Process and system for refining acrylic acid

Abstract

The present invention relates to a process for refining acrylic acid comprising the following steps: a) contacting acrylic acid process gas with a coolant from the top of a purification column and a column bottom stream of an absorption column in countercurrent to form a first coolant and a first gas phase; wherein the first gas phase is contacted with a raffinate phase from an extraction column in countercurrent to form a second coolant and a second gas phase; the second gas phase is contacted with a top spray of the absorption column in countercurrent to form a third coolant and a third gas phase; b) introducing a part of the third coolant into the top of the absorption column and another part into the lower part of the extraction column to form an extract phase and a raffinate phase, wherein the raffinate phase is returned to the upper or middle or lower part of the absorption column; c) introducing the extract phase from step b) from the column bottom into the upper or middle or lower part of a solvent recovery column; d) introducing the column bottom stream of the absorption column from step a) into the upper or middle part of the purification column for purification to obtain refined acrylic acid.

Description

Technical Field

[0001] This invention relates to methods and systems for refining acrylic acid. More specifically, this invention relates to a method and system for refining acrylic acid that is simple in overall process flow, environmentally friendly, and low in cost. Background Technology

[0002] Acrylic acid is an unsaturated fatty acid, an important industrial derivative of propylene, and a crucial organic chemical raw material. Containing active double bonds and carboxyl functional groups, acrylic acid is particularly suitable for preparing superabsorbent materials, dispersants, flocculants, and thickeners. Ester products derived from acrylic acid are widely used in surface coatings, fiber auxiliaries, adhesives, leather, and paper industries; while polyacrylic acid (salts) derived from acrylic acid are used in superabsorbent resins, detergents, and water treatment agents.

[0003] There are more than a dozen methods for producing acrylic acid, including the chloroethanol process, the ketene process, and the Reppe process. Currently, all large-scale acrylic acid production plants worldwide use the propylene gas-phase oxidation method. This method uses propylene and air as raw materials, and the oxidation reaction takes place in a fixed-bed catalyst bed in the presence of steam and other inert gases. The reaction consists of two steps:

[0004] In the first step, propylene is oxidized by oxygen to acrolein in the presence of a MoBiFe composite oxide catalyst:

[0005] CH2=CHCH3+O2→CH2=CHCHO+H2O, the heat of reaction is: 3.4×10 5 J / mol.

[0006] In the second step, in the presence of the MoVWCu composite oxide catalyst, acrolein is further oxidized to acrylic acid:

[0007] 2CH2=CHCHO + O2 → 2CH2=CHCOOH, the heat of reaction is: 2.52 × 10 5 J / mol.

[0008] The reactor outlet yields an acrylic acid gaseous mixture, whose main components are acrylic acid gas, nitrogen, aldehydes, carboxylic acids, carbon dioxide, carbon monoxide, and oxygen. This acrylic acid gaseous mixture is then purified and separated to obtain the acrylic acid product.

[0009] Currently, the commonly used methods for the gas-phase separation of acrylic acid mainly include three different technical routes: organic solvent absorption distillation, water absorption azeotropic distillation, and water absorption extractive distillation.

[0010] Organic solvent absorption distillation technology has the advantages of a short process and relatively low energy consumption; however, it requires the use of solvents to absorb acrylic acid, operates at high temperatures, is prone to polymerization of acrylic acid, and has a short operating cycle. Water absorption azeotropic distillation technology has the advantages of a short process and low investment costs; however, it requires the use of azeotropic agents, has higher energy consumption, and higher operating costs. Water absorption extractive distillation technology has the advantages of low energy consumption and low operating costs; however, it has the disadvantages of a longer process, higher investment costs, and higher consumption of extractants and polymerization inhibitors.

[0011] In Chinese patent CN1165808A, a mixture of diphenyl ether and biphenyl is used as an absorbent to absorb acrylic acid, and then a relatively pure acrylic acid is separated by distillation. This method requires the use of environmentally harmful solvents, and expensive polymerization inhibitors need to be added at each step to prevent acrylic acid polymerization.

[0012] Chinese patent CN101260036A discloses an improved process for the refining unit in an acrylic acid production plant. This method involves cooling the acrylic acid gas generated in the second acrylic acid reactor in a reactant cooler, absorbing it in an absorption tower, and then allowing the lower liquid to enter a light component fractionation tower for azeotropic distillation of water, acetic acid, and acrylic acid using toluene as the azeotropic agent. Finally, relatively pure acrylic acid is separated by rectification. This method requires the use of toluene as a solvent, consumes a large amount of steam during water removal, resulting in high energy consumption and increased production costs. Furthermore, it generates a large amount of acidic wastewater during operation, increasing environmental costs.

[0013] Chinese patent CN102775295B discloses a method for purifying acrylic acid. This method includes a two-tower process: an absorption tower and a purification tower. By coupling the cooling, absorption, and purification processes of acrylic acid, a device consisting of two towers is used to complete the recovery and purification of acrylic acid. Simultaneously, water is recycled as both the absorbent and coolant, eliminating the use of other solvents (extractants, azeotropic agents) and avoiding solvent pollution. This method has a relatively simple process, reducing equipment investment and operating costs. However, because this method uses an aqueous acetic acid solution from the top of the absorption tower as the absorbent, the acrylic acid content in the exhaust gas at the top of the tower is relatively high (approximately 0.3 wt%), increasing propylene consumption and thus significantly increasing production costs.

[0014] Chinese patent CN109232232A discloses a method for refining acrylic acid, including steps such as high-concentration gas quenching absorption, low-concentration gas reabsorption, and purification of acrylic acid process gas. This method employs two absorption steps and utilizes extraction and stripping processes to treat and recover subsequent acidic wastewater. While this method recovers some acrylic acid and reduces overall loss, the simultaneous use of high-concentration and low-concentration absorption towers in its absorption process creates a relatively complex system, increasing equipment investment. Furthermore, the introduction of demineralized water for washing, while reducing losses in the top tail gas, indirectly increases wastewater discharge, raises treatment costs, and is detrimental to environmental protection requirements.

[0015] Therefore, there is a great need to develop a new method and system for refining acrylic acid, which has significant practical and economic value due to its simple overall process, low equipment investment, low energy consumption, and low auxiliary material consumption, and is suitable for large-scale industrial production. Summary of the Invention

[0016] To address the above problems, a first aspect of the present invention provides a method for refining acrylic acid, comprising the following steps:

[0017] a) An acrylic acid process gas, optionally from the oxidation reactor, is countercurrently contacted with a coolant from the top of the purification tower (C2) and a bottom stream from the absorption tower (C1) in the lower part of the absorption tower (C1) to form a first coolant and a first gas phase.

[0018] The first coolant enters the bottom stream of the absorption tower (C1), and the first gas phase comes into countercurrent contact with the raffinate phase from the extraction tower (C3) to form a second coolant and a second gas phase.

[0019] The second coolant enters the bottom stream of the absorption tower (C1), and the second gas phase comes into countercurrent contact with the spray liquid at the top of the absorption tower (C1) to form a third coolant and a third gas phase;

[0020] b) A portion of the third coolant is introduced into the top of the absorption tower (C1) as the top spray liquid, and another portion is introduced into the lower part of the extraction tower (C3) for extraction and separation to form an extract phase and a raffinate phase, wherein the raffinate phase is returned from the top of the extraction tower (C3) to the upper, middle or lower part of the absorption tower (C1).

[0021] c) The extract phase from step b) is introduced from the bottom of the extraction column (C3) into the upper, middle or lower part of the solvent recovery column (C4) for solvent recovery;

[0022] d) Introduce the bottom stream of the absorption tower (C1) from step a) into the upper or middle section of the purification tower (C2) for purification, so as to obtain refined acrylic acid in the side stream of the purification tower (C2) and obtain heavy components in the bottom of the purification tower (C2); and

[0023] e) Optionally, the heavy components in the bottom of the purification tower (C2) in step d) are introduced into the thin-film evaporator (C5) for secondary evaporation, and then introduced from the lower part of the thin-film evaporator (C5) into the middle part of the heavy component decomposition unit (C6) for decomposition treatment.

[0024] In a preferred embodiment, step a) further includes recycling or venting the third gas phase through multiple channels;

[0025] Preferably, the multi-path recycling or venting includes introducing the third gas phase into the upstream reactor; and / or introducing the third gas phase into the waste gas treatment unit; and / or introducing the third gas phase into the lower part of the solvent recovery tower (C4) as a desorption gas;

[0026] More preferably, the multi-path recycling or venting includes dividing the third gas phase into three paths: the first path is introduced into the upstream reactor as circulating tail gas to participate in the proportioning, the second path is introduced into the waste gas treatment unit for treatment, and the third path is introduced into the lower part of the solvent recovery tower (C4) as gas for desorption.

[0027] In a preferred embodiment, step b) further includes introducing another portion of the third coolant into the middle of the absorption tower (C1) for use as a spray liquid in the tower.

[0028] In a preferred embodiment, step c) further includes:

[0029] The desorbed gas phase obtained during the solvent recovery process is introduced from the top of the solvent recovery tower (C4) into the bottom, lower, or middle section of the absorption tower (C1); and / or

[0030] The desorbed extractant obtained during the solvent recovery process is cooled and then introduced into the upper part of the extraction tower (C3).

[0031] In a preferred embodiment, the solvent recovery in step c) includes heating the extract phase from step b) to allow it to come into full contact with and mix with the desorption gas introduced into the solvent recovery tower (C4);

[0032] Preferably, the gas introduced into the solvent recovery tower (C4) for desorption is from the third gas phase or an external gas in step a) of claim 1, wherein the external gas is optionally selected from air and / or nitrogen.

[0033] In a preferred embodiment, step d) further includes introducing part or all of the light component solution obtained after condensing the vapor phase at the top of the purification tower (C2) into the bottom of the absorption tower (C1).

[0034] In a preferred embodiment, step e) further includes introducing some or all of the acrylic acid-containing light component generated in the thin-film evaporator (C5) from the top of the thin-film evaporator (C5) into the lower part of the purification column (C2); and

[0035] Optionally, step e) further includes introducing some or all of the acrylic acid-containing light component generated in the recombination cleavage unit (C6) from the top of the recombination cleavage unit (C6) into the lower part of the absorption tower (C1).

[0036] In a preferred embodiment, the temperature of the acrylic acid process gas is 160°C-250°C; and / or

[0037] The concentration of acrylic acid in the third coolant is 1-10 wt%, preferably 1-8 wt%, more preferably 2-6 wt%; and / or

[0038] The content of acrylic acid in the third gas phase is no more than 0.1 wt%, preferably no more than 0.08 wt%, more preferably no more than 0.06 wt%, and most preferably no more than 0.01 wt%; and / or

[0039] The concentration of acrylic acid in the bottom stream of the absorption tower (C1) is 75-90 wt%; and / or

[0040] The third gas phase temperature is 50-70℃, preferably 53-68℃, more preferably 55-65℃; and / or

[0041] The absorber (C1) has a bottom temperature of 75-90°C, preferably 78-88°C, more preferably 80-85°C, a top temperature of 55-70°C, preferably 58-68°C, more preferably 60-65°C, a bottom pressure of 115-135 kPa, preferably 120-130 kPa, more preferably 124-128 kPa, and a top pressure of 100-130 kPa, preferably 110-125 kPa, more preferably 115-124 kPa; and / or

[0042] The purification column (C2) has a reboiler temperature of 75-90°C, preferably 78-88°C, more preferably 80-85°C, a top temperature of 55-70°C, preferably 58-68°C, more preferably 60-65°C, a reboiler pressure of 10-20 kPa, preferably 12-18 kPa, more preferably 15-16 kPa, and a top pressure of 1-10 kPa, preferably 2-8 kPa, more preferably 4-5 kPa; and / or

[0043] The extraction column (C3) has a reboiler temperature of 10-50°C, preferably 15-40°C, more preferably 20-35°C, a top temperature of 10-50°C, preferably 15-40°C, more preferably 20-35°C, a reboiler pressure of 250-350 kPa, preferably 280-320 kPa, more preferably 300-310 kPa, and a top pressure of 150-250 kPa, preferably 180-220 kPa, more preferably 200-210 kPa; and / or

[0044] The solvent recovery tower (C4) has a bottom temperature of 140-250°C, preferably 150-200°C, more preferably 150-180°C, a top temperature of 70-100°C, preferably 75-95°C, more preferably 80-90°C, and a bottom pressure of 110-150 kPa, preferably 120-145 kPa, more preferably 130-140 kPa; and / or

[0045] The reboiler temperature of the thin-film evaporator (C5) is 90-130℃, preferably 100-120℃, more preferably 105-115℃; the top temperature is 70-110℃, preferably 80-100℃, more preferably 85-95℃; the reboiler pressure is 10-30KPa, preferably 15-25KPa, more preferably 20-22KPa; and the top pressure is 10-30KPa, preferably 15-25KPa, more preferably 20-22KPa; and / or

[0046] The recombinant splitter (C6) has a reboiler temperature of 160-200℃, preferably 170-195℃, more preferably 188-190℃, a top temperature of 160-200℃, preferably 170-195℃, more preferably 180-190℃, a reboiler pressure of 80-110KPa, preferably 90-100KPa, more preferably 98-99KPa, and a top pressure of 80-110KPa, preferably 90-100KPa, more preferably 98-99KPa.

[0047] In a preferred embodiment, the volume ratio of the portion of the third coolant introduced to the top of the absorption tower (C1) as the top spray liquid to the portion introduced to the bottom of the extraction tower (C3) for extraction and separation is 1:(0.01-0.1); and / or.

[0048] The extractant used in step b) is selected from the group consisting of: cyclohexane, n-heptane, butyl acetate, isobutyl acetate, dimethyl carbonate, dibutyl ether, benzyl methacrylate, hexanediol diacrylate, anisole, diisooctyl phosphate, tributyl phosphate, trioctyl tert-amine, dimethyl terephthalate, diethyl terephthalate, dimethyl phthalate, diethyl phthalate, dimethyl isophthalate and diethyl isophthalate, isooctyl acrylate, butyl acrylate, and butanol.

[0049] In a preferred embodiment, polymerization inhibitor air and / or polymerization inhibitor are added to the absorption tower (C1) and / or purification tower (C2) and / or extraction tower (C3) and / or solvent recovery tower (C4).

[0050] In a preferred embodiment, the method does not use an azeotropic agent and / or does not require additional water.

[0051] A second aspect of the invention provides a system for refining acrylic acid, comprising:

[0052] -Absorption tower (C1),

[0053] -Purification tower (C2),

[0054] -Extraction tower (C3),

[0055] - Solvent recovery tower (C4),

[0056] -The first pipeline (101) connected to the lower part of the absorption tower (C1),

[0057] -A second pipeline (102) connecting the bottom of the absorption tower (C1) to the upper or middle part of the purification tower (C2),

[0058] -A fifth pipeline (105) connecting the lower part of the absorption tower (C1) and the extraction tower (C3),

[0059] -A sixth pipeline (106) connecting the upper, middle, or lower part of the absorption tower (C1) to the top of the extraction tower (C3), and

[0060] - A seventh pipeline (107) connecting the bottom of the extraction tower (C3) to the upper, middle or lower part of the solvent recovery tower (C4).

[0061] In a preferred embodiment, the system for refining acrylic acid further includes:

[0062] - A third pipeline (103) connecting the lower part of the absorption tower (C1) to the top of the purification tower (C2); and / or

[0063] - A fourth pipeline (104) connecting the bottom, lower or middle section of the absorber (C1) to the top of the solvent recovery tower (C4); and / or

[0064] - An eighth pipeline (108) connecting the upper part of the extraction tower (C3) to the bottom of the solvent recovery tower (C4); and / or

[0065] - A ninth pipeline (109) connected to the solvent recovery tower (C4) or a ninth pipeline (109) connecting the top of the absorption tower (C1) to the bottom of the solvent recovery tower (C4); and / or

[0066] - The tenth pipeline (110) connected to the top of the absorption tower (C1); and / or

[0067] - The eleventh pipeline (111) is connected to the top of the absorption tower (C1).

[0068] In a preferred embodiment, the system for refining acrylic acid further includes:

[0069] - Thin-film evaporator (C5),

[0070] -Recombination splitter (C6),

[0071] - The twelfth pipeline (112) connecting the bottom of the purification tower (C2) to the upper part of the thin-film evaporator (C5),

[0072] -The fourteenth pipeline (114) connecting the lower part of the thin-film evaporator (C5) to the middle part of the recombination and splitting device (C6), and

[0073] - The sixteenth pipeline (116) connected to the retort of the column reactor (C6).

[0074] In a preferred embodiment, the system for refining acrylic acid further includes:

[0075] - A thirteenth pipeline (113) connecting the lower part of the purification column (C2) to the top of the thin-film evaporator (C5); and / or

[0076] - The fifteenth pipeline (115) connects the lower part of the absorption tower (C1) to the top of the recombination and splitting device (C6).

[0077] Compared with the prior art, the present invention has the following advantages:

[0078] 1) In the method and system for refining acrylic acid of the present invention, the rapid cooling process, absorption process, and purification process of the acrylic acid gas-phase mixture are deeply coupled. The rapid cooling, absorption, and separation processes of acrylic acid are completed through an absorption tower and a purification tower. An extractant is introduced, and an auxiliary extraction tower is used to reduce the concentration of the absorption spray, thereby enhancing the absorption effect and reducing the loss of acrylic acid in the tail gas. The overall process flow is simple, the system equipment is few, and the equipment investment and operating costs are significantly reduced.

[0079] 2) This invention does not introduce any process water; the water generated by the reaction in the system is recycled, and no wastewater is produced. Since no azeotropic agents are used, the subsequent purification and separation process is very simple. It has the advantages of low energy consumption and low environmental costs, making it a green and clean production process that meets the needs of certain high-end products. It has significant practicality and economic benefits and is easy to scale up for industrial production.

[0080] 3) This invention employs an extraction process to reduce the acrylic acid content in the spray absorption liquid, thereby increasing the absorption effect and reducing the loss of acrylic acid in the exhaust gas. The overall extraction process is conducted under mild conditions, the extractant is easy to recover and reuse, it is easy to operate, and the overall energy and material consumption is low, resulting in significant effects and a substantial reduction in production unit costs.

[0081] 4) This invention is simple and easy to implement, with mild process conditions and simple maintenance and operation. It is safe and reliable in operation and suitable for large-scale industrial production. Attached Figure Description

[0082] Figure 1 This is a schematic diagram of the overall process for refining acrylic acid in Embodiment 1 of the present invention.

[0083] Figure 2 This is a schematic diagram of the absorption tower in Embodiment 1 of the present invention. Detailed Implementation Plan

[0084] This disclosure can be more readily understood by referring to the following detailed description of preferred embodiments of the invention and the included examples.

[0085] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of any conflict, the definitions in this specification shall prevail.

[0086] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion.

[0087] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0088] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0089] Furthermore, the indefinite articles “a” and “an” preceding an element or component in this document do not impose any requirement on the quantity (i.e., number of occurrences) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.

[0090] Methods for refining acrylic acid

[0091] The first aspect of the present invention provides a method for refining acrylic acid, comprising the following steps:

[0092] a) An acrylic acid process gas, optionally from the oxidation reactor, is countercurrently contacted with a coolant from the top of the purification tower (C2) and a bottom stream from the absorption tower (C1) in the lower part of the absorption tower (C1) to form a first coolant and a first gas phase.

[0093] The first coolant enters the bottom stream of the absorption tower (C1), and the first gas phase comes into countercurrent contact with the raffinate phase from the extraction tower (C3) to form a second coolant and a second gas phase.

[0094] The second coolant enters the bottom stream of the absorption tower (C1), and the second gas phase comes into countercurrent contact with the spray liquid at the top of the absorption tower (C1) to form a third coolant and a third gas phase;

[0095] b) A portion of the third coolant is introduced into the top of the absorption tower (C1) as the top spray liquid, and another portion is introduced into the lower part of the extraction tower (C3) for extraction and separation to form an extract phase and a raffinate phase, wherein the raffinate phase is returned from the top of the extraction tower (C3) to the upper, middle or lower part of the absorption tower (C1).

[0096] c) The extract phase from step b) is introduced from the bottom of the extraction column (C3) into the upper, middle or lower part of the solvent recovery column (C4) for solvent recovery;

[0097] d) Introduce the bottom stream of the absorption tower (C1) from step a) into the upper or middle section of the purification tower (C2) for purification, so as to obtain refined acrylic acid in the side stream of the purification tower (C2) and obtain heavy components in the bottom of the purification tower (C2); and

[0098] e) Optionally, the heavy components in the bottom of the purification tower (C2) in step d) are introduced into the thin-film evaporator (C5) for secondary evaporation, and then introduced from the lower part of the thin-film evaporator (C5) into the middle part of the heavy component decomposition unit (C6) for decomposition treatment.

[0099] In the method of this invention, the enrichment of acrylic acid process gas in the absorption tower (C1) is not a simple absorption process, nor is it a traditional gas absorption process. Instead, it is divided into a quenching process (achieved through the countercurrent contact) and an absorption process. The quenching process involves circulating a large amount of low-temperature liquid phase (approximately 70-90°C) with a gas phase at approximately 160°C-250°C in the tower bottom, lowering the gas phase temperature. This causes a large amount of acrylic acid, acetic acid, and other organic substances to rapidly condense and precipitate directly, significantly reducing the gas flow rate and simplifying the absorption process. A small amount of uncondensed acrylic acid and acetic acid gaseous phase continues to rise with the inert gas and comes into countercurrent contact with the spray liquid. The acrylic acid is then fully absorbed step-by-step using the principle of partial pressure difference and phase equilibrium. This invention utilizes the pressure difference between acrylic acid and other gases in the gas-liquid phase of the process gas. Through the principle of gas-liquid phase equilibrium, acrylic acid is separated from the reaction product gas. The reactant mixture containing gaseous acrylic acid is fully absorbed through gas-liquid countercurrent, maximizing the absorption of acrylic acid gas in the mixture and dissolving it in the liquid to form a solution. The undissolved components remain in the gas phase.

[0100] In a preferred embodiment, step a) further includes recycling or venting the third gas phase through multiple channels;

[0101] Preferably, the multi-path recycling or venting includes introducing the third gas phase into the upstream reactor; and / or introducing the third gas phase into the waste gas treatment unit; and / or introducing the third gas phase into the lower part of the solvent recovery tower (C4) as a desorption gas;

[0102] More preferably, the multi-path recycling or venting includes dividing the third gas phase into three paths: the first path is introduced into the upstream reactor as circulating tail gas to participate in the proportioning, the second path is introduced into the waste gas treatment unit for treatment, and the third path is introduced into the lower part of the solvent recovery tower (C4) as gas for desorption.

[0103] In a preferred embodiment, step b) further includes introducing another portion of the third coolant into the middle of the absorber (C1) for use as a spray liquid in the tower. By further configuring the spray liquid in the tower, the cooling effect on the gas phase can be further enhanced.

[0104] In a preferred embodiment, step c) further includes:

[0105] The desorbed gas phase obtained during the solvent recovery process is introduced from the top of the solvent recovery tower (C4) into the bottom, lower, or middle section of the absorption tower (C1); and / or

[0106] The desorbed extractant obtained during the solvent recovery process is cooled and then introduced into the upper part of the extraction tower (C3).

[0107] In a preferred embodiment, the solvent recovery in step c) includes heating the extract phase from step b) to allow it to come into full contact with and mix with the desorption gas introduced into the solvent recovery tower (C4);

[0108] Preferably, the gas introduced into the solvent recovery tower (C4) for desorption is from the third gas phase or an external gas in step a) of claim 1, wherein the external gas is optionally selected from air and / or nitrogen.

[0109] The extraction phase is circulated and heated with the introduced desorption gas to ensure full contact and mixing between the gas and liquid phases. The acrylic acid is released from the liquid phase through high temperature and is quickly carried away by the circulating gas phase, thus achieving solvent regeneration.

[0110] In a preferred embodiment, step d) further includes introducing part or all of the light component solution (containing acrylic acid, acetic acid, water, etc.) obtained after condensing the vapor phase at the top of the purification tower (C2) into the bottom of the absorption tower (C1).

[0111] In a preferred embodiment, step e) further includes introducing some or all of the acrylic acid-containing light component generated in the thin-film evaporator (C5) from the top of the thin-film evaporator (C5) into the lower part of the purification column (C2); and

[0112] Optionally, step e) further includes introducing some or all of the acrylic acid-containing light component generated in the recombination cleavage unit (C6) from the top of the recombination cleavage unit (C6) into the lower part of the absorption tower (C1).

[0113] In this invention, the recombination decomposer (C6) is used to decompose the dimer. Its function is to heat and decompose the acrylic acid dimer at high temperature to further recover acrylic acid products and reduce material consumption.

[0114] In a preferred embodiment, the temperature of the acrylic acid process gas is 160°C-250°C; and / or

[0115] The concentration of acrylic acid in the third coolant is 1-10 wt%, preferably 1-8 wt%, more preferably 2-6 wt%, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any concentration between these concentrations; and / or.

[0116] The acrylic acid content in the third gas phase is no more than 0.1 wt%, preferably no more than 0.08 wt%, more preferably no more than 0.06 wt%, and most preferably no more than 0.01 wt%, for example, no more than 0.01 wt%, no more than 0.02 wt%, no more than 0.03 wt%, no more than 0.04 wt%, no more than 0.05 wt%, no more than 0.06 wt%, no more than 0.07 wt%, no more than 0.08 wt%, no more than 0.09 wt%, or any content between these values; and / or

[0117] The concentration of acrylic acid in the bottom stream of the absorption tower (C1) is 75-90 wt%; and / or

[0118] The temperature of the third gas phase is 50-70°C, preferably 53-68°C, more preferably 55-65°C; and / or

[0119] The absorber (C1) has a bottom temperature of 75-90°C, preferably 78-88°C, more preferably 80-85°C, a top temperature of 55-70°C, preferably 58-68°C, more preferably 60-65°C, a bottom pressure of 115-135 kPa, preferably 120-130 kPa, more preferably 124-128 kPa, and a top pressure of 100-130 kPa, preferably 110-125 kPa, more preferably 115-124 kPa; and / or

[0120] The purification column (C2) has a reboiler temperature of 75-90°C, preferably 78-88°C, more preferably 80-85°C, a top temperature of 55-70°C, preferably 58-68°C, more preferably 60-65°C, a reboiler pressure of 10-20 kPa, preferably 12-18 kPa, more preferably 15-16 kPa, and a top pressure of 1-10 kPa, preferably 2-8 kPa, more preferably 4-5 kPa; and / or

[0121] The extraction column (C3) has a reboiler temperature of 10-50°C, preferably 15-40°C, more preferably 20-35°C, a top temperature of 10-50°C, preferably 15-40°C, more preferably 20-35°C, a reboiler pressure of 250-350 kPa, preferably 280-320 kPa, more preferably 300-310 kPa, and a top pressure of 150-250 kPa, preferably 180-220 kPa, more preferably 200-210 kPa; and / or

[0122] The solvent recovery tower (C4) has a bottom temperature of 140-250°C, preferably 150-200°C, more preferably 150-180°C, a top temperature of 70-100°C, preferably 75-95°C, more preferably 80-90°C, and a bottom pressure of 110-150 kPa, preferably 120-145 kPa, more preferably 130-140 kPa; and / or

[0123] The reboiler temperature of the thin-film evaporator (C5) is 90-130℃, preferably 100-120℃, more preferably 105-115℃; the top temperature is 70-110℃, preferably 80-100℃, more preferably 85-95℃; the reboiler pressure is 10-30KPa, preferably 15-25KPa, more preferably 20-22KPa; and the top pressure is 10-30KPa, preferably 15-25KPa, more preferably 20-22KPa; and / or

[0124] The recombinant splitter (C6) has a reboiler temperature of 160-200℃, preferably 170-195℃, more preferably 188-190℃, a top temperature of 160-200℃, preferably 170-195℃, more preferably 180-190℃, a reboiler pressure of 80-110KPa, preferably 90-100KPa, more preferably 98-99KPa, and a top pressure of 80-110KPa, preferably 90-100KPa, more preferably 98-99KPa.

[0125] In a preferred embodiment, the volume ratio of the portion of the third coolant introduced to the top of the absorption tower (C1) as the top spray liquid to the portion introduced to the bottom of the extraction tower (C3) for extraction and separation is 1:(0.01-0.1); and / or.

[0126] The extractant used in step b) is selected from the group consisting of: cyclohexane, n-heptane, butyl acetate, isobutyl acetate, dimethyl carbonate, dibutyl ether, benzyl methacrylate, hexanediol diacrylate, anisole, diisooctyl phosphate, tributyl phosphate, trioctyl tert-amine, dimethyl terephthalate, diethyl terephthalate, dimethyl phthalate, diethyl phthalate, dimethyl isophthalate and diethyl isophthalate, isooctyl acrylate, butyl acrylate, and butanol.

[0127] In a more preferred embodiment, the volume ratio of the portion introduced into the top of the absorption tower (C1) as the top spray liquid, the portion introduced into the lower part of the extraction tower (C3) for extraction and separation, and the portion introduced into the middle part of the absorption tower (C1) as the spray liquid in the tower is 1:(0.01-0.1):(0.01-0.1).

[0128] In this invention, in order to increase the absorption effect, the selectivity of the extractant is utilized to extract some or all of the low-concentration spray liquid with acrylic acid and acetic acid into the extract phase, which further reduces the concentration of the spray liquid, increases the mass transfer driving force of absorption, and thus reduces the loss of acrylic acid in the exhaust gas at the top of the tower.

[0129] In the extraction tower of this invention, the spray liquid serves as the dispersed phase, fully contacting and mixing with the extractant. The extracted spray liquid is returned to the upper part of the absorption tower as spray liquid; the extractant phase enters the solvent regeneration tower (desorption tower), where the acrylic acid and extractant are separated by utilizing the difference in relative volatility. The desorbed gaseous acrylic acid is sent to the absorption tower for recovery using the recycled process tail gas as a medium, while the extractant is returned to the extraction tower for reuse.

[0130] In a preferred embodiment, polymerization-inhibiting air and / or polymerization inhibitors are added to the absorption tower (C1) and / or purification tower (C2) and / or extraction tower (C3) and / or solvent recovery tower (C4). The addition of polymerization-inhibiting air and / or polymerization inhibitors prevents acrylic acid self-polymerization in the towers. Preferably, in this invention, polymerization-inhibiting air can be added to the bottom of the acrylic acid purification tower, reboiler, thin-film evaporator, and recombinant decomposition unit; a measured amount of polymerization inhibitor can be added to the top gaseous product and reflux liquid; and a certain amount of reflux liquid, along with a measured amount of polymerization inhibitor pumped by the polymerization inhibitor feed pump, can be sprayed into the top condenser, side-stream condenser, and tail gas condenser to more effectively prevent polymerization in the towers.

[0131] In a preferred embodiment, the polymerization inhibitor may be selected from one or more of the following groups: PZ, HQ, AI-61R, AI-61A, ZJ-701, and MQ.

[0132] In a preferred embodiment, the method does not use an azeotropic agent and / or does not require additional water.

[0133] System for refining acrylic acid

[0134] A second aspect of the invention provides a system for refining acrylic acid, comprising:

[0135] -Absorption tower (C1),

[0136] -Purification tower (C2),

[0137] -Extraction tower (C3),

[0138] - Solvent recovery tower (C4),

[0139] -The first pipeline (101) connected to the lower part of the absorption tower (C1),

[0140] -A second pipeline (102) connecting the bottom of the absorption tower (C1) to the upper or middle part of the purification tower (C2),

[0141] -A fifth pipeline (105) connecting the lower part of the absorption tower (C1) and the extraction tower (C3),

[0142] -A sixth pipeline (106) connecting the upper, middle, or lower part of the absorption tower (C1) to the top of the extraction tower (C3), and

[0143] - A seventh pipeline (107) connecting the bottom of the extraction tower (C3) to the upper, middle or lower part of the solvent recovery tower (C4).

[0144] In a preferred embodiment, the system for refining acrylic acid further includes:

[0145] - A third pipeline (103) connecting the lower part of the absorption tower (C1) to the top of the purification tower (C2); and / or

[0146] - A fourth pipeline (104) connecting the bottom, lower or middle section of the absorber (C1) to the top of the solvent recovery tower (C4); and / or

[0147] - An eighth pipeline (108) connecting the upper part of the extraction tower (C3) to the bottom of the solvent recovery tower (C4); and / or

[0148] - A ninth pipeline (109) connected to the solvent recovery tower (C4) or a ninth pipeline (109) connecting the top of the absorption tower (C1) to the bottom of the solvent recovery tower (C4); and / or

[0149] - The tenth pipeline (110) connected to the top of the absorption tower (C1); and / or

[0150] - The eleventh pipeline (111) is connected to the top of the absorption tower (C1).

[0151] In a preferred embodiment, the system for refining acrylic acid further includes:

[0152] - Thin-film evaporator (C5),

[0153] -Recombination splitter (C6),

[0154] - The twelfth pipeline (112) connecting the bottom of the purification tower (C2) to the upper part of the thin-film evaporator (C5),

[0155] -The fourteenth pipeline (114) connecting the lower part of the thin-film evaporator (C5) to the middle part of the recombination and splitting device (C6), and

[0156] - The sixteenth pipeline (116) connected to the retort of the column reactor (C6).

[0157] In a preferred embodiment, the system for refining acrylic acid further includes:

[0158] - A thirteenth pipeline (113) connecting the lower part of the purification column (C2) to the top of the thin-film evaporator (C5); and / or

[0159] - The fifteenth pipeline (115) connects the lower part of the absorption tower (C1) to the top of the recombination and splitting device (C6).

[0160] As detailed above, this invention provides an improved method and system for purifying acrylic acid. Through deep coupling of absorption and extraction, and absorption and distillation processes, the water generated in the reaction is recycled to rapidly cool, absorb, and purify the acrylic acid process gas, yielding an acrylic acid product with a purity of over 99.5%. The entire process does not use azeotropic agents or require additional water replenishment, and zero wastewater discharge is achieved through temperature control at the top of the absorption tower.

[0161] The invention will be described in detail through the following embodiments and combined embodiments that are obvious from corresponding dependent and other references:

[0162] Implementation Scheme 1. A method for refining acrylic acid, comprising the following steps:

[0163] a) An acrylic acid process gas, optionally from the oxidation reactor, is countercurrently contacted with a coolant from the top of the purification tower (C2) and a bottom stream from the absorption tower (C1) in the lower part of the absorption tower (C1) to form a first coolant and a first gas phase.

[0164] The first coolant enters the bottom stream of the absorption tower (C1), and the first gas phase comes into countercurrent contact with the raffinate phase from the extraction tower (C3) to form a second coolant and a second gas phase.

[0165] The second coolant enters the bottom stream of the absorption tower (C1), and the second gas phase comes into countercurrent contact with the spray liquid at the top of the absorption tower (C1) to form a third coolant and a third gas phase;

[0166] b) A portion of the third coolant is introduced into the top of the absorption tower (C1) as the top spray liquid, and another portion is introduced into the lower part of the extraction tower (C3) for extraction and separation to form an extract phase and a raffinate phase, wherein the raffinate phase is returned from the top of the extraction tower (C3) to the upper, middle or lower part of the absorption tower (C1).

[0167] c) The extract phase from step b) is introduced from the bottom of the extraction column (C3) into the upper, middle or lower part of the solvent recovery column (C4) for solvent recovery;

[0168] d) Introduce the bottom stream of the absorption tower (C1) from step a) into the upper or middle section of the purification tower (C2) for purification, so as to obtain refined acrylic acid in the side stream of the purification tower (C2) and obtain heavy components in the bottom of the purification tower (C2); and

[0169] e) Optionally, the heavy components in the bottom of the purification tower (C2) in step d) are introduced into the thin-film evaporator (C5) for secondary evaporation, and then introduced from the lower part of the thin-film evaporator (C5) into the middle part of the heavy component decomposition unit (C6) for decomposition treatment.

[0170] 2. The method of embodiment 1, wherein step a) further includes recycling or venting the third gas phase through multiple channels;

[0171] Preferably, the multi-path recycling or venting includes introducing the third gas phase into the upstream reactor; and / or introducing the third gas phase into the waste gas treatment unit; and / or introducing the third gas phase into the lower part of the solvent recovery tower (C4) as a desorption gas;

[0172] More preferably, the multi-path recycling or venting includes dividing the third gas phase into three paths: the first path is introduced into the upstream reactor as circulating tail gas to participate in the proportioning, the second path is introduced into the waste gas treatment unit for treatment, and the third path is introduced into the lower part of the solvent recovery tower (C4) as gas for desorption.

[0173] 3. The method of embodiment 1 or 2, wherein step b) further includes introducing another portion of the third coolant into the middle of the absorption tower (C1) for use as a spray liquid in the tower.

[0174] 4. The method of embodiment 1 or 2, wherein step c) further includes:

[0175] The desorbed gas phase obtained during the solvent recovery process is introduced from the top of the solvent recovery tower (C4) into the bottom, lower, or middle section of the absorption tower (C1); and / or

[0176] The desorbed extractant obtained during the solvent recovery process is cooled and then introduced into the upper part of the extraction tower (C3).

[0177] 5. The method of embodiment 1 or 2, wherein the solvent recovery in step c) includes, under heating, fully contacting and mixing the extract phase in step b) with the desorption gas introduced into the solvent recovery tower (C4);

[0178] Preferably, the gas introduced into the solvent recovery tower (C4) for desorption is from the third gas phase or an external gas in step a) of Embodiment 1, wherein the external gas is optionally selected from air and / or nitrogen.

[0179] 6. The method of embodiment 1 or 2, wherein step d) further includes introducing part or all of the light component solution obtained after condensing the vapor phase at the top of the purification tower (C2) into the bottom of the absorption tower (C1).

[0180] 7. The method of embodiment 1 or 2, wherein step e) further includes introducing some or all of the acrylic acid-containing light component generated in the thin-film evaporator (C5) from the top of the thin-film evaporator (C5) into the lower part of the purification column (C2); and

[0181] Optionally, step e) further includes introducing some or all of the acrylic acid-containing light component generated in the recombination cleavage unit (C6) from the top of the recombination cleavage unit (C6) into the lower part of the absorption tower (C1).

[0182] 8. The method of embodiment 1 or 2, wherein the temperature of the acrylic acid process gas is 160°C-250°C; and / or

[0183] The concentration of acrylic acid in the third coolant is 1-10 wt%, preferably 1-8 wt%, more preferably 2-6 wt%; and / or

[0184] The content of acrylic acid in the third gas phase is no more than 0.1 wt%, preferably no more than 0.08 wt%, more preferably no more than 0.06 wt%, and most preferably no more than 0.01 wt%; and / or

[0185] The concentration of acrylic acid in the bottom stream of the absorption tower (C1) is 75-90 wt%; and / or

[0186] The temperature of the third gas phase is 50-70°C, preferably 53-68°C, more preferably 55-65°C; and / or

[0187] The absorber (C1) has a bottom temperature of 75-90°C, preferably 78-88°C, more preferably 80-85°C, a top temperature of 55-70°C, preferably 58-68°C, more preferably 60-65°C, a bottom pressure of 115-135 kPa, preferably 120-130 kPa, more preferably 124-128 kPa, and a top pressure of 100-130 kPa, preferably 110-125 kPa, more preferably 115-124 kPa; and / or

[0188] The purification column (C2) has a reboiler temperature of 75-90°C, preferably 78-88°C, more preferably 80-85°C, a top temperature of 55-70°C, preferably 58-68°C, more preferably 60-65°C, a reboiler pressure of 10-20 kPa, preferably 12-18 kPa, more preferably 15-16 kPa, and a top pressure of 1-10 kPa, preferably 2-8 kPa, more preferably 4-5 kPa; and / or

[0189] The extraction column (C3) has a reboiler temperature of 10-50°C, preferably 15-40°C, more preferably 20-35°C, a top temperature of 10-50°C, preferably 15-40°C, more preferably 20-35°C, a reboiler pressure of 250-350 kPa, preferably 280-320 kPa, more preferably 300-310 kPa, and a top pressure of 150-250 kPa, preferably 180-220 kPa, more preferably 200-210 kPa; and / or

[0190] The solvent recovery tower (C4) has a bottom temperature of 140-250°C, preferably 150-200°C, more preferably 150-180°C, a top temperature of 70-100°C, preferably 75-95°C, more preferably 80-90°C, a bottom pressure of 110-150 kPa, preferably 120-145 kPa, more preferably 130-140 kPa, and a top pressure of 110-150 kPa, preferably 120-145 kPa, more preferably 130-140 kPa; and / or

[0191] The reboiler temperature of the thin-film evaporator (C5) is 90-130℃, preferably 100-120℃, more preferably 105-115℃; the top temperature is 70-110℃, preferably 80-100℃, more preferably 85-95℃; the reboiler pressure is 10-30KPa, preferably 15-25KPa, more preferably 20-22KPa; and the top pressure is 10-30KPa, preferably 15-25KPa, more preferably 20-22KPa; and / or

[0192] The recombinant splitter (C6) has a reboiler temperature of 160-200℃, preferably 170-195℃, more preferably 188-190℃, a top temperature of 160-200℃, preferably 170-195℃, more preferably 180-190℃, a reboiler pressure of 80-110KPa, preferably 90-100KPa, more preferably 98-99KPa, and a top pressure of 80-110KPa, preferably 90-100KPa, more preferably 98-99KPa.

[0193] 9. The method of embodiment 1 or 2, wherein the volume ratio of the portion of the third coolant introduced to the top of the absorption tower (C1) as the top spray liquid to the portion introduced to the lower part of the extraction tower (C3) for extraction and separation is 1:(0.01-0.1); and / or.

[0194] The extractant used in step b) is selected from the group consisting of: cyclohexane, n-heptane, butyl acetate, isobutyl acetate, dimethyl carbonate, dibutyl ether, benzyl methacrylate, hexanediol diacrylate, anisole, diisooctyl phosphate, tributyl phosphate, trioctyl tert-amine, dimethyl terephthalate, diethyl terephthalate, dimethyl phthalate, diethyl phthalate, dimethyl isophthalate and diethyl isophthalate, isooctyl acrylate, butyl acrylate, and butanol.

[0195] 10. The method of embodiment 1 or 2, wherein antipolymerization air and / or antipolymerization agent are added to the absorption tower (C1) and / or purification tower (C2) and / or extraction tower (C3) and / or solvent recovery tower (C4).

[0196] 11. The method of embodiment 1 or 2, which does not use an azeotropic agent and / or does not require additional water.

[0197] 12. A system for refining acrylic acid, comprising:

[0198] -Absorption tower (C1),

[0199] -Purification tower (C2),

[0200] -Extraction tower (C3),

[0201] - Solvent recovery tower (C4),

[0202] -The first pipeline (101) connected to the lower part of the absorption tower (C1),

[0203] -A second pipeline (102) connecting the bottom of the absorption tower (C1) to the upper or middle part of the purification tower (C2),

[0204] -A fifth pipeline (105) connecting the lower part of the absorption tower (C1) and the extraction tower (C3),

[0205] -A sixth pipeline (106) connecting the middle or lower part of the absorption tower (C1) to the top of the extraction tower (C3), and

[0206] - A seventh pipeline (107) connecting the bottom of the extraction tower (C3) to the upper, middle or lower part of the solvent recovery tower (C4).

[0207] 13. The system for refining acrylic acid according to embodiment 12, further comprising:

[0208] - A third pipeline (103) connecting the lower part of the absorption tower (C1) to the top of the purification tower (C2); and / or

[0209] - A fourth pipeline (104) connecting the bottom, lower or middle section of the absorber (C1) to the top of the solvent recovery tower (C4); and / or

[0210] - An eighth pipeline (108) connecting the upper part of the extraction tower (C3) to the bottom of the solvent recovery tower (C4); and / or

[0211] - A ninth pipeline (109) connected to the solvent recovery tower (C4) or a ninth pipeline (109) connecting the top of the absorption tower (C1) to the bottom of the solvent recovery tower (C4); and / or

[0212] - The tenth pipeline (110) connected to the top of the absorption tower (C1); and / or

[0213] - The eleventh pipeline (111) is connected to the top of the absorption tower (C1).

[0214] 14. The system for refining acrylic acid according to embodiment 12 or 13, further comprising:

[0215] - Thin-film evaporator (C5),

[0216] -Recombination splitter (C6),

[0217] - The twelfth pipeline (112) connecting the bottom of the purification tower (C2) to the upper part of the thin-film evaporator (C5),

[0218] -The fourteenth pipeline (114) connecting the lower part of the thin-film evaporator (C5) to the middle part of the recombination and splitting device (C6), and

[0219] - The sixteenth pipeline (116) connected to the retort of the column reactor (C6).

[0220] 15. The system for refining acrylic acid according to embodiment 14, further comprising:

[0221] - A thirteenth pipeline (113) connecting the lower part of the purification column (C2) to the top of the thin-film evaporator (C5); and / or

[0222] - The fifteenth pipeline (115) connects the lower part of the absorption tower (C1) to the top of the recombination and splitting device (C6).

[0223] Preferred embodiment

[0224] The preferred embodiments of this application will be further described in detail below with reference to the accompanying drawings. The following description is exemplary and not intended to limit the application. Any other similar situations also fall within the protection scope of this application.

[0225] Example 1

[0226] A method for refining acrylic acid includes the following steps:

[0227] a) Rapid cooling absorption step

[0228] Acrylic acid process gas 11 at 220°C from the upstream oxidation reactor is contacted countercurrently with the coolant recovered from the top of purification tower C2 in the lower part of absorption tower C1 for rapid cooling absorption, thereby cooling and absorbing acrylic acid, part of acetic acid and water in the process gas to form a first coolant and an uncooled first gas phase.

[0229] The uncooled first gas phase rises in the absorption tower C1, and during the upward movement, it comes into countercurrent contact with the raffinate phase from the extraction tower C3 to form a second coolant and an uncooled second gas phase;

[0230] The second coolant enters the bottom stream of the absorption tower C1. The second gas phase first comes into countercurrent contact with the spray liquid in the absorption tower C1, and then comes into countercurrent contact with the spray liquid at the top of the absorption tower C1 to form a third coolant and a third gas phase (the temperature of the third gas phase is 65°C).

[0231] The third coolant is divided into three streams: most of it is pumped back to the top of the absorption tower C1 as top spray liquid, a small portion is sent to the middle of the absorption tower C1 as middle spray liquid, and an even smaller portion is sent to the extraction tower C3 for separation and purification. The volume ratio of the portion pumped back to the top of the absorption tower C1, the portion sent to the middle of the absorption tower C1, and the portion sent to the extraction tower C3 is 20:1:0.5.

[0232] The third gas phase is divided into three paths: the first path is introduced into the upstream reactor as circulating tail gas 12 to participate in the proportioning; the second path 13 is introduced into the waste gas treatment unit for treatment (the acrylic acid content in this part is 0.1-0.15 wt%); and the third path 14 is introduced into the lower part of the solvent recovery tower C4 as gas for desorption.

[0233] The polymerization inhibitor hydroquinone (HQ) is added to the absorption tower C1;

[0234] The purification tower C2 contains hydroquinone (HQ) as a polymerization inhibitor and polymerization-inhibiting air.

[0235] b) Extraction steps

[0236] Extraction is performed using tributyl phosphate as the extractant, with a large amount of acrylic acid and acetic acid entering the extract phase. A raffinate containing a very low concentration of acrylic acid is obtained at the top of extraction column C3. This raffinate is returned from the top of extraction column C3 to the middle of absorption column C1 as an absorbent, to be countercurrently contacted with the second gas phase.

[0237] c) Solvent recovery steps

[0238] The extract phase from step b) is introduced from the bottom of extraction column C3 into the upper part of solvent recovery column C4. The extract phase is heated thoroughly to desorb the acrylic acid gas phase. The desorbed gas phase 15 is returned from the top of solvent recovery column C4 to the lower part of absorption column C1 to recover the acrylic acid gas phase therein. The desorbed extractant is then returned from the bottom of solvent recovery column C4 to extraction column C3 for recycling.

[0239] d) Purification steps

[0240] The bottom stream from step a) (a mixed solution containing acrylic acid, acetic acid, and water, wherein the acrylic acid content is 87.5 wt%) is introduced from the bottom of the absorption tower C1 into the upper part of the purification tower C2 for purification. The light and heavy components are separated. The light component solution containing acrylic acid and acetic acid obtained after vapor condensation at the top of the purification tower C2 is entirely returned to the bottom of the absorption tower C1 as the absorbent for the absorption tower.

[0241] The gas phase extracted from the side stream of purification tower C2 is condensed to obtain acrylic acid product 16 with a purity of 99.5%.

[0242] The bottom of purification column C2 yielded heavy components containing acrylic acid, acrylic acid dimer, etc.

[0243] e) Recombinant component processing steps

[0244] The heavy components from the bottom of purification tower C2 in step d) are introduced into thin-film evaporator C5 for secondary evaporation, and then introduced from the bottom of thin-film evaporator C5 into the middle of recombinant cell cracking unit C6 for cracking treatment. Specifically, a portion of the light components containing acrylic acid generated in thin-film evaporator C5 is introduced from the top of thin-film evaporator C5 into the bottom of purification tower C2, and a portion of the light components containing acrylic acid generated in recombinant cell cracking unit C6 is introduced from the top of recombinant cell cracking unit C6 into the bottom of absorption tower (C1). The remaining heavy components are discharged into the waste liquid treatment unit for treatment.

[0245] System for refining acrylic acid

[0246] A system for refining acrylic acid, used to implement the method for refining acrylic acid as described above. The system for refining acrylic acid comprises the following components:

[0247] -Absorption tower (C1),

[0248] -Purification tower (C2),

[0249] -Extraction tower (C3),

[0250] - Solvent recovery tower (C4),

[0251] - Thin-film evaporator (C5),

[0252] -Recombination splitter (C6),

[0253] -The first pipeline (101) connected to the lower part of the absorption tower (C1),

[0254] -A second pipeline (102) connecting the bottom of the absorption tower (C1) to the upper part of the purification tower (C2),

[0255] -A third pipeline (103) connecting the lower part of the absorption tower (C1) to the top of the purification tower (C2),

[0256] -A fourth pipeline (104) connecting the lower part of the absorption tower (C1) to the top of the solvent recovery tower (C4),

[0257] -A fifth pipeline (105) connecting the upper part of the absorption tower (C1) to the lower part of the extraction tower (C3),

[0258] -A sixth pipeline (106) connecting the middle of the absorption tower (C1) to the top of the extraction tower (C3),

[0259] -A seventh pipeline (107) connecting the bottom of the extraction tower (C3) to the upper part of the solvent recovery tower (C4),

[0260] - An eighth pipeline (108) connecting the upper part of the extraction tower (C3) to the bottom of the solvent recovery tower (C4),

[0261] - A ninth pipeline (109) connecting the top of the absorption tower (C1) to the bottom of the solvent recovery tower (C4),

[0262] - The tenth pipeline (110) connected to the top of the absorption tower (C1),

[0263] - The eleventh pipeline (111) connected to the top of the absorption tower (C1),

[0264] - The twelfth pipeline (112) connecting the bottom of the purification tower (C2) to the upper part of the thin-film evaporator (C5),

[0265] -The thirteenth pipeline (113) connecting the lower part of the purification tower (C2) to the top of the thin-film evaporator (C5),

[0266] -The fourteenth pipeline (114) connecting the lower part of the thin-film evaporator (C5) to the middle part of the recombination and splitting device (C6),

[0267] - The fifteenth pipeline (115) connecting the lower part of the absorption tower (C1) to the top of the recombination and splitting device (C6), and

[0268] - The sixteenth pipeline (116) connected to the retort of the column reactor (C6).

[0269] In the preferred embodiment 1 described above, the operating parameters of each tower are shown in Table 1 below:

[0270] Table 1

[0271]

[0272] In the preferred embodiment 1 described above, the operating parameters of each pipeline are shown in Table 2 below:

[0273] Table 2

[0274]

[0275] Test Result Comparison

[0276] The technical advantages and disadvantages of the method for refining acrylic acid of the present invention are compared with those of the prior art method CN102775295B, and the conclusions are shown in Table 3 below:

[0277] Table 3

[0278]

[0279]

[0280] Testing revealed that the method for refining acrylic acid according to this invention improves the absorption process and eliminates the need for azeotropic agents, thus preventing wastewater generation and ultimately yielding an acrylic acid product with a purity of over 99.5%. Compared to traditional processes, both cost reduction and auxiliary material consumption are lower. In particular, compared to the prior art CN102775295B, cost reduction is further reduced by approximately 20%. Therefore, this invention possesses significant advantages, including low energy consumption, environmental friendliness, low cost, strong practicality, and ease of large-scale industrial production, achieving remarkable beneficial effects.

[0281] The foregoing examples are merely illustrative, serving to explain some features of this disclosure. The appended claims are intended to claim the broadest possible scope, and the embodiments presented herein are merely illustrative of selected implementations based on combinations of all possible embodiments. Therefore, the applicant intends that the appended claims are not limited by the selection of examples illustrating the features of this application. As used in the claims, the term "comprising" and its semantic variations logically also include different and varying terms, such as, but not limited to, "basically constitutes" or "consisting of". Numerical ranges are provided where necessary, and these ranges also include sub-ranges within them. Variations within these ranges are also self-evident to those skilled in the art and should not be considered as a donation to the public, and such variations should be interpreted as being covered by the appended claims where possible. Furthermore, advancements in technology may result in alternatives or sub-equivalents not currently considered due to inaccuracies in linguistic expression, and such variations should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for refining acrylic acid, comprising the following steps: a) An acrylic acid process gas, optionally from the oxidation reactor, is countercurrently contacted with a coolant from the top of the purification tower (C2) and a bottom stream from the absorption tower (C1) in the lower part of the absorption tower (C1) to form a first coolant and a first gas phase; The first coolant enters the bottom stream of the absorption tower (C1), and the first gas phase comes into countercurrent contact with the raffinate phase from the extraction tower (C3) to form a second coolant and a second gas phase. The second coolant enters the bottom stream of the absorption tower (C1), and the second gas phase comes into countercurrent contact with the spray liquid at the top of the absorption tower (C1) to form a third coolant and a third gas phase; b) A portion of the third coolant is introduced into the top of the absorption tower (C1) as the top spray liquid, and another portion is introduced into the lower part of the extraction tower (C3) for extraction and separation to form an extract phase and a raffinate phase, wherein the raffinate phase is returned from the top of the extraction tower (C3) to the upper, middle or lower part of the absorption tower (C1). c) The extract phase from step b) is introduced from the bottom of the extraction column (C3) into the upper, middle or lower part of the solvent recovery column (C4) for solvent recovery; d) Introduce the bottom stream of the absorption tower (C1) from step a) into the upper or middle section of the purification tower (C2) for purification, so as to obtain refined acrylic acid in the side stream of the purification tower (C2) and obtain heavy components in the bottom of the purification tower (C2); and e) Optionally, the heavy components in the bottom of the purification tower (C2) in step d) are introduced into the thin film evaporator (C5) for secondary evaporation, and then introduced from the lower part of the thin film evaporator (C5) into the middle part of the heavy component decomposition unit (C6) for decomposition treatment. Step c) further includes: The desorbed extractant obtained during the solvent recovery process is cooled and then introduced into the upper part of the extraction tower (C3); and The solvent recovery in step c) includes heating the extract phase from step b) to allow it to come into full contact with the desorption gas introduced into the solvent recovery tower (C4).

2. The method of claim 1, wherein step a) further includes recycling or venting the third gas phase through multiple channels.

3. The method of claim 2, wherein the multi-channel recycling or venting comprises introducing the third gas phase into the upstream reactor; and / or introducing the third gas phase into the waste gas treatment unit; and / or introducing the third gas phase into the lower part of the solvent recovery tower (C4) as a gas for desorption.

4. The method of claim 2, wherein the multi-path recycling or venting includes dividing the third gas phase into three paths: the first path is introduced into the upstream reactor as circulating tail gas to participate in the proportioning, the second path is introduced into the waste gas treatment unit for treatment, and the third path is introduced into the lower part of the solvent recovery tower (C4) as gas for desorption.

5. The method of any one of claims 1-4, wherein step b) further comprises introducing another portion of the third coolant into the middle of the absorption tower (C1) for use as a spray liquid in the tower.

6. The method of any one of claims 1-4, wherein step c) further comprises: The desorbed gas phase obtained during the solvent recovery process is introduced from the top of the solvent recovery tower (C4) into the bottom, lower or middle part of the absorption tower (C1).

7. The method of any one of claims 1-4, wherein the gas introduced into the solvent recovery tower (C4) for desorption is derived from the third gas phase or an external gas in step a) of claim 1, wherein the external gas is optionally selected from air and / or nitrogen.

8. The method of any one of claims 1-4, wherein step d) further comprises introducing part or all of the light component solution obtained after condensing the vapor phase at the top of the purification tower (C2) into the bottom of the absorption tower (C1).

9. The method of any one of claims 1-4, wherein step e) further comprises introducing some or all of the acrylic acid-containing light component generated in the thin-film evaporator (C5) from the top of the thin-film evaporator (C5) into the lower part of the purification column (C2); and Optionally, step e) further includes introducing some or all of the acrylic acid-containing light component generated in the recombination cleavage unit (C6) from the top of the recombination cleavage unit (C6) into the lower part of the absorption tower (C1).

10. The method of any one of claims 1-4, wherein the temperature of the acrylic acid process gas is 160°C-250°C; and / or The concentration of acrylic acid in the third coolant is 1-10 wt%; and / or The content of acrylic acid in the third gas phase does not exceed 0.1 wt%; and / or The concentration of acrylic acid in the bottom stream of the absorption tower (C1) is 75-90 wt%; and / or The temperature of the third gas phase is 50-70°C; and / or The absorber (C1) has a bottom temperature of 75-90℃, a top temperature of 55-70℃, a bottom pressure of 115-135 kPa, and a top pressure of 100-130 kPa; and / or The purification column (C2) has a reboiler temperature of 75-90℃, a top temperature of 55-70℃, a reboiler pressure of 10-20 kPa, and a top pressure of 1-10 kPa; and / or The extraction column (C3) has a bottom temperature of 10-50℃, a top temperature of 10-50℃, a bottom pressure of 250-350 kPa, and a top pressure of 150-250 kPa; and / or The solvent recovery tower (C4) has a bottom temperature of 140-250℃, a top temperature of 70-100℃, a bottom pressure of 110-150 kPa, and a top pressure of 110-150 kPa; and / or The reboiler temperature of the thin-film evaporator (C5) is 90-130℃, the top temperature is 70-110℃, the reboiler pressure is 10-30 kPa, and the top pressure is 10-30 kPa; and / or The recombinant splitter (C6) has a bottom temperature of 160-200℃, a top temperature of 160-200℃, a bottom pressure of 80-110 KPa, and a top pressure of 80-110 KPa.

11. The method of claim 10, wherein the concentration of acrylic acid in the third coolant is 1-8 wt%.

12. The method of claim 10, wherein the concentration of acrylic acid in the third coolant is 2-6 wt%.

13. The method of claim 10, wherein the content of acrylic acid in the third gas phase does not exceed 0.08 wt%.

14. The method of claim 10, wherein the content of acrylic acid in the third gas phase does not exceed 0.06 wt%.

15. The method of claim 10, wherein the content of acrylic acid in the third gas phase does not exceed 0.01 wt%.

16. The method of claim 10, wherein the temperature of the third gas phase is 53-68°C.

17. The method of claim 10, wherein the temperature of the third gas phase is 55-65°C.

18. The method of claim 10, wherein the bottom temperature of the absorption tower (C1) is 78-88°C.

19. The method of claim 10, wherein the bottom temperature of the absorption tower (C1) is 80-85°C.

20. The method of claim 10, wherein the top temperature of the absorption tower (C1) is 58-68°C.

21. The method of claim 10, wherein the top temperature of the absorption tower (C1) is 60-65°C.

22. The method of claim 10, wherein the pressure at the bottom of the absorption tower (C1) is 120-130 kPa.

23. The method of claim 10, wherein the pressure at the bottom of the absorption tower (C1) is 124-128 kPa.

24. The method of claim 10, wherein the pressure at the top of the absorption tower (C1) is 110-125 kPa.

25. The method of claim 10, wherein the pressure at the top of the absorption tower (C1) is 115-124 kPa.

26. The method of claim 10, wherein the bottom temperature of the purification column (C2) is 78-88°C.

27. The method of claim 10, wherein the bottom temperature of the purification column (C2) is 80-85°C.

28. The method of claim 10, wherein the top temperature of the purification column (C2) is 58-68°C.

29. The method of claim 10, wherein the top temperature of the purification column (C2) is 60-65°C.

30. The method of claim 10, wherein the reboiler pressure of the purification column (C2) is 12-18 kPa.

31. The method of claim 10, wherein the reboiler pressure of the purification column (C2) is 15-16 kPa.

32. The method of claim 10, wherein the pressure at the top of the purification column (C2) is 2-8 kPa.

33. The method of claim 10, wherein the pressure at the top of the purification column (C2) is 4-5 kPa.

34. The method of claim 10, wherein the bottom temperature of the extraction column (C3) is 15-40°C.

35. The method of claim 10, wherein the bottom temperature of the extraction column (C3) is 20-35°C.

36. The method of claim 10, wherein the top temperature of the extraction column (C3) is 15-40°C.

37. The method of claim 10, wherein the top temperature of the extraction column (C3) is 20-35°C.

38. The method of claim 10, wherein the pressure of the bottom of the extraction column (C3) is 280-320 kPa.

39. The method of claim 10, wherein the pressure at the bottom of the extraction column (C3) is 300-310 kPa.

40. The method of claim 10, wherein the top pressure of the extraction column (C3) is 180-220 kPa.

41. The method of claim 10, wherein the top pressure of the extraction column (C3) is 200-210 kPa.

42. The method of claim 10, wherein the bottom temperature of the solvent recovery tower (C4) is 150-200°C.

43. The method of claim 10, wherein the bottom temperature of the solvent recovery tower (C4) is 150-180°C.

44. The method of claim 10, wherein the top temperature of the solvent recovery tower (C4) is 75-95°C.

45. The method of claim 10, wherein the top temperature of the solvent recovery tower (C4) is 80-90°C.

46. ​​The method of claim 10, wherein the reboiler pressure of the solvent recovery tower (C4) is 120-145 kPa.

47. The method of claim 10, wherein the reboiler pressure of the solvent recovery tower (C4) is 130-140 kPa.

48. The method of claim 10, wherein the top pressure of the solvent recovery tower (C4) is 120-145 kPa.

49. The method of claim 10, wherein the top pressure of the solvent recovery tower (C4) is 130-140 kPa.

50. The method of claim 10, wherein the bottom temperature of the thin-film evaporator (C5) is 100-120°C.

51. The method of claim 10, wherein the bottom temperature of the thin-film evaporator (C5) is 105-115°C.

52. The method of claim 10, wherein the top temperature of the thin-film evaporator (C5) is 80-100°C.

53. The method of claim 10, wherein the top temperature of the thin-film evaporator (C5) is 85-95°C.

54. The method of claim 10, wherein the pressure of the bottom of the thin-film evaporator (C5) is 15-25 kPa.

55. The method of claim 10, wherein the pressure of the bottom column of the thin-film evaporator (C5) is 20-22 kPa.

56. The method of claim 10, wherein the top pressure of the thin-film evaporator (C5) is 15-25 kPa.

57. The method of claim 10, wherein the top pressure of the thin-film evaporator (C5) is 20-22 kPa.

58. The method of claim 10, wherein the recombinant splitter (C6) has a reboiler temperature of 170-195°C.

59. The method of claim 10, wherein the recombinant splitter (C6) has a reboiler temperature of 188-190°C.

60. The method of claim 10, wherein the top temperature of the recombination splitter (C6) is 170-195°C.

61. The method of claim 10, wherein the top temperature of the recombination splitter (C6) is 180-190°C.

62. The method of claim 10, wherein the reboiler pressure of the recombination splitter (C6) is 90-100 kPa.

63. The method of claim 10, wherein the reboiler pressure of the recombination splitter (C6) is 98-99 kPa.

64. The method of claim 10, wherein the top pressure of the recombination splitter (C6) is 90-100 kPa.

65. The method of claim 10, wherein the top pressure of the recombination splitter (C6) is 98-99 kPa.

66. The method of any one of claims 1-4, wherein the volume ratio of the portion of the third coolant introduced to the top of the absorption tower (C1) as the top spray liquid to the portion introduced to the lower part of the extraction tower (C3) for extraction and separation is 1:(0.01-0.1); and / or The extractant used in step b) is selected from the group consisting of: cyclohexane, n-heptane, butyl acetate, isobutyl acetate, dimethyl carbonate, dibutyl ether, benzyl methacrylate, hexanediol diacrylate, anisole, diisooctyl phosphate, tributyl phosphate, trioctyl tert-amine, dimethyl terephthalate, diethyl terephthalate, dimethyl phthalate, diethyl phthalate, dimethyl isophthalate and diethyl isophthalate, isooctyl acrylate, butyl acrylate, and butanol.

67. The method of any one of claims 1-4, wherein antipolymerization air and / or antipolymerization agent are added to the absorption tower (C1) and / or purification tower (C2) and / or extraction tower (C3) and / or solvent recovery tower (C4).

68. The method of any one of claims 1-4, wherein no azeotropic agent is used and / or no additional water is added.

69. A system for refining acrylic acid, comprising: - Absorption tower (C1). - Purification tower (C2). - Extraction tower (C3). - Solvent recovery tower (C4). - The first pipeline (101) is connected to the lower part of the absorption tower (C1). - A second pipeline (102) connecting the bottom of the absorption tower (C1) to the upper or middle part of the purification tower (C2). - A fifth pipeline (105) connecting the lower part of the absorption tower (C1) and the extraction tower (C3). -A sixth pipeline (106) connecting the upper, middle, or lower part of the absorption tower (C1) to the top of the extraction tower (C3), and - A seventh pipeline (107) connecting the bottom of the extraction tower (C3) to the upper, middle or lower part of the solvent recovery tower (C4).

70. The system for refining acrylic acid according to claim 69, further comprising: - A third pipeline (103) connecting the lower part of the absorption tower (C1) to the top of the purification tower (C2); and / or -A fourth pipeline (104) connecting the bottom, lower or middle section of the absorber (C1) to the top of the solvent recovery tower (C4); and / or - An eighth pipeline (108) connecting the upper part of the extraction tower (C3) to the bottom of the solvent recovery tower (C4); and / or - A ninth pipeline (109) connected to the solvent recovery tower (C4) or a ninth pipeline (109) connecting the top of the absorption tower (C1) to the bottom of the solvent recovery tower (C4); and / or - The tenth pipeline (110) connected to the top of the absorption tower (C1); and / or - The eleventh pipeline (111) is connected to the top of the absorption tower (C1).

71. The system for refining acrylic acid according to claim 69 or 70, further comprising: - Thin film evaporator (C5). - Recombination splitter (C6). - The twelfth pipeline (112) connects the bottom of the purification tower (C2) to the upper part of the thin film evaporator (C5). -The fourteenth pipeline (114) connecting the lower part of the thin-film evaporator (C5) to the middle part of the recombination and splitting device (C6), and - The sixteenth pipeline (116) connected to the retort of the column reactor (C6).

72. The system for refining acrylic acid according to claim 71, further comprising: - A thirteenth pipeline (113) connecting the lower part of the purification column (C2) to the top of the thin-film evaporator (C5); and / or - The fifteenth pipeline (115) connects the lower part of the absorption tower (C1) to the top of the recombination and splitting device (C6).

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