Acylation process

Abstract

The invention concerns a process for the manufacture of an acylated polysaccharide which comprises. (a) reacting a polysaccharide with an acylating agent to produce an acylated polysaccharide and (b) washing the acylated polysaccharide with water containing from 0.05 to 15 mg/l Ca.sup.2+-ions (c) recovering the washed acylated polysaccharide and an aqueous phase containing carboxylic acid from step (b).

Claims

1. A process for manufacturing an acylated polysaccharide and recovering a permeate containing carboxylic acid comprising: (a) reacting a polysaccharide with an acylating agent to produce an acylated polysaccharide, wherein the polysaccharide is cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and sodium, potassium, calcium or ammonium salts of cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose or starch, wherein the acylation agent comprises at least one organic acidic compound selected from the group consisting of acetic anhydride and acetic acid, and a mineral acid comprising sulphuric acid; (b) quenching, precipitating and washing the acylated polysaccharide with water containing from 0.05 to 8 mg/l Ca.sup.2+-ions; and (c) recovering the washed acylated polysaccharide and a combined aqueous phase from the quenching, precipitating and washing containing carboxylic acid from step (b), wherein concentration of carboxylic acid in the combined aqueous phase is 5 to 40 wt. %, wherein the combined aqueous phase is treated by nanofiltration or reverse osmosis to recover a permeate containing carboxylic acid and wherein the process is carried out in the substantial absence of a surface active substance, wherein concentration of the surface-active substance in the combined aqueous phase is equal to or lower than 150 ppm, wherein there is an absence of lignosulfates, wherein all water used to wash the acylated polysaccharide contains from 0.05 to 8 mg/l Ca.sup.2+-ions; wherein the combined aqueous phase contains from 10 to 20000 mg/l SO.sub.4.sup.2-ions.

2. The process of claim 1, wherein the acylating agent is acetic acid anhydride.

3. The process according to claim 1, wherein the polysaccharide is cellulose or starch.

4. The process according to claim 1, wherein step (a) is carried out in the presence of at least one acidic compound.

5. The process according to claim 1, wherein the concentration of the surface-active substance in the aqueous phase is equal to or lower than 105 ppm.

6. The process according to claim 1, wherein the aqueous phase before filtration contains from 10 to 40 wt. % acetic acid, and from 10 to 20000 mg/l SO.sub.4.sup.2-ions.

7. The process according to claim 6, wherein the aqueous phase further comprises organic impurities with a minimal molecular weight from more than 100 g/mol to more than 300 g/mol.

8. The process according to claim 1, wherein the nanofiltration or reverse osmosis filtration is carried out employing a membrane with a capacity to filter organic impurities with a molecular weight from more than 100 g/mol to more than 300 g/mol.

9. The process according to claim 1, wherein the volume reduction in the nanofiltration or reverse osmosis is from 50% to 99%.

10. The process according to claim 1, wherein the concentration of surface active substance in the aqueous phase is equal to or lower than 50 ppm, wherein anions present in the combined aqueous phase to form salts with the Ca.sup.2+ ions consist of at least one member selected from the group consisting of SO.sub.4.sup.2, CO.sub.3.sup.2, HCO.sub.3.sup.2, and PO.sub.4.sup.3.

11. The process according to claim 4, wherein the at least one acidic compound is selected from the group consisting of acetic acid and sulfuric acid.

12. The process according to claim 1, wherein the nanofiltration or reverse osmosis filtration is carried out employing a membrane with a capacity to filter organic impurities with a molecular weight of more than 300 g/mol.

13. The process according to claim 1, wherein the process is carried out in the absence of surface-active substance.

14. The process according to claim 1, wherein the polysaccharide (PS) has formula PS(OH).sub.3-x and reacts with the acylation agent to form the acylated polysaccharide of formula PS(OH).sub.3-x(OCOR).sub.x, wherein x denotes the degree of substitution of the hydroxyl groups in the polysaccharide and is from 0.5 to 3.

15. The process according to claim 1, wherein the polysaccharide is cellulose.

16. The process according to claim 1, wherein the water for quenching, precipitating and washing the acetylated polysaccharide contains from 0.05 to 5 mg/l Ca.sup.2+-ions, wherein the polysaccharide is cellulose, wherein the acylation agent comprises sulphuric acid; wherein the carboxylic acid comprises acetic acid; wherein the polysaccharide and the acylation agent react to produce a reaction mixture comprising the acylated cellulose; wherein the reaction mixture was quenched with a solution of acetic acid and water, wherein the acylated cellulose was precipitated from the quenched reaction mixture; wherein the aqueous phase before filtration contains from 5 to 40 wt. % acetic acid, from 0.05 to 5 mg/l Ca.sup.2+-ions, and from 10 to 16000 mg/l SO.sub.4.sup.2-ions, wherein the nanofiltration or reverse osmosis filtration is carried out employing a membrane with a capacity to filter organic impurities with a molecular weight from more than 100 g/mol to more than 300 g/mol.

17. A process for recovering acylated polysaccharide and recovering a permeate containing carboxylic acid, the process comprising: (a) reacting a polysaccharide with an acylating agent to produce an acylated polysaccharide, wherein the polysaccharide is cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and sodium, potassium, calcium or ammonium salts of cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose or starch, wherein the acylation agent comprises at least one organic acidic compound selected from the group consisting of acetic anhydride and acetic acid, and a mineral acid comprising sulphuric acid; (b) quenching, precipitating and washing the acylated polysaccharide with water containing from 0.05 to 8 mg/l Ca.sup.2+-ions; and (c) recovering the washed acylated polysaccharide and a combined aqueous phase from the quenching, precipitating and washing containing carboxylic acid from step (b), wherein concentration of carboxylic acid in the combined aqueous phase is 5 to 40 wt. %; (d) treating the combined aqueous phase by nanofiltration or reverse osmosis to recover a permeate containing carboxylic acid to provide a purified aqueous phase containing carboxylic acid, wherein the process is carried out in the substantial absence of a surface active substance, wherein concentration of the surface-active substance in the combined aqueous phase is equal to or lower than 150 ppm, wherein there is an absence of lignosulfates; and (e) subjecting the purified aqueous phase to at least one further purification step, wherein all water used to wash the acylated polysaccharide contains from 0.05 to 8 mg/l Ca.sup.2+-ions; wherein the combined aqueous phase contains from 10 to 20000 mg/l SO.sub.4.sup.2-ions.

18. The process according to claim 17, wherein the purification step is selected from the group consisting of extraction, drying, washing, distillation, or combinations thereof.

19. The process according to claim 17, wherein the water for quenching, precipitating and washing the acetylated polysaccharide contains from 0.05 to 5 mg/l Ca.sup.2+-ions.

20. A process for the acetylation of polysaccharides and recovering a permeate containing carboxylic acid, the process comprising: (a) reacting a polysaccharide with acetic anhydride to produce an acetylated polysaccharide, wherein the polysaccharide is cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, and sodium, potassium, calcium or ammonium salts of cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose or starch, wherein the acylation agent comprises at least one organic acidic compound selected from the group consisting of acetic anhydride and acetic acid, and a mineral acid comprising sulphuric acid; (b) quenching, precipitating and washing the acetylated polysaccharide with water containing from 0.05 to 8 mg/l Ca.sup.2+-ions; and (c) recovering the washed acetylated polysaccharide and a combined aqueous phase from the quenching, precipitating and washing containing carboxylic acid from step (b), wherein concentration of carboxylic acid in the combined aqueous phase is 5 to 40 wt. %; (d) treating the combined aqueous phase by nanofiltration or reverse osmosis to recover a permeate containing acetic acid to provide a purified aqueous phase containing acetic acid, wherein the process is carried out in the substantial absence of a surface active substance, wherein concentration of the surface-active substance in the combined aqueous phase is equal to or lower than 150 ppm, wherein there is an absence of lignosulfates; and (e) subjecting the purified aqueous phase to at least one further purification step (f) converting the acetic acid obtained in step (e) into acetic anhydride; and (g) reacting a polysaccharide with the acetic anhydride obtained in step (f), wherein all water used to wash the acylated polysaccharide contains from 0.05 to 8 mg/l Ca.sup.2+-ions; wherein the combined aqueous phase contains from 10 to 20000 mg/l SO.sub.4.sup.2-ions.

21. The process of claim 20, wherein the polysaccharide is cellulose.

22. The process of claim 20, wherein the acetylation is further carried out in the presence of at least one acidic compound selected from the group consisting of acetic acid and sulfuric acid.

23. The process according to claim 20, wherein the water for quenching, precipitating and washing the acetylated polysaccharide contains from 0.05 to 5 mg/l Ca.sup.2+-ions.

24. A process for manufacturing an acylated polysaccharide and recovering a permeate containing carboxylic acid comprising: (a) reacting a polysaccharide with an acylating agent to produce an acylated polysaccharide; (b) quenching, precipitating and washing the acylated polysaccharide with water containing from 0.05 to 8 mg/l Ca.sup.2+-ions; and (c) quenching, precipitating and recovering the washed acylated polysaccharide and a combined aqueous phase from the quenching, precipitating and washing containing carboxylic acid from step (b); wherein the polysaccharide (PS) has formula PS(OH).sub.3-x and reacts with the acylation agent to form the acylated polysaccharide of formula PS(OH).sub.3-x(OCOR).sub.x, wherein x denotes the degree of substitution of the hydroxyl groups in the polysaccharide and is from 0.5 to 3; wherein the acylation agent comprises at least one member selected from the group consisting of carboxylic acid anhydrides of formula (RCO).sub.2O, carboxylic acids, carboxylic acid halides, and carbonylimidazoles, and the acylation agent comprises mineral acid comprising sulfuric acid; wherein R of the acylation agent and the acylated polysaccharide is an aliphatic or cycloaliphatic radical containing 1 to 18 carbon atoms, an araliphatic radical containing 7 to 12 carbon atoms, an aromatic radical containing 6 to 12 carbon atoms; wherein R may be optionally substituted by one or more of halogens, NO.sub.2, phenyl, COOR.sup.1, OR.sup.1 or an aromatic radical containing from 1 to 12 carbon atoms substituted by a C.sub.1-6 aliphatic group, wherein R.sup.1 is a C.sub.1-C.sub.4 alkyl radical optionally substituted by one or more halogens; wherein the process is carried out in the substantial absence of a surface active substance, wherein the combined aqueous phase is treated by nanofiltration or reverse osmosis to recover a permeate containing carboxylic acid and wherein the process is carried out in the substantial absence of a surface active substance, wherein concentration of the surface-active substance in the combined aqueous phase is equal to or lower than 150 ppm, wherein there is an absence of lignosulfates; wherein all water used to wash the acylated polysaccharide contains from 0.05 to 8 mg/l Ca.sup.2+-ions; wherein the combined aqueous phase contains from 10 to 20000 mg/l SO.sub.4.sup.2-ions.

Description

(1) The examples hereafter are intended to illustrate the invention in a non-limitative manner.

EXAMPLE 1

(2) Cellulose was pre-treated in acetic acid with sulphuric acid as described in A. Hummel, Industrial processes, Macromolecular Symposia, 2004, Vol 208(1), p. 61-80. The activated cellulose was then reacted with a mixture of acetic acid and acetic acid anhydride at a temperature of 45-85 C. After completed reaction, the reaction mixture was quenched with a solution of 60 wt. % of acetic acid in water. The Ca.sup.2+-content of the water used for the aqueous acid solution was 4.6 mg/l. The reaction mixture was then poured into water containing 4.6 mg/l Ca.sup.2+-ions and 16 wt. % acetic acid, and the cellulose acetate precipitates. The precipitated cellulose acetate was washed with water containing 4.6 mg/l Ca.sup.2+-ions and dried. The combined aqueous phase from quenching, precipitation and washing contained approximately 30% acetic acid. The aqueous phase was filtered with a 5 m filter and then subjected to batch mode reverse osmosis using an AK4040 membrane (Osmonics Desal). A VR of 96.3% was achieved, while no decrease in permeate quality or increase of operation pressure or differential pressure of the 5 m filter, which would have indicated membrane or filter blockage, was observed. A foam test was performed to control the efficiency of the reverse osmosis: 1 part of permeate was diluted with 4 parts of water and shaken. The foam standing time of the permeate throughout the reverse osmosis step at all VR values was 5 sec, whereas the foam standing time of the aqueous phase before reverse osmosis was more than 300 seconds, indicating an efficient removal of organic impurities. The permeate was subjected to liquid/liquid extraction with diethylether and subsequent distillation to yield glacial acetic acid. During the extraction and distillation, no clogging, encrusting or fouling of the equipment was observed.