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. 10-2020-0159107, filed on November 24, 2020, with the Korean Intellectual Property Office, 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 of propylene, and the demand for acrylic acid as a raw material for superabsorbent polymers, coatings, adhesives, etc., has increased. In particular, superabsorbent polymers are used in hygiene products such as diapers.

[0004] Currently, a considerable number of chemical products are produced using raw materials derived from fossil fuels such as coal or oil. However, in order to prevent global warming and protect the environment, the use of recyclable biological resources as carbon sources as an alternative to existing fossil fuels has recently gained attention. For example, methods have been explored to develop methods using biomass resources such as starchy biomass from corn or wheat, carbohydrate biomass from sugarcane, and cellulose biomass from rapeseed residue or rice straw as raw materials.

[0005] In other words, research is currently underway on breaking through existing petrochemical-based manufacturing processes and producing chemical products using environmentally friendly raw materials, in order to achieve excellent performance in terms of environmental protection and 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 in the liquid phase through esterification in the absence of water and catalysts. Furthermore, as lactic acid is concentrated and its concentration increases, it reacts as lactic acid oligomers. Dehydration occurs during lactic acid oligomerization, and lactic acid oligomerization occurs when lactic acid is concentrated in the absence of water.

[0008] When lactic acid oligomers are introduced into reactors used to produce acrylic acid, scaling occurs and the reaction yield decreases. Therefore, methods to reduce the content of lactic acid oligomers in the production of acrylic acid are being investigated.

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

[0010] Alternatively, a distillation column can be used to separate the vaporized lactic acid aqueous solution by utilizing the boiling point difference, thus eliminating the presence of oligomers. However, the oligomerization reaction of lactic acid still occurs in this column, leading to the concentration of lactic acid oligomers and causing a temperature rise in the lower part of the distillation column.

[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 in production.

[0012] Existing technical documents

[0013] Patent documents

[0014] (Patent Document 1) International Patent Application Publication No. 2005-095320 Summary of the Invention

[0015] Technical issues

[0016] This application aims to provide 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: supplying a lactic acid feedstock to the upper part of a distillation column; supplying water to the lower part of the distillation column; supplying a first lactic acid vapor vapor vaporized in the distillation column to a reactor; and supplying a second lactic acid aqueous solution that has not been vaporized in the distillation column to the middle part of the distillation column.

[0019] Beneficial effects

[0020] According to one embodiment of this application, the method for producing acrylic acid uses a distillation column that utilizes boiling point differences for separation. Specifically, to address the problem of temperature rise in the lower part of the distillation column during operation, water and concentrated lactic acid feedstock are supplied separately, rather than as an aqueous solution of lactic acid. Therefore, by supplying water to the lower part of the distillation column, thereby decomposing a portion of the concentrated lactic acid oligomers in the lower part into lactic acid, the temperature in the lower part of the distillation column can be reduced.

[0021] In particular, lactic acid thermally decomposes at high temperatures (approximately 200°C to above 250°C) and produces byproducts such as propionic acid. However, by supplying water separately to the lower part of the distillation column as described above, the temperature of the lower part of the distillation column and the temperature of the distillation column can be reduced, which inhibits the production of byproducts caused by the thermal decomposition of lactic acid.

[0022] Furthermore, the method for producing acrylic acid according to this application uses a distillation column instead of a vaporizer, and can prevent the formation of lactic acid oligomers during the vaporization of the lactic acid aqueous solution. In addition, by introducing the concentrated lactic acid raw material into the distillation column as is, acrylic acid can be produced without a separate dilution device. Attached Figure Description

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

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

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

[0026] <Figure Labels>

[0027] 100: Distillation Column

[0028] 200: Heat exchanger

[0029] 1: Liquid lactic acid aqueous solution

[0030] 2: Water

[0031] 3: First lactic acid vapor

[0032] 4: Second lactic acid aqueous solution Detailed Implementation

[0033] This instruction manual will be described in more detail below.

[0034] In this specification, unless otherwise stated to the contrary, a description that a part "contains" certain components means that other components may also be contained, without excluding other components.

[0035] In this specification, "p to q" means the range of "greater than or equal to p and less than or equal to q".

[0036] The embodiments of this disclosure will be described in detail below with reference to the accompanying drawings, enabling those skilled in the art to readily implement this disclosure. However, this disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0037] One embodiment of this application provides a method for producing acrylic acid, the method comprising: supplying a lactic acid feedstock to the upper part of a distillation column; supplying water to the lower part of the distillation column; supplying a first lactic acid vapor vapor vaporized in the distillation column to a reactor; and supplying a second lactic acid aqueous solution that has not been vaporized in the distillation column to the middle part of the distillation column.

[0038] According to one embodiment of this application, the method for producing acrylic acid uses a distillation column that utilizes boiling point differences for separation. In particular, to address the problem of temperature rise in the lower part of the distillation column during operation, water is supplied to the lower part of the distillation column instead of being supplied as an aqueous solution of lactic acid. Furthermore, by decomposing a portion of the lactic acid oligomers concentrated in the lower part into lactic acid, the temperature in the lower part of the distillation column can be reduced.

[0039] Figure 1 This is a schematic diagram of a method for producing acrylic acid according to one embodiment of this application. Specifically, Figure 1 Using a four-stage distillation column 100, the steps can be specifically identified as: (1) supplying lactic acid feedstock to the distillation column 100; (2) supplying water to the lower part of the distillation column; (3) supplying first lactic acid vapor vapor vaporized in the distillation column to the reactor; and (4) supplying a second lactic acid aqueous solution that has not been vaporized in the distillation column to the middle part of the distillation column.

[0040] In one embodiment of this application, the lactic acid raw material comprises: water; lactic acid; and lactic acid oligomers, and may contain up to 20 parts by weight of water per 100 parts by weight of the lactic acid raw material.

[0041] 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.

[0042] 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 lactic acid dimers to 100-mers.

[0043] Lactic acid is a substance that is polymerized in the liquid phase through esterification without a catalyst or even without water, and all substances formed by the polymerization of lactic acid can be represented as lactic acid oligomers.

[0044] In one embodiment of this application, the lactic acid raw material comprises: water; lactic acid; and lactic acid oligomers, and based on 100 parts by weight of the lactic acid raw material, it may contain 20 parts by weight or less, preferably 18 parts by weight or less, more preferably 13 parts by weight or less of water.

[0045] In one embodiment of this application, the lactic acid raw material comprises: water; lactic acid; and lactic acid oligomers, and based on 100 parts by weight of the lactic acid raw material, it may contain 0 parts by weight or more, preferably 1 part by weight or more, and more preferably 1.5 parts by weight or more of water.

[0046] The method for producing acrylic acid according to this application introduces concentrated lactic acid feedstock into a distillation column as is, and by minimizing the water content in the lactic acid feedstock within the aforementioned range, acrylic acid can be produced without a separate lactic acid dilution unit.

[0047] In one embodiment of the method for producing acrylic acid provided in this application, the temperature of the upper part of the distillation column is higher than or equal to 150°C and lower than or equal to 200°C, and the temperature of the lower part of the distillation column is higher than or equal to 200°C and lower than or equal to 250°C.

[0048] In another embodiment, the temperature of the upper part of the distillation column can be higher than or equal to 150°C and lower than or equal to 200°C, preferably higher than or equal to 155°C and lower than or equal to 190°C, more preferably higher than or equal to 160°C and lower than or equal to 185°C, and most preferably higher than or equal to 170°C and lower than or equal to 180°C.

[0049] In another embodiment, the temperature of the lower part of the distillation column can be higher than or equal to 200°C and lower than or equal to 250°C, preferably higher than or equal to 210°C and lower than or equal to 245°C, more preferably higher than or equal to 220°C and lower than or equal to 245°C, and most preferably higher than or equal to 230°C and lower than or equal to 245°C.

[0050] Lactic acid decomposes thermally at high temperatures (approximately 200°C to 250°C and above) and produces byproducts such as propionic acid. However, this application, as described above, can reduce the temperature of the lower part of the distillation column and the overall temperature of the distillation column by separately supplying water to the lower part of the distillation column. Furthermore, by having the upper and lower parts of the distillation column with the aforementioned temperature range, the generation of byproducts caused by the thermal decomposition of lactic acid can be suppressed.

[0051] In one embodiment of the present application, the method for producing acrylic acid is provided in which the ratio of lactic acid to lactic acid oligomer in the first lactic acid vapor is from 100:0 to 95:5.

[0052] The first lactic acid vapor is a substance obtained by separating lactic acid feedstock introduced into a distillation column using the boiling point difference, and the first lactic acid vapor may contain water, lactic acid, and lactic acid oligomers.

[0053] In another embodiment, the ratio of lactic acid to lactic acid oligomer in the first lactic acid vapor can be from 100:0 to 95:5, and most preferably 100:0.

[0054] The method for producing acrylic acid according to this application uses a distillation column instead of a vaporizer, and can prevent the formation of lactic acid oligomers during the vaporization of the lactic acid aqueous solution. Furthermore, in the production of gaseous acrylic acid, the occurrence of scaling in the reactor can be minimized by reducing the oligomer content, and the reaction yield can be maximized.

[0055] In one embodiment of the method for producing acrylic acid provided in this application, the ratio of lactic acid to lactic acid oligomer in the second lactic acid aqueous solution is from 1:99 to 20:80.

[0056] The second lactic acid aqueous solution contains oligomers that are concentrated in the lower part of the distillation column but not vaporized in the distillation column. In this application, the concentrated oligomers can be decomposed back into lactic acid by introducing water directly into the lower part of the distillation column, which can directly reduce the temperature of the lower part of the distillation column.

[0057] In addition, by resupplying the second lactic acid aqueous solution to the middle of the distillation column, the distillation column can be operated with minimal lactic acid loss.

[0058] In one embodiment of this application, the distillation column has only a reboiler and no condenser, and can refer to an evaporator for heating and evaporating the liquid rich in high-boiling-point components extracted from the bottom of the distillation column, returning the generated vapor to the bottom of the distillation column, and extracting the remaining liquid as effluent, and can use distillation columns commonly used in the art without limitation.

[0059] In one embodiment of the present application, a method for producing acrylic acid is provided, wherein the distillation column is formed having 3 to 7 stages, with the upper stage being the first stage, the middle stage being the stage between the upper and lower stages, and the lower stage being the last stage.

[0060] The distillation column according to this application can be configured to have 5 stages, and there is no limitation on the number of stages of the distillation column, such as 10 stages or 15 stages. In this case, the upper stage refers to the uppermost stage of the distillation column, the lower stage refers to the lowermost stage of the distillation column, and the middle stage refers to all stages other than the upper and lower stages.

[0061] In one embodiment of the method for producing acrylic acid provided in this application, the internal pressure of the distillation column is greater than or equal to 0.1 bar and less than or equal to 2.0 bar.

[0062] In another embodiment, the internal pressure of the distillation column can be greater than or equal to 0.1 bar and less than or equal to 2.0 bar, preferably greater than or equal to 0.3 bar and less than or equal to 1.8 bar.

[0063] As described above, by ensuring the internal pressure of the distillation column meets the aforementioned range, the decomposition of lactic acid can be minimized due to the appropriate temperature in the vaporizer, and by subsequently reducing the pressure difference with the reactor, the capacity of the compressor used can be set to an appropriate range.

[0064] Lactic acids are highly corrosive, especially at temperatures above 200°C. Therefore, the materials used in distillation columns and reactors are preferably those with a certain degree of resistance to lactic acids. Examples of materials resistant to lactic acids include austenitic stainless steels, ferritic stainless steels, duplex stainless steels, nickel alloys, titanium, zirconium, tantalum, titanium alloys, gold, and platinum. The resulting vapor composition containing lactic acid can be contacted with a catalyst and converted into other useful chemical products. Examples of products derived from lactic acids include acrylic acid and pyruvic acid.

[0065] In one embodiment of the method for producing acrylic acid provided in this application, the first lactic acid vapor comprises: water; lactic acid; and lactic acid oligomer, and based on 100 parts by weight of the first lactic acid vapor, it comprises greater than or equal to 5 parts by weight and less than or equal to 80 parts by weight of lactic acid and lactic acid oligomer.

[0066] In another embodiment, the first lactic acid vapor comprises: water; lactic acid; and lactic acid oligomers, and based on 100 parts by weight of the first lactic acid vapor, it may contain greater than or equal to 5 parts by weight and less than or equal to 80 parts by weight, preferably greater than or equal to 10 parts by weight and less than or equal to 75 parts by weight, more preferably greater than or equal to 30 parts by weight and less than or equal to 70 parts by weight of lactic acid and lactic acid oligomers.

[0067] The method for producing acrylic acid is highly effective by using a first lactic acid vapor with the content range of lactic acid substances as described above, and by having an appropriate amount subsequently supplied to the reactor. Furthermore, the method is highly economically feasible by introducing an appropriate amount of water into the reactor.

[0068] In one embodiment of the present application, a method for producing acrylic acid is provided, wherein acrylic acid is produced by a dehydration reaction of the first lactic acid vapor after the step of supplying first lactic acid vapor, which is vaporized in a distillation column, to a reactor.

[0069] In other words, the method for producing acrylic acid according to this disclosure breaks through existing petrochemical-based manufacturing processes and produces acrylic acid based on lactic acid, an environmentally friendly raw material. Therefore, it achieves excellent performance in terms of environmental protection while also ensuring sustainability. Specifically, by using a distillation column and introducing water separately to the lower part of the distillation column, the content of lactic acid oligomers introduced into the reactor is minimized, the acrylic acid yield is maximized, and scaling in the reactor is suppressed.

[0070] The production method disclosed herein is particularly useful for synthesizing acrylic acid, and specifically, acrylic acid can be prepared by contacting a lactic acid-containing vapor composition obtained in this disclosure with a dehydration catalyst. The generated reaction gas is collected and liquefied by cooling or contacting with a collection liquid, and after purification processes such as extraction, distillation, or 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.

[0071] The embodiments of this disclosure will be described in detail below so that those skilled in the art can readily implement this disclosure. However, this disclosure may be implemented in various different forms and is not limited to the embodiments described herein.

[0072] <Preparation Example>

[0073] The following examples and comparative examples are simulated by Aspen Plus from Aspen Technology Inc.

[0074] Example 1

[0075] The distillation column is configured with five stages, featuring only reboilers and no condensers. Purified, concentrated lactic acid feedstock is introduced into the first stage (top stage) of the distillation column without a dilution step. Water is introduced into the fifth stage (bottom stage) of the distillation column to lower the operating temperature by partially decomposing lactic acid oligomers at the bottom of the column.

[0076] The upper stream is obtained as a gas phase (first lactic acid vapor) and used as feed to the reactor. The lower stream (second lactic acid aqueous solution) is reintroduced into the distillation column to operate without lactic acid loss, and the number of stages for the reintroduction of the lower stream during operation is the second stage.

[0077] The internal pressure of the distillation column used is 1.5 bar.

[0078] The operation process of Example 1 can be performed in Figure 1 Confirmed in China, such as Figure 1 As shown, the flow rates of liquid lactic acid aqueous solution 1, water 2, first lactic acid vapor 3 and second lactic acid aqueous solution 4, as well as the composition of each flow, are shown in Table 1 below.

[0079] [Table 1]

[0080]

[0081] Comparative Example 1

[0082] Except that the lactic acid feedstock and water are not introduced separately, the purified concentrated lactic acid feedstock is diluted in water to prepare an aqueous solution with 40% lactic acid feedstock (lactic acid and lactic acid oligomers), and this aqueous solution is introduced into the first stage (top stage) of the distillation column, and water is not introduced into the fifth stage (bottom stage) of the distillation column, and the operation is carried out in the same manner as in Example 1.

[0083] The internal pressure of the distillation column used is 1.5 bar.

[0084] Specifically, the operation method can be found in Figure 2 Confirmed in [the process]. Concentrated lactic acid feedstock, diluted in water to prepare an aqueous solution containing 40% lactic acid feedstock (lactic acid and lactic acid oligomers), was introduced into stream 1, and it was confirmed that no water was introduced as [the desired result]. Figure 1 The process of stream 2. For example... Figure 2 As shown, the flow rates of liquid lactic acid aqueous solution 1, first lactic acid vapor 3, and second lactic acid aqueous solution 4, as well as the composition of each flow, are shown in Table 2 below.

[0085] [Table 2]

[0086]

[0087] Comparative Example 2

[0088] The purified concentrated lactic acid feedstock was diluted in water to prepare an aqueous solution containing 40% lactic acid feedstock (lactic acid and lactic acid oligomers). This aqueous solution was introduced into a heat exchanger, where 3% was vaporized, and the unvaporized liquid was recycled. The flow rate of the recycled liquid was approximately 50 times that of the liquid lactic acid aqueous solution, and the recycled liquid was introduced into the heat exchanger after encountering the diluted lactic acid aqueous solution. The vapor phase of lactic acid vaporized in the heat exchanger was used as the reactor feed.

[0089] The heat exchanger used operates at a pressure of 1.5 bar and a temperature of 217°C.

[0090] Specifically, the operation method can be found in Figure 3 It can be confirmed that, unlike Example 1 and Comparative Example 1, the operation of using a heat exchanger 200 instead of a distillation column is confirmed.

[0091] The composition and content of the lactic acid vapor (first lactic acid vapor) supplied to the final reactor by the various methods of Example 1, Comparative Example 1 and Comparative Example 2 are described in Table 3 below, and the temperature of the reboiler of the distillation column used is also described in Table 3 below.

[0092] [Table 3]

[0093]

[0094] Table 3 confirms the composition and content of the final lactic acid vapor supplied to the reactor feed. Specifically, it confirms that in Comparative Example 1, where lactic acid oligomers were separated using a distillation column, the lactic acid feedstock contained approximately 38% by weight of lactic acid and 1.8% by weight of lactic acid oligomers, reducing the oligomer content to around 3%. However, as the reboiler temperature of the distillation column increased to nearly 360°C, the lactic acid was likely to undergo thermal decomposition (lactic acid decomposes at temperatures above 200°C to 250°C), and a loss of lactic acid subsequently supplied to the reactor feed was confirmed.

[0095] In Example 1 of Table 3, introducing water to the bottom of the distillation column decomposes the lactic acid oligomers concentrated in the lower part of the distillation column. This lowers the temperature in the lower part of the distillation column, and it can be confirmed that the reboiler temperature is reduced to approximately 240°C, compared to approximately 360°C in Comparative Example 1. Furthermore, there are almost no lactic acid oligomers in the composition of the lactic acid vapor in the reactor feed. Additionally, it can be confirmed that although the flow rates of the introduced lactic acid aqueous solution 1 and water 2 are the same as in Comparative Example 1, the difference lies in the introduction of water 2 to the bottom of the distillation column.

[0096] In Comparative Example 2 in Table 3, the lactic acid raw material (lactic acid and lactic acid oligomers) was about 39% by weight. However, based on the lactic acid raw material, only 34% by weight of lactic acid was present, with the remainder being lactic acid oligomers. It can be confirmed that the problem of high lactic acid oligomer content is generated, with the proportion of lactic acid oligomers in the lactic acid raw material being about 14%.

[0097] In other words, the method for producing acrylic acid according to one embodiment of this application uses a distillation column for separation based on boiling point difference. In particular, to address the problem of temperature rise in the lower part of the distillation column during operation, water and concentrated lactic acid feedstock are supplied separately rather than as an aqueous solution of lactic acid to the distillation column. Therefore, it can be confirmed that by supplying water to the lower part of the distillation column, a portion of the lactic acid oligomers concentrated in the lower part of the distillation column is decomposed into lactic acid, thereby reducing the temperature in the lower part of the distillation column.

[0098] Furthermore, the method for producing acrylic acid according to this application uses a distillation column instead of a vaporizer, and it can be confirmed that this method can prevent the formation of lactic acid oligomers during the vaporization of the lactic acid aqueous solution. Moreover, by introducing the concentrated lactic acid raw material into the distillation column as is, acrylic acid can be produced without a separate dilution device.

Claims

1. A method for producing acrylic acid, the method comprising: The step of supplying lactic acid feedstock to the top of the distillation column; The step of supplying water separately to the lower part of the distillation column; The step of supplying the first lactic acid vapor vapor, vaporized in the distillation column, to the reactor; and The step of supplying the second lactic acid aqueous solution that has not been vaporized in the distillation column to the middle of the distillation column. The distillation column has a reboiler but no condenser. The lactic acid raw material comprises: water; lactic acid; and lactic acid oligomers, and based on 100 parts by weight of the lactic acid raw material, it contains less than 20 parts by weight of water.

2. The method for producing acrylic acid according to claim 1, wherein, The temperature of the upper part of the distillation column is higher than or equal to 150°C and lower than or equal to 200°C, and the temperature of the lower part of the distillation column is higher than or equal to 200°C and lower than or equal to 250°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 vapor is 100:0 to 95:

5.

4. The method for producing acrylic acid according to claim 1, wherein, The ratio of lactic acid to lactic acid oligomer in the second lactic acid aqueous solution is 1:99 to 20:

80.

5. The method for producing acrylic acid according to claim 1, wherein, The internal pressure of the distillation column is greater than or equal to 0.1 bar and less than or equal to 2.0 bar.

6. The method for producing acrylic acid according to claim 1, wherein, The distillation column is formed with 3 to 7 stages, the upper part is the first stage, the middle part is the stage between the upper part and the lower part, and the lower part is the last stage.

7. The method for producing acrylic acid according to claim 1, wherein, The first lactic acid vapor comprises: water; lactic acid; and lactic acid oligomers, and based on 100 parts by weight of the first lactic acid vapor, it comprises greater than or equal to 5 parts by weight and less than or equal to 80 parts by weight of lactic acid and lactic acid oligomers.

8. The method for producing acrylic acid according to claim 1, wherein after the step of supplying the first lactic acid vapor vapor vaporized in the distillation column to the reactor, the method generates acrylic acid by a dehydration reaction of the first lactic acid vapor vapor.

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