Methods for preparing acrylic acid

Abstract

A method for preparing acrylic acid is provided, comprising: dehydrating an aqueous lactic acid solution in a reaction unit to prepare a reaction product stream; passing the reaction product stream sequentially through a cooling unit and a purification unit, and supplying the discharge stream of the purification unit to an acrylic acid separation tower; and separating unreacted lactic acid into a side discharge stream and acrylic acid into an top discharge stream in the acrylic acid separation tower.

Description

[Technical Field]

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2021-0137936, filed on October 15, 2021, the entire contents of which are incorporated herein by reference as a part of the specification. Technical Field

[0004] This invention relates to a method for preparing acrylic acid, and more specifically, to a method for preparing acrylic acid by the dehydration reaction of lactic acid, which effectively removes byproducts while reducing acrylic acid loss. [Background Technology]

[0005] Acrylic acid is used as a polymer raw material in fibers, adhesives, paints, fiber processing, leather, building materials, and other applications, and its demand is constantly growing. In addition, acrylic acid is also used as a raw material for absorbent resins, and is widely used in industry for absorbent products such as diapers and sanitary napkins, water-retaining agents in agriculture and horticulture, and industrial waterproofing materials.

[0006] Traditional methods for preparing acrylic acid generally involve oxidizing propylene in air. However, this method converts propylene into acrolein through a gas-contact oxidation reaction, followed by a gas-contact oxidation reaction of acrolein to produce acrylic acid. Furthermore, this method produces acetic acid as a byproduct, which is difficult to separate from acrylic acid. Additionally, methods for preparing acrylic acid using propylene rely on propylene obtained through refining crude oil, a fossil resource. Considering recent increases in crude oil prices and global warming, this method presents challenges related to raw material costs and environmental pollution.

[0007] Therefore, methods for preparing acrylic acid from carbon-neutral biomass feedstocks have been investigated. For example, there is a method for preparing acrylic acid (AA) via the gaseous dehydration reaction of lactic acid (LA). This method generally involves the intramolecular dehydration reaction of lactic acid at temperatures above 300°C in the presence of a catalyst. The dehydration reaction of lactic acid produces reaction products containing acrylic acid, and depending on the conversion rate, unreacted lactic acid is present in the reaction products. When unreacted lactic acid is present in the reaction products, the economic feasibility of this method can be improved simply by recovering the lactic acid during the separation process. However, because lactic acid rapidly oligomerizes at high temperatures and concentrations, it is difficult to recover the lactic acid. [Summary of the Invention]

[0008] [Technical Issues]

[0009] One object of the present invention is to provide a method for efficiently recovering unreacted lactic acid from the reaction products generated in the preparation of acrylic acid by the dehydration reaction of lactic acid, so as to solve the problems mentioned in the background art.

[0010] [Technical Solution]

[0011] In one general aspect, a method for preparing acrylic acid includes: dehydrating an aqueous solution of lactic acid in a reaction unit to prepare a reaction product stream; passing the reaction product stream sequentially through a cooling unit and a purification unit, and supplying the discharge stream of the purification unit to an acrylic acid separation tower; and separating unreacted lactic acid into a side discharge stream and acrylic acid into an top discharge stream in the acrylic acid separation tower.

[0012] [Beneficial Effects]

[0013] According to the method for preparing acrylic acid of the present invention, when recovering lactic acid from reaction products containing acrylic acid, the recovery rate of unreacted lactic acid can be improved by controlling the amount of time exposed to high temperature at high concentration to minimize the oligomerization reaction of lactic acid. [Attached Image Description]

[0014] Figure 1 This is a process flow diagram of a method for preparing acrylic acid according to an exemplary embodiment of the present invention.

[0015] Figure 2 This is a process flow diagram of the method for preparing acrylic acid based on a comparative example.

Detailed Implementation Methods

[0016] The terms and words used in the specification and claims of this invention should not be construed as having a general or dictionary meaning, but should be interpreted as having a meaning and concept consistent with the technical concept of the invention, based on the principle that the inventors are able to properly define the concepts of the terms in order to best describe their own invention.

[0017] The term "flow" in this invention can refer to fluid flow in a process or to the fluid itself flowing in a pipe. Specifically, "flow" can refer to both the fluid itself flowing in a pipe connecting various devices and the fluid flow. Furthermore, the fluid can include any one or more components of gas, liquid, and solid.

[0018] In the following text, reference will be made to Figure 1 The invention will be described in more detail to provide a better understanding of it.

[0019] According to the present invention, a method for preparing acrylic acid is provided. More specifically, the method may include: dehydrating an aqueous lactic acid solution in a reaction unit 10 to prepare a reaction product stream; passing the reaction product stream sequentially through a cooling unit 20 and a purification unit 30, and supplying the discharge stream of the purification unit 30 to an acrylic acid separation tower 100; and separating unreacted lactic acid into a side discharge stream and acrylic acid into an upper discharge stream in the acrylic acid separation tower 100.

[0020] Specifically, the traditional method for preparing acrylic acid generally involves oxidizing propylene in air. However, this method converts propylene into acrolein through a gas-contact oxidation reaction, and then further oxidizes the acrolein to produce acrylic acid. Furthermore, this method produces acetic acid as a byproduct, which is difficult to separate from acrylic acid. Additionally, the method of preparing acrylic acid using propylene relies on propylene obtained through refining crude oil, a fossil resource, as a raw material. Considering recent increases in crude oil prices and global warming, this method presents issues related to raw material costs and environmental pollution.

[0021] To address the problems of traditional methods for preparing acrylic acid, methods for preparing acrylic acid from carbon-neutral biomass feedstocks have been investigated. For example, there is a method for preparing acrylic acid (AA) via the gaseous dehydration reaction of lactic acid (LA). This method generally involves the intramolecular dehydration reaction of lactic acid at high temperatures in the presence of a catalyst. The dehydration reaction of lactic acid produces reaction products containing acrylic acid, and depending on the conversion rate, unreacted lactic acid is included in the reaction products. When unreacted lactic acid is present in the reaction products, the economic feasibility of this method can be improved simply by recovering the lactic acid during the separation process. However, because lactic acid rapidly oligomerizes at high temperatures and high concentrations, it is difficult to recover the lactic acid.

[0022] Therefore, in order to solve the conventional problems, this invention provides a method for separating lactic acid from a reaction product containing acrylic acid prepared by a lactic acid dehydration reaction, wherein the exposure time of high-concentration lactic acid to high temperature is shortened to prevent lactic acid oligomerization, thereby improving the recovery rate of unreacted lactic acid.

[0023] According to an exemplary embodiment of the present invention, an aqueous solution of lactic acid is supplied to reaction unit 10 and subjected to a dehydration reaction to prepare a reaction product containing acrylic acid. Here, the dehydration reaction can be carried out as a gas-phase reaction in the presence of a catalyst. For example, the concentration of lactic acid in the aqueous solution can be 10% by weight or more, 20% by weight or more, or 30% by weight or more, and 40% by weight or less, 50% by weight or less, 60% by weight or less, or 70% by weight or less. When lactic acid is present at a high concentration, oligomers such as dimers and trimers are formed through an equilibrium reaction, so that lactic acid can be used in the form of an aqueous solution with concentrations within the above-mentioned ranges.

[0024] The reactor may include a reactor capable of carrying out a typical lactic acid dehydration reaction. The reactor may include a reaction tube filled with a catalyst, through which a reaction gas containing the volatile components of an aqueous lactic acid solution, as a feedstock, is passed, allowing the lactic acid to be dehydrated via a gas-phase contact reaction to produce acrylic acid. In addition to lactic acid, the reaction gas may also include any one or more diluent gases such as water vapor, nitrogen, and air for adjusting concentration.

[0025] The reactor operating conditions can be those of a common lactic acid dehydration reaction. Here, the reactor operating temperature can refer to the set temperature of the heating medium, etc., used to control the reactor temperature.

[0026] The catalyst used in the dehydration reaction of lactic acid may include one or more catalysts selected from the group consisting of sulfate catalysts, phosphate catalysts, and nitrate catalysts. As specific examples, sulfates may include Na₂SO₄, K₂SO₄, CaSO₄, and Al₂(SO₄)₃; phosphates may include Na₃PO₄, Na₂HPO₄, NaH₂PO₄, K₃PO₄, K₂HPO₄, KH₂PO₄, CaHPO₄, Ca₃(PO₄)₂, AlPO₄, CaH₂P₂O₇, and Ca₂P₂O₇; and nitrates may include NaNO₃, KNO₃, and Ca(NO₃)₂. Furthermore, the catalyst may be supported on a support. The support may include one or more catalysts selected from the group consisting of diatomaceous earth, alumina, silica, titanium dioxide, carbides, and zeolites.

[0027] The reaction products prepared by the dehydration reaction of lactic acid may contain water (H2O), gaseous byproducts, low-boiling byproducts, high-boiling byproducts, and unreacted lactic acid, in addition to acrylic acid as the desired product.

[0028] The method of preparing acrylic acid via lactic acid dehydration reaction can ensure raw material competitiveness and solve environmental pollution problems compared with the traditional method of propylene oxidation in air. However, the lactic acid conversion rate is low and various byproducts are generated, reducing the yield of acrylic acid. Therefore, it is necessary to develop a method that improves economic feasibility. To this end, this invention provides a method that improves economic feasibility by increasing the recovery rate of unreacted lactic acid.

[0029] According to an exemplary embodiment of the present invention, the reaction product stream is passed sequentially through a cooling unit 20 and a purification unit 30, and the discharge stream from the purification unit 30 can be supplied to an acrylic acid separation tower 100 to recover lactic acid.

[0030] According to an exemplary embodiment of the present invention, the cooling unit 20 may include one or more cooling towers to which the reaction product stream can be supplied and cooled. Specifically, the reaction product prepared by the lactic acid dehydration reaction is a gaseous phase and can be condensed in the cooling tower. The gaseous byproducts can be separated to the upper part of the cooling tower, the liquid condensate can be discharged to the lower part of the cooling tower, and the condensate can be supplied to the downstream purification unit 30. Here, the gaseous byproducts may include water, carbon monoxide, carbon dioxide, dilution gas, acetaldehyde, etc., as gaseous components.

[0031] According to an exemplary embodiment of the present invention, the purification unit 30 may include a water separation tower and a low-boiling-point separation tower. For example, the water separation tower may separate water from the reaction products by distillation or extraction.

[0032] When water is separated from the reaction products by extraction in a water separation tower, an additional extractant is supplied to the water separation tower. This extractant can be used to separate the acrylic acid contained in the reaction product stream into the top discharge stream of the water separation tower. Furthermore, a step of recovering the extractant can be performed.

[0033] The extractant may comprise one or more of the following: benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butyl acetate, isobutyl 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. As a specific example, the extractant may be toluene.

[0034] The method of supplying the extractant to the water separator and performing extraction can be any known method, for example, any method such as cross-flow, counter-flow and co-flow can be used without particular limitation.

[0035] The reaction product stream and the extractant can be contacted in a water separation column to separate the extractant and the extraction residue. For example, the extractant can be acrylic acid dissolved in the extractant, and the extractant can be discharged as the top discharge stream of the water separation column. Here, the top discharge stream of the water separation column can be supplied to a low-boiling-point separation column after the extractant has been removed.

[0036] Furthermore, the extraction residue, which is water-containing wastewater, can be separated into the lower discharge stream of a water separation tower. Here, aqueous byproducts can be separated from the water and discharged together in the lower part of the water separation tower.

[0037] The upper discharge stream of the water separator is supplied to the low-boiling-point separator, and the low-boiling-point byproducts can be removed by distillation. The reaction product from which the low-boiling-point byproducts have been removed can be discharged as the lower discharge stream of the low-boiling-point separator. Here, the discharge stream from the purification unit 30 supplied to the acrylic acid separator 100 can be the lower discharge stream of the low-boiling-point separator.

[0038] The reaction product stream can be passed sequentially through cooling unit 20 and purification unit 30 to remove gaseous byproducts, water and low-boiling-point byproducts.

[0039] The effluent from the refining unit 30 may contain acrylic acid, unreacted lactic acid, and high-boiling-point byproducts. The content of unreacted lactic acid in the effluent from the refining unit 30 varies with the conversion rate of lactic acid, depending on the reaction and process conditions in the reaction unit 10. For example, it may be more than 0.5% by weight, more than 2% by weight, or more than 5% by weight, and less than 10% by weight, less than 15% by weight, or less than 20% by weight. Therefore, when unreacted lactic acid is present in the reaction products, it should be recovered or removed during the separation process. However, it is conventionally difficult to recover unreacted lactic acid, and in most cases, unreacted lactic acid is removed together with high-boiling-point byproducts. In this invention, unreacted lactic acid is recovered at a high recovery rate to improve the economic feasibility of the method.

[0040] According to an exemplary embodiment of the present invention, the discharge stream of the purification unit 30 may be supplied to the acrylic acid separation tower 100 to recover lactic acid. Specifically, the acrylic acid separation tower 100 may be used to separate acrylic acid from the reaction products and to recover and reuse unreacted lactic acid.

[0041] The operating conditions of the acrylic acid separation tower 100 can be adjusted according to the composition of the discharge stream from the purification unit 30 to improve the separation efficiency of each component.

[0042] The operating pressure of the acrylic acid separation tower 100 can be above 10 Torr, above 30 Torr, or above 50 Torr, and below 80 Torr, below 100 Torr, or below 200 Torr. When the acrylic acid separation tower 100 operates at the above-mentioned operating pressure range, the separation efficiency of acrylic acid, unreacted lactic acid, and high-boiling-point by-products in the acrylic acid separation tower 100 can be relatively high, and side reactions occurring at high temperatures can be suppressed.

[0043] The discharge stream from the refining unit 30 can be supplied to a section that accounts for 40% or more, 50% or more, 60% or more, or 65% or more and less than 80%, 85% or less, or 90% of the total number of sections in the acrylic acid separation tower 100. Here, the total number of sections in the acrylic acid separation tower 100 can be 10 to 70. For example, when the total number of sections in the acrylic acid separation tower 100 is 100, the top section can be section 1, the bottom section can be section 100, and sections accounting for 60% to 80% of the total number of sections in the acrylic acid separation tower 100 can refer to sections 60 to 80 of the acrylic acid separation tower 100. By controlling the supply section of the discharge stream from the refining unit 30 to the acrylic acid separation tower 100 within the above-mentioned range, the separation efficiency of acrylic acid, lactic acid, and high-boiling-point by-products in the acrylic acid separation tower 100 is improved.

[0044] In acrylic acid separation tower 100, acrylic acid can be separated from the top discharge stream, lactic acid can be separated from the side discharge stream, and high-boiling-point by-products can be separated from the bottom discharge stream.

[0045] The side discharge stream of the acrylic acid separation tower 100 can be discharged to a section that is 20% or more, 30% or more, 50% or more, or 55% or more and less than 70%, 75% or less, or less than 80% of the total number of sections of the acrylic acid separation tower 100. By controlling the discharge section of the side discharge stream of the acrylic acid separation tower 100 within the above range, high-purity unreacted lactic acid is separated to the side and recovered. Therefore, the time that lactic acid is exposed to high temperatures can be minimized, and the loss of lactic acid discharged to the lower part along with high-boiling-point byproducts can be minimized.

[0046] The content of unreacted lactic acid in the side discharge stream of acrylic acid separation tower 100 can be more than 70%, 70% to 90%, or 75% to 90% of the content of unreacted lactic acid in the discharge stream of purification unit 30. The unreacted lactic acid separated into the side discharge stream of acrylic acid separation tower 100 can be mixed with an aqueous lactic acid solution and supplied to reaction unit 10. The recovery of unreacted lactic acid as a side discharge stream of acrylic acid separation tower 100 and its reuse in reaction unit 10 improves the economic feasibility of the method.

[0047] The upper discharge stream of acrylic acid separation tower 100 is passed through a condenser, and a portion of the stream is returned to acrylic acid separation tower 100 to separate acrylic acid from the remaining stream. Furthermore, a portion of the lower discharge stream of acrylic acid separation tower 100 is passed through a reboiler and returned to acrylic acid separation tower 100 to separate high-boiling-point byproducts from the remaining stream.

[0048] The flow ratio of the stream that passes through the reboiler and is returned to the acrylic acid separation tower 100 to the stream that has not been returned and separated from the acrylic acid separation tower 100 in the upper discharge stream can be 0.8 or more, 0.85 or more, or 0.95 or more, and 1.3 or less, 1.4 or less, or 1.5 or less. As described above, by controlling the flow ratio of the stream that passes through the reboiler and is returned to the acrylic acid separation tower 100 to the stream that has not been returned and separated from the acrylic acid separation tower 100 in the upper discharge stream, the time that unreacted lactic acid spends in the lower reboiler of the acrylic acid separation tower 100, which operates at high temperature, is reduced, thereby preventing the oligomerization reaction of lactic acid.

[0049] According to an exemplary embodiment of the present invention, in the method for preparing acrylic acid, if necessary, devices such as distillation columns, condensers, reboilers, valves, pumps, separators and mixers may be further installed.

[0050] The method for preparing acrylic acid according to the present invention has been described and explained above in the accompanying drawings. However, the description and explanation in the drawings are only for understanding the core structure of the present invention. In addition to the methods and apparatus shown above and in the drawings, other methods and apparatus that are not separately described and explained can also be appropriately applied and used to implement the method for preparing acrylic acid according to the present invention.

[0051] The present invention will be described in more detail below by way of examples. However, the following examples are provided for illustrative purposes, 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.

[0052] Example

[0053] Example 1

[0054] according to Figure 1 The process flow diagram shown illustrates the method for preparing acrylic acid using the Aspen Plus simulator from Aspen Technology, Inc.

[0055] Specifically, an aqueous lactic acid solution and nitrogen (N2) as a diluent gas are supplied to reaction unit 10 to prepare a reaction product containing acrylic acid (AA) through a dehydration reaction. The effluent stream from reaction unit 10 containing the reaction product is supplied to cooling unit 20 to remove gaseous byproducts, and the reaction product with the gaseous byproducts removed is supplied to purification unit 30. In purification unit 30, water and low-boiling-point byproducts are removed from the reaction product, and the effluent stream from purification unit 30 with the water and low-boiling-point byproducts removed is supplied to the 15th section of acrylic acid separation tower 100. At this point, the total number of sections in acrylic acid separation tower 100 is 20.

[0056] The upper discharge stream from the acrylic acid separation tower 100 is passed through a condenser, and a portion of the stream is returned to the acrylic acid separation tower 100 to separate acrylic acid from the remaining stream. Furthermore, a portion of the lower discharge stream from the acrylic acid separation tower 100 is passed through a reboiler and returned to the acrylic acid separation tower 100 to separate high-boiling-point byproducts from the remaining stream. Additionally, a side discharge stream containing unreacted lactic acid is separated and sent to the 13th section of the acrylic acid separation tower 100. This side discharge stream is mixed with an aqueous lactic acid solution and supplied to the first reaction unit 10. At this time, the flow rate ratio of the stream returned to the acrylic acid separation tower 100 after passing through the reboiler to the stream from the upper discharge stream of the acrylic acid separation tower 100 that has not been returned and from which acrylic acid has been separated is controlled at 1.3.

[0057] The temperature, pressure, and flow rate (kg / hr) of each component in each logistics process are shown in Table 1 below:

[0058] [Table 1]

[0059]

[0060] Example 2

[0061] The method is carried out in the same manner as in Example 1, except that the discharge stream of the purification unit 30 is supplied to the 10th section of the acrylic acid separation tower 100 and the side discharge stream containing unreacted lactic acid is separated to the 8th section of the acrylic acid separation tower 100.

[0062] At this point, the temperature, pressure, and flow rate (kg / hr) of each component in each logistics are shown in Table 2 below:

[0063] [Table 2]

[0064]

[0065] Comparative example

[0066] Comparative Example 1

[0067] according to Figure 2 The process flow diagram shown illustrates the method for preparing acrylic acid using the Aspen Plus simulator from Aspen Technology, Inc.

[0068] Specifically, an aqueous lactic acid solution and nitrogen (N2) as a diluent gas are supplied to the reaction unit to prepare a reaction product containing acrylic acid (AA) through a dehydration reaction. The effluent from the reaction unit containing the reaction product stream is supplied to a cooling unit to remove gaseous byproducts, and the reaction product with the gaseous byproducts removed is supplied to a purification unit. In the purification unit, water and low-boiling-point byproducts are removed from the reaction product, and the effluent from the purification unit with water and low-boiling-point byproducts removed is supplied to the third section of the acrylic acid separation tower 100. At this point, the acrylic acid separation tower 100 has a total of 10 sections.

[0069] The upper discharge stream from acrylic acid separation tower 100 is passed through a condenser, and a portion of the stream is returned to acrylic acid separation tower 100 to separate acrylic acid from the remaining stream. Additionally, a portion of the lower discharge stream from acrylic acid separation tower 100 is passed through a reboiler and returned to acrylic acid separation tower 100 to separate high-boiling-point byproducts and unreacted lactic acid from the remaining stream and supply them to lactic acid recovery tower 200.

[0070] The upper discharge stream from the lactic acid recovery tower 200 is passed through a condenser, with a portion of the stream being returned to the lactic acid recovery tower 200, and unreacted lactic acid recovered from the remaining stream. Additionally, a portion of the lower discharge stream from the lactic acid recovery tower 200 is passed through a reboiler and returned to the lactic acid recovery tower 200, separating high-boiling-point byproducts from the remaining stream. The lactic acid recovered from the upper discharge stream of the lactic acid recovery tower 200 is mixed with an aqueous lactic acid solution and supplied to the reaction unit.

[0071] The temperature, pressure, and flow rate (kg / hr) of each component in each logistics process are shown in Table 3 below:

[0072] [Table 3]

[0073]

[0074] Referring to Tables 1 to 3, in Examples 1 and 2, where unreacted lactic acid was recovered from the reaction product by the method for preparing acrylic acid according to the present invention, the purity of acrylic acid was confirmed to be 99.9% to 100%, and the recovery rate of lactic acid was above 75%. In particular, in Example 1, where the supply section of the discharge stream from the purification unit 30 was controlled to be 65% to 85% of the total number of sections of the acrylic acid separation tower 100, the discharge section of the side discharge stream from the acrylic acid separation tower 100 was controlled to be 55% to 75%, and the flow ratio of the stream that passed through the reboiler and was returned to the acrylic acid separation tower 100 to the stream that was not returned and separated in the upper discharge stream of the acrylic acid separation tower 100 was controlled to be 1 to 1.5, the purity of acrylic acid reached 100%, and the recovery rate of lactic acid was high.

[0075] In contrast, in Comparative Example 1, a conventionally designed facility for recovering unreacted lactic acid discharged from the lower part of the acrylic acid separation tower 100 along with high-boiling-point byproducts, the lower discharge stream of the acrylic acid separation tower 100 is supplied to a downstream lactic acid separation tower where lactic acid is recovered. This increases the amount of time the product is exposed to high temperatures at high concentrations, thereby increasing the equilibrium reaction rate. For example, high concentrations of unreacted lactic acid are discharged from the lower part of the acrylic acid separation tower 100 at high temperatures, and the unreacted lactic acid is reheated in the downstream tower, thereby promoting the oligomerization reaction of lactic acid and reducing the recovery rate of unreacted lactic acid, while using additional energy.

Claims

1. A process for producing acrylic acid, the process comprising: dehydrating an aqueous lactic acid solution in a reaction unit to produce a reaction product stream; passing the reaction product stream sequentially through a cooling unit and a refining unit, and supplying the effluent stream of the refining unit to an acrylic acid separation column; and separating unreacted lactic acid as a side draw stream and separating acrylic acid as an upper draw stream in the acrylic acid separation column, wherein the side draw stream of the acrylic acid separation column is drawn from a stage that is from 20% to 80% of the total number of stages of the acrylic acid separation column.

2. The process for producing acrylic acid as claimed in claim 1, wherein, The effluent stream of the refining unit is supplied to a stage that is from 40% to 90% of the total number of stages of the acrylic acid separation column.

3. The process for producing acrylic acid as claimed in claim 1, wherein, The effluent stream of the refining unit is supplied to a stage that is from 65% to 85% of the total number of stages of the acrylic acid separation column.

4. The process for producing acrylic acid as claimed in claim 1, wherein, The side draw stream of the acrylic acid separation column is drawn from a stage that is from 55% to 75% of the total number of stages of the acrylic acid separation column.

5. The process for producing acrylic acid as claimed in claim 1, wherein, The operating pressure of the acrylic acid separation column is from 10 to 200 Torr.

6. The process for producing acrylic acid as claimed in claim 1, wherein, The flow ratio of a stream that passes through a reboiler and is refluxed to the acrylic acid separation column to a stream that is not refluxed and separates acrylic acid from the upper draw stream of the acrylic acid separation column is from 0.8 to 1.

5.

7. The process for producing acrylic acid as claimed in claim 1, wherein, The unreacted lactic acid that is separated as the side draw stream of the acrylic acid separation column is mixed with the aqueous lactic acid solution and supplied to the reaction unit.

8. The process for producing acrylic acid as claimed in claim 1, wherein, A high boiling by-product is separated from the lower draw stream of the acrylic acid separation column.

9. The process for producing acrylic acid as claimed in claim 1, wherein, The reaction product stream comprises acrylic acid, water, a gaseous by-product, a low boiling by-product, a high boiling by-product, and unreacted lactic acid.

10. The process for producing acrylic acid as claimed in claim 9, wherein, The cooling unit removes the gaseous by-product from the reaction product stream and the refining unit removes water and the low boiling by-product from the reaction product stream.

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