CN-122003396-A - Method for purifying acrylic acid by recycling recycle gas

Abstract

The invention relates to a method for purifying acrylic acid by recycling a recycle gas, comprising steps a) to f). First, acrylic acid is a component of the Product Gas Mixture (PGM), which also contains minor components and optionally water. In step a), the Product Gas Mixture (PGM) is separated in a separation column (T-Kol) into a crude acrylic acid stream (RAS) and a minor component stream (NKS). Then, according to step b), a crude acrylic acid stream (RAS) is withdrawn from the separation column (T-Kol). According to step c), at least a portion of the minor component stream (NKS) is supplied to the cleavage column (S-Kol) from the tray of the separation column (T-Kol). In a cleavage column (S-Kol), cleavage of at least a portion of the minor component stream (NKS) is carried out according to step d) to give monomeric acrylic acid. According to step e), the monomeric acrylic acid is taken off as a constituent of the recycle gas stream (KGS) at the top of the cleavage column (S-Kol). In step f), at least a portion of the circulating gas stream (KGS) is supplied into the separation column (T-Kol), wherein at least a portion of the circulating gas stream (KGS) is supplied into the separation column (T-Kol) above the location where the Product Gas Mixture (PGM) is supplied into the separation column (T-Kol).

Inventors

• S.W. Beck
• L. Schultz
• T blaschke
• U. HARMON

Assignees

• 巴斯夫欧洲公司

Dates

Publication Date

20260508

Application Date

20241001

Priority Date

20231011

Claims (15)

1. 1. A process for purifying acrylic acid comprising steps a) to f): a) Separating a Product Gas Mixture (PGM) containing acrylic acid and a minor component into a crude acrylic acid stream (RAS) and a minor component stream (NKS) in a separation column (T-Kol), B) Withdrawing the crude acrylic acid stream (RAS) from the separation column (T-Kol), C) Supplying at least a part of said minor component stream (NKS) from the tray of said separation column (T-Kol) into a cleavage column (S-Kol), D) Cleaving at least a portion of the minor component stream (NKS) in the cleavage column (S-Kol) to obtain monomeric acrylic acid, E) A Stripping Gas Stream (SGS) is supplied at the tray of the cracking column (S-Kol), and a recycle gas stream (KGS) comprising the Stripping Gas Stream (SGS) and monomeric acrylic acid is taken off at the top of the cracking column (S-Kol). F) Supplying at least a portion of the circulating gas stream (KGS) withdrawn in step e) into the separation column (T-Kol), wherein at least a portion of the circulating gas stream (KGS) is supplied into the separation column (T-Kol) above the location where the Product Gas Mixture (PGM) is supplied into the separation column (T-Kol).
2. 2. The process according to claim 1, wherein the crude acrylic acid stream (RAS) from step b) is supplied to a device (V1), and the process further comprises step g): g) Further purifying the crude acrylic acid stream (RAS) in the device (V1) to obtain purified Acrylic Acid (AAS) and mother acid (MS).
3. 3. The method according to claim 2, further comprising steps h) and i): h) Withdrawing the mother acid (MS) from the device (V1) and optionally separating the mother acid (MS) into two mother acid streams (MS-a and MS-b), I) Recycling the mother acid (MS) or the optional mother acid stream (MS-a) into the separation column (T-Kol), wherein at least a portion of the mother acid (MS) or the optional mother acid stream (MS-a) is fed into the separation column (T-Kol) above the point of withdrawal from the crude acrylic acid stream (RAS) in step b).
4. 4. A method according to claim 3, wherein in step i) the mother acid (MS) is separated into two mother acid streams (MS-a and MS-b), and the method further comprises step j): j) The mother acid stream (MS-b) is fed to the cleavage column (S-Kol).
5. 5. The method according to any one of claims 1 to 4, comprising a further step a 1) before step a): a1 Supplying a Product Gas Mixture (PGM) into a device (V2), quenching the Product Gas Mixture (PGM) in the device (V2), withdrawing the quenched Product Gas Mixture (PGM) from the device (V2), and supplying the quenched Product Gas Mixture (PGM) into the separation column (T-Kol), Part of the minor component stream (NKS) from step a) is introduced as quench liquid into the plant (V2) to obtain a quenched Product Gas Mixture (PGM).
6. 6. The method according to any one of claim 4 to 6, wherein, At least 80 wt.% of the mother acid (MS) or optionally the mother acid stream (MS-a) is recycled to the separation column (T-Kol).
7. 7. Method according to any one of claims 1 to 6, characterized in that part of the circulating gas stream (KGS) from step e) is supplied to the device (V2), wherein in the device (V2) the circulating gas stream (KGS) is preferably combined with quenched Product Gas Mixture (PGM), and the mixture thus obtained is subsequently supplied to the separation column (T-Kol).
8. 8. The method according to any one of claims 1 to 7, wherein, The separation column (T-Kol) is designed as I) A rectifying tower, Ii) a distillation column, and/or Iii) And a condensing tower.
9. 9. The method according to any one of claims 1 to 8, wherein, I) In the separation column (T-Kol) and/or Ii) in the cleavage column (S-Kol), Dual-flow trays and/or cross-flow trays are used as internal components for the separation to be effective.
10. 10. The process according to any one of claims 1 to 9, wherein the process for purifying acrylic acid comprises preparing acrylic acid, wherein a Product Gas Mixture (PGM) comprising acrylic acid, water vapour and minor components is produced by heterogeneously catalyzed gas phase partial oxidation of at least one C 3 precursor of acrylic acid with molecular oxygen over a solid catalyst at elevated temperature.
11. 11. The method of claim 10, wherein the C 3 precursor of the acrylic acid is propylene and/or acrolein.
12. 12. The method according to any one of claims 1 to 11, wherein, I) The crude acrylic acid stream (RAS) according to step b) comprises at least 90% by weight of acrylic acid and water, acetic acid, diacrylic acid, propionic acid and 2-furfuraldehyde, and/or Ii) said mother acid (MS) according to step d) comprises at least 90% by weight of acrylic acid and water, acetic acid, diacrylic acid, propionic acid and 2-furfuraldehyde.
13. 13. The apparatus for purifying acrylic acid according to any one of claims 1 to 12, comprising -A separation column (T-Kol), -A cleavage column (S-Kol), Connecting the tray of the separation column (T-Kol) to the first line (L1) of the cracking column (S-Kol), -A second line (L2) leading from the cracking column (S-Kol), wherein the second line (L2) is connected to the separation column (T-Kol) and leads to the separation column (T-Kol) above the feed point of the Product Gas Mixture (PGM).
14. 14. The apparatus of claim 13, further comprising -Means (V1), -A third line (L3) connecting said separation column (T-Kol) and said device (V1), -A fourth line (L4) leading from the device (V1) and split into two lines (L4-a and L4-b), wherein the line (L4-a) is connected to the separation column (T-Kol) and opens into the separation column above the line (L3).
15. 15. The apparatus of claim 14, further comprising -Means (V2), A fifth line (L5) connecting said device (V2) and said separation column (T-Kol), wherein said fifth line (L5) is used for feeding said Product Gas Mixture (PGM), -A branch of the second line (L2) leading from the cracking column (S-Kol), wherein said branch leads to the device (V2), -A branch of the first line (L1) leading from the separation column (T-Kol), wherein the branch leads to the device (V2).

Description

Method for purifying acrylic acid by recycling recycle gas Description The invention relates to a method for purifying acrylic acid by recycling a recycle gas, comprising steps a) to f). First, acrylic acid is a component of the Product Gas Mixture (PGM), which also contains minor components and optionally water. In step a), the Product Gas Mixture (PGM) is separated in a separation column (T-Kol) into a crude acrylic acid stream (RAS) and a minor component stream (NKS). Then, according to step b), a crude acrylic acid stream (RAS) is withdrawn from the separation column (T-Kol). According to step c), at least a portion of the minor component stream (NKS) is supplied to the cleavage column (S-Kol) from the tray of the separation column (T-Kol). In a cleavage column (S-Kol), cleavage of at least a portion of the minor component stream (NKS) is carried out according to step d) to give monomeric acrylic acid. According to step e), the monomeric acrylic acid is taken off as a constituent of the recycle gas stream (KGS) at the top of the cleavage column (S-Kol). In step f), at least a portion of the circulating gas stream (KGS) is supplied into the separation column (T-Kol), wherein at least a portion of the circulating gas stream (KGS) is supplied into the separation column (T-Kol) above the location where the Product Gas Mixture (PGM) is supplied into the separation column (T-Kol). Acrylic acid is an important base chemical. Because of their highly reactive double bonds and acid functions, they are particularly suitable for the preparation of polymers as monomers. For example, in the amount of acrylic monomer produced, a majority is esterified (e.g., to give an adhesive, dispersion, or lacquer) prior to polymerization. Only a small fraction is polymerized directly (e.g. forming a "superabsorbent"). Although direct polymerization of acrylic acid generally requires a monomer of high purity, the purity requirement for acrylic acid is not as high if the acrylic acid is esterified prior to polymerization. Acrylic acid is obtained mainly by heterogeneously catalyzed gas phase partial oxidation of the C 3 precursor of acrylic acid with molecular oxygen at elevated temperature over a catalyst in the solid state of aggregation. The term "C 3 precursor" includes those compounds which are formally obtainable by reduction of acrylic acid. During the preparation, these C 3 precursors are diluted in the gaseous state, typically with inert gases such as nitrogen, CO 2, saturated hydrocarbons and/or water vapor, mixed with molecular oxygen at elevated temperature and optionally elevated pressure, passed over a transition metal mixed oxide catalyst, and oxidatively converted to a product gas mixture containing acrylic acid and minor components such as furfural, benzaldehyde and maleic anhydride from which acrylic acid must be separated. Thus, the acrylic acid obtained is not a pure product, but rather a mixture as described above, which contains, in addition to acrylic acid (generally ≡90% or ≡95% of the total weight), typical by-products of gas phase oxidation, such as water, lower aldehydes (e.g. furfural, acrolein or methacrolein, benzaldehyde), lower carboxylic acids (e.g. acetic acid, propionic acid) and the like, and oligomers of acrylic acid. The reason for the formation of acrylic acid oligomers is that acrylic acid present in the condensed phase forms acrylic acid oligomers (Michael adducts) by reversible Michael addition reactions on itself and on dimers formed in the process, as well as oligomers by free radical polymerization. The presence of water (an unavoidable by-product of the vapor phase catalytic oxidation to acrylic acid) and the high temperature promote the formation of acrylic acid oligomers. Since the corresponding oligomers have a higher boiling point than acrylic acid, they accumulate during the separation of acrylic acid by distillation and during the fractional condensation of the product gas mixture produced by gas-phase catalytic oxidation in the high boiling range (for example in the bottom liquid). DE 10 2014 114 193 A1 and the EP patent EP-B3 201 167 issued thereto describe a similar process for the preparation of acrylic acid, in which a temperature-controlled mother acid stream is taken off from a crystallization device for obtaining purified acrylic acid and is led to an absorption column and a cleavage column. In addition, a secondary component stream containing oligomeric acrylic acid is fed to the cleavage column to obtain monomeric acrylic acid. Using the stripping gas stream, the monomeric acrylic acid is introduced as a component of the recycle gas stream into a quenching device, where it is mixed with the product gas stream, and the resulting mixture is then introduced into the bottom of the absorption column. However, DE 10 2014 114 193 A1 does not disclose that at least a portion of the recycle gas stream which is withdrawn from the cleavage column and contains monomeric acrylic acid