Process for the recovery of carboxylic acid and wood treatment process

Abstract

Process for the recovery of carboxylic acid, in particular acetic acid containing carboxylic anhydride in particular acetic anhydride and other impurities, which comprises: (a) treating a fraction, in particular a fraction originating from a wood treatment process, containing carboxylic acid and impurities with a metal salt in the presence of water, (b) treating at least part of the fraction obtained from step (a) to remove metal salt and, (c) treating at least part of the fraction obtained from step (b) by distillation, stripping or membrane separation to recover at least a purified carboxylic acid fraction.

Claims

1-15: (canceled)

16. A process for the recovery of carboxylic acid containing carboxylic anhydride, and other impurities, the process comprising: (a) treating a fraction containing carboxylic acid and impurities with a metal salt in the presence of water; (b) treating at least part of the fraction obtained from step (a) to remove metal salt; and (c) treating at least part of the fraction obtained from step (b) by distillation, stripping or membrane separation to recover at least a purified carboxylic acid fraction.

17. The process according to claim 16, wherein the metal salt is an alkali salt.

18. The process according to claim 16, wherein the carboxylic acid fraction introduced into step (a) contains chlorinated compounds corresponding to from 3 to 2000 ppm molar equivalents of chlorine atoms relative to carboxylic acid.

19. The process according to claim 18, wherein the amount of metal salt supplied to step (a) is from 10 to 10000 equivalents relative to the molar amount of chlorine atoms contained in the chlorinated compounds.

20. The process according to claim 16, wherein the fraction introduced into step (a) contains terpenes, terpenoids, and mixtures thereof.

21. The process according to claim 20, wherein the fraction introduced into step (a) contains from 50 to 1500 ppm by weight of the terpenes, terpenoids, and mixtures thereof.

22. The process according to claim 16, wherein the amount of water present in step (a) is from 0.8 to 1.2 molar equivalents of carboxylic acid anhydride present in the fraction supplied to step (a).

23. The process according to claim 16, wherein the metal salt is separated in step (b) by evaporation.

24. The process according to claim 16, wherein the metal salt is removed as a solid from the fraction obtained by step (a) and/or from the residue obtained from an evaporation operation of step (b), and/or wherein the metal salt is removed as a liquid stream containing the metal salt obtained from the evaporation residue of an evaporation operation of step (b).

25. The process according to claim 23, which comprises withdrawing a gas stream comprising carboxylic acid and impurities from the evaporation of step (b) and feeding at least part of the gas stream into step (c) wherein the gas stream fed into step (c) comprises less than 1 ppm wt. of halogen.

26. The process according to claim 16, wherein water is added to the fraction obtained by step (b) prior to step (c).

27. The process according to claim 26, wherein the amount of the water is from 1 to 25 wt. %, calculated on the total mass of the fraction obtained by step (b).

28. The process according to claim 16 further comprising withdrawing the purified carboxylic acid fraction as a side stream or a bottom stream from step (c).

29. The process according to claim 16 further comprising recovering a carboxylic acid/carboxylic anhydride mixture containing other impurities from a wood treatment process and separating said mixture into a first fraction consisting essentially of carboxylic anhydride and optionally recycling said first fraction to the wood treatment process, and a second fraction containing carboxylic acid, impurities originating from wood and carboxylic anhydride, and introducing at least part of said second fraction into step (a).

30. The process for the manufacture of treated wood comprising the process for the recovery of carboxylic acid according to claim 16.

31. The process according to claim 16, wherein acetic acid and acetic anhydride are recovered.

32. The process according to claim 16, wherein the fraction in step (a) is from a wood treatment process.

33. The process according to claim 17, wherein the metal salt is sodium acetate.

34. The process according to claim 27, wherein the amount of water is from 7 wt. % to 12 wt. %.

Description

EXAMPLE

[0046] A continuous flow of a fraction containing carboxylic acid and impurities, which is liquid effluent from a wood acetylation process, containing 50 wt. % acetic acid, 49 wt. % acetic anhydride and 1 wt. % of terpenes, terpene derived impurities and other organic impurities is submitted to a first distillation, employing a distillation column made of titanium.

[0047] This distillation column is equipped with structured packing which equals 20 theoretical stages. The chosen reflux ratio is 3. The column is operated at an pressure of 0.5 bar abs. at the top of the column. From this first distillation column a condensed stream is withdrawn at 93.6 C. with an acetic acid content of 98 wt. %, 20 ppm of chlorine (expressed as chlorine atoms) and the remaining rest is acetic anhydride, terpenes and terpenoids.

[0048] As step (a), in an intermediate treatment vessel, the top product of the first distillation is treated with a small amount of water in order to react with the remaining acetic anhydride. To the same intermediate treatment vessel, a flow of a 50% NaOH solution in water is added to the fraction obtained to provide 200 molar equivalents Na+ relative to the molar amount of chlorine atoms contained in the chlorinated compounds of the top product of the first distillation. The flowrates of water and NaOH solution to the intermediate vessel are calculated such that the water content reaction mixture is 1.05 eq relative to the content of acetic anhydride while maintaining the appropriate amount of NaOH.

[0049] In a step (b), the fraction obtained by step (a) is fed into a natural flow evaporator which is operated at a pressure of 0.3 bar abs. The fraction obtained by step (b) is substantially free of halogen, in particular chloride.

[0050] A small side stream of 0.5 wt. % of the liquid evaporation residue is withdrawn from the evaporator, cooled down to 30 C. and passed over a filter. Since the formed NaCl is basically indissoluble in acetic acid at low water concentration, it is removed as a precipitated salt by the filtration step. The dissolved Na-Acetate passes the filter and is recycled to the intermediate treatment vessel in which step (a) is performed.

[0051] The water content of the vapor fraction obtained by step (b) is further increased up to 10 wt % and submitted to step (c).

[0052] To perform step (c), the fraction obtained by step (b) and enriched with water is fed as vapor stream into a distillation column, This distillation column is equipped with structured packing which equals 35 theoretical stages. The chosen reflux ratio is 5. The column is operated at a pressure of 0.2 bar abs. at the top of the column.

[0053] From this distillation column a condensed overhead stream is withdrawn at 60.3 C. with a water content of 95%. wt. This stream contains more than 80% of all terpenes, terpene derived impurities and other organic impurities which were contained in the fraction fed to step (c).

[0054] The acetic acid, withdrawn at the bottom of the column of step (c) with a concentration of 99.5%, is substantially free of halogen, in particular chloride, containing less than 20% of all terpene and other organic impurities which were contained in the fraction fed to step (c).

[0055] The material is stored in a stainless steel vessel and has the corrosiveness of pure acetic acid. No coloration of the product is observed over time.