Method for preparing acrylic acid

Abstract

The present disclosure relates to a method for preparing acrylic acid, and the method for preparing acrylic acid includes: a step of preparing a reaction product containing acrylic acid by supplying lactic acid into a reactor and performing a dehydration reaction; a step of supplying a reactor discharge stream containing the reaction product to a cooling tower and condensing the reaction product to transfer a lower discharge stream containing a condensate to an acrylic acid purification unit and supplying an uncondensed substance discharged as an upper discharge stream to a distillation tower; and, in the distillation tower, circulating the lower discharge stream containing acrylic acid to the cooling tower, and removing acetaldehyde from the upper discharge stream.

Description

Technical Field

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0167556, filed in the Korean Intellectual Property Office on December 3, 2020, the entire contents of which are incorporated into this specification by reference.

[0002] The present disclosure relates to a method for preparing acrylic acid, and more particularly, to a method for preventing acrylic acid loss while effectively removing acetaldehyde generated as a by-product when preparing acrylic acid through a dehydration reaction of lactic acid. Background Art

[0003] Acrylic acid is used as a raw material for polymers used in fibers, adhesives, coatings, fiber processing, leather, building materials, etc., and demand for it is expanding. In addition, acrylic acid is also used as a raw material for absorbent polymers, and is widely used industrially in applications such as absorbent materials such as diapers and sanitary napkins, water retaining agents for agricultural and horticultural uses, and waterstops for industrial uses.

[0004] The existing method for preparing acrylic acid generally uses a method of oxidizing propylene with air, however, this method is a method of converting propylene into acrolein using a gas phase catalytic oxidation reaction and subjecting the reaction product to a gas phase catalytic oxidation reaction to prepare acrylic acid, and this method produces acetic acid as a by-product that is difficult to separate from acrylic acid. In addition, the method for preparing acrylic acid using propylene uses propylene obtained by refining fossil resource crude oil, which has problems in terms of raw material cost or environmental pollution in view of the recent rise in crude oil prices or global warming.

[0005] In view of the above, a method for preparing acrylic acid from a carbon-neutral biomass raw material has been studied. For example, a method for preparing acrylic acid (AA) by a gas phase dehydration reaction of lactic acid (LA) may be included. The method is a method for preparing acrylic acid by an intramolecular dehydration reaction of lactic acid, usually at a high temperature of more than 300°C and in the presence of a catalyst. However, during the dehydration reaction of lactic acid, a side reaction occurs in addition to the dehydration reaction, and the side reaction produces acetaldehyde (ACHO) as a reaction product as a byproduct in addition to acrylic acid. The problem with this is that the byproduct acetaldehyde produced by the dehydration reaction of lactic acid promotes the formation of polymers during the purification process of acrylic acid, resulting in a decrease in the quality and productivity of the product.

[0006] Prior art literature

[0007] Patent Literature

[0008] (Patent Document 1) JP 2014-189513 A Summary of the invention

[0009] Technical issues

[0010] The present disclosure is made in view of the problems mentioned in the background art, and aims to provide a method for effectively removing acetaldehyde as a by-product when preparing acrylic acid through a dehydration reaction of lactic acid and minimizing the loss amount of acrylic acid in this process.

[0011] Technical Solution

[0012] One embodiment of the present disclosure provides a method for preparing acrylic acid, the method comprising: a step of preparing a reaction product containing acrylic acid by supplying lactic acid to a reactor and performing a dehydration reaction; a step of supplying a reactor effluent stream containing the reaction product to a cooling tower and condensing the reaction product to transfer a lower effluent stream containing the condensate to an acrylic acid purification unit and supplying an uncondensed substance discharged as an upper effluent stream to a distillation tower; and, in the distillation tower, circulating the lower effluent stream containing acrylic acid to the cooling tower and removing acetaldehyde from the upper effluent stream.

[0013] Beneficial Effects

[0014] According to the method for preparing acrylic acid disclosed herein, the reaction product containing acrylic acid is condensed in a cooling tower, and by operating the cooling tower to minimize the amount of acetaldehyde flowing to the lower part, the amount of acetaldehyde transferred to the acrylic acid purification unit can be reduced. Thus, the quality and productivity of the product can be improved by preventing the formation of polymers in the acrylic acid purification process caused by acetaldehyde.

[0015] Furthermore, in order to operate the cooling tower so as to minimize the amount of acetaldehyde flowing to the lower portion, a certain amount of water flows to the upper portion of the cooling tower, where the loss of acrylic acid occurs. In this regard, the present disclosure can prevent the loss of acrylic acid by placing a distillation tower above the cooling tower, recovering acrylic acid to the lower portion of the distillation tower, and recycling the acrylic acid back to the cooling tower.

[0016] Furthermore, by controlling the operating conditions of the cooling tower and the distillation tower in the present disclosure, acrylic acid can be recovered without increasing the amount of process energy used by utilizing the heat removed from the cooler below the cooling tower as a heat source required for the reboiler below the distillation tower. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 and Figure 2 Each of them is a process flow chart of a method for preparing acrylic acid according to one embodiment of the present disclosure.

[0018] Figure 3 It is a process flow chart of the method for preparing acrylic acid according to the comparative example.

[0019] <Reference Numbers>

[0020] 10: Reactor

[0021] 20: Cooling Tower

[0022] 21: First Cooler

[0023] 22: Second cooler

[0024] 30: Distillation Tower

[0025] 31: Reboiler

[0026] 32: Condenser DETAILED DESCRIPTION

[0027] The terms or words used in the specification and claims of the present disclosure shall not be restrictively interpreted as commonly used or dictionary meanings, but shall be interpreted as meanings and concepts corresponding to the technical ideas of the present disclosure based on the principle that the inventor can appropriately define the concepts of the terms in order to describe the present invention in the best possible manner.

[0028] In the present disclosure, the term "upper part" may refer to a part corresponding to a height of more than 50% of the total height of a container or device, and the term "lower part" may refer to a part corresponding to a height of less than 50% of the total height of a container or device.

[0029] In the present disclosure, the term "flow" may refer to the flow of a fluid in a process, or may refer to the fluid itself flowing in a pipeline. Specifically, flow may refer to both the fluid itself flowing in a pipeline connecting various devices and the flow of a fluid. In addition, fluid may refer to a gas, a liquid, etc. The case of a fluid containing a solid component is not excluded.

[0030] In the following, reference will be made to Figure 1 and Figure 2 The present disclosure is described in more detail in order to illustrate the present disclosure.

[0031] One embodiment of the present disclosure provides a method for preparing acrylic acid. More specifically, the method may include: a step of preparing a reaction product containing acrylic acid by supplying lactic acid to a reactor 10 and performing a dehydration reaction; supplying a discharge stream of the reactor 10 containing the reaction product to a cooling tower 20 and condensing the reaction product to transfer a lower discharge stream containing a condensate to an acrylic acid purification unit, and supplying an uncondensed substance discharged as an upper discharge stream to a distillation tower 30; and, in the distillation tower 30, circulating the lower discharge stream containing acrylic acid to the cooling tower 20, and removing acetaldehyde from the upper discharge stream.

[0032] Specifically, the existing method for preparing acrylic acid generally uses a method of oxidizing propylene with air, however, this method is a method of converting propylene into acrolein using a gas phase catalytic oxidation reaction, and subjecting the reaction product to a gas phase catalytic oxidation reaction to prepare acrylic acid, and this method produces acetic acid as a by-product that is difficult to separate from acrylic acid. In addition, the method of preparing acrylic acid using propylene uses propylene obtained by refining fossil resource crude oil, which has problems in terms of raw material cost or environmental pollution in view of the recent increase in crude oil prices or global warming.

[0033] In order to solve the problems of the existing method for preparing acrylic acid, a method for preparing acrylic acid from a carbon-neutral biomass raw material has been studied. For example, a method for preparing acrylic acid (AA) by a gas phase dehydration reaction of lactic acid (LA) can be included. The method is a method for preparing acrylic acid by an intramolecular dehydration reaction of lactic acid, usually at a high temperature and in the presence of a catalyst. However, during the dehydration reaction of lactic acid, a side reaction also occurs here in addition to the dehydration reaction, and in addition to acrylic acid, the side reaction produces acetaldehyde (ACHO) as a reaction product as a by-product. The problem that exists in this way is that the by-product acetaldehyde produced by the dehydration reaction of lactic acid promotes the formation of polymers during the purification process of acrylic acid, so that the quality and productivity of the product decrease. Therefore, the separation of acetaldehyde before purifying acrylic acid has been studied, where water needs to flow to the upper part of the cooling tower 20 in order to effectively separate acetaldehyde, and there is a problem of losing acrylic acid in the process.

[0034] In view of the above problems, the present disclosure aims to provide a method for preparing acrylic acid, which can effectively remove acetaldehyde generated as a by-product in the manufacturing process while preparing acrylic acid through a dehydration reaction of lactic acid, and also improve the quality and productivity of the product by preventing the loss of acrylic acid.

[0035] According to one embodiment of the present disclosure, a reaction product containing acrylic acid can be prepared by supplying lactic acid to the reactor 10 and performing a dehydration reaction. Here, the lactic acid can be introduced into the reactor 10 in the state of an aqueous solution, or the dehydration reaction can be performed in a gas phase reaction in the presence of a catalyst. For example, the lactic acid can be introduced into the reactor 10 as a lactic acid aqueous solution containing 10% to 90% by mass or 20% to 80% by mass of lactic acid.

[0036] The reactor 10 may be a reactor capable of performing a conventional dehydration reaction of lactic acid, and examples thereof may include a stirred reactor, a fixed bed reactor, a fluidized bed reactor, etc. In addition, the reactor 10 may include a reaction tube filled with a catalyst, and when a reaction gas containing volatile components of a raw material lactic acid aqueous solution passes through the reaction tube, lactic acid is dehydrated using a gas phase catalytic reaction to produce acrylic acid. In addition to lactic acid, the reaction gas may also contain any one or more dilution gases among water vapor, nitrogen, and air for concentration adjustment.

[0037] As for the working conditions of the reactor 10, the reactor may be operated under the conventional dehydration reaction conditions of lactic acid, for example, the temperature may be from 250° C. to 500° C., 250° C. to 450° C., or 300° C. to 400° C. Here, the working temperature of the reactor 10 may refer to the set temperature of a heat medium or the like for controlling the temperature of the reactor 10. In addition, the working pressure of the reactor 10 may be 30 kPa to 1000 kPa, 50 kPa to 500 kPa, or 60 kPa to 300 kPa.

[0038] Examples of the catalyst used in the lactic acid dehydration reaction may include one or more types selected from sulfate catalysts, phosphate catalysts, and nitrate catalysts. As a specific example, sulfate may include Na 2 SO 4 , K 2 SO 4 、CaSO 4 and Al 2 (SO 4 ) 3 , phosphates can include Na 3 PO 4 、Na 2 HPO 4 、NaH 2 PO 4 , K 3 PO 4 , K 2 HPO 4 , KH 2 PO 4 、CaHPO 4 , Ca 3 (PO 4 ) 2 、AlPO 4 , CaH 2 P 2 O 7 and Ca 2 P 2 O 7 , nitrates can include NaNO 3 、KNO 3 and Ca(NO 3 ) 2 In addition, the catalyst may be supported on a carrier. Examples of the carrier may include one or more types selected from diatomaceous earth, alumina, silica, titania, calcium carbide, and zeolite.

[0039] The reaction product produced by the lactic acid dehydration reaction may contain by-products such as water (H 2O), acetaldehyde (ACHO), carbon monoxide (CO), carbon dioxide (CO 2 ), diluent gas and high boiling point substances. Here, the content of acetaldehyde contained in the reaction product can be about 5% to 60% relative to the content of acrylic acid. Therefore, a purification process is required for separating acrylic acid from the reaction product.

[0040] According to one embodiment of the present disclosure, the discharge stream of the reactor 10 containing the reaction product may be supplied to the cooling tower 20 for cooling before being transferred to the acrylic acid purification unit. Specifically, since the discharge stream of the reactor 10 containing the reaction product is discharged in a gas phase, it may be supplied to the cooling tower 20 and condensed by cooling. The condensate condensed in this process is transferred to the acrylic acid purification unit as a lower discharge stream of the cooling tower 20, and the uncondensed matter may be discharged as an upper discharge stream and supplied to the distillation tower 30. Here, the condensate may contain acrylic acid, as well as water, high boiling point substances, etc. as by-products, and the uncondensed matter may contain acetaldehyde, water, carbon monoxide, carbon dioxide, diluent gas, etc.

[0041] The cooling tower 20 may be operated under conditions that minimize the content of acetaldehyde in the downstream discharge stream. Specifically, the downstream discharge stream of the cooling tower 20 is transferred to an acrylic acid purification unit to purify acrylic acid, and there is a problem in that the quality and productivity of the product are reduced due to the promotion of polymer formation caused by acetaldehyde during the acrylic acid purification process. In this regard, the present disclosure minimizes the content of acetaldehyde flowing out as the downstream discharge stream of the cooling tower 20 by controlling the operating conditions of the cooling tower 20. For example, the flow rate of acetaldehyde in the downstream discharge stream of the cooling tower 20 may be 3% or less, from 0.1% to 2.5%, or from 0.5% to 2%, relative to the flow rate of acetaldehyde in the discharge stream of the reactor 10.

[0042] In order to minimize the content of acetaldehyde in the lower discharge stream of the cooling tower 20, it is necessary to include a certain amount of water in the upper discharge stream of the cooling tower 20. Specifically, when a certain amount of water is included in the upper discharge stream of the cooling tower 20, acetaldehyde having a boiling point lower than that of water is mainly included in the upper discharge stream of the cooling tower 20. On the other hand, in order to include most of the acetaldehyde without including water in the upper discharge stream of the cooling tower 20, it is necessary to increase the number of stages in the cooling tower 20 to improve the separation efficiency, or it is necessary to change the type to a distillation tower type by adding a reboiler, which is inefficient. Therefore, the present disclosure can minimize the amount of acetaldehyde flowing out as the lower discharge stream of the cooling tower 20 using an effective method of including a certain amount of water in the upper discharge stream of the cooling tower 20. For example, the flow rate of water in the upper discharge stream of the cooling tower 20 may be from 20% to 50%, 30% to 50%, or 35% to 50% relative to the flow rate of water in the discharge stream of the reactor 10.

[0043] In addition, when the cooling tower 20 is operated so that a certain amount of water is included in the upper discharge flow of the cooling tower 20, acrylic acid can flow out together as the upper discharge flow of the cooling tower 20. For example, the flow rate of acrylic acid in the upper discharge flow of the cooling tower 20 can be from 5% to 50%, 20% to 50%, or 30% to 50% relative to the flow rate of acrylic acid in the discharge flow of the reactor 10. Therefore, in order to reduce the content of acetaldehyde in the lower part of the cooling tower 20 before transferring the reaction product to the acrylic acid purification unit, the loss of excessive acrylic acid has been avoided in the art. In view of the above situation, the present disclosure additionally installs a distillation tower 30 and supplies the upper discharge flow of the cooling tower 20 to the distillation tower 30, and acrylic acid flowing to the upper part of the cooling tower 20 can be recovered.

[0044] The operating pressure of the cooling tower 20 may be, for example, from 30 kPa to 1000 kPa, 50 kPa to 500 kPa, or 60 kPa to 300 kPa. By operating the cooling tower 20 within the above range, the amount of acetaldehyde flowing to the lower portion can be minimized while including a certain amount of water in the upper discharge flow of the cooling tower 20.

[0045] A portion of the lower discharge flow of the cooling tower 20 flows back to the cooling tower 20 after passing through one or more coolers, and the remaining flow may be transferred to the acrylic acid purification unit. For example, a portion of the lower discharge flow of the cooling tower 20 may flow back to the cooling tower 20 after passing through the first cooler 21 or the first cooler 21 and the second cooler 22. Here, the operating conditions of the first cooler 21, the operating conditions of the second cooler 22, and the reflux ratio of the lower portion of the cooling tower 20 may be appropriately adjusted according to the operating conditions of the cooling tower 20.

[0046] In each of the first cooler 21 and the second cooler 22, one or more types of cooling water selected from, for example, cooling water, chilled water, and brine can be used as a refrigerant. As a specific example, relatively cheap cooling water can be used in the first cooler 21 and the second cooler 22.

[0047] The purification unit may include, for example, a step of separating water to remove water contained in the lower discharge stream of the cooling tower 20 and a step of separating high-boiling substances, whereby acrylic acid separated at a high purity can be obtained.

[0048] According to one embodiment of the present disclosure, the uncondensed matter not condensed in the cooling tower 20 may be discharged as an upper discharge stream of the cooling tower 20 and supplied to the distillation tower 30. Here, the distillation tower 30 may be used to separate and recover acrylic acid contained in the upper discharge stream of the cooling tower 20.

[0049] Specifically, acrylic acid separated in the distillation tower 30 is discharged as a lower discharge stream of the distillation tower 30 and circulated to the cooling tower 20 , and acetaldehyde, carbon monoxide, carbon dioxide, diluent gas, etc. may be discharged as an upper discharge stream of the distillation tower 30 .

[0050] The upper discharge flow of the distillation tower 30 passes through the condenser 32, a part of the flow may be refluxed to the distillation tower 30, and the remaining flow may be discharged. Here, the reflux ratio of the upper part of the distillation tower 30 may be appropriately adjusted according to the operating conditions of the distillation tower 30.

[0051] The upper discharge stream of the distillation column 30 may pass through an additional purification process as needed, and by purifying acetaldehyde contained in the upper discharge stream of the distillation column 30 and selling acetaldehyde separately, the production cost of acrylic acid can be reduced and competitiveness can be ensured.

[0052] The lower discharge stream of the distillation tower 30 is heated by the reboiler 31 before being circulated to the cooling tower 20, and then a part of the stream may be circulated to the cooling tower 20, and the remaining stream may be refluxed to the distillation tower 30. Here, the reflux ratio of the lower portion of the distillation tower 30 may be appropriately adjusted according to the operating conditions of the distillation tower 30.

[0053] In addition, the discharge stream of the distillation tower 30 is heat-exchanged with a part of the lower discharge stream of the cooling tower 20 in one or more coolers installed below the cooling tower 20 before being circulated to the cooling tower 20, without using a separate reboiler 31, and then a part of the stream is circulated to the cooling tower 20, and the remaining stream may be refluxed to the distillation tower 30. As a specific example, the lower discharge stream of the distillation tower 30 is supplied to the first cooler 21 as a refrigerant before being circulated to the cooling tower 20, and is heat-exchanged with a part of the lower discharge stream of the cooling tower 20 by countercurrent, cocurrent or crosscurrent, and a part of the stream is circulated to the cooling tower 20, and the remaining stream may be refluxed to the distillation tower 30. Specifically, acrylic acid discharged to the upper part of the cooling tower 20 is included in wastewater and discharged from the process, or needs to be recovered by a distillation process, which consumes additional energy, however, as described above, by utilizing the heat removed from the cooler below the cooling tower 20 as a heat source required for the reboiler 31 below the lower part of the distillation tower 30 described above, acrylic acid can be recovered without increasing the amount of process energy used.

[0054] The operating pressure of the distillation tower 30 may be from 10 kPa to 900 kPa, 30 kPa to 600 kPa, or 40 kPa to 200 kPa. By operating the distillation tower 30 within the above range, as much acrylic acid as possible can be recovered as the downstream discharge flow of the distillation tower 30 and circulated to the cooling tower 20.

[0055] The flow rate of acrylic acid in the upper discharge stream of the distillation column 30 may be 3% or less, from 0.1% to 3%, or from 0.1% to 1.5% relative to the flow rate of acrylic acid in the discharge stream of the reactor 10. By recovering as much acrylic acid as possible in the distillation column 30 as described above, the loss of acrylic acid can be prevented.

[0056] In order to heat exchange the lower discharge flow of the distillation tower 30 and a part of the lower discharge flow of the cooling tower 20, the operating pressures of the distillation tower 30 and the cooling tower 20 may be controlled. For example, the operating pressure of the distillation tower 30 may be controlled to be lower than the operating pressure of the cooling tower 20. As a specific example, the operating pressure of the distillation tower 30 may be controlled to be 20 kPa to 900 kPa, 30 kPa to 500 kPa, or 50 kPa to 200 kPa lower than the operating pressure of the cooling tower 20. By controlling the operating pressures of the distillation tower 30 and the cooling tower 20 within the above range, the lower discharge flow of the distillation tower 30 and a part of the lower discharge flow of the cooling tower 20 may be heat exchanged due to the temperature difference, whereby acrylic acid may be recovered in the distillation tower 30 without increasing the amount of energy used and circulated to the cooling tower 20. In addition, the amount of refrigerant used may be reduced by heat exchange between the lower discharge flow of the distillation tower 30 and a part of the lower discharge flow of the cooling tower 20.

[0057] According to one embodiment of the present disclosure, in the method for preparing acrylic acid, devices such as a distillation column, a condenser, a reboiler, a valve, a pump, a separator, and a mixer may be further installed as needed.

[0058] In the above, the method for preparing acrylic acid according to the present disclosure is described and illustrated in the accompanying drawings, however, these descriptions and illustrations only describe or illustrate basic components for understanding the present disclosure, and in addition to the processes and devices described and illustrated above, processes and devices that are not separately described and illustrated can be appropriately applied and used to realize the method for preparing acrylic acid according to the present disclosure.

[0059] Hereinafter, the present disclosure will be described in more detail with reference to embodiments. However, the following embodiments are for illustrative purposes only, and it is obvious to those skilled in the art that various changes and modifications can be made within the category and scope of the technical idea of ​​the present disclosure, and the scope of the present disclosure is not limited thereto.

[0060] Example

[0061] Example 1

[0062] for Figure 1 The process flow chart shown in FIG. 1 was used to simulate the process of preparing acrylic acid using Aspen Plus simulation software (simulator) from Aspen Technology Inc.

[0063] Specifically, lactic acid and nitrogen (N) as a diluent gas were mixed. 2 ) is supplied to the reactor 10 and a reaction product containing acrylic acid (AA) is prepared through a dehydration reaction, and an exhaust stream of the reactor 10 containing the reaction product is supplied to a cooling tower 20.

[0064] The discharge stream of the reactor 10 was condensed in the cooling tower 20, and the uncondensed matter was discharged as an upper discharge stream and supplied to the distillation tower 30. In addition, the condensate was discharged from the cooling tower 20 as a lower discharge stream at a temperature of 117° C., a part of the stream was refluxed to the cooling tower 20 after passing through the first cooler 21, and the remaining stream was supplied to the acrylic acid purification unit. Here, the operating pressure of the cooling tower 20 was controlled at 200 kPa.

[0065] In the distillation tower 30, the lower discharge stream of 113° C. containing acrylic acid passed through the reboiler 31, a part of the stream was refluxed to the distillation tower 30, and the remaining stream was circulated to the cooling tower 20. In addition, the upper discharge stream containing acetaldehyde in the distillation tower 30 passed through the condenser 32, a part of the stream was refluxed to the distillation tower 30, and the remaining stream was discharged. Here, the operating pressure of the distillation tower 30 was controlled at 190 kPa.

[0066] As a result, the flow rate (kg / hr) of each component in each stream is shown in Table 1 below.

[0067] [Table 1]

[0068] 1-1 1-2 1-3 1-4 1-5 <![CDATA[N 2 ]]> 101.2 0.0 101.2 101.2 0.0 <![CDATA[CO / CO 2 ]]> 28.7 0.0 28.6 28.7 0.0 ACHO 14.0 0.2 13.7 13.8 0.1 <![CDATA[H 2 The]]> 597.2 538.0 59.3 244.9 185.6 AA 240.5 238.0 2.5 56.6 54.1 High boiling point substances 18.5 16.6 1.9 5.8 3.9 sum 1000.1 792.8 207.2 451.0 243.7

[0069] The sum is a value obtained by rounding the value obtained in the Aspen Plus simulation software to one decimal place.

[0070] When referring to Table 1, it was confirmed that in Example 1, the amount of acetaldehyde in the lower discharge stream of the cooling tower 20 transferred to the purification unit was very small, about 1.4% of the acetaldehyde contained in the reaction product, and the loss of acrylic acid was confirmed to be very small, the amount of acrylic acid flowing out as the upper discharge stream of the distillation tower 30 was about 1% of the acrylic acid contained in the reaction product.

[0071] Example 2

[0072] for Figure 2 The process for preparing acrylic acid was simulated using the process flow chart shown in Aspen Plus simulation software from Aspen Technology Inc.

[0073] Specifically, lactic acid and nitrogen (N) as a diluent gas were mixed. 2) is supplied to the reactor 10 and a reaction product containing acrylic acid (AA) is prepared through a dehydration reaction, and an exhaust stream of the reactor 10 containing the reaction product is supplied to a cooling tower 20.

[0074] The reactor 10 discharge stream was condensed in the cooling tower 20, and the uncondensed matter was discharged as an upper discharge stream and supplied to the distillation tower 30. In addition, the condensate was discharged from the cooling tower 20 as a lower discharge stream at a temperature of 117° C., a part of the stream was refluxed to the cooling tower 20 after passing through the first cooler 21 and the second cooler 22, and the remaining stream was supplied to the acrylic acid purification unit. Here, the operating pressure of the cooling tower 20 was controlled at 200 kPa.

[0075] In the distillation tower 30, the lower discharge stream of 96° C. containing acrylic acid is supplied to the first cooler 21, and heat-exchanged with a part of the lower discharge stream of the cooling tower 20, a part of the stream is refluxed to the distillation tower 30, and the remaining stream is circulated to the cooling tower 20. In addition, the upper discharge stream containing acetaldehyde in the distillation tower 30 passes through the condenser 32, a part of the stream is refluxed to the distillation tower 30, and the remaining stream is discharged. Here, the operating pressure of the distillation tower 30 is controlled at 110 kPa.

[0076] As a result, the flow rate (kg / hr) of each component in each stream is shown in Table 2 below.

[0077] [Table 2]

[0078] 2-1 2-2 2-3 2-4 2-5 <![CDATA[N 2 ]]> 101.2 0.0 101.2 101.2 0.0 <![CDATA[CO / CO 2 ]]> 28.7 0.0 28.6 28.7 0.0 ACHO 14.0 0.2 13.7 13.9 0.1 <![CDATA[H 2 The]]> 597.2 537.7 59.5 238.6 179.1 AA 240.5 238.0 2.5 55.1 52.6 High boiling point substances 18.5 16.8 1.6 5.8 4.1 sum 1000.1 792.7 207.1 443.3 235.9

[0079] When referring to Table 2, it is confirmed that, as in Example 1, also in Example 2, the loss of acrylic acid is very small, while the amount of acetaldehyde in the lower discharge stream of the cooling tower 20 transferred to the purification unit is reduced.

[0080] In addition to this, by subjecting the lower discharge stream of the distillation tower 30 and a part of the lower discharge stream of the cooling tower 20 to heat exchange in the first cooler 21, acrylic acid discharged to the upper portion of the cooling tower 20 can be recovered without using additional energy, thereby using the heat of about 33233 kcal / hr removed from the first cooler 21 as the heat supplied to the reboiler 31 in Example 1.

[0081] Comparative Example

[0082] Comparative Example 1

[0083] for Figure 3 The process for preparing acrylic acid was simulated using the process flow chart shown in Aspen Plus simulation software from Aspen Technology Inc.

[0084] Specifically, lactic acid and nitrogen as a diluent gas are supplied to the reactor 10 and a reaction product including acrylic acid (AA) is prepared through a dehydration reaction, and an exhaust stream of the reactor 10 including the reaction product is supplied to the cooling tower 20 .

[0085] The discharge stream of the reactor 10 is condensed in the cooling tower 20, the uncondensed matter is discharged as the upper discharge stream, the condensate in the cooling tower 20 is discharged as the lower discharge stream, and a part of the stream is refluxed to the cooling tower 20 after passing through the first cooler 21, and the remaining stream is supplied to the acrylic acid purification unit. Here, the operating pressure of the cooling tower 20 is controlled at 200 kPa, and the amount of acetaldehyde flowing out as the lower discharge stream of the cooling tower 20 is minimized by controlling the circulation flow rate of the lower discharge stream of the cooling tower 20 after passing through the first cooler 21 and circulating to the cooling tower 20.

[0086] As a result, the flow rates of the components in the respective streams are shown in Table 3 below.

[0087] [Table 3]

[0088] 3-1 3-2 3-3 <![CDATA[N 2 ]]> 101.2 0.0 101.2 <![CDATA[CO / CO 2 ]]> 28.7 0.0 28.6 ACHO 14.0 0.2 13.7 <![CDATA[H 2 The]]> 597.2 537.7 59.5 AA 240.5 227.6 12.9 High boiling point substances 18.5 17.1 1.4 sum 1000.1 782.6 217.3

[0089] Comparative Example 2

[0090] The operation was performed in the same manner as in Comparative Example 1 except that the circulation flow rate of the lower exhaust flow of the cooling tower 20 circulated to the cooling tower 20 after passing through the first cooler 21 was increased.

[0091] As a result, the flow rate of each component in each stream is shown in Table 4 below.

[0092] [Table 4]

[0093]

[0094]

[0095] When referring to Tables 3 and 4, the circulation flow rate of the lower discharge stream of the cooling tower 20 circulated to the cooling tower 20 after passing through the first cooler 21 was adjusted in Comparative Example 1 to minimize the amount of acetaldehyde in the lower discharge stream of the cooling tower 20 as in the embodiment, and it was confirmed that the amount of acrylic acid flowing out as the upper discharge stream of the cooling tower 20 was very high, which was about 5.4% of the acrylic acid contained in the reaction product.

[0096] Furthermore, in Comparative Example 2, it was confirmed that when the amount of acrylic acid flowing out as the upper discharge flow of the cooling tower 20 was minimized compared to Comparative Example 1, the amount of acetaldehyde in the lower discharge flow of the cooling tower 20 was very high, about 12% of the acetaldehyde contained in the reaction product.

Claims

1. A method for preparing acrylic acid, the method comprising: a step of preparing a reaction product containing acrylic acid by supplying lactic acid into a reactor and performing a dehydration reaction; A step of supplying a reactor effluent stream containing the reaction product to a cooling tower and condensing the reaction product to transfer a lower effluent stream containing the condensate to an acrylic acid purification unit and supplying an uncondensed substance discharged as an upper effluent stream to a distillation tower; and In the distillation tower, a lower discharge stream containing acrylic acid is circulated to the cooling tower, and acetaldehyde is removed from an upper discharge stream, Wherein, the working pressure of the distillation tower is 20 kPa to 900 kPa lower than the working pressure of the cooling tower, Wherein, the working pressure of the distillation tower is 10kPa to 900kPa, Wherein, the working pressure of the cooling tower is 30kPa to 1000kPa, wherein a portion of the lower discharge flow of the cooling tower flows back to the cooling tower after passing through the first cooler, The lower discharge stream of the distillation tower is supplied to the first cooler and heat-exchanged with a portion of the lower discharge stream of the cooling tower before being circulated to the cooling tower, a portion of the stream is circulated to the cooling tower and the remaining stream is refluxed to the distillation tower.

2. The method for preparing acrylic acid according to claim 1, wherein: A portion of the lower discharge flow of the cooling tower that has passed through the first cooler further passes through a second cooler and flows back to the cooling tower.

3. The method for preparing acrylic acid according to claim 1, wherein: The lower discharge stream of the distillation tower is heated by a reboiler before being circulated to the cooling tower, and then a part of the stream is circulated to the cooling tower and the remaining stream is refluxed to the distillation tower.

4. The method for preparing acrylic acid according to claim 1, wherein: The flow rate of acetaldehyde in the lower discharge flow of the cooling tower is 3% or less relative to the flow rate of acetaldehyde in the discharge flow of the reactor.

5. The method for preparing acrylic acid according to claim 1, wherein: The flow rate of acrylic acid in the upper discharge stream of the distillation column is 3% or less relative to the flow rate of acrylic acid in the discharge stream of the reactor.

Images