Process for the recovery of carboxylic acid and wood treatment process

Abstract

The present invention concerns a process for the recovery of carboxylic acid from a fraction comprising carboxylic acid and impurities, and a process for the manufacture of treated wood, which comprise the step of submitting a fraction containing carboxylic acid and impurities to a gas stripping operation.

Claims

1-16: (canceled)

17. A process for recovering carboxylic acid from a fraction containing carboxylic acid and impurities, the process comprising submitting said fraction to a gas stripping operation, and recovering at least a purified carboxylic acid fraction.

18. The process according to claim 17, further comprising an additional separation step prior to the gas stripping operation.

19. The process according to claim 17, further comprising an additional step of pretreating the fraction containing the carboxylic acid and the impurities to be introduced in the gas stripping operation with an aqueous phase.

20. The process according to claim 19, wherein the fraction containing the carboxylic acid and the impurities further contains carboxylic anhydride, wherein the content of the carboxylic anhydride in the fraction containing the carboxylic acid and the impurities prior to the addition of the aqueous phase is less than 20 weight %.

21. The process according to claim 19, wherein the amount of the aqueous phase is controlled such that the water content of the fraction obtained is from 0.01 weight % to 20 weight %.

22. The process according to claim 17, wherein the fraction containing the carboxylic acid and the impurities further contains halogenated impurities.

23. The process according to claim 17, wherein the fraction containing the carboxylic acid and the impurities further contains terpenes, terpenoids, or both.

24. The process according to claim 17, wherein the fraction containing the carboxylic acid and the impurities contains at least one impurity selected from the group consisting of wood preservatives, preservation agents, or combinations thereof.

25. The process according to claim 17, wherein the gas stripping operation comprises at least one gas selected from the group consisting of air, oxygen, CO.sub.2, exhaust gas, and inert gases.

26. The process according to claim 17, wherein the gas stripping operation is performed continuously in a countercurrent or co-current way, or batchwise.

27. The process according to claim 17, wherein the carboxylic acid fraction submitted to the gas stripping operation has a temperature of from 10 to 90° C. in the gas stripping operation.

28. The process according to claim 17, wherein the carboxylic acid fraction containing the carboxylic acid and the impurities originates from an acylation process, the acylation process concerns acylation of materials comprising polysaccharides.

29. The process according to claim 28, wherein the process from which the carboxylic acid fraction containing the carboxylic acid and the impurities originates is a wood treatment process.

30. The process according to claim 17, further comprising withdrawing a mixture rich in carboxylic anhydride as a side stream or a bottom stream from a separation step.

31. The process according to claim 30, which further comprises recycling the mixture rich in carboxylic anhydride to a wood treatment process.

32. A process for manufacturing treated wood comprising the process according to claim 17.

33. The process according to claim 17, wherein the carboxylic acid is acetic acid.

34. The process according to claim 22, wherein the halogenated impurities are selected from the group consisting of hydrogen halides, carboxylic acid halides, and mixtures thereof.

35. The process according to claim 28, wherein the acylation process is an acetylation process.

36. The process according to claim 28, wherein the polysaccharides are selected from starch, cellulose, or combinations thereof.

Description

[0024] The following list is non-limiting and summarizes some preferred embodiments, process variants and aspects described before:

Embodiment A

[0025] Stripping of fraction containing carboxylic acid and impurities

Embodiment B

[0026] Distillation of a fraction containing carboxylic acid and impurities to obtain a fraction containing carboxylic acid and a reduced amount of impurities; stripping of the fraction containing carboxylic acid and a reduced amount of impurities.

[0027] This embodiment is particularly preferred, in particular if the fraction containing carboxylic acid and impurities contains equal to or more than 50 weight % of carboxylic acid anhydride.

Embodiment C

[0028] Distillation of a fraction containing carboxylic acid and impurities to obtain a fraction containing carboxylic acid and a reduced amount of impurities; addition of an aqueous phase; stripping of the pretreated fraction containing carboxylic acid and a reduced amount of impurities.

[0029] This embodiment is particularly preferred, in particular if the fraction containing carboxylic acid and impurities contains equal to or more than 50 weight % of carboxylic acid anhydride.

Embodiment D

[0030] Stripping of a fraction containing carboxylic acid and impurities to obtain a fraction containing carboxylic acid and a reduced amount of impurities; distillation of the fraction containing carboxylic acid and a reduced amount of impurities.

Embodiment E

[0031] Addition of an aqueous phase to a fraction containing carboxylic acid and impurities; distillation of the pretreated fraction; stripping the pretreated fraction containing carboxylic acid and impurities.

Embodiment F

[0032] Stripping of a fraction containing carboxylic acid and impurities to obtain a fraction containing carboxylic acid and a reduced amount of impurities; distillation of the fraction; stripping of the pretreated fraction.

Embodiment G

[0033] Stripping of a fraction containing carboxylic acid and impurities to obtain a fraction containing carboxylic acid and a reduced amount of impurities; distillation of the fraction; addition of an aqueous phase to the fraction; stripping of the pretreated fraction.

[0034] In a preferred aspect, the fraction being submitted to stripping, which is either the fraction containing carboxylic acid and impurities or a fraction containing carboxylic acid and a reduced amount of impurities, comprises equal to or more than 50 weight %, preferably equal to or more than 60 weight %, and more preferably equal to or more than 70 weight %, and most preferably equal to or more than 80 weight % of a mixture consisting of carboxylic acid anhydride and carboxylic acid. In one aspect, the fraction submitted to a stripping step consists of a mixture consisting of carboxylic acid anhydride and carboxylic acid, thus the content of the mixture in the fraction containing carboxylic acid and impurities or carboxylic acid and a reduced amount of impurities is 100 weight %. In another aspect, the fraction submitted to a stripping step comprises equal to or less than 99 weight %, preferably equal to or less than 97 weight %, and more preferably equal to or less than 95 weight % of a mixture consisting of carboxylic acid anhydride and carboxylic acid. In one aspect, the fraction submitted to a stripping step comprises equal to or less than 92 weight % of a mixture consisting of carboxylic acid anhydride and carboxylic acid. In yet another aspect, which is preferred in some embodiments, the fraction submitted to a stripping step comprises equal to or less than 90 weight % of a mixture consisting of carboxylic acid anhydride and carboxylic acid. The mixture consisting of carboxylic acid anhydride and carboxylic acid generally has a weight ratio of carboxylic acid anhydride versus carboxylic acid of from 1:99 to 99:1. Often, the content of carboxylic acid anhydride in the mixture consisting of carboxylic acid anhydride and carboxylic acid is equal to or greater than 1 weight %, preferably equal to or greater than 10 weight % , more preferably equal to or greater than 30%, and most preferably equal to or greater than 45 weight %. Generally, the content of carboxylic acid anhydride in the mixture consisting of carboxylic acid anhydride and carboxylic acid is equal to or lower than 99 weight %, preferably equal to or lower than 80 weight % , more preferably equal to or lower than 70%, and most preferably equal to or lower than 50 weight %. Often, the content of carboxylic acid in the mixture consisting of carboxylic acid anhydride and carboxylic acid is equal to or greater than 1 weight %, preferably equal to or greater than 10 weight % , more preferably equal to or greater than 30%, and most preferably equal to or greater than 45 weight %. Generally, the content of carboxylic acid in the mixture consisting of carboxylic acid anhydride and carboxylic acid is equal to or lower than 99 weight %, preferably equal to or lower than 80 weight % , more preferably equal to or lower than 70%, and most preferably equal to or lower than 50 weight %. It is understood that the weight fractions of carboxylic acid and carboxylic acid anhydride in the mixture consisting of carboxylic acid anhydride and carboxylic acid make up the sum of 100 weight % of the mixture consisting of carboxylic acid anhydride and carboxylic acid.

[0035] Often, the purified carboxylic acid fraction recovered by the process according to the present invention is sufficiently pure to use in downstream processes such as the production of carboxylic acid anhydride. In this case, no further steps are required to recover the purified carboxylic acid fraction after the stripping operation. If necessary, the purified carboxylic acid fraction can be further purified by additional separation steps such as distillation or liquid-liquid-extraction.

[0036] In one aspect of the present invention, at least one impurity contained in the fraction containing carboxylic acid and impurities was applied to the wood. In particular, the at least one impurity contained in the fraction containing carboxylic acid and impurities which was applied to the wood originates from one or more wood preservatives or wood preservation agents. Often, the at least one impurity was applied to the wood before the wood treatment process. Application of wood preservatives or wood preservation agents for preserving the wood, and thus, impurities originating therefrom, e.g. during shipping of the wood to the wood treatment plant (and thus, before the wood treatment process), is common. Examples of impurities which originate from such wood preservatives and/or wood preservative agents are Benzalkonium chloride, iodocarb, Propiconazole, Iodofon, Propylene Glycol, Dipropylene glycol methyl ether, Dipropylene glycol, Didecyl-dimethly ammonium chloride, 5-Chloro-2-methyl-4-isothiazolin-3-one, 2-Methyl-4-isothiazolin-3-one, Petroleum distillates, ethyl alcohol, Chlorothalonil, Methylene Bis Thiocyanate, Sodium nitrite, Guazatine and Phosphonic acid. The process according to the present invention substantially reduces or removes the content of the at least one impurity applied to the wood.

[0037] The invention also concerns a process for the manufacture of treated wood, e.g. as disclosed in EP-A-0680810, in particular acetylated wood, which comprises the process for the recovery of carboxylic acid according to the invention. Generally, wood is treated with carboxylic acid anhydride, in particular acetic anhydride, by which an effluent rich in carboxylic anhydride and carboxylic acid, also comprising other impurities, is generated next to the treated wood product. This effluent is advantageously treated by the process according to the present invention as fraction containing carboxylic acid and impurities to generate at least a purified carboxylic acid. In one aspect, the purified carboxylic acid is used, either directly or after other process steps, such as separation steps, as reaction medium in the process for the manufacture of treated wood. In another aspect, the purified carboxylic acid is used, either directly or after other process steps, such as separation steps, for the manufacture of carboxylic acid anhydride by known processes, for example ketene process. The carboxylic acid anhydride generated by these aspects is then recycled to its originating process, in particular into the wood treatment process. In another aspect, it is used for other processes. A side stream rich in carboxylic acid anhydride, as generated during the process according to the present invention, for example by a separation step as described in the second embodiment, can also be recycled. For the recycling of said side stream, the side stream can be used as recovered, or after further treatment steps. The side stream can be recycled to the originating process, which is in particular a wood treatment process. In another aspect, the side stream rich in carboxylic acid anhydride is used for other processes.

[0038] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0039] The following examples further illustrate the invention but are not to be construed as limiting its scope.

Example 1

[0040] 250 mL of a liquid phase containing 50/50 w/w acetic acid anhydride and acetic acid and 2000 mg/L acetyl chloride (mixture Ml) were left to stand at room temperature under an argon blanket, measured for acetyl chloride. Argon was bubbled through the mixture using a glass fritt at 1 L/min for 1 hour, and the mixture (mixture M2) was again measured for acetyl chloride.

TABLE-US-00001 Total Amount Time acetylchlorid Step [h] Process step GC-MS-SIM 1 0 Initial measurement Initial concentration 2 1 Leaving to stand under Initial concentration argon blanket 1 hour 3 2 1 hour bubbling argon 0 ppm

[0041] The content of acetyl chloride was measured by GC-MS in SIM-SCAN-mode using external standard calibration (mass spectrometer Agilent MSD-5975, gas chromatograph Agilent 7890 using HP-5 capillary column).

Example 2

[0042] To 200 mL of a liquid phase originating from a wood acetylation process containing 50/50 w/w acetic acid anhydride and acetic acid, 200 μl of acetyl chloride were added to bring the concentration of acetyl chloride to 1000 mg/L (mixture M3). Dry Air was bubbled through the mixture using a glass fritt at 1 L/min for 90 minutes hour, and the mixture was measured for acetyl chloride at 1, 30, 60 and 90 minutes (after 90 minutes: M4).

TABLE-US-00002 Total Time Step [h] Process step Chloride 1  0 Initial measurement 1141 ppm 2  1 min Bubbling air 1 L/min 1135 ppm 3 30 min Bubbling air 1 L/min  760 ppm 4 60 min Bubbling air 1 L/min  634 ppm 5 90 min Bubbling air 1 L/min   0 ppm

[0043] The content of chloride was measured by titration (Metrohm Titroprocessor 686, 0.01 m AgNO3 titration agent).

Example 3

[0044] A 250 mL sample of M1, M2, M3, M4 and technical grade acetic acid was submitted to a corrosion test according to the following procedure:

[0045] Procedure 3a: The sample was contacted at 70° C. temperature with coupons of AlSI316L, A1S1904L, Alloy C276 and alloy C22. After 650 hours, the coupons contacted with samples M1 and M3 showed extensive pitting, while for samples M2, M4 and technical grade acetic acid, no pitting was observed.

[0046] Procedure 3b: Samples M2, M4 and technical grade acetic acid were contacted at 115° C. temperature with coupons of AlSI316L, AlSI904L, Alloy C276 and alloy C22. After 650 hours, the coupons contacted with samples M2 and M4 showed no deterioation of the coupons, similar to the coupons contacted with technical grade acetic acid.