CN118201903A - Method for producing high-purity (meth) acrylic acid - Google Patents

Abstract

A process for producing (meth) acrylic acid is provided, comprising: contacting a mixed gas containing (meth) acrylic acid with water in an absorption column 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 the lower portion of the absorption column and supplying the solution to a crystallizer, and discharging the second aqueous (meth) acrylic acid solution from the side portion of the absorption column; supplying the second aqueous (meth) acrylic acid solution to a water separation column to obtain a distillate comprising (meth) acrylic acid and high-boiling by-products; supplying the distillate to a high boiling point by-product separation column, and supplying an upper vent stream of the high boiling point by-product separation column containing (meth) acrylic acid to the crystallizer; purified (meth) acrylic acid is obtained in the crystallizer, and a part of the mother liquor recovered in the crystallizer is circulated to the absorption column and the remaining part is circulated to the water separation column.

Description

Method for producing high-purity (meth) acrylic acid

Cross Reference to Related Applications

The present application claims the benefit of priority from korean patent application No.10-2022-0109514, filed 8/30/2022, and korean patent application No.10-2023-0107059, filed 8/16/2023, which are incorporated herein in their entirety as part of the present specification.

Technical Field

The present invention relates to a method for producing high-purity (meth) acrylic acid.

Background

(Meth) acrylic acid is generally produced by a method of subjecting a compound such as propane, propylene and (meth) acrolein to a gas-phase oxidation reaction in the presence of a catalyst. For example, propane, propylene, etc. are converted into (meth) acrylic acid by (meth) acrolein by a gas phase oxidation reaction in the presence of a suitable catalyst, 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 (such as acetic acid, low boiling by-products, and high boiling by-products) generated by the reaction is obtained in the latter stage of the reactor.

The mixed gas containing (meth) acrylic acid is contacted with an absorption solvent such as water in an absorption column to recover the (meth) acrylic acid aqueous solution. Further, as a subsequent method for recovering (meth) acrylic acid contained in the aqueous (meth) acrylic acid solution, processes such as extraction, distillation, and purification are generally included. In order to improve the recovery efficiency of (meth) acrylic acid, various methods of adjusting process conditions, process sequences, and the like have been proposed.

However, since the absorption solvent such as water used in the absorption column has a high specific heat, separation of by-products from the aqueous (meth) acrylic acid solution containing water by distillation or the like requires a significantly high energy consumption. Meanwhile, when the subsequent process is simplified and shortened in order to reduce the energy consumption amount, the energy consumption amount may be reduced, but it is difficult to obtain high-purity (meth) acrylic acid.

In addition, acetic acid and high boiling point byproducts, which are main byproducts of the (meth) acrylic acid production process, are separated and removed so that they do not accumulate in the system, and in the process, a loss of the desired product (meth) acrylic acid is caused.

Therefore, there is an urgent need to introduce a technology that can reduce the energy consumption in the entire process while also minimizing the loss of high purity (meth) acrylic acid from the aqueous (meth) acrylic acid solution.

Disclosure of Invention

Technical problem

In order to solve the problems mentioned in the background art, it is an object of the present invention to provide a method for recovering (meth) acrylic acid, which can further reduce the energy consumption in the purification process while ensuring high purity of (meth) acrylic acid at a high recovery rate.

Technical proposal

In one general aspect, a method of preparing (meth) acrylic acid includes: contacting a mixed gas containing (meth) acrylic acid with water in an absorption column 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 the lower portion of the absorption column and supplying the solution to a crystallizer, and discharging the second aqueous (meth) acrylic acid solution from the side portion of the absorption column; supplying the second aqueous (meth) acrylic acid solution to a water separation column to obtain a distillate comprising (meth) acrylic acid and high-boiling by-products; supplying the distillate to a high boiling point by-product separation column, and supplying an upper vent stream of the high boiling point by-product separation column including (meth) acrylic acid to a crystallizer; purified (meth) acrylic acid is obtained in a crystallizer, and a part of the mother liquor recovered in the crystallizer is circulated to an absorption column and the remaining part is circulated to a water separation column.

Advantageous effects

According to the method for preparing (meth) acrylic acid of the present invention, the amount of water introduced into the absorption column for purifying (meth) acrylic acid is minimized, and a portion of the aqueous (meth) acrylic acid solution discharged from the absorption column is directly supplied to the crystallizer without performing a distillation process, thereby reducing the energy consumption in the entire process.

In addition, a water separation column and a layer separator may be provided after the absorption column to separate and remove acetic acid as a by-product, and thus, the loss of (meth) acrylic acid discharged from the upper portion of the absorption column may be reduced as compared with the case where all acetic acid is discharged from the upper portion of the absorption column.

In addition, the high boiling point by-products may be separated after the water separation column to prevent the high boiling point by-products from accumulating in the system and the upper vent stream of the high boiling point by-products is supplied again to crystallize, thereby further reducing the loss of (meth) acrylic acid.

Drawings

Fig. 1 is a process flow chart illustrating a method of preparing (meth) acrylic acid according to an exemplary embodiment of the present invention.

Fig. 2 to 4 are process flow charts showing a method of preparing (meth) acrylic acid according to comparative examples of the present invention.

Detailed Description

The terms and words used in the specification and claims of the present invention should not be construed restrictively to have a common or dictionary meaning, but should be construed to have a meaning and concept conforming to the technical idea of the present invention based on the principle that the inventors can properly define the concepts of the terms in order to describe their own invention in the best manner.

The term "stream" in the present invention may refer to the fluid flow in a process or may refer to the fluid itself flowing in a pipe. In particular, a stream may refer to the fluid itself and the fluid flow flowing in the conduit connecting each device. In addition, a fluid may refer to a gas or a liquid, and the case where a solid substance is contained in the fluid is not excluded.

Meanwhile, in a device such as an absorption column, a degassing column, a distillation column or a distillation column, and a crystallizer, unless otherwise specified, "lower portion" of the device means a point from the top to the bottom of the device at a height of 95% to 100%, particularly the lowest portion (bottom). Also, unless specifically stated otherwise, the "upper portion" of the device refers to the point from the top to the bottom of the device at a height of 0% to 5%, specifically the highest point (top).

Hereinafter, the present invention will be described in more detail for better understanding of the present invention.

The method of preparing (meth) acrylic acid according to an exemplary embodiment of the present invention may include: contacting a mixed gas containing (meth) acrylic acid with water in an absorption column 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 the lower portion of the absorption column and supplying the solution to a crystallizer, and discharging the second aqueous (meth) acrylic acid solution from the side portion of the absorption column; supplying the second aqueous (meth) acrylic acid solution to a water separation column to obtain a distillate comprising (meth) acrylic acid and high-boiling by-products; supplying the distillate to a high boiling point by-product separation column, and supplying an upper vent stream of the high boiling point by-product separation column including (meth) acrylic acid to a crystallizer; purified (meth) acrylic acid is obtained in a crystallizer, and a part of the mother liquor recovered in the crystallizer is circulated to an absorption column and the remaining part is circulated to a water separation column.

Hereinafter, various processes that may be included in exemplary embodiments of the present invention will be described with reference to fig. 1 and the like.

First, a method of preparing (meth) acrylic acid according to an exemplary embodiment of the present invention may include: the mixed gas containing (meth) acrylic acid is contacted with water in an absorption column to obtain a first aqueous (meth) acrylic acid solution and a second aqueous (meth) acrylic acid solution. Here, the mixed gas containing (meth) acrylic acid refers to a generic term for the gas phase components discharged from the reactor 10 for producing (meth) acrylic acid by the gas phase oxidation reaction. Specifically, the mixed gas may contain (meth) acrylic acid, unreacted raw material compounds, (meth) acrolein, inert gases, carbon monoxide, carbon dioxide, water vapor, various organic by-products (acetic acid, low-boiling by-products, high-boiling by-products, etc.), and the like. Herein, the "low boiling point by-product" (light end) or "high boiling point by-product" (heavy end) is a by-product that may be generated in the process for producing and recovering the (meth) acrylic acid of interest, and may be a compound having a higher or lower molecular weight than the (meth) acrylic acid.

Specifically, a mixed gas containing (meth) acrylic acid can be prepared as follows.

First, a reaction gas including an oxygen-containing gas and a raw material compound is supplied to a reactor 10 provided with a catalyst through a reaction gas supply line 1, and a gas phase oxidation reaction is performed in the reactor 10 in the presence of the catalyst to obtain a mixed gas containing (meth) acrylic acid.

Here, the oxygen-containing gas may be air. The raw material compound may be one or more compounds selected from propane, propylene, butane, 1-butene, t-butene, and (meth) acrolein, and specifically, the raw material compound may contain propylene. Meanwhile, the reaction gas supplied to the reactor 10 may further include a recycle gas recovered and recycled from the upper portion of the absorption tower 100.

The recycle gas may come from an upper portion of the absorber 100 described later. That is, the mixed gas is contacted with water as an absorption solvent in the absorption column 100, and the non-condensable gas insoluble in water may be discharged as an upper discharge stream 110 of the absorption column 100. The non-condensable gas may contain impurities such as acetic acid, inert gases, unreacted starting compounds and a minimum content of (meth) acrylic acid. The recycle gas may be supplied to the reactor 10 so that it may be used for the gas phase oxidation reaction for producing (meth) acrylic acid performed in the reactor.

That is, when acetic acid is discharged from the upper portion of the absorption tower 100, the content of (meth) acrylic acid discharged from the upper portion of the absorption tower 100 tends to increase as the discharge amount of acetic acid increases. This means the loss of (meth) acrylic acid. As described later, according to the present invention, since acetic acid in the system can be further separated and removed by the water separation column and the layer separator after the absorption column, the acetic acid in the system does not need to be forcibly discharged to the upper discharge stream 110 of the absorption column, and specifically, an amount of acetic acid sufficient to minimize the (meth) acrylic acid content in the upper discharge stream 110 of the absorption column can be discharged as the upper discharge stream 110. Accordingly, the content of (meth) acrylic acid discharged and lost from the upper portion of the absorption column 100 can be minimized.

At the same time, a portion 3 of the absorber upper vent stream 110 may be supplied to the cooling tower 20 and the remainder may be supplied to the exhaust incinerator for disposal.

A water supply line 5 is provided at an upper portion of the cooling tower 20, and water used as an absorption solvent in the absorption tower may be supplied from the water supply line 5 to the cooling tower 20. In cooling tower 20, the water may be contacted with non-condensable gases contained in a portion 3 of the absorber upper vent stream 110. As described above, the non-condensable gases may include acetic acid and a minimum amount of (meth) acrylic acid, and these components are dissolved in water and may be discharged as an aqueous solution as a lower discharge stream of the cooling tower 20. Thereafter, the lower effluent stream 6 of the cooling tower 20 can be supplied to the absorber tower 100.

The water required in the absorption tower 100 may be supplied through a water supply line 5 provided at an upper portion of the cooling tower 20. The water may include, in particular, water such as tap water and deionized water, and may include recycled process water introduced from other processes (e.g., aqueous phase recycled from extraction processes and/or distillation processes). In addition, the absorption solvent may include small amounts of organic byproducts (e.g., acetic acid) introduced from other processes.

Meanwhile, most of acetic acid contained in the non-condensable gas by contact with water in the cooling tower 20 is removed by being dissolved in water, and the gas not dissolved in water is discharged as a recycle gas through the recycle gas transfer line 4 provided at an upper portion of the cooling tower 20. The recycle gas may be supplied to the reactor 10 so that it may be used for the gas phase oxidation reaction for producing (meth) acrylic acid performed in the reactor. The recycle gas may be mixed with the reaction gas and supplied to the reactor, and may be supplied to the reactor through a line 4 separate from the line 1 for supplying the reaction gas.

Thereafter, a process of obtaining an aqueous solution of (meth) acrylic acid by supplying a mixed gas containing (meth) acrylic acid as a gas phase oxidation reaction product to the absorption column 100 through the reactor discharge line 2 and contacting the gas with water as an absorption solvent in the absorption column 100 may be performed. Specifically, the mixed gas may contain (meth) acrylic acid, organic by-products such as acetic acid and acrolein, and water vapor.

Here, the kind of the absorption column 100 may be determined in consideration of the contact efficiency of the mixed gas with the absorption solvent, etc., and may be, for example, a packed column type absorption column or a multistage tray type absorption column. For packing the inside of the tower absorber, packing such as raschig rings, pall rings, saddle packing, wire mesh packing, and structured packing may be applied.

Further, in consideration of the efficiency of the absorption process, the mixed gas 2 may be supplied to the lower portion of the absorption tower 100, and water as an absorption solvent may be supplied to the upper portion of the absorption tower 100.

Meanwhile, the absorption tower 100 may be operated at an internal pressure of 1 bar to 1.5 bar or 1 bar to 1.3 bar, and an internal temperature of 50 ℃ to 100 ℃ or 50 ℃ to 90 ℃ in consideration of condensation conditions of (meth) acrylic acid, moisture content based on saturated water vapor pressure, and the like.

Meanwhile, according to an exemplary embodiment of the present invention, by the absorption process performed in the absorption tower 100, the first aqueous (meth) acrylic acid solution discharged from the lower portion of the absorption tower 100 and the second aqueous (meth) acrylic acid solution discharged from the side portion of the absorption tower 100 may be obtained.

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

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

The content of (meth) acrylic acid in the first aqueous (meth) acrylic acid solution is higher than the content of (meth) acrylic acid in the aqueous (meth) acrylic acid solution discharged from the conventional absorption column. In particular, by setting the content of (meth) acrylic acid in the first (meth) acrylic acid aqueous solution to 75% by weight or more, the first (meth) acrylic acid aqueous solution can be directly supplied to the crystallizer 300 without performing a separate purification process or separation process on the first (meth) acrylic acid aqueous solution, and thus, the total process energy can be reduced, and also high-purity (meth) acrylic acid can be obtained in the crystallizer 300.

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

Meanwhile, as described above, the upper discharge stream of the absorption column 100 may contain a non-condensable gas that is insoluble in water as an absorption solvent in the absorption column 100, and the non-condensable gas may contain acetic acid, an inert gas, unreacted raw material compounds, and a minimum content of (meth) acrylic acid.

In general, in order to obtain high-purity (meth) acrylic acid, acetic acid is usually discharged as much as possible into the upper discharge stream of the absorption column. However, when the amount of acetic acid discharged to the upper portion of the absorption tower 100 increases and exceeds a certain level, the content of (meth) acrylic acid discharged to the upper portion of the absorption tower 100 increases, and thus, the amount of (meth) acrylic acid lost in the absorption tower also increases. Accordingly, the present invention can minimize the content of (meth) acrylic acid lost in the absorption column by controlling the amount of acetic acid contained in the upper vent stream of the absorption column 100. That is, the content of acetic acid in the vent stream in the upper portion of the absorption column can be controlled so that the content of (meth) acrylic acid lost to the upper portion of the absorption column can be minimized. In addition, since acetic acid can be further separated and removed by the water separation column and the layer separator after the later-described absorption column, the problem that acetic acid accumulates in the system and acts as an impurity can be solved.

From this point of view, the flow rate ratio of acetic acid discharged to the upper portion of the absorption column may be 20 to 80% by weight, specifically 30 to 60% by weight, based on the flow rate of acetic acid introduced to the absorption column. Meanwhile, the content of (meth) acrylic acid contained in the upper discharge stream of the absorption column may be 0.1 to 0.5% by weight, specifically, 0.2 to 0.3% by weight.

Meanwhile, the first aqueous (meth) acrylic acid solution may be supplied to the crystallizer 300 through the lower discharge stream 130 of the absorption column, and the second aqueous (meth) acrylic acid solution may be introduced into the process of obtaining a distillate comprising (meth) acrylic acid and high boiling point by-products through the side discharge stream 120 of the absorption column.

That is, by discharging the first and second aqueous solutions of (meth) acrylic acid having different (meth) acrylic acid contents from the absorption tower 100, respectively, the amount of energy consumption consumed in the subsequent process can be reduced. In particular, since the first (meth) acrylic acid aqueous solution has a high concentration of (meth) acrylic acid content, it can be directly supplied to the crystallizer 300 without performing a separate purification process or separation process on the first (meth) acrylic acid aqueous solution, and thus, the total process energy can be reduced, and also high purity (meth) acrylic acid can be obtained in the crystallizer 300. This is possible because, as described above, the content of (meth) acrylic acid in the aqueous first (meth) acrylic acid solution is high.

In addition, the aqueous first (meth) acrylic acid solution also contains a certain amount of water. Since the mother liquor separated from the purified (meth) acrylic acid in the crystallizer 300 is circulated to the absorption column as described later, the amount of water contained in the second aqueous (meth) acrylic acid solution decreases the amount of water contained in the mother liquor, and thus, the amount of energy consumption involved in the purification process of the second aqueous (meth) acrylic acid solution decreases.

Specifically, the method of preparing (meth) acrylic acid according to one exemplary embodiment of the present invention may include supplying a first aqueous (meth) acrylic acid solution to a crystallizer 300 and crystallizing to obtain purified (meth) acrylic acid and a mother liquor separated from the purified (meth) acrylic acid. In the present specification, the (meth) acrylic acid crystallized in the crystallizer may refer to purified (meth) acrylic acid in some cases.

The (meth) acrylic acid contained in the first aqueous (meth) acrylic acid solution supplied to the crystallizer 300 may be recrystallized by a crystallization process, and purified high-purity (meth) acrylic acid is obtained. In addition, not only the first aqueous (meth) acrylic acid solution but also an upper discharge stream of a high-boiling by-product separation column containing a high content of (meth) acrylic acid discharged from an upper portion of a high-boiling by-product separation column 600 described later may be introduced into the crystallizer 300.

The crystallization process may be performed under ordinary conditions.

The crystallization method for obtaining a product by crystallization in the present invention is not limited to suspension crystallization and layer crystallization, and may be continuous or batch-wise, and may be performed in one stage or two or more stages. As a non-limiting example, (meth) acrylic acid may be dynamically crystallized and provided as purified (meth) acrylic acid.

Specifically, in order to dynamically crystallize (meth) acrylic acid before crystallization, an aqueous solution of (meth) acrylic acid may be first allowed to flow on the inner wall of the tube in the form of a falling film. In addition, the temperature of the tube may be adjusted to below the condensation point of (meth) acrylic acid to form crystals in the inner wall of the tube. Then, the temperature of the tube may be raised to near the condensation point of (meth) acrylic acid, causing condensation (sweat) of about 5% by weight of (meth) acrylic acid. In addition, the mother liquor condensed from the tube is removed, and crystals formed in the inner wall of the tube are recovered, thereby obtaining purified (meth) acrylic acid of high purity. The mother liquor may refer to an aqueous solution of (meth) acrylic acid introduced into the crystallizer 300, in which purified (meth) acrylic acid has been removed. Thus, the mother liquor may contain (meth) acrylic acid, acetic acid, and high boiling point by-products in addition to water, and the (meth) acrylic acid herein may be residual (meth) acrylic acid that is not crystallized in the crystallizer 300.

The separation of the mother liquor from the crystallized and purified (meth) acrylic acid can be performed using a solid-liquid separation device, for example, a belt filter, a centrifuge, or the like. Purified (meth) acrylic acid may be recovered as (meth) acrylic acid recovery stream 310 and mother liquor may be withdrawn from crystallizer 300 via a mother liquor discharge stream.

According to an exemplary embodiment of the present invention, a portion of the mother liquor discharged from the crystallizer 300 may be recycled to the absorption column 100 through the first mother liquor recovery line 320, and the remaining mother liquor may be recycled to the water separation column 500 through the second mother liquor recovery line 330. Here, as will be described later, the water separation column 500 is a device for obtaining a distillate containing (meth) acrylic acid and high-boiling by-products by supplying all or part of the second aqueous (meth) acrylic acid solution and distilling the solution.

Meanwhile, the mother liquor discharged from the crystallizer 300 may contain 50 to 80 wt%, specifically, 60 to 75 wt% of (meth) acrylic acid. In addition, the mother liquor may comprise 20 to 50 wt%, specifically 25 to 40wt% of water. In addition, the mother liquor exiting the crystallizer 300 may contain a residual amount of organic byproducts.

According to an exemplary embodiment of the present invention, the second aqueous (meth) acrylic acid solution may be introduced through a process of obtaining a distillate comprising (meth) acrylic acid and high boiling point by-products.

Meanwhile, according to an exemplary embodiment of the present invention, the process of obtaining a distillate comprising (meth) acrylic acid and high boiling point byproducts may be performed by including: a portion of the second aqueous (meth) acrylic acid solution is supplied to the extraction column 400 as an extraction column supply stream 170, and the remaining portion is supplied to the water separation column 500 as a water separation column supply stream 160; contacting the extraction solvent and the extraction column feed stream in the extraction column 400 and supplying an extract stream comprising the extract to the water separation column 500; and separating in the water separation column 500 an upper effluent stream 510 of the water separation column comprising water and a distillate comprising (meth) acrylic acid and high boiling by-products as a lower effluent stream 520 of the water separation column.

That is, the second (meth) acrylic acid aqueous solution is separated and supplied to the extraction column 400 and the water separation column 500, thereby reducing the energy consumption of the subsequent process, and also achieving effective separation of byproducts such as acetic acid. Specifically, the flow rate of the extraction column supply stream 170 supplied to the extraction column to the flow rate of the second (meth) acrylic acid aqueous solution may be 20 to 60% by weight. When the flow rate ratio is 20 wt% or more, the flow rate introduced into the water separation column 500 is reduced, and the energy consumed by the distilled water having a high specific heat in the water separation column 500 can be reduced. Meanwhile, when the flow ratio is 60wt% or less, acetic acid as a by-product is effectively separated to the upper portion of the water separation column 500, and the amount of acetic acid introduced into the high boiling point by-product separation column 600 may be minimized. Accordingly, the acetic acid content in the upper effluent stream of the high boiling by-product separation column 600 is reduced, and thus, high purity purified (meth) acrylic acid can be obtained in the crystallizer 300.

Meanwhile, the extraction column 400 removes most of the water contained in the extraction column supply stream 170 without using a large amount of energy and supplies it to the water separation column 500, thereby saving energy for azeotropic distillation in the water separation column 500 described later. In this regard, the extraction in extraction column 400 is preferably performed by contacting the extraction solvent with the extraction column feed stream by a liquid-liquid contact process in terms of improving the energy efficiency of the overall process.

Here, the extraction solvent may be a hydrocarbon solvent which forms an azeotrope with water and organic by-products (acetic acid, etc.) and does not form an azeotrope with (meth) acrylic acid, but can sufficiently extract (meth) acrylic acid, and in addition, in the extraction process, it is also advantageous that the boiling point thereof is 10 to 120 ℃. Specifically, the extraction solvent may be one or more solvents selected from benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methyl isobutyl 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.

In addition, as the extraction column 400, an extraction apparatus according to a liquid-liquid contact method may be used. Non-limiting examples of extraction devices may include a karl reciprocating plate column (Karr reciprocating plate column), a rotary disk contactor (rotary-disk contactor), a Scheibel column, a Kuhni column, a spray extraction column, a packed extraction column, a pulsed packed column, a mixer-settler train (bank of mixer-settler), a mixer, a centrifuge (centrifugal countercurrent extractor), and the like.

In this way, most of the water in the extraction column supply stream 170 supplied to the extraction column 400 is removed, resulting in an extract from which (meth) acrylic acid is extracted by the extraction solvent, and this extract may be supplied as extract stream 410 to the water separation column 500. In particular, the extract may comprise (meth) acrylic acid, acetic acid, an extract solvent and high boiling by-products.

In addition, water contained in the extraction column feed stream 170 through the extraction process may be recovered as raffinate. The recovered raffinate may be discharged as a raffinate stream 420 and introduced into a layer separator 550, which is described later. Since water is recovered in the extraction process, the operational burden of the distillation process described later can be reduced to reduce energy consumption.

Subsequently, according to an exemplary embodiment of the present invention, the water separation column supply stream 160 and the extract stream 410 in the second aqueous (meth) acrylic acid solution are supplied to the water separation column 500, and these streams may be subjected to a distillation process.

The flow rate of water in the stream supplied to the water separation column 500 may be 30 to 70 wt%, specifically 40 to 60 wt%, based on the flow rate of water introduced to the absorption column. When the flow ratio of water is less than 30 wt%, acetic acid in the water separation column 500 may be difficult to separate, and when the flow ratio is more than 70 wt%, the energy consumption amount for water consumption in the distilled water separation column 500 and the high boiling by-product separation column 600 may increase.

That is, by controlling the flow rate and content of water contained in the stream supplied to the water separation column 500, byproducts such as acetic acid in the water separation column 500 can be effectively removed, and finally, high-purity purified (meth) acrylic acid can be obtained. At the same time, the energy consumption required for distilled water in the water separation column 500 and the high boiling point by-product separation column 600, which will be described later, can be minimized, thereby reducing the total energy cost.

The distillation process in the water separation column 500 for the stream supplied to the water separation column 500 may be a process of separating an upper fraction comprising water, hydrophobic azeotropic solvent and acetic acid and a lower fraction comprising (meth) acrylic acid and high boiling byproducts by azeotropic distillation.

In accordance with the present invention, it is advantageous to conduct distillation in the water separation column 500 in the presence of a hydrophobic azeotropic solvent because the azeotropic solvent, water, and organic byproducts (e.g., acetic acid) can be recovered simultaneously in the process.

Here, the hydrophobic azeotropic solvent is a hydrophobic solvent which can form an azeotrope with water and acetic acid but not with (meth) acrylic acid, and a hydrocarbon solvent satisfying the physical properties can be applied without limitation. In addition, the hydrophobic azeotropic solvent may have a lower boiling point than (meth) acrylic acid, and may have a boiling point of preferably 10 to 120 ℃.

According to the present invention, the hydrophobic azeotropic solvent may be one or more solvents selected from benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butyl acetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methyl isobutyl 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.

In addition, the hydrophobic azeotropic solvent may be the same as or different from the extraction solvent applied to the extraction column 400. However, in view of productivity according to a continuous process or the like, it is preferable that the hydrophobic azeotropic solvent is the same as the extraction solvent. When the same compound is thus used as the azeotropic solvent and the extraction solvent, at least a part of the azeotropic solvent distilled and recovered in the water separation column 500 may be supplied to the lower portion of the extraction column 400 and used as a part of the extraction solvent.

When the hydrophobic azeotropic solvent is added to the above-mentioned water separation column 500, the azeotrope of (meth) acrylic acid and water is broken. Thus, the water, acetic acid, and hydrophobic azeotropic solvent used for azeotropic distillation in the mother liquor may form an azeotrope together and be recovered as the upper fraction of the water separation column 500. In addition, a lower fraction containing (meth) acrylic acid and high boiling point by-products may be recovered to the lower portion of the water separation column 500.

The upper fraction of the water separation column thus recovered may be supplied to the layer separator 550 through the upper discharge stream 510 of the water separation column, and the lower fraction of the water separation column may be supplied to the high boiling by-product separation column 600 through the lower discharge stream 520 of the water separation column.

Here, the layer separator 550 is a liquid-liquid layer separator, and a device that separates fluids that are not mixed with each other by a density difference using gravity, centrifugal force, or the like, wherein a relatively light liquid may be separated to an upper portion of the layer separator 550, and a relatively heavy liquid may be separated to a lower portion of the layer separator 550. Specifically, the upper vent stream 510 of the water separation column supplied to the layer separator 550 may be separated into an organic layer comprising a hydrophobic azeotropic solvent and an aqueous layer comprising water and acetic acid.

In addition, the organic layer separated from the layer separator 550 is discharged as a discharge stream 560 of the layer separator, a portion of the discharge stream 560 of the layer separator may be supplied to an upper portion of the water separation column 500 and reused as an azeotropic solvent, and the remaining portion may be supplied to the extraction column 400 and reused as an extraction solvent.

Meanwhile, in the layer separator 550, a part of the aqueous layer including water and acetic acid may be supplied to the upper portion of the absorption tower 100 and used as an absorption solvent, and the remaining part may be discharged as wastewater.

Here, acetic acid may be contained in the aqueous layer, and the concentration of acetic acid contained in the aqueous layer may vary based on the kind of azeotropic solvent, the reflux ratio of the column installed in the water separation column 500, and the like. 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, more preferably 3 to 10% by weight.

That is, according to an exemplary embodiment of the present invention, acetic acid may be discharged through the upper discharge stream of the absorption column 100, or may be discharged through azeotropic distillation performed by the water separation column 500 and the layer separator 550. Thus, acetic acid accumulated in the system can be removed more effectively than a method of removing only acetic acid at the upper part of the absorption column, thereby obtaining purified (meth) acrylic acid therefrom with high purity. In addition, process flexibility can be ensured as compared with an attempt to discharge the total amount of acetic acid in the system to the upper portion of the absorption column, and this has an advantage of minimizing (meth) acrylic acid lost from the upper portion of the absorption column.

From this point of view, the total flow rate of acetic acid introduced into the absorption column 100 may be the same as the sum of the flow rate of acetic acid in the upper discharge stream of the absorption column 100 and the flow rate of acetic acid contained in the water layer of the layer separator 550 and discharged stream.

Meanwhile, a method of preparing (meth) acrylic acid according to an exemplary embodiment of the present invention may include: the lower vent stream 520 of the water separation column 500 is supplied to the high boiling by-product separation column 600, and the upper vent stream of the high boiling by-product separation column 600 containing (meth) acrylic acid is supplied to the crystallizer 300.

The lower effluent stream of the water separation column 500 may be distilled through the high boiling by-product separation column 600, separated into a lower fraction containing high boiling by-products and an upper fraction containing high (meth) acrylic acid content by removing the high boiling by-products. The upper fraction may be supplied to the crystallizer 300 through the upper vent stream 610 of the high boiling by-product separation column, and the content of (meth) acrylic acid contained in the upper vent stream 510 of the high boiling by-product separation column may be 90 to 99% by weight, specifically, 95 to 99% by weight.

That is, since the amount of water contained in each stream has been reduced in the process after the absorption column 100 and also a large amount of water has been removed by the extraction column 400 and the water separation column 500, the content of water in the upper discharge stream 610 of the high boiling by-product separation column is controlled to be low, and thus, it can be achieved that the high concentration (meth) acrylic acid stream can be directly introduced into the crystallizer 300. By introducing the upper vent stream 610 of the high boiling by-product separation column into the crystallizer 300, the loss of (meth) acrylic acid can be reduced to a maximum.

Meanwhile, the first aqueous (meth) acrylic acid solution discharged from the lower part of the absorption column and the upper discharge stream of the high boiling point by-product separation column may be separately supplied as separate streams to the crystallizer 300, and these streams may also form a mixed stream and be supplied to the crystallizer 300.

The content of (meth) acrylic acid contained in the upper discharge stream of the high boiling point by-product separation column may be higher than the content of (meth) acrylic acid contained in the first aqueous (meth) acrylic acid solution, and when the first aqueous (meth) acrylic acid solution discharged from the lower portion of the absorption column forms a mixed stream with the upper discharge stream of the high boiling point by-product separation column and is supplied to the crystallizer, the content of (meth) acrylic acid in the mixed stream may be 85 to 99% by weight. Thus, the mixed stream can be introduced directly into the crystallizer without a separate distillation process.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are provided to illustrate the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be made without departing from the scope and spirit of the invention, and the scope of the invention is not limited thereto.

Example 1

The process for the preparation of (meth) acrylic acid was simulated using an Aspen Plus simulator provided by Aspen according to the process scheme shown in fig. 1.

Specifically, a reaction gas containing air and a raw material compound (propylene) is supplied to a reactor 10 provided with a catalyst through a reaction gas supply line 1, and a recycle gas from a cooling tower 20 is supplied to the reactor 10 through a recycle gas delivery line 4. By the gas phase oxidation reaction performed in the reactor 10, a mixed gas 2 having a composition containing (meth) acrylic acid (6.6 mol%), water (16.4 mol%), a high boiling substance (0.09 mol%) and an inert gas (76.3 mol%) was obtained.

The mixed gas 2 was fed to the 11 th stage from the top of the absorption column 100 at a temperature of 164 ℃. In the absorption column 100, the mixed gas is 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 added to the absorption column 100 is supplied through the lower discharge stream 6 of the cooling column and the water layer from the later-described layer separator 550, and is supplied to the upper portion of the absorption column 100 at a flow rate of 10.6 wt% of the mass flow rate of the mixed gas 2. At this time, the pressure in the upper portion of the absorption column 100 was 1.1 bar, and the temperature in the lower portion of the absorption column 100 was 82 ℃.

Meanwhile, in the absorption column 100, the non-condensable gas containing the water-insoluble component is separated as an upper discharge stream 110 of the absorption column, and a part 3 of the upper discharge stream of the absorption column is supplied to the cooling column 20, and the remaining part is discharged out of the system.

In the cooling tower 20, the non-condensable gases contained in a portion 3 of the upper effluent stream of the absorber are dissolved in water. At this time, water is supplied through the water supply line 5. In the cooling tower 20, a water-insoluble gas is supplied to the reactor 10 through the recycle gas transfer line 4, and a lower discharge stream 6 of the cooling tower containing water and water-soluble components (acetic acid and (meth) acrylic acid that is not dissolved in water in the absorption tower) is supplied to an upper portion of the absorption tower 100.

Meanwhile, the above-mentioned first (meth) acrylic acid aqueous solution contains (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 is supplied as the lower discharge stream 130 of the absorption column to the crystallizer 300. At this time, the lower vent stream 130 of the absorber forms a mixed stream with the upper vent stream 610 of the high boiling by-product separation column and is supplied to the crystallizer 300. The content of (meth) acrylic acid in the mixed stream was 88.6% by weight.

The (meth) acrylic acid recovery stream 310 containing (meth) acrylic acid is obtained by the crystallization process performed in the crystallizer 300, and the content of (meth) acrylic acid in the (meth) acrylic acid recovery stream 310 is 99.5% by weight or more. Finally, 99.5 wt% or more of (meth) acrylic acid is obtained from the crystallizer 300.

In addition, a mother liquor separated from (meth) acrylic acid is obtained in the crystallizer 300. At this time, 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 is split into two and supplied to the absorption column 100 and the water separation column 500 through the first mother liquor recovery line 320 and the second mother liquor recovery line 330, respectively.

Meanwhile, the above-mentioned second (meth) acrylic acid aqueous solution contains (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 a height of 64% from the top to the bottom of the absorption column 100 is supplied as a side discharge stream 120 of the absorption column to the extraction column 400 and the water separation column 500. At this time, the side discharge stream 120 of the absorber containing the second aqueous (meth) acrylic acid solution is split into two, 45% by weight of the total weight of the second aqueous (meth) acrylic acid solution is supplied as an extraction column supply stream 170 to the extraction column 400, and the remaining 55% by weight of the second aqueous (meth) acrylic acid solution is supplied as a water separation column supply stream 160 to the water separation column 500. At the same time, the mass flow of the side offtake stream 120 of the absorber is 0.77 times the mass flow of the lower offtake stream 130 of the absorber.

By an extraction process performed in the extraction column 400 in the presence of an extraction solvent (toluene), a raffinate stream 420 comprising water and an extract stream 410 comprising toluene and (meth) acrylic acid are obtained. At this time, the extraction solvent (toluene) supplied to the lower portion of the extraction column 400 is supplied at a flow rate of 4.32 times the mass flow rate of water in the second aqueous (meth) acrylic acid solution supplied to the extraction column 400. The raffinate stream 420 is supplied to a later-described layer separator 550, and the extract stream 410 is mixed with the aforementioned water separation column supply stream 160 and supplied to the water separation column 500.

In the water separation column 500, an upper discharge stream 510 of the water separation column containing toluene, water and acetic acid and a lower discharge stream 520 of the water separation column containing (meth) acrylic acid and high boiling by-products are obtained by performing azeotropic distillation in the presence of a hydrophobic azeotropic solvent (toluene). At this time, the hydrophobic azeotropic solvent supplied to the water separation column 500 is supplied at a flow rate 1.5 times the mass flow rate of the extraction solvent supplied to the extraction column 400.

The upper effluent stream 510 of the water separation column is supplied to a layer separator 550 and separated into an aqueous layer 570 comprising water and acetic acid and an organic layer 560 comprising toluene. A part of the aqueous layer is supplied to the absorption tower 100, and the remaining part is discharged as wastewater. Meanwhile, the organic layer is supplied to the extraction column 400 and the water separation column 500.

Meanwhile, the lower discharge stream 520 of the above-mentioned water separation column is supplied to the high boiling by-product separation column 600, resulting in an upper discharge stream 610 of the high boiling by-product separation column containing (meth) acrylic acid and a lower discharge stream 620 of the high boiling by-product separation column containing the high boiling by-product. As described above, the upper vent stream 610 of the high boiling by-product separation column is mixed with the lower vent stream 130 of the absorber column and supplied to the crystallizer 300. At this time, the content of (meth) acrylic acid in the upper discharge stream 610 of the high boiling by-product separation column was 99.2% by weight.

As a result, the energy used in the water separation column 500 was 369.1kcal/kgAA, the energy used in the high boiling by-product separation column 600 was 82.3kcal/kg AA, and the energy used in the crystallizer 300 was 130.5kcal/kgAA, and thus 581.8kcal/kgAA was used in total.

Comparative example 1

The process for the preparation of (meth) acrylic acid was simulated using an Aspen Plus simulator provided by Aspen according to the process scheme shown in fig. 2.

Specifically, in comparative example 1, the reaction product 2 obtained by the same process as in example 1 was added to the absorption column under the same conditions (operation condition and flow rate of water added to the absorption column), but the aqueous (meth) acrylic acid solution was obtained not from the side and bottom of the absorption column 100 but only from the bottom of the absorption column.

The aqueous (meth) acrylic acid solution is supplied to a degasser 150 to obtain an upper effluent stream of the degasser containing low boiling by-products, and a lower effluent stream 160 of the degasser containing the aqueous (meth) acrylic acid solution from which low boiling by-products are removed. At this time, the upper discharge stream from the deaerator has a flow rate of 13.6 wt% compared to the mass flow rate of water added to the absorber, and the lower discharge stream 160 of the deaerator has a flow rate of 2.3 times the mass flow rate of water added to the absorber. The lower vent stream 160 of the degasser comprises (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%).

The lower vent stream 160 of the degasser is supplied to a water separation column 500 and subjected to azeotropic distillation in the presence of a hydrophobic azeotropic solvent (toluene) to obtain an upper vent stream 510 of the water separation column containing toluene, water and acetic acid, and a lower vent stream 520 of the water separation column containing (meth) acrylic acid and high boiling by-products. At this time, the hydrophobic azeotropic solvent (toluene) is supplied to the upper portion of the water separation column 500 at a flow rate 2.1 times the flow rate of the degassing column lower portion discharge stream 160.

The upper effluent stream 510 of the water separation column is supplied to a layer separator 550 to obtain an aqueous layer 570 comprising water and acetic acid and an organic layer 560 comprising toluene. A portion of the aqueous layer 570 is supplied to the absorber 100 and the remaining portion is discharged as wastewater. At the same time, the organic layer 560 is recycled to the water separation column 500.

At the same time, the lower effluent stream 520 of the water separation column is supplied to the high boiling by-product separation column 600, resulting in a lower effluent stream 620 of the high boiling by-product separation column containing high boiling by-products and an upper effluent stream 610 of the high boiling by-product separation column containing (meth) acrylic acid. The content of (meth) acrylic acid in the upper discharge stream 610 of the high boiling by-product separation column is 99.5% by weight or more, and finally 99.5% by weight or more of (meth) acrylic acid is obtained from the high boiling by-product separation column 600.

As a result, the energy used in the water separation column 500 was 683.6kcal/kgAA, and the energy used in the high boiling by-product separation column 600 was 179.5kcal/kgAA, and therefore 863.1kcal/kgAA was used in total.

Comparative example 2

The process for the preparation of (meth) acrylic acid was simulated using an Aspen Plus simulator from Aspen according to the process flow shown in figure 3.

In comparative example 2, the lower discharge stream 160 of the deaeration column having the same composition as comparative example 1 was divided into two paths at 35 wt% and 65 wt% of the total weight of the lower discharge stream 160 of the deaeration column, respectively, and supplied to the extraction column 400 and the water separation column 500, respectively.

By an extraction process performed in the extraction column 400 in the presence of an extraction solvent (toluene), a raffinate stream 420 comprising water and an extract stream 410 comprising toluene and (meth) acrylic acid are obtained. At this time, the extraction solvent is supplied to the lower portion of the extraction column 400 at a flow rate 4.1 times the mass flow rate of water in the lower portion of the degassing column effluent stream 160, and the lower portion of the degassing column effluent stream 160 is branched to the upper portion of the extraction column 400 and supplied. Raffinate stream 420 is supplied to layer separator 550 and extract stream 410 is mixed with the lower effluent stream of the degasser split to water separation column 500 and supplied to water separation column 500.

In the water separation column 500, an upper discharge stream 510 of the water separation column containing toluene, water and acetic acid and a lower discharge stream 520 of the water separation column containing (meth) acrylic acid and high boiling by-products are obtained by performing azeotropic distillation in the presence of a hydrophobic azeotropic solvent (toluene). At this time, the hydrophobic azeotropic solvent is supplied to the upper portion of the water separation column 500 at a mass flow rate 2.1 times the mass flow rate of the extraction solvent supplied to the extraction column 400.

The upper effluent stream 510 of the water separation column is supplied to a layer separator 550 to obtain an aqueous layer 570 comprising water and acetic acid and an organic layer 560 comprising toluene. A part of the aqueous layer is supplied to the absorption tower 100, and the remaining part is discharged as wastewater. Meanwhile, the organic layer 560 is supplied to the water separation column 500 and the extraction column 400.

At the same time, the lower effluent stream 520 of the water separation column is supplied to the high boiling by-product separation column 600, resulting in a lower effluent stream 620 of the high boiling by-product separation column containing high boiling by-products and an upper effluent stream 610 of the high boiling by-product separation column containing (meth) acrylic acid. The content of (meth) acrylic acid in the upper discharge stream 610 of the high boiling by-product separation column is 99.5% by weight or more, and finally 99.5% by weight or more of (meth) acrylic acid is obtained from the high boiling by-product separation column 600.

As a result, the energy used in the water separation column 500 was 474.5kcal/kgAA, and the energy used in the high boiling by-product separation column 600 was 179.5kcal/kg AA, and therefore, a total of 654kcal/kg AA was used.

Comparative example 3

The process flow shown in fig. 4 was used to simulate the process of (meth) acrylic acid production using Aspen Plus simulator from Aspen.

Specifically, in comparative example 3, the flow rate of the second (meth) acrylic acid aqueous solution discharged to the side of the absorption column was 0.23 times the mass flow rate of the first (meth) acrylic acid aqueous solution discharged to the bottom of the absorption column.

The first aqueous (meth) acrylic acid solution is supplied as a lower discharge stream 130 of the absorber to a degasser 150. The lower vent stream 130 of the absorber is degassed in the degasser 150, the low boiling by-products are supplied to the absorber 100 as the upper vent stream 170 of the degasser, and the aqueous (meth) acrylic acid solution of the low boiling by-products that have been degassed is supplied to the water separation column 500 as the lower vent stream 160 of the degasser. At this point, the lower vent stream 160 of the degasser comprises (meth) acrylic acid (73 wt%), acetic acid (2.4 wt%), water (23.3 wt%), furfural (0.6 wt%) and maleic acid (0.7 wt%).

Meanwhile, the second aqueous (meth) acrylic acid solution is supplied to the extraction column 400 as the side discharge stream 120 of the absorption column. The second aqueous (meth) acrylic acid solution contains (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%).

By an extraction process performed in the extraction column 400 in the presence of an extraction solvent (toluene), a raffinate stream 420 comprising water and an extract stream 410 comprising toluene and (meth) acrylic acid are obtained. At this time, the extraction solvent 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 portion of the extraction column was supplied to the lower portion of the extraction column. Raffinate stream 420 is supplied to layer separator 550 and extract stream 410 is supplied to water separation column 500. At this time, extract stream 410 is mixed with lower discharge stream 160 of the above-described degasser and supplied as a mixed stream to water separation column 500.

In the water separation column 500, an upper discharge stream 510 of the water separation column containing toluene, water and acetic acid and a lower discharge stream 520 of the water separation column containing (meth) acrylic acid and high boiling by-products are obtained by performing azeotropic distillation in the presence of a hydrophobic azeotropic solvent (toluene). At this time, the hydrophobic azeotropic solvent is supplied to the upper portion of the water separation column 500 at a mass flow rate 2.45 times the mass flow rate of the extraction solvent supplied to the extraction column 400 described above.

The upper effluent stream 510 of the water separation column is supplied to a layer separator 550 to obtain an aqueous layer comprising water and acetic acid, and an organic layer 560 comprising toluene. A part of the aqueous layer is supplied to the absorption tower 100, and the remaining part is discharged as wastewater. At the same time, the organic layer is recycled to the water separation column 500 and the extraction column 400.

At the same time, the lower effluent stream 520 of the water separation column is supplied to the high boiling by-product separation column 600, resulting in a lower effluent stream 620 of the high boiling by-product separation column containing high boiling by-products and an upper effluent stream 610 of the high boiling by-product separation column containing (meth) acrylic acid. The content of (meth) acrylic acid in the upper discharge stream 610 of the high boiling by-product separation column is 99.5% by weight or more, and finally 99.5% by weight or more of (meth) acrylic acid is obtained from the high boiling by-product separation column 600.

As a result, the energy used in the water separation column 500 was 455.9kcal/kgAA, and the energy used in the high boiling by-product separation column 600 was 179.5kcal/kgAA, and therefore, the energy of 635.5kcal/kgAA was used in total.

In comparative example 3, it was confirmed that although the lower discharge stream of the water separation column was not introduced into the crystallizer as in comparative examples 1 and 2, 99.5 wt% or more of (meth) acrylic acid could be obtained by the high boiling by-product separation column, but the total energy consumption was increased as compared with example 1 further provided with the crystallizer.

Claims (10)

1. A process for preparing (meth) acrylic acid, the process comprising:

Contacting a mixed gas containing (meth) acrylic acid with water in an absorption column 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 the lower portion of the absorption column and supplying the solution to a crystallizer, and discharging the second aqueous (meth) acrylic acid solution from the side portion of the absorption column;

Supplying the second aqueous (meth) acrylic acid solution to a water separation column to obtain a distillate comprising (meth) acrylic acid and high-boiling by-products;

Supplying the distillate to a high boiling point by-product separation column, and supplying an upper vent stream of the high boiling point by-product separation column containing (meth) acrylic acid to the crystallizer; and

Purified (meth) acrylic acid is obtained in the crystallizer, and a part of the mother liquor recovered in the crystallizer is circulated to the absorption column and the remaining part is circulated to the water separation column.

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

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

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

5. The process for producing (meth) acrylic acid according to claim 1,

Wherein the first aqueous (meth) acrylic acid solution discharged from the lower portion of the absorption column forms a mixed stream with the upper discharge stream of the high boiling point by-product separation column and is supplied to the crystallizer,

The content of (meth) acrylic acid in the mixed stream is 85 to 99% by weight.

6. The method for producing (meth) acrylic acid according to claim 1, wherein a flow rate ratio of acetic acid discharged to an upper portion of the absorption column is 20 to 80% by weight based on a flow rate of acetic acid introduced into the absorption column.

7. The method for producing (meth) acrylic acid according to claim 1, wherein the obtaining a distillate comprising (meth) acrylic acid and high-boiling by-products comprises:

Supplying a portion of the second aqueous (meth) acrylic acid solution to an extraction column as an extraction column supply stream, and supplying the remaining portion to a water separation column as a water separation column supply stream;

contacting an extraction solvent and the extraction column feed stream in the extraction column and supplying an extract stream comprising an extract to the water separation column;

An upper discharge stream of the water separation column containing water and a distillate containing (meth) acrylic acid and high boiling by-products as a lower discharge stream of the water separation column are separated in the water separation column.

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

9. The process for producing (meth) acrylic acid according to claim 7, wherein an upper discharge stream of the water separation column is supplied to a layer separator, a part of an aqueous layer containing water and acetic acid is circulated to the absorption column, and the remaining part is discharged as waste water.

10. The process for producing (meth) acrylic acid according to claim 7, wherein an extraction solvent and the extraction column supply stream are contacted in the extraction column to further obtain a raffinate stream comprising a raffinate, and the raffinate stream is supplied to a layer separator.