Process for the production of acrylic acid

Abstract

The present application relates to a process for the production of acrylic acid.

Description

Technical Field

[0001] This application claims priority and benefit to Korean Patent Application No. 10-2020-0159080, filed with the Korean Intellectual Property Office on November 24, 2020, the entire contents of which are incorporated herein by reference.

[0002] This application relates to a method for producing acrylic acid. Background Technology

[0003] Acrylic acid is typically produced through the oxidative dehydrogenation reaction of propylene. The demand for acrylic acid as a raw material for superabsorbent polymers, coatings, adhesives, etc., is increasing. In particular, superabsorbent polymers are used in hygiene products such as diapers.

[0004] To date, a significant number of chemical products are produced using feedstocks derived from fossil fuels such as coal or oil. However, in the context of mitigating global warming and protecting the environment, the use of recyclable bio-derived resources as carbon sources as alternatives to existing fossil fuels has recently garnered attention. For example, methods have been explored for developing feedstocks that utilize biomass resources including starchy biomass such as corn or wheat, carbohydrate biomass such as sugarcane, and cellulosic biomass such as rapeseed residue or rice straw.

[0005] In other words, research is currently underway to break away from existing petrochemical-based manufacturing processes and produce chemical products based on environmentally friendly raw materials in order to achieve superior performance in terms of environmental protection while also achieving sustainability.

[0006] One type of reaction that produces other chemical products from lactic acid can include a gas-phase reaction, in which the lactic acid feedstock is evaporated and contacted in a gaseous state with a catalyst to obtain the product. For example, as a technique for producing acrylic acid using lactic acid, a gas-phase dehydration reaction using a solid catalyst is known, and the dehydration reaction of lactic acid is primarily studied as a gas-phase reaction.

[0007] Lactic acid is a substance that polymerizes through esterification in the liquid phase under anhydrous and catalyst-free conditions. As lactic acid is concentrated and its concentration increases, it reacts as lactic acid oligomers. Dehydration occurs during lactic acid oligomerization, and oligomerization occurs when lactic acid is concentrated under anhydrous conditions.

[0008] When lactic acid oligomers are introduced into the reactor for acrylic acid production, scaling occurs in the reactor, reducing the reaction yield. Therefore, research is underway on methods to reduce the lactic acid oligomer content in acrylic acid production.

[0009] In order to reduce the content of lactic acid oligomers, lactic acid is introduced into the vaporizer in the form of an aqueous solution of lactic acid. However, the low-boiling-point water is vaporized first in the vaporizer, and then the lactic acid is vaporized. Since the lactic acid is concentrated in the liquid phase during the vaporization process, the problem of generating lactic acid oligomers still exists.

[0010] In addition, a distillation column that utilizes boiling point difference for separation can be used to ensure that the vaporized lactic acid aqueous solution does not contain oligomers. However, the lactic acid oligomerization reaction still occurs in this column, the lactic acid oligomers are concentrated, and the temperature rise in the lower part of the distillation column is a problem.

[0011] Therefore, in view of the above, research is underway to reduce the content of lactic acid oligomers and increase the yield of acrylic acid.

[0012] Existing technical documents

[0013] Patent documents

[0014] International Patent Application Publication No. 2005-095320 Summary of the Invention

[0015] Technical issues

[0016] This application relates to a method for producing acrylic acid.

[0017] Technical solution

[0018] One embodiment of this application provides a method for producing acrylic acid, the method comprising: step 1, preparing a first lactic acid aqueous solution by diluting a lactic acid raw material with water; step 2, subjecting the first lactic acid aqueous solution to heat exchange to form vaporized second lactic acid vapor and unvaporized third lactic acid aqueous solution; step 3, including the unvaporized third lactic acid aqueous solution in the aqueous solution of step 1; and step 4, supplying an absorbent to the vaporized second lactic acid vapor and absorbing it to form absorbed fourth lactic acid aqueous solution and unabsorbed fifth lactic acid vapor.

[0019] The absorbent is water or an aqueous solution of lactic acid.

[0020] Beneficial effects

[0021] In a method for producing acrylic acid according to one embodiment of this application, lactic acid oligomers contained in the gaseous lactic acid aqueous solution are absorbed by increasing the process of supplying an absorbent to the gaseous lactic acid aqueous solution vaporized by a heat exchanger, and the content of oligomers in the lactic acid aqueous solution is reduced before being supplied to the reactor feed.

[0022] In particular, by absorbing the oligomers contained in the lactic acid vapor (second lactic acid vapor) vaporized by the heat exchanger through the absorption process, the content of lactic acid oligomers in the lactic acid vapor is reduced, thereby reducing scaling in the vaporizer and reaction unit. Furthermore, by including a high content of lactic acid monomers, the yield of acrylic acid produced is increased and losses are minimized, thus increasing economic feasibility. Attached Figure Description

[0023] Figure 1 This is a schematic diagram illustrating a method for producing acrylic acid according to one embodiment of this application.

[0024] Figure 2 This is a schematic diagram illustrating a method for producing acrylic acid according to Comparative Example 1 of this application.

[0025] Figure 3 This is a schematic diagram illustrating a method for producing acrylic acid according to Comparative Example 2 of this application.

[0026] <Figure Labels>

[0027] 100: Heat exchanger

[0028] 200: Absorption device

[0029] 300: Dilution tank

[0030] 400: Decomposition Tank

[0031] 1: Lactic acid raw materials

[0032] 2: Water

[0033] 3: Liquid lactic acid aqueous solution

[0034] 4: First lactic acid aqueous solution

[0035] 5: Second lactic acid vapor

[0036] 6: Absorbent liquid

[0037] 7: Fifth lactic acid vapor

[0038] 8: Fourth lactic acid aqueous solution

[0039] 9: Third lactic acid aqueous solution (liquid circulation flow) Detailed Implementation

[0040] This instruction manual will be described in more detail below.

[0041] In this specification, the description that a part "contains" certain ingredients means that it can further contain other ingredients, without excluding other ingredients, unless otherwise specified.

[0042] In this specification, "p to q" means the range of "greater than or equal to p and less than or equal to q".

[0043] In the following, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings to enable those skilled in the art to readily implement the present disclosure. However, the present disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0044] One embodiment of this application provides a method for producing acrylic acid, the method comprising: step 1, preparing a first lactic acid aqueous solution by diluting a lactic acid raw material with water; step 2, subjecting the first lactic acid aqueous solution to heat exchange to form a vaporized second lactic acid vapor and an unvaporized third lactic acid aqueous solution; step 3, including the unvaporized third lactic acid aqueous solution in the aqueous solution of step 1; and step 4, supplying an absorbent to the vaporized second lactic acid vapor and absorbing it to form an absorbed fourth lactic acid aqueous solution and an unabsorbed fifth lactic acid vapor, wherein the absorbent is water or a lactic acid aqueous solution.

[0045] In an acrylic acid production method according to one embodiment of this application, lactic acid oligomers contained in the second lactic acid vapor are absorbed by increasing the process of supplying absorbent to the second lactic acid vapor vapor that has been vaporized in a heat exchanger, and the content of oligomers in the second lactic acid vapor is reduced before being supplied to the reactor feed before the fifth lactic acid vapor is supplied.

[0046] In particular, by absorbing the oligomers contained in the lactic acid vapor (second lactic acid vapor) vaporized by the heat exchanger through the absorption process, the content of lactic acid oligomers in the lactic acid vapor is reduced, thereby reducing scaling in the vaporizer and reaction unit. Furthermore, by including a high content of lactic acid monomers, the yield of acrylic acid produced is increased and losses are minimized, thus increasing economic feasibility.

[0047] One embodiment of this application provides step 1, which involves preparing a first aqueous lactic acid solution by diluting a lactic acid feedstock with water.

[0048] In one embodiment of this application, the lactic acid raw material may comprise water, lactic acid, and lactic acid oligomers.

[0049] In this application, lactic acid is an organic compound having an asymmetric carbon atom bonded with four atomic groups: carboxyl, hydroxyl, methyl, and hydrogen, including both D-lactic acid and L-lactic acid, and may refer to a single lactic acid monomer.

[0050] In this application, lactic acid oligomers refer to substances obtained by reacting lactic acid with each other to form dimers, trimers, etc., and lactic acid oligomers can refer to dimers to 100-mers of lactic acid.

[0051] Lactic acid is a substance that can polymerize in the liquid phase through esterification, even in the absence of anhydrous substances and catalysts. Substances formed through the polymerization of lactic acid can be classified as lactic acid oligomers. In other words, apart from a single lactic acid monomer, all substances formed through the polymerization of lactic acid can be defined as lactic acid oligomers.

[0052] In one embodiment of this application, step 1 is a step of diluting with water in the state of lactic acid raw material, and may refer to a step of minimizing oligomers by increasing the water content generated during the equilibrium reaction process of lactic acid oligomer formation.

[0053] In one embodiment of this application, the first lactic acid aqueous solution comprises water and a lactic acid raw material, the lactic acid raw material comprising lactic acid and lactic acid oligomers, and the content of the lactic acid raw material is greater than or equal to 30 parts by weight and less than or equal to 99 parts by weight based on 100 parts by weight of the first lactic acid aqueous solution.

[0054] In another embodiment, based on 100 parts by weight of the first lactic acid aqueous solution, the content of the lactic acid raw material can be greater than or equal to 50 parts by weight and less than or equal to 99 parts by weight, preferably greater than or equal to 60 parts by weight and less than or equal to 99 parts by weight, more preferably greater than or equal to 70 parts by weight and less than or equal to 99 parts by weight.

[0055] In one embodiment of this application, the first lactic acid aqueous solution may refer to a lactic acid aqueous solution comprising all the first lactic acid aqueous solutions prepared by diluting the lactic acid raw material in step 1, as well as the liquid circulation stream of the third lactic acid aqueous solution that has not been vaporized in the heat exchanger and the liquid circulation stream of the absorbent used in the absorption process described later.

[0056] In one embodiment of the acrylic acid production method provided in this application, the ratio of lactic acid to lactic acid oligomer in the first lactic acid aqueous solution is 1:99 to 20:80.

[0057] In another embodiment, the ratio of lactic acid to lactic acid oligomer in the first lactic acid aqueous solution can be in the range of 1:99 to 20:80, 3:97 to 20:80, and 5:95 to 20:80.

[0058] As described above, the first lactic acid aqueous solution is an aqueous solution that mixes three types of lactic acid aqueous solutions. Since the proportion of lactic acid oligomers in the third lactic acid aqueous solution contained in the liquid circulation stream is relatively high, the proportion of lactic acid oligomers in the first lactic acid aqueous solution can be relatively high.

[0059] Figure 1This is a schematic diagram illustrating a method for producing acrylic acid according to one embodiment of this application. In particular, step 1 may be the step of preparing an aqueous solution 4 of step 1, which comprises all the liquid lactic acid aqueous solution 3 produced by diluting the lactic acid raw material with water, a liquid stream 9 of the unvaporized third lactic acid aqueous solution produced in step 2 described later, and an absorbed fourth lactic acid aqueous solution 8 produced in step 4 described later.

[0060] In other words, as described above, by recycling both the third and fourth lactic acid aqueous solutions in each step back to step 1 via a liquid flow, the loss of lactic acid can be minimized.

[0061] As described above, step 1 can correspond to the step of diluting the lactic acid feedstock with water before introducing it into the heat exchange step (step 2 described later).

[0062] One embodiment of this application provides step 2, which involves heat exchange of a first aqueous lactic acid solution to form vaporized second lactic acid vapor and an unvaporized third aqueous lactic acid solution.

[0063] Here, step 2 may include the process of heat exchange via a heat exchanger.

[0064] In one embodiment of this application, the heat exchanger may be one or more selected from falling film evaporators, scraped film evaporators, thermosiphon evaporators, and forced circulation evaporators, but is not limited thereto, as long as it is capable of vaporizing the first lactic acid aqueous solution.

[0065] In other words, in one embodiment of this application, step 2 is the step of vaporizing the aqueous solution from step 1. The reaction for producing acrylic acid from lactic acid is primarily a gas-phase reaction; therefore, step 2 can be a step related to the process of vaporizing the liquid aqueous solution from step 1 into a gas phase.

[0066] A method for producing acrylic acid according to one embodiment of this application includes a recycling process, wherein the aqueous solution of step 1 comprises a first lactic acid aqueous solution from the initial process under normal conditions. In subsequent recycling processes, the aqueous solution of step 1 may comprise one or more of the first lactic acid aqueous solution, a third lactic acid aqueous solution (described later), and a fourth lactic acid aqueous solution (described later).

[0067] In one embodiment of this application, the vaporized second lactic acid vapor and the unvaporized third lactic acid aqueous solution are formed by vaporizing the aqueous solution of step 1. The vaporized second lactic acid vapor maintains a low lactic acid oligomer content compared to the unvaporized third lactic acid aqueous solution.

[0068] In the step of vaporizing the liquid-aqueous solution in step 1 via a heat exchanger, the water, which has a lower boiling point, is vaporized first, while the lactic acid, which has a relatively higher boiling point, is vaporized later. As the water vaporizes, the lactic acid concentrates to form lactic acid oligomers. When these lactic acid oligomers are included in the vaporized second lactic acid vapor, they may be introduced into the subsequent reactor, causing scaling and reducing the reaction yield of acrylic acid. Therefore, reducing the content of lactic acid oligomers in the vaporized second lactic acid vapor in step 4, described later, is a technical feature of this disclosure.

[0069] In other words, the content of lactic acid oligomers is high even after vaporization in step 2, which may cause problems. Therefore, this application includes step 4, which involves absorption by an absorption device to reduce the content of lactic acid oligomers in the second lactic acid vapor.

[0070] In one embodiment of this application, the unvaporized third lactic acid aqueous solution is returned from the heat exchanger to the aqueous solution contained in step 1 via a liquid circulation stream, thus acrylic acid can be produced without loss of lactic acid feedstock.

[0071] In one embodiment of the acrylic acid production method provided in this application, the heat exchanger has an internal pressure greater than or equal to 0.3 bar and less than or equal to 3 bar, and an internal temperature greater than or equal to 150°C and less than or equal to 300°C.

[0072] In another embodiment, the heat exchanger may have an internal pressure greater than or equal to 0.3 bar and less than or equal to 3.0 bar, preferably greater than or equal to 0.5 bar and less than or equal to 2.5 bar, and more preferably greater than or equal to 1.0 bar and less than or equal to 1.5 bar.

[0073] In another embodiment, the internal temperature of the heat exchanger can be 200°C or higher, preferably 210°C or higher, and more preferably 215°C or higher, and can be 300°C or lower.

[0074] By adjusting the pressure of the heat exchanger to the aforementioned range, the temperature of the heat exchanger can be appropriately maintained within the aforementioned range, and the pressure difference with the subsequent reactor can be reduced, thereby appropriately forming the capacity of the compressor for subsequent processes. Furthermore, by adjusting the temperature of the heat exchanger to the aforementioned range, the aqueous solution contained within the heat exchanger from step 1 can be vaporized, and the yield of acrylic acid may increase because the lactic acid feedstock is not decomposed.

[0075] In one embodiment of the acrylic acid production method provided in this application, the second lactic acid vapor contains water and a lactic acid raw material, which contains lactic acid and lactic acid oligomers, and the content of the lactic acid raw material can be greater than or equal to 15 parts by weight and less than or equal to 80 parts by weight based on 100 parts by weight of the second lactic acid vapor.

[0076] In another embodiment, based on 100 parts by weight of the second lactic acid vapor, the content of the lactic acid raw material can be greater than or equal to 15 parts by weight and less than or equal to 80 parts by weight, preferably greater than or equal to 17 parts by weight and less than or equal to 75 parts by weight, more preferably greater than or equal to 20 parts by weight and less than or equal to 60 parts by weight.

[0077] In one embodiment of the acrylic acid production method provided in this application, the ratio of lactic acid to lactic acid oligomer in the second lactic acid vapor is from 80:20 to 95:5. Here, this ratio may refer to a weight ratio.

[0078] In another embodiment, the ratio of lactic acid to lactic acid oligomer in the second lactic acid vapor can be in the range of 80:20 to 95:5, 81:19 to 93:7, and 82:18 to 90:10.

[0079] The second lactic acid vapor is included in the reactor for the subsequent production of acrylic acid, ensuring that the proportion of lactic acid feedstock in the second lactic acid vapor state vaporized in step 2 and the proportion of lactic acid contained in the feedstock meet the aforementioned ranges, and that the amount and quantity of water introduced into the reactor are appropriate. Subsequently, through the absorption process described later, the second lactic acid vapor can have a minimized proportion of lactic acid oligomers.

[0080] In one embodiment of this application, the unvaporized third lactic acid aqueous solution can be returned to the aqueous solution contained in step 1 by a liquid stream, and the first lactic acid aqueous solution can contain the unvaporized third lactic acid aqueous solution.

[0081] The third lactic acid aqueous solution forms lactic acid oligomers through the oligomerization reaction of concentrated lactic acid and is recycled without vaporization. Based on 100 parts by weight of the third lactic acid aqueous solution, the third lactic acid aqueous solution may contain greater than or equal to 90 parts by weight and less than or equal to 99 parts by weight of lactic acid oligomers.

[0082] Next, water is introduced into the first lactic acid aqueous solution containing the third lactic acid aqueous solution (i.e., this can be defined as the aqueous solution of step 1) for dilution, and through the equilibrium reaction, the content of lactic acid oligomers in the lactic acid aqueous solution introduced into the heat exchanger can be reduced as much as possible.

[0083] Figure 1This is a schematic diagram illustrating a method for producing acrylic acid according to one embodiment of this application. Specifically, step 2 is a step of heat exchange of the aqueous solution 4 from step 1 to form vaporized second lactic acid vapor 5 and unvaporized third lactic acid aqueous solution 9, and step 3 can represent a liquid circulation flow containing the unvaporized third lactic acid aqueous solution 9 in the aqueous solution of step 1.

[0084] One embodiment of this application may include step 4, which involves supplying an absorbent to vaporized second lactic acid vapor and absorbing it to form an absorbed fourth lactic acid aqueous solution and an unabsorbed fifth lactic acid vapor.

[0085] In one embodiment of this application, an absorbent is supplied to the second lactic acid vapor to form an absorbed fourth lactic acid aqueous solution with a high lactic acid oligomer content. The process of recycling the fourth lactic acid aqueous solution back to step 1 provides an economically superior process without loss of raw materials. Furthermore, unabsorbed fifth lactic acid vapor is formed through the absorption process, i.e., step 4. Therefore, the lactic acid oligomer content in the fifth lactic acid vapor is minimized, and the reaction yield can be increased by using the fifth lactic acid vapor in the subsequent acrylic acid production process.

[0086] In other words, even if vaporization is carried out in step 2, the content of lactic acid oligomers is still high in the second lactic acid vapor state, which may cause problems. Therefore, this application includes step 4, which involves absorption by an absorption device to reduce the content of lactic acid oligomers in the second lactic acid vapor.

[0087] In one embodiment of this application, the absorbed fourth lactic acid aqueous solution may contain water and lactic acid raw material, and the fourth lactic acid aqueous solution may be returned to the aqueous solution contained in step 1 by a circulating stream together with the absorbent.

[0088] In one embodiment of the acrylic acid production method provided in this application, the absorption device may be one or more selected from rotary drum, spray drum, packed tower and plate tower.

[0089] In one embodiment of this application, the absorption device may be a packed tower or a multi-stage absorption tower.

[0090] The absorption process involves absorbing and decomposing lactic acid oligomers in the second lactic acid vapor to increase the lactic acid monomer content. An absorbent liquid can be used during the absorption process; the absorbent liquid can be water or an aqueous lactic acid solution.

[0091] The acrylic acid production method according to this application adds a process to further reduce the content of lactic acid oligomers through the absorption process, reduces the occurrence of scaling in the reactor used for the final acrylic acid production process, increases the reaction yield, and minimizes the loss of lactic acid relative to the introduced lactic acid feedstock by increasing the content of vaporized lactic acid, thereby maximizing economic feasibility.

[0092] In one embodiment of the acrylic acid production method provided in this application, a fifth lactic acid vapor can be formed through an absorption process. This fifth lactic acid vapor comprises water and a lactic acid feedstock, which comprises lactic acid and lactic acid oligomers. Based on 100 parts by weight of the fifth lactic acid vapor, the content of the lactic acid feedstock can be greater than or equal to 10 parts by weight and less than or equal to 80 parts by weight.

[0093] In another embodiment, based on 100 parts by weight of the fifth lactic acid vapor, the content of the lactic acid raw material can be greater than or equal to 15 parts by weight and less than or equal to 80 parts by weight, preferably greater than or equal to 17 parts by weight and less than or equal to 80 parts by weight, more preferably greater than or equal to 20 parts by weight and less than or equal to 75 parts by weight.

[0094] The fifth lactic acid vapor is the final aqueous solution of lactic acid in a vaporized state before the production of acrylic acid. The lactic acid raw material content in the fifth lactic acid vapor meets the above-mentioned range, and the amount of lactic acid raw material itself introduced is appropriate. By appropriately adjusting the water content to a suitable range, excellent economic feasibility was achieved in the subsequent production of acrylic acid.

[0095] In one embodiment of the acrylic acid production method provided in this application, the ratio of lactic acid to lactic acid oligomer in the fifth lactic acid vapor is from 100:0 to 90:10.

[0096] In another embodiment, the ratio of lactic acid to lactic acid oligomer in the fifth lactic acid vapor can be from 100:0 to 90:10, preferably from 100:0 to 95:5, and more preferably from 100:0 to 97:3.

[0097] In other words, the acrylic acid production method according to this disclosure breaks through the existing petrochemical-based manufacturing process and produces acrylic acid based on the environmentally friendly feedstock lactic acid. Therefore, it achieves excellent performance in terms of environmental protection and sustainability. The fifth lactic acid vapor is the final state of lactic acid vapor introduced into the reactor. Through the above absorption process, the acrylic acid production method according to this application adds a process to further reduce the content of lactic acid oligomers, which can reduce scaling in the reactor used in the final acrylic acid production process and improve the reaction yield.

[0098] In one embodiment of the acrylic acid production method provided in this application, the absorption device has an internal pressure greater than or equal to 0.3 bar and less than or equal to 3.0 bar, and an internal temperature greater than or equal to 100°C and less than or equal to 230°C.

[0099] In another embodiment, the absorption device may have an internal pressure greater than or equal to 0.3 bar and less than or equal to 3.0 bar, preferably greater than or equal to 0.5 bar and less than or equal to 2.5 bar, and more preferably greater than or equal to 1.0 bar and less than or equal to 1.5 bar.

[0100] By adjusting the pressure of the absorption device to the above range, the pressure difference with the reactor can be reduced, and the capacity of the compressor for subsequent processes can be appropriately formed.

[0101] In another embodiment, the absorption device may have an internal temperature of 100°C or higher and 230°C or lower, preferably 110°C or higher and 220°C or lower, more preferably 120°C or higher and 200°C or lower.

[0102] In one embodiment of the acrylic acid production method provided in this application, an absorbent is supplied to vaporized second lactic acid vapor and absorbed to form an absorbed fourth lactic acid aqueous solution and an unabsorbed fifth lactic acid vapor, and the fourth lactic acid aqueous solution is included in the aqueous solution of step 1.

[0103] In other words, as described above, the first lactic acid aqueous solution in step 1 may contain a fourth lactic acid aqueous solution.

[0104] Figure 1 This is a schematic diagram illustrating a method for producing acrylic acid according to one embodiment of this application. Specifically, step 4 may include supplying vaporized second lactic acid vapor 5 to an absorption device 200 and absorbing it through an absorption liquid 6. As a result, the absorbed fourth lactic acid aqueous solution 8 is recycled back to step 1 via a circulating stream to form the aqueous solution 4 of step 1. Finally, in the final acrylic acid production process, the unabsorbed fifth lactic acid vapor 7 has a minimized lactic acid oligomer content.

[0105] The production method disclosed herein is particularly suitable for synthesizing acrylic acid. Specifically, the lactic acid-containing vapor composition obtained in this disclosure can be contacted with a dehydration catalyst to prepare acrylic acid. The generated reaction gases are collected and liquefied by cooling or contact with a collection liquid, and after purification processes such as extraction, distillation, and crystallization, high-purity acrylic acid can be obtained. The produced acrylic acid is widely used as a raw material for water-absorbing polymers, coatings, adhesives, etc.

[0106] Embodiments of this disclosure will be described in detail below to enable those skilled in the art to readily implement it. However, this disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0107] Preparation Examples

[0108] The following examples and comparative models were simulated using Aspen Plus from Aspen Technology Inc.

[0109] Comparative Example 1

[0110] like Figure 2 As shown, purified lactic acid feedstock is diluted in water to prepare a liquid lactic acid aqueous solution 3 containing 40% lactic acid feedstock. This aqueous solution is introduced into a heat exchanger, where 2% of it is vaporized. The unvaporized liquid is recirculated 9 at a flow rate approximately 50 times that of the liquid lactic acid aqueous solution 3. The recirculated liquid stream merges with the heat exchanger feed and is introduced into the heat exchanger. Subsequently, the vaporized gaseous lactic acid material stream in the heat exchanger is used as the reactor feed.

[0111] The heat exchanger used operates at a pressure of 1.5 bar, a temperature of 217°C, and a calorie content of 0.5 mm kcal / hr.

[0112] The operation process of Comparative Example 1 can be performed in Figure 2 Confirmed in China. (As...) Figure 2 As shown in Table 1, the flow rates of the liquid lactic acid aqueous solution 3, aqueous solution 4, third lactic acid aqueous solution 9, and fifth lactic acid vapor 7 in step 1, as well as the composition of each material flow, are shown below.

[0113] [Table 1]

[0114]

[0115] Comparative Example 2

[0116] like Figure 3 As shown, purified lactic acid raw material 1 is diluted in water 2 to prepare a liquid lactic acid aqueous solution 3 with 40% lactic acid raw material. The aqueous solution is introduced into a heat exchanger, where 2% of it is vaporized and the unvaporized liquid is recycled 9.

[0117] The recirculated liquid stream is introduced into the decomposition tank 400, where lactic acid oligomers are decomposed by water contained in the liquid lactic acid aqueous solution 3. Lactic acid oligomers generated in the heat exchanger are partially decomposed in the decomposition tank and reintroduced into the heat exchanger. The vaporized gaseous lactic acid stream is used as reactor feed.

[0118] The operation process of Comparative Example 2 can be performed in Figure 3 Confirmed in China, such as Figure 3 As shown in Table 2, the flow rates of the liquid lactic acid aqueous solution 3, aqueous solution 4, third lactic acid aqueous solution 9, and fifth lactic acid vapor 7 in step 1, as well as the composition of each material flow, are shown below.

[0119] [Table 2]

[0120]

[0121] Comparative Example 3

[0122] When diluting lactic acid feedstock 1 in water 2, a portion of water 2 is replaced with steam, and the remaining conditions are the same as in Comparative Example 2. Due to the increased temperature in dilution tank 300, there is an advantage in reducing the size of the dilution tank, but the flow rates and compositions are the same as in Table 2 of Comparative Example 2.

[0123] Example 1

[0124] When the purified lactic acid feedstock was diluted in water, unlike in Comparative Example 1, a small amount of water was introduced to prepare a liquid lactic acid aqueous solution with 56% lactic acid feedstock. This aqueous solution was then introduced into the heat exchanger. The remaining water was used as the absorbent, and the total amount of water introduced remained constant, ensuring that the concentration of lactic acid in the reactor feed was maintained at 40%.

[0125] Two percent of the liquid is vaporized in the heat exchanger, and the unvaporized liquid is recycled and introduced back into the heat exchanger. The vaporized gaseous lactic acid stream in the heat exchanger contains water, lactic acid, and lactic acid oligomers, and is then introduced into the absorption unit. The absorbent is introduced into the absorption unit to absorb and separate the oligomers in the gas phase. Water and lactic acid flow out as gas (fifth lactic acid vapor) and are used as reactor feed. The flow rate of the recycled liquid is approximately the same as that of the liquid lactic acid aqueous solution (…). Figure 1 50 times that of the No. 3 material flow.

[0126] The heat exchanger used operates at a pressure of 1.5 bar, a temperature of 238°C, and a calorie content of 0.5 mm kcal / hr.

[0127] The operation process of Example 1 can be performed in Figure 1 Confirmed in China, such as Figure 1 As shown in Table 3, the flow rates of liquid lactic acid aqueous solution 3, first lactic acid aqueous solution 4, second lactic acid vapor 5, absorbent (water) 6, fourth lactic acid aqueous solution 8, third lactic acid aqueous solution 9 and fifth lactic acid vapor 7, as well as the composition of each material flow, are shown in Table 3.

[0128] [Table 3]

[0129]

[0130] Example 2

[0131] Except that an aqueous solution of lactic acid is used instead of water as the absorbent, the procedure is the same as in Example 1.

[0132] The heat exchanger used operates at a pressure of 1.5 bar, a temperature of 231°C, and a calorie content of 0.5 mm kcal / hr.

[0133] Similar to Example 1, also in accordance with Figure 1The operation process of Example 2, the flow rates of liquid lactic acid aqueous solution 3, first lactic acid aqueous solution 4, second lactic acid vapor 5, absorbent (lactic acid aqueous solution) 6, fourth lactic acid aqueous solution 8, third lactic acid aqueous solution 9 and fifth lactic acid vapor 7, and the composition of each material flow are shown in Table 4 below.

[0134] [Table 4]

[0135]

[0136] Based on the composition and content of the final lactic acid vapor produced in each of Comparative Example 1, Comparative Example 2, Example 1, and Example 2, the feed to the reactor was prepared ( Figures 1 to 3 The 7th material flow in each of them is shown in Table 5 below.

[0137] [Table 5]

[0138]

[0139] Table 5 shows that in Comparative Example 1, the total content of lactic acid raw material (lactic acid and lactic acid oligomers) was approximately 39% by weight. However, the lactic acid content was only 85% of the raw material, with the remainder being lactic acid oligomers. It was confirmed that the content of lactic acid oligomers was relatively high among lactic acid substances, approximately 14%.

[0140] In Comparative Example 2 in Table 5, it was confirmed that the content of oligomers decreased compared to Comparative Example 1. This was due to the addition of the process of decomposing oligomers in the decomposition tank. However, as confirmed in Table 5, the proportion of lactic acid oligomers in the lactic acid substances was still approximately 8.5%, and it was confirmed that a considerable amount of lactic acid oligomers were contained in the fifth lactic acid vapor itself.

[0141] In Comparative Example 3, when the lactic acid raw material 1 was diluted in water 2, steam was used to replace part of the water 2, and the other conditions were the same as in Comparative Example 2. Due to the increased temperature of the dilution tank 300, it has the advantage of reducing the size of the dilution tank, but the flow rates and composition are the same as in Comparative Example 2. The proportion of lactic acid oligomers in the lactic acid substances is still about 8.5%, and it was confirmed that a considerable amount of lactic acid oligomers are contained in the fifth lactic acid vapor itself.

[0142] Table 5 shows Example 1, which describes the absorption process disclosed in this application, wherein water is used as the absorbent. Similar to Comparative Example 1, the content of the lactic acid feedstock (lactic acid and lactic acid oligomers) was 40% by weight. It was confirmed that the lactic acid oligomer content in the reactor feed decreased, with a lactic acid ratio of 98% and a lactic acid oligomer ratio of 2% based on the lactic acid feedstock.

[0143] Furthermore, Example 2 in Table 5 describes the absorption process disclosed in this application, wherein an aqueous lactic acid solution is used as the absorbent. Similar to Example 1, the content of the lactic acid feedstock (lactic acid and lactic acid oligomers) is 40% by weight. It was confirmed that the content of lactic acid oligomers in the reactor feed decreased, and based on the lactic acid feedstock, the lactic acid proportion was 99% and the lactic acid oligomer proportion was 1%.

[0144] In other words, it is confirmed that in the acrylic acid production method according to one embodiment of this application, by increasing the process of supplying absorbent to the vaporized liquid solution of the gaseous lactic acid solution after passing through a heat exchanger, the lactic acid oligomers contained in the liquid solution are absorbed, thereby reducing the content of oligomers in the liquid solution of the lactic acid solution before being fed to the reactor.

[0145] Specifically, it was confirmed that by absorbing the oligomers contained in the lactic acid vapor (second lactic acid vapor) vaporized through the heat exchanger, the content of lactic acid oligomers in the lactic acid vapor was reduced, thereby reducing scaling in the vaporizer and reaction unit. Furthermore, by including a high content of lactic acid monomers, the yield of acrylic acid produced was increased, losses were minimized, and economic feasibility was enhanced.

[0146] Furthermore, when the absorbent is supplied before the heat exchanger step, the content of lactic acid oligomers in the vaporized lactic acid vapor may also decrease. However, such a process requires a separate decomposition unit, and there is also the disadvantage of increasing the size of the decomposition unit due to the residence time required for decomposition.

[0147] Furthermore, compared to the case where steam is supplied as the absorbent before the heat exchanger step, there is an effect of reducing energy consumption. However, compared to the case where steam is supplied, the disclosure of this application has significantly superior performance in reducing the oligomer content in the feed.

Claims

1. A method for producing acrylic acid, the method comprising: Step 1: Prepare a first lactic acid aqueous solution by diluting the lactic acid raw material with water; Step 2: The first lactic acid aqueous solution is subjected to heat exchange to form vaporized second lactic acid vapor and unvaporized third lactic acid aqueous solution; Step 3: The unvaporized third lactic acid aqueous solution is included in the aqueous solution of step 1; as well as Step 4: Supply absorbent liquid to the vaporized second lactic acid vapor and absorb it to form absorbed fourth lactic acid aqueous solution and unabsorbed fifth lactic acid vapor. Step 4 includes the absorption process using an absorption device; and The internal pressure of the absorption device is greater than or equal to 0.3 bar and less than or equal to 3 bar, and the internal temperature is greater than or equal to 100°C and less than or equal to 230°C. The absorbed fourth lactic acid aqueous solution is contained in the aqueous solution of step 1. The first lactic acid aqueous solution contains water and lactic acid raw material; The lactic acid raw material comprises lactic acid and lactic acid oligomers; and Based on 100 parts by weight of the first lactic acid aqueous solution, the content of the lactic acid raw material is greater than or equal to 30 parts by weight and less than or equal to 99 parts by weight. The unabsorbed fifth lactic acid vapor is supplied to the reactor used for the production of acrylic acid. The absorbent is water or an aqueous solution of lactic acid.

2. The method for producing acrylic acid according to claim 1, wherein, Step 2 includes a heat exchange process using a heat exchanger; and The internal pressure of the heat exchanger is greater than or equal to 0.3 bar and less than or equal to 3 bar, and the internal temperature is greater than or equal to 150°C and less than or equal to 300°C.

3. The method for producing acrylic acid according to claim 1, wherein, The ratio of lactic acid to lactic acid oligomer in the first lactic acid aqueous solution is 1:99 to 30:

70.

4. The method for producing acrylic acid according to claim 1, wherein, The weight ratio of lactic acid to lactic acid oligomer in the second lactic acid vapor is 80:20 to 95:

5.

5. The method for producing acrylic acid according to claim 1, wherein, The ratio of lactic acid to lactic acid oligomer in the fifth lactic acid vapor is from 100:0 to 90:

10.

6. The method for producing acrylic acid according to claim 1, wherein, The fifth lactic acid vapor contains water and lactic acid raw material; The lactic acid raw material comprises lactic acid and lactic acid oligomers; and Based on 100 parts by weight of the fifth lactic acid vapor, the content of the lactic acid raw material is greater than or equal to 10 parts by weight and less than or equal to 80 parts by weight.

7. The method for producing acrylic acid according to claim 2, wherein, The heat exchanger is selected from one or more of the following: falling film evaporator, scraped film evaporator, thermosiphon evaporator, and forced circulation evaporator.

8. The method for producing acrylic acid according to claim 1, wherein, The absorption device is selected from one or more of the following: rotary drum, packed tower, and plate tower.

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