)acrylic acid solution. The water introduced into the absorption tower 100 was supplied via the lower discharge stream 6 of the cooling tower and a water layer from a layer separation device 550 described below, and the water was supplied to the upper part of 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 upper part of the absorption tower 100 was 1.1 bar, and the temperature at the lower part of the absorption tower 100 was 82°C.

[0086] 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 was supplied to a cooling tower 20, and the remainder was discharged outside the system.

[0087] In the cooling tower 20, non-condensable gases contained in a portion 3 of the absorber upper discharge stream were dissolved in water. Here, the water was supplied via a water supply line 5. The gases not dissolved in water in the cooling tower 20 were supplied to the reactor 10 via a recycle gas transfer line 4, and the cooling tower lower discharge stream 6 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.

[0088] Meanwhile, the first (meth)acrylic acid aqueous solution contained (meth)acrylic acid (79.2 wt%), acetic acid (2.2 wt%), water (17 wt%), furfural (0.7 wt%), and maleic acid (0.8 wt%), and was supplied to crystallization apparatus 300 as bottom discharge stream 130 from the absorber. Here, bottom discharge stream 130 from the absorber was mixed with top discharge stream 610 from a high-boiling by-product separation tower, which will be described later, and supplied to crystallization apparatus 300. The (meth)acrylic acid content in the mixed stream was 88.6 wt%.

[0089] A (meth)acrylic acid recovery stream 310 containing (meth)acrylic acid was obtained by the crystallization process performed in the crystallization apparatus 300, and the content of (meth)acrylic acid in the (meth)acrylic acid recovery stream 310 was 99.5 wt % or more. Finally, 99.5 wt % or more of (meth)acrylic acid was obtained from the crystallization apparatus 300.

[0090] Furthermore, a mother liquor was obtained by separating the (meth)acrylic acid from the crystallization apparatus 300. The mother liquor contained (meth)acrylic acid (63.2 wt%), water (25.3 wt%), acetic acid (3.9 wt%), furfural (3.1 wt%), and maleic acid (4.5 wt%). The mother liquor was branched and supplied to the absorption tower 100 and the water separation tower 500 via a first mother liquor recovery line 320 and a second mother liquor recovery line 330, respectively.

[0091] Meanwhile, the second aqueous (meth)acrylic acid solution contained (meth)acrylic acid (43.8 wt%), acetic acid (4.3 wt%), water (50.9 wt%), furfural (0.4 wt%), and maleic acid (0.03 wt%), and was supplied to the extraction tower 400 and the water separation tower 500 as a side discharge stream 120 of the absorption tower 64% of the height downward from the top of the absorption tower 100. Here, the side discharge stream 120 of the absorption tower containing the second aqueous (meth)acrylic acid solution was branched, and 45 wt% of the total weight of the second aqueous (meth)acrylic acid solution was supplied to the extraction tower 400 as the extraction tower feed stream 170, and the remaining 55 wt% of the second aqueous (meth)acrylic acid solution was supplied to the water separation tower 500 as the water separation tower feed stream 160. Meanwhile, the mass flow rate of the side discharge stream 120 of the absorption tower was 0.77 times the mass flow rate of the bottom discharge stream 130 of the absorption tower.

[0092] The extraction step performed in the extraction tower 400 in the presence of an extraction solvent (toluene) produced a raffinate stream 420 containing water and an extract stream 410 containing toluene and (meth)acrylic acid. The extraction solvent (toluene) supplied to the lower part of the extraction tower 400 was supplied at a flow rate 4.32 times the mass flow rate of water in the second aqueous (meth)acrylic acid solution supplied to the extraction tower 400. The raffinate stream 420 was supplied to a layer separation apparatus 550, which will be described later, and the extract stream 410 was mixed with the water separation tower feed stream 160 and supplied to the water separation tower 500.

[0093] Azeotropic distillation was carried out in the presence of a hydrophobic azeotropic solvent (toluene) in the water separation tower 500, yielding a water separation tower top discharge stream 510 containing toluene, water, and acetic acid, and a water separation tower bottom discharge stream 520 containing (meth)acrylic acid and high-boiling by-products. The hydrophobic azeotropic solvent was supplied to the water separation tower 500 at a flow rate 1.5 times the mass flow rate of the extraction solvent supplied to the extraction tower 400.

[0094] The top effluent stream 510 from the water separation tower was fed to a layer separation apparatus 550, where it was separated into an aqueous layer 570 containing water and acetic acid and an organic layer 560 containing toluene. A portion of the aqueous layer was fed to an absorption tower 100, and the remainder was discharged as wastewater to the outside of the system. Meanwhile, the organic layer was fed to an extraction tower 400 and a water separation tower 500.

[0095] Meanwhile, the above-mentioned bottom discharge stream 520 from the water separation tower was supplied to a high-boiling by-product separation tower 600 to obtain a top discharge stream 610 from the high-boiling by-product separation tower containing (meth)acrylic acid and a bottom discharge stream 620 from the high-boiling by-product separation tower containing high-boiling by-products. The top discharge stream 610 from the high-boiling by-product separation tower was mixed with the bottom discharge stream 130 from the absorption tower as described above and supplied to the crystallization apparatus 300. Here, the content of (meth)acrylic acid in the top discharge stream 610 from the high-boiling by-product separation tower was 99.2 wt%.

[0096] As a result, the energy consumed in the water separation tower 500 was 369.1 kcal / kg AA, the energy consumed in the high boiling point by-product separation tower 600 was 82.3 kcal / kg AA, and the energy consumed in the crystallization apparatus 300 was 130.5 kcal / kg AA, for a total of 581.8 kcal / kg AA.

[0097] (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.

[0098] Specifically, in Comparative Example 1, the reaction product 2 obtained in the same steps as in Example 1 was introduced into an absorption tower under the same conditions (operating conditions and the flow rate of water introduced into the absorption tower), but the aqueous (meth)acrylic acid solution was not obtained from the side and bottom of the absorption tower 100, and was obtained only from the bottom of the absorption tower.

[0099] The aqueous (meth)acrylic acid solution was supplied to a 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 160 containing the aqueous (meth)acrylic acid solution from which the low-boiling by-products had been removed were obtained. The upper discharge stream from the degassing tower had a flow rate of 13.6 wt% of the mass flow rate of water fed 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 fed into the absorption tower. The lower discharge stream 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%).

[0100] The bottom discharge stream 160 from the degassing tower was supplied to a water separation tower 500 and subjected to azeotropic distillation in the presence of a hydrophobic azeotropic solvent (toluene) to obtain a top discharge stream 510 from the water separation tower containing toluene, water, and acetic acid, and a bottom discharge stream 520 from the water separation tower containing (meth)acrylic acid and high-boiling by-products. Here, the hydrophobic azeotropic solvent (toluene) was supplied to the top of the water separation tower 500 at a flow rate 2.1 times the flow rate of the bottom discharge stream 160 from the degassing tower.

[0101] The top discharge stream 510 from the water separation tower was fed to a layer separation apparatus 550 to obtain an aqueous layer 570 containing water and acetic acid and an organic layer 560 containing toluene. A portion of the aqueous layer 570 was fed to an absorption tower 100, and the remainder was discharged to the outside of the system as wastewater. Meanwhile, the organic layer 560 was recycled to the water separation tower 500.

[0102] Meanwhile, bottom discharge stream 520 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 finally, 99.5 wt % or more of (meth)acrylic acid was obtained from high-boiling by-product separation tower 600.

[0103] As a result, the energy consumed in the water separation tower 500 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.

[0104] (Comparative Example 2) The (meth)acrylic acid production process was simulated using an Aspen Plus simulator manufactured by Aspen Corporation, following the process flow illustrated in FIG.

[0105] In Comparative Example 2, the bottom discharge stream 160 of the degassing tower, which had 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 400 and the water separation tower 500, respectively.

[0106] The extraction process in the extraction tower 400 was carried out in the presence of an extraction solvent (toluene), yielding a raffinate stream 420 containing water and an extract stream 410 containing toluene and (meth)acrylic acid. The extraction solvent was supplied to the bottom of the extraction tower 400 at a flow rate 4.1 times the mass flow rate of water in the degassing tower bottom discharge stream 160, which was branched and supplied to the top of the extraction tower 400. The raffinate stream 420 was supplied to a layer separation apparatus 550, and the extract stream 410 was mixed with the degassing tower bottom discharge stream, which was branched and supplied to the water separation tower 500, and then supplied to the water separation tower 500.

[0107] Azeotropic distillation was carried out in the presence of a hydrophobic azeotropic solvent (toluene) in the water separation tower 500 to obtain an upper discharge stream 510 from the water separation tower containing toluene, water, and acetic acid, and a lower discharge stream 520 from the water separation tower containing (meth)acrylic acid and high-boiling by-products. The hydrophobic azeotropic solvent was supplied to the upper part of the water separation tower 500 at a mass flow rate 2.1 times the mass flow rate of the extraction solvent supplied to the extraction tower 400.

[0108] The top discharge stream 510 from the water separation tower was fed to a layer separation apparatus 550 to obtain an aqueous layer 570 containing water and acetic acid and an organic layer 560 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 560 was fed to a water separation tower 500 and an extraction tower 400.

[0109] Meanwhile, bottom discharge stream 520 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 finally, 99.5 wt % or more of (meth)acrylic acid was obtained from high-boiling by-product separation tower 600.

[0110] As a result, the energy consumed in the water separation tower 500 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 of energy consumed.

[0111] (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.

[0112] Specifically, in Comparative Example 3, the flow rate of the second aqueous (meth)acrylic acid solution discharged to the side of the absorption tower was 0.23 times the mass flow rate of the first aqueous (meth)acrylic acid solution discharged to the bottom of the absorption tower.

[0113] The first (meth)acrylic acid aqueous solution was supplied to a degassing tower 150 as a bottom discharge stream 130 from the absorber. The bottom discharge stream 130 from the absorber was degassed in the degassing tower 150, and the low-boiling by-products were supplied to the absorption tower 100 as a top discharge stream 170 from the degassing tower. The (meth)acrylic acid aqueous solution from which the low-boiling by-products had been degassed was supplied to a water separation tower 500 as a bottom discharge stream 160 from the degassing tower. The bottom discharge stream 160 from the degassing tower contained (meth)acrylic acid (73 wt%), acetic acid (2.4 wt%), water (23.3 wt%), furfural (0.6 wt%), and maleic acid (0.7 wt%).

[0114] Meanwhile, the second aqueous (meth)acrylic acid solution was fed to extraction tower 400 as absorber side draw stream 120. The second aqueous (meth)acrylic acid solution contained (meth)acrylic acid (26.4 wt%), acetic acid (4.1 wt%), water (68.8 wt%), furfural (0.14 wt%), and maleic acid (0.03 wt%).

[0115] The extraction process performed in the extraction tower 400 in the presence of an extraction solvent (toluene) produced a raffinate stream 420 containing water and an extract stream 410 containing toluene and (meth)acrylic acid. The extraction solvent was supplied to the lower part of the extraction tower at a flow rate 3.35 times the mass flow rate of water in the second aqueous (meth)acrylic acid solution supplied to the upper part of the extraction tower. The raffinate stream 420 was supplied to a layer separation apparatus 550, and the extract stream 410 was supplied to a water separation tower 500. The extract stream 410 was mixed with the bottom discharge stream 160 from the degassing tower and supplied to the water separation tower 500 as a combined stream.

[0116] Azeotropic distillation was carried out in the presence of a hydrophobic azeotropic solvent (toluene) in the water separation tower 500 to obtain an upper discharge stream 510 from the water separation tower containing toluene, water, and acetic acid, and a lower discharge stream 520 from the water separation tower containing (meth)acrylic acid and high-boiling by-products. The hydrophobic azeotropic solvent was supplied to the upper part of the water separation tower 500 at a flow rate 2.45 times the mass flow rate of the extraction solvent supplied to the extraction tower 400.

[0117] The top discharge stream 510 from the water separation tower was fed to a layer separation apparatus 550, which produced an aqueous layer 570 containing water and acetic acid and an organic layer 560 containing toluene. A portion of the aqueous layer was fed to the absorption tower 100, and the remainder was discharged to the outside of the system as wastewater. Meanwhile, the organic layer was recycled to the water separation tower 500 and the extraction tower 400.

[0118] Meanwhile, bottom discharge stream 520 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 finally, 99.5 wt % or more of (meth)acrylic acid was obtained from high-boiling by-product separation tower 600.

[0119] As a result, the energy consumed in the water separation tower 500 was 455.9 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 635.5 kcal / kg AA.

[0120] In Comparative Example 3, unlike Comparative Examples 1 and 2, the bottom discharge stream of the water separation tower was not introduced into a crystallization apparatus, but 99.5 wt% or more of (meth)acrylic acid was obtained through a high-boiling by-product separation tower. However, it was confirmed that the total energy consumption increased compared to Example 1, which further included a crystallization apparatus.

Claims

1. contacting a mixed gas containing (meth)acrylic acid and high-boiling by-products with water in an absorption tower to obtain a first aqueous (meth)acrylic acid solution and a second aqueous (meth)acrylic acid solution; Discharging the first aqueous (meth)acrylic acid solution from a bottom of the absorption tower and supplying it to a crystallization device, and discharging the second aqueous (meth)acrylic acid solution from a side of the absorption tower; feeding the second aqueous (meth)acrylic acid solution to a water separation column to obtain a distillate containing (meth)acrylic acid and high-boiling by-products; feeding the distillate to a high-boiling by-product separation column, and feeding the top discharge stream of the high-boiling by-product separation column containing the (meth)acrylic acid to the crystallization apparatus; obtaining purified (meth)acrylic acid in the crystallization apparatus, and circulating a portion of the mother liquor recovered in the crystallization apparatus to the absorption tower and the remainder to the water separation tower.

2. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the first aqueous (meth)acrylic acid solution has a (meth)acrylic acid content of 75% by weight to 95% by weight, and the second aqueous (meth)acrylic acid solution has a (meth)acrylic acid content of 30% by weight to 60% by weight.

3. 2. The method for producing (meth)acrylic acid according to claim 1, wherein the second aqueous (meth)acrylic acid solution is discharged from a side portion of the absorption tower at a height of 40% to 80% downward from the top of the absorption tower.

4. 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.

5. the first aqueous (meth)acrylic acid solution discharged from the bottom of the absorption tower and the top discharge stream of the high-boiling by-product separation tower are supplied to the crystallization apparatus as a mixed stream; The method for producing (meth)acrylic acid according to claim 1, wherein the content of (meth)acrylic acid in the mixed stream is 85 to 99% by weight.

6. The mixed gas further contains acetic acid, The method for producing (meth)acrylic acid according to claim 1, wherein a flow rate ratio of the acetic acid discharged from the upper part of the absorption tower based on a flow rate of the acetic acid introduced into the absorption tower is 20% by weight to 80% by weight.

7. The step of obtaining a distillate containing (meth)acrylic acid and high-boiling by-products comprises: feeding a portion of the second aqueous (meth)acrylic acid solution to an extraction tower as an extraction tower feed stream and feeding the remainder to a water separation tower as a water separation tower feed stream; contacting an extractant with the extraction tower feed stream in the extraction tower and feeding an extract stream containing an extract to the water separation tower; 2. The method for producing (meth)acrylic acid according to claim 1, comprising a step of separating, in the water separation tower, a top discharge stream from the water separation tower containing water and the distillate containing (meth)acrylic acid and high-boiling by-products as a bottom discharge stream from the water separation tower.

8. 8. The method for producing (meth)acrylic acid according to claim 7, wherein a flow rate ratio of the extraction tower feed stream supplied to the extraction tower to a flow rate of the second aqueous (meth)acrylic acid solution is 20% by weight to 60% by weight.

9. The mixed gas further contains acetic acid, 8. The method for producing (meth)acrylic acid according to claim 7, wherein the top discharge stream of the water separation tower is fed to a layer separation device, a part of the aqueous layer containing water and acetic acid is recycled to the absorption tower, and the remainder is discharged as wastewater.

10. 8. The method for producing (meth)acrylic acid according to claim 7, wherein the extraction solvent and the extraction tower feed stream are contacted in the extraction tower to further obtain a raffinate stream containing a raffinate, and the raffinate stream is fed to a layer separation device.

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