Method for preparing acrylic acid

Abstract

Provided is a method for preparing an acrylic acid including: dehydrating a lactic acid aqueous solution in a reaction unit to prepare a reaction product stream; passing the reaction product stream through a cooling unit and a refining unit sequentially and supplying a discharge stream from the refining unit to an acrylic acid separation column; and separating an unreacted lactic acid as a side discharge stream and separating the acrylic acid as an upper discharge stream in the acrylic acid separation column.

Description

Acrylic acid manufacturing method

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2021-0137936, filed October 15, 2021, the entire contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention relates to a method for producing acrylic acid, and more specifically, to a method for producing acrylic acid through a dehydration reaction of lactic acid, while reducing the loss of acrylic acid and effectively removing byproducts.

[0005] Acrylic acid is a polymer raw material used in fibers, adhesives, paints, textile processing, leather, and construction materials, and its demand is growing. Furthermore, acrylic acid is also used as a raw material for absorbent resins, widely used industrially in absorbent products such as paper diapers and sanitary pads, as well as in agricultural and horticultural water retention agents and industrial water-repellents.

[0006] Conventional acrylic acid manufacturing methods typically involve air oxidation of propylene. However, this method involves converting propylene into acrolein through a gas-phase catalytic oxidation reaction, which is then subjected to a gas-phase catalytic oxidation reaction to produce acrylic acid. However, acetic acid is produced as a byproduct, which is difficult to separate from acrylic acid. Furthermore, the method for manufacturing acrylic acid using propylene uses propylene, which is obtained by refining crude oil, a fossil resource, as a raw material, and considering recent issues such as rising crude oil prices and global warming, there are problems in terms of raw material costs and environmental pollution.

[0007] In this regard, research has been conducted on methods for producing acrylic acid from carbon-neutral biomass raw materials. For example, there is a method for producing acrylic acid (AA) through a gas-phase dehydration reaction of lactic acid (LA). This method generally produces acrylic acid through an intramolecular dehydration reaction of lactic acid at high temperatures above 300°C and in the presence of a catalyst. The dehydration reaction of lactic acid produces a reaction product containing acrylic acid, and depending on the conversion rate, the reaction product contains unreacted lactic acid. If the reaction product contains unreacted lactic acid, it must be recovered in a separation process to improve the economic feasibility of the process. However, lactic acid undergoes rapid oligomerization at high concentrations and high temperatures, making its recovery difficult.

[0008] The problem to be solved in the present invention is to provide a method for effectively recovering and reusing unreacted lactic acid from a reaction product produced by producing acrylic acid through a dehydration reaction of lactic acid in order to solve the problems mentioned in the technology that forms the background of the above invention.

[0009] According to one embodiment of the present invention for solving the above problem, the present invention provides a method for producing acrylic acid, comprising the steps of: producing a reaction product stream by dehydrating a lactic acid aqueous solution in a reaction unit; sequentially passing the reaction product stream through a cooling unit and a purification unit, and supplying a discharge stream from the purification unit to an acrylic acid separation tower; and separating unreacted lactic acid as a side discharge stream and acrylic acid as an upper discharge stream from the acrylic acid separation tower.

[0010] According to the method for producing acrylic acid of the present invention, in recovering lactic acid from a reaction product containing acrylic acid, the recovery rate of unreacted lactic acid can be increased by controlling the time of exposure to high temperature in a high concentration state to minimize the oligomerization reaction of lactic acid.

[0011] Figure 1 is a process flow diagram according to a method for manufacturing acrylic acid in one embodiment of the present invention.

[0012] Figure 2 is a process flow diagram according to the acrylic acid manufacturing method in a comparative example.

[0013] The terms or words used in the description and claims of the present invention should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0014] In the present invention, the term "stream" may refer to the flow of fluid within a process, and may also refer to the fluid itself flowing within a pipe. Specifically, the stream may refer to both the fluid itself flowing within the pipe connecting each device and the flow of the fluid. Furthermore, the fluid may include one or more components of gas, liquid, and solid.

[0015]

[0016] Hereinafter, to help understand the present invention, the present invention will be described in more detail with reference to FIG. 1.

[0017] According to the present invention, a method for producing acrylic acid is provided. More specifically, the method may include the steps of: producing a reaction product stream by dehydrating an aqueous lactic acid solution in a reaction unit (10); sequentially passing the reaction product stream 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 as a side discharge stream and separating acrylic acid as an upper discharge stream from the acrylic acid separation tower (100).

[0018] Specifically, the conventional method for manufacturing acrylic acid is generally a method for oxidizing propylene in the air, but this method converts propylene into acrolein through a gas-phase catalytic oxidation reaction, and manufactures acrylic acid by subjecting this to a gas-phase catalytic oxidation reaction. However, acetic acid is produced as a by-product, and this has the problem of being difficult to separate from acrylic acid. In addition, the method for manufacturing acrylic acid using propylene uses propylene obtained by refining crude oil, a fossil resource, as a raw material, and considering recent issues such as the rise in crude oil prices and global warming, there are problems in terms of raw material costs and environmental pollution.

[0019] To address the problems of the conventional acrylic acid production methods, research has been conducted on methods for producing acrylic acid from carbon-neutral biomass raw materials. For example, there is a method for producing acrylic acid (AA) through a gas-phase dehydration reaction of lactic acid (LA). This method typically produces acrylic acid through an intramolecular dehydration reaction of lactic acid at high temperatures and in the presence of a catalyst. The dehydration reaction of lactic acid produces a reaction product containing acrylic acid, and depending on the conversion rate, the reaction product contains unreacted lactic acid. If the reaction product contains unreacted lactic acid, it must be recovered through a separation process to improve the economic feasibility of the process. However, lactic acid undergoes rapid oligomerization at high concentrations and temperatures, making its recovery difficult.

[0020] Accordingly, in order to solve the above-mentioned conventional problem, the present invention provides a method for separating lactic acid from a reaction product including acrylic acid produced through a dehydration reaction of lactic acid, thereby preventing oligomerization of lactic acid by shortening the time for which high-concentration lactic acid is exposed to high temperature, thereby improving the recovery rate of unreacted lactic acid.

[0021] According to one embodiment of the present invention, a lactic acid aqueous solution may be supplied to the reaction unit (10) to undergo a dehydration reaction to produce a reaction product containing acrylic acid. At this time, the dehydration reaction may be performed as a gas phase reaction in the presence of a catalyst. For example, the lactic acid concentration of the lactic acid aqueous solution may be 10 wt% or more, 20 wt% or more, or 30 wt% or more, and 40 wt% or less, 50 wt% or less, 60 wt% or less, or 70 wt% or less. When the lactic acid is present at a high concentration, oligomers such as dimers and trimers are formed by an equilibrium reaction, and thus the lactic acid may be used in the form of an aqueous solution having a concentration within the above range.

[0022] The above reactor may include a reactor capable of performing a conventional dehydration reaction of lactic acid, and the reactor may include a reaction tube filled with a catalyst, and a reaction gas containing volatile components of a raw material lactic acid aqueous solution may be passed through the reaction tube to dehydrate lactic acid through a gas phase contact reaction to produce acrylic acid. The reaction gas may further include, in addition to lactic acid, one or more dilution gases selected from the group consisting of steam, nitrogen, and air for concentration adjustment.

[0023] The operating conditions of the above reactor may be set under typical lactic acid dehydration reaction conditions. In this case, the operating temperature of the reactor may refer to the set temperature of a heat medium, etc., used to control the temperature of the reactor.

[0024] The catalyst used in the dehydration reaction of the lactic acid may include, for example, at least one selected from the group consisting of a sulfate-based catalyst, a phosphate-based catalyst, and a nitrate-based catalyst. As a specific example, the sulfate may include Na2SO4, K2SO4, CaSO4, and Al2(SO4)3, the phosphate may include Na3PO4, Na2HPO4, NaH2PO4, K3PO4, K2HPO4, KH2PO4, CaHPO4, Ca3(PO4)2, AlPO4, CaH2P2O7, and Ca2P2O7, and the nitrate may include NaNO3, KNO3, and Ca(NO3)2. In addition, the catalyst may be supported on a support. The support may include, for example, at least one selected from the group consisting of diatomaceous earth, alumina, silica, titanium dioxide, carbide, and zeolite.

[0025] The reaction product manufactured through the dehydration reaction of the above lactic acid may further include water (H2O), gaseous by-products, low-boiling-point by-products, high-boiling-point by-products, and unreacted lactic acid in addition to the desired product, acrylic acid.

[0026] The method of producing acrylic acid through the dehydration of lactic acid can secure raw material competitiveness and alleviate environmental pollution compared to conventional air oxidation of propylene. However, the conversion rate of lactic acid is low, and various byproducts are generated, resulting in a low acrylic acid yield. Therefore, process development is necessary to improve economic feasibility. To address this issue, the present invention provides a method for improving economic feasibility by increasing the recovery rate of unreacted lactic acid.

[0027] According to one embodiment of the present invention, the reaction product stream sequentially passes through a cooling unit (20) and a purification unit (30), and the discharge stream of the purification unit (30) is supplied to an acrylic acid separation tower (100) to recover lactic acid.

[0028] According to one embodiment of the present invention, the cooling unit (20) may include one or more cooling towers, and the reaction product stream may be supplied to the cooling towers and cooled. Specifically, the reaction product produced through the dehydration reaction of the lactic acid may be condensed in a gaseous state through the cooling tower. A gaseous byproduct may be separated from the upper portion of the cooling tower, and a liquid condensate may be discharged from the lower portion, and the condensate may be supplied to a purification unit (30) at the rear end. At this time, the gaseous byproduct may include gas components such as water, carbon monoxide, carbon dioxide, dilution gas, and acetaldehyde.

[0029] According to one 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 product through distillation or extraction.

[0030] When separating water from the reaction product through extraction in the water separation tower, a separate extractant is supplied to the water separation tower, and the acrylic acid contained in the reaction product stream can be separated into an upper discharge stream of the water separation tower using the extractant. In addition, a further step for recovering the extractant may be performed.

[0031] The extractant may include, for example, at least one selected from the group consisting of benzene, toluene, xylene, n-heptane, cycloheptane, cycloheptene, 1-heptene, ethylbenzene, methylcyclohexane, n-butylacetate, isobutylacetate, isobutyl acrylate, n-propyl acetate, isopropyl acetate, methylisobutyl 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 isopropylbutyl ether. As a specific example, the extractant may be toluene.

[0032] Any known method can be used to supply the extractant to the water separation tower and extract the water. For example, any method such as cross current, counter current, or co-current can be used without any special restrictions.

[0033] The reaction product stream and the extractant can be brought into contact with each other in the water separation tower to separate the extractant and the raffinate. For example, the extractant may be acrylic acid dissolved in the extractant, and the extractant may be discharged as a top discharge stream from the water separation tower. In this case, the top discharge stream from the water separation tower may be supplied to a low-boiling-point separation tower after removing the extractant.

[0034] Additionally, the above-mentioned residual liquid is wastewater containing water and can be separated into the lower portion of the water separation tower. At this time, water and water-soluble byproducts can be separated and discharged together from the lower portion of the water separation tower.

[0035] The above low-boiling-point separation tower can receive the upper discharge stream of the water separation tower and remove low-boiling-point by-products through distillation, and the reaction product from which the low-boiling-point by-products have been removed can be discharged as the lower discharge stream of the low-boiling-point separation tower. In this case, the discharge stream of the purification unit (30) supplied to the acrylic acid separation tower (100) can be the lower discharge stream of the low-boiling-point separation tower.

[0036] The above reaction product stream may sequentially pass through a cooling unit (20) and a purification unit (30) to remove gaseous byproducts, water, and low-boiling-point byproducts.

[0037] The discharge stream of the purification unit (30) may include acrylic acid, unreacted lactic acid, and high-boiling-point by-products. The content of unreacted lactic acid in the discharge stream of the purification unit (30) varies depending on the conversion rate of lactic acid in the reaction unit (10) that varies depending on the reaction and process conditions, and may be, for example, 0.5 wt% or more, 2 wt% or more, or 5 wt% or more, and 10 wt% or less, 15 wt% or less, or 20 wt% or less. In this way, if unreacted lactic acid exists in the reaction product, it must be recovered or removed in a separation process. However, in the past, it was difficult to recover the unreacted lactic acid, and most of it was removed together with the high-boiling-point by-products. In the present invention, the economic feasibility of the process is improved by recovering the unreacted lactic acid at a high recovery rate.

[0038] According to one embodiment of the present invention, the discharge stream of the purification unit (30) may be supplied to an acrylic acid separation tower (100) to recover lactic acid. Specifically, the acrylic acid separation tower (100) may be configured to separate acrylic acid from the reaction product and recover unreacted lactic acid for reuse.

[0039] The operating conditions of the above acrylic acid separation tower (100) can be adjusted to increase the separation efficiency in separating each component according to the composition of the discharge stream of the purification unit (30).

[0040] The operating pressure of the acrylic acid separation tower (100) may be 10 torr or more, 30 torr or more, or 50 torr or more and 80 torr or less, 100 torr or less, or 200 torr or less. When the acrylic acid separation tower (100) is operated at an operating pressure within the above range, the separation efficiency is high in separating acrylic acid, unreacted lactic acid, and high-boiling-point by-products in the acrylic acid separation tower (100), and side reactions occurring at high temperatures can be suppressed.

[0041] The discharge stream of the purification unit (30) may be supplied in stages of 40% or more, 50% or more, 60% or more, or 65% or more and 80% or less, 85% or less, or 90% or less of the total number of stages of the acrylic acid separation tower (100). At this time, the total number of stages of the acrylic acid separation tower (100) may be 10 to 70 stages. For example, when the total number of stages of the acrylic acid separation tower (100) is 100 stages, the top stage may be stage 1, the bottom stage may be stage 100, and stages of 60% to 80% of the total number of stages of the acrylic acid separation tower (100) may mean stages 60 to 80 of the acrylic acid separation tower (100). By controlling the supply end of the purification unit (30) discharge stream supplied to the acrylic acid separation tower (100) within the above range, the separation efficiency of acrylic acid, lactic acid, and high-boiling-point by-products in the acrylic acid separation tower (100) can be increased.

[0042] In the above acrylic acid separation tower (100), acrylic acid can be separated from the upper discharge stream, lactic acid can be separated from the side discharge stream, and high-boiling-point by-products can be separated from the lower discharge stream.

[0043] The side discharge stream of the acrylic acid separation tower (100) may be discharged in stages of 20% or more, 30% or more, 50% or more, or 55% or more and 70% or less, 75% or less, or 80% or less of the total number of stages of the acrylic acid separation tower (100). By controlling the discharge stage of the side discharge stream of the acrylic acid separation tower (100) within the above range, high-purity unreacted lactic acid can be separated to the side and recovered, thereby minimizing the time that lactic acid is exposed to high temperatures while minimizing the loss of lactic acid discharged downward together with high-boiling-point by-products.

[0044] The content of unreacted lactic acid included in the side discharge stream of the acrylic acid separation tower (100) may be 70% or more, 70% to 90%, or 75% to 90% of the content of unreacted lactic acid included in the discharge stream of the purification unit (30). The unreacted lactic acid separated into the side discharge stream in the acrylic acid separation tower (100) may be mixed with the aqueous lactic acid solution and supplied to the reaction unit (10). By recovering the unreacted lactic acid into the side discharge stream of the acrylic acid separation tower (100) and reusing it in the reaction unit (10), the economic efficiency of the process can be improved.

[0045] The upper discharge stream of the acrylic acid separation tower (100) passes through a condenser, and a portion of the stream is refluxed to the acrylic acid separation tower (100), and acrylic acid can be separated from the remaining stream. In addition, a portion of the lower discharge stream of the acrylic acid separation tower (100) passes through a reboiler, and is refluxed to the acrylic acid separation tower (100), and high-boiling-point by-products can be separated from the remaining stream.

[0046] The flow rate ratio of the stream that passes through the reboiler and is refluxed to the acrylic acid separation tower (100) compared to the flow rate of the stream that separates acrylic acid without being refluxed among the upper discharge streams of the acrylic acid separation tower (100) may 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 rate ratio of the stream that passes through the lower reboiler and is refluxed compared to the flow rate of the stream that separates acrylic acid without being refluxed among the upper discharge streams of the acrylic acid separation tower (100), the time for unreacted lactic acid to pass through the lower reboiler of the acrylic acid separation tower (100) operated at a high temperature can be reduced, thereby preventing the oligomerization reaction of lactic acid from proceeding.

[0047] According to one embodiment of the present invention, in the acrylic acid manufacturing method, if necessary, additional devices such as a distillation tower, a condenser, a reboiler, a valve, a pump, a separator, and a mixer may be additionally installed.

[0048] Above, the method for producing acrylic acid according to the present invention has been described and illustrated in the drawings, but the description and illustration of the drawings describe and illustrate only the core components for understanding the present invention, and in addition to the processes and devices described and illustrated in the drawings, processes and devices not described and illustrated separately can be appropriately applied and utilized to carry out the method for producing acrylic acid according to the present invention.

[0049]

[0050] Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present invention, and the scope of the present invention is not limited to these examples alone.

[0051]

[0052] Example

[0053] Example 1

[0054] According to the process flow diagram shown in Fig. 1, the acrylic acid manufacturing process was simulated using Aspen Plus simulator from Aspen.

[0055] Specifically, a lactic acid aqueous solution and nitrogen (N2) as a dilution gas were supplied to the reaction unit (10) to produce a reaction product including acrylic acid (AA) through a dehydration reaction. The reaction unit (10) discharge stream including the reaction product stream was supplied to the cooling unit (20) to remove gaseous byproducts, and the reaction product from which the gaseous byproducts were removed was supplied to the purification unit (30). In the purification unit (30), water and low-boiling-point byproducts were removed from the reaction product, and the purification unit (30) discharge stream from which the water and low-boiling-point byproducts were removed was supplied to stage 15 of the acrylic acid separation tower (100). At this time, the total number of stages of the acrylic acid separation tower (100) is 20 stages.

[0056] In the acrylic acid separation tower (100), the upper discharge stream passed through a condenser, and some of the stream was refluxed to the acrylic acid separation tower (100), and acrylic acid was separated from the remaining stream. In addition, some of the lower discharge stream of the acrylic acid separation tower (100) passed through a reboiler and refluxed to the acrylic acid separation tower (100), and high-boiling-point by-products were separated from the remaining stream. In addition, a side discharge stream containing unreacted lactic acid was separated from stage 13 of the acrylic acid separation tower (100), and the side discharge stream of the acrylic acid separation tower (100) was mixed with the lactic acid aqueous solution and supplied to the reaction unit (10). At this time, the ratio of the flow rate of the stream that is not refluxed and separates acrylic acid among the upper discharge streams of the acrylic acid separation tower (100) to the flow rate of the stream that passes through the reboiler and is refluxed to the acrylic acid separation tower (100) was controlled to 1.3.

[0057] The temperature and pressure of each stream and the flow rate (kg / hr) of each component within each stream are shown in Table 1 below.

[0058] 1234Temperature (℃) 907713397Pressure (torr) 760707070Mass flow rate (kg / hr)Acrylic acid 1022.51000.00.022.5Lactic acid 100.00.022.176.0Lactic acid oligomer 0.00.02.00.0High boiling point by-product 30.00.030.00.0Total 1152.51000.054.198.5

[0059]

[0060] Example 2

[0061] In the above Example 1, the same method as in the above Example 1 was performed except that the discharge stream of the purification unit (30) was supplied to stage 10 of the acrylic acid separation tower (100), and the side discharge stream containing unreacted lactic acid was separated to stage 8 of the acrylic acid separation tower (100).

[0062] At this time, the temperature and pressure of each stream and the flow rate (kg / hr) of each component within each stream are shown in Table 2 below.

[0063] 1234Temperature (℃) 907713397Pressure (torr) 760707070Mass flow rate (kg / hr)Acrylic acid 1022.5999.60.022.9Lactic acid 100.00.422.175.6Lactic acid oligomer 0.00.02.00.0High boiling point by-product 30.00.030.00.0Total 1152.51000.054.198.5

[0064]

[0065] Comparative example

[0066] Comparative Example 1

[0067] According to the process flow diagram shown in Fig. 2, the acrylic acid manufacturing process was simulated using Aspen Plus simulator from Aspen.

[0068] Specifically, a lactic acid aqueous solution and nitrogen (N2) as a dilution gas were supplied to the reaction unit (10) to produce a reaction product including acrylic acid (AA) through a dehydration reaction. The reaction unit (10) discharge stream including the reaction product stream was supplied to a cooling unit (20) to remove gaseous byproducts, and the reaction product from which the gaseous byproducts had been removed was supplied to a purification unit (30). In the purification unit (30), water and low-boiling-point byproducts were removed from the reaction product, and the purification unit (30) discharge stream from which the water and low-boiling-point byproducts had been removed was supplied to three stages of an acrylic acid separation tower (100). At this time, the total number of stages of the acrylic acid separation tower (100) is 10 stages.

[0069] The upper discharge stream from the acrylic acid separation tower (100) passed through a condenser, and a portion of the stream was refluxed to the acrylic acid separation tower (100), and acrylic acid was separated from the remaining stream. In addition, a portion of the lower discharge stream from the acrylic acid separation tower (100) passed through a reboiler and refluxed to the acrylic acid separation tower (100), and high-boiling-point by-products and unreacted lactic acid were separated from the remaining stream and supplied to the lactic acid recovery tower (200).

[0070] The upper discharge stream from the lactic acid recovery tower (200) passed through a condenser, and a portion of the stream was refluxed to the lactic acid recovery tower (200), and unreacted lactic acid was recovered from the remaining stream. In addition, a portion of the lower discharge stream from the lactic acid recovery tower (200) passed through a reboiler, and was refluxed to the lactic acid recovery tower (200), and high-boiling-point by-products were separated from the remaining stream. The lactic acid recovered from the upper discharge stream of the lactic acid recovery tower (200) was mixed with the lactic acid aqueous solution and supplied to the reaction unit (10).

[0071] The temperature and pressure of each stream and the flow rate (kg / hr) of each component within each stream are shown in Table 3 below.

[0072] 12345Temperature (℃)909011797133Pressure (torr)7601201207070Mass flow rate (kg / hr)Acrylic acid1022.5998.124.424.40.0Lactic acid100.01.996.172.621.6Lactic acid oligomer0.00.02.00.03.9High boiling point by-product30.00.030.00.030.0Total1152.51000.0152.597.055.5

[0073]

[0074] Referring to Tables 1 to 3 above, in the case of Examples 1 and 2 in which unreacted lactic acid is recovered from the reaction product by the acrylic acid production method according to the present invention, it was confirmed that the purity of the acrylic acid was 99.9% to 100%, and the recovery rate of lactic acid was 75% or higher. In particular, in the case of Example 1 in which the supply stage of the discharge stream of the purification unit (30) was controlled to a stage corresponding to 65% to 85% of the total number of stages of the acrylic acid separation tower (100), the discharge stage of the side discharge stream of the acrylic acid separation tower (100) was controlled to 55% to 75%, and the ratio of the flow rate of the stream that separates acrylic acid without being refluxed among the upper discharge streams of the acrylic acid separation tower (100) and passes through the reboiler and is refluxed to the acrylic acid separation tower (100) was controlled to 1 to 1.5, it was confirmed that the purity of the acrylic acid reached 100%, and the recovery rate of lactic acid was even higher.

[0075] In comparison, in the case of Comparative Example 1, it was arbitrarily designed to recover unreacted lactic acid discharged together with high-boiling-point by-products from the bottom of the conventional acrylic acid separation tower (100), and the bottom discharge stream of the acrylic acid separation tower (100) was supplied to the lactic acid separation tower at the rear, and lactic acid was recovered from the lactic acid separation tower, so that the high-concentration unreacted lactic acid was discharged at a high temperature from the bottom of the acrylic acid separation tower (100) and was heated again in the tower at the rear, and the time of exposure to high temperature in a high-concentration state became longer, so that the oligomerization reaction of lactic acid was promoted as the equilibrium reaction rate increased, and there was a problem that the recovery rate of unreacted lactic acid decreased, and there was a problem that additional energy was used.

Claims

1. A step of producing a reaction product stream by dehydrating a lactic acid aqueous solution in a reaction section; The above reaction product stream sequentially passes through a cooling unit and a purification unit, and the step of supplying the discharge stream of the purification unit to an acrylic acid separation tower; and A method for producing acrylic acid, comprising the step of separating unreacted lactic acid as a side discharge stream and separating acrylic acid as a top discharge stream in the acrylic acid separation tower.

2. In paragraph 1, A method for producing acrylic acid, wherein the discharge stream from the above purification unit is supplied in a range of 40% to 90% of the total number of stages of the above acrylic acid separation tower.

3. In paragraph 1, A method for producing acrylic acid, wherein the discharge stream from the above purification unit is supplied to 65% to 85% of the total number of stages of the above acrylic acid separation tower.

4. In paragraph 1, A method for producing acrylic acid, wherein the side discharge stream of the acrylic acid separation tower is discharged in stages of 20% to 80% of the total number of stages of the acrylic acid separation tower.

5. In paragraph 1, A method for producing acrylic acid, wherein the side discharge stream of the acrylic acid separation tower is discharged in stages of 55% to 75% of the total number of stages of the acrylic acid separation tower.

6. In paragraph 1, A method for producing acrylic acid, wherein the operating pressure of the acrylic acid separation tower is 10 torr to 200 torr.

7. In paragraph 1, A method for producing acrylic acid, wherein the flow rate ratio of a stream that separates acrylic acid without being refluxed among the upper discharge streams of the acrylic acid separation tower and a stream that passes through a reboiler and is refluxed to the acrylic acid separation tower is 0.8 to 1.

5.

8. In paragraph 1, A method for producing acrylic acid, wherein unreacted lactic acid separated as a side discharge stream from the acrylic acid separation tower is mixed with the lactic acid aqueous solution and supplied to a reaction unit.

9. In paragraph 1, A method for producing acrylic acid by separating high-boiling-point by-products from the bottom discharge stream of the above acrylic acid separation tower.

10. In paragraph 1, A method for producing acrylic acid, wherein the above reaction product stream comprises acrylic acid, water, gaseous by-products, low boiling point by-products, high boiling point by-products, and unreacted lactic acid.

11. In paragraph 10, A method for producing acrylic acid, wherein the cooling unit removes gaseous byproducts from the reaction product stream, and the purification unit removes water and low-boiling-point byproducts from the reaction product stream.