Process of producing xylose and dissolving pulp

Patent metadata

Field	Value
Publication number	US-9068236-B2
Application number	US-200913125152-A
Country	US
Kind code	B2
Filing date	Oct 20, 2009
Priority date	Oct 21, 2008
Publication date	Jun 30, 2015
Grant date	Jun 30, 2015

Abstract

The present invention relates to a process for the production of xylose and dissolving pulp from xylan-containing biomass, such as hardwood. The invention is based on prehydrolysis of the xylan-containing biomass with SO 2 in specified conditions, followed by chromatographic fractionation, nanofiltration or precipitation crystallization of the xylose-containing prehydrolyzate to obtain a xylose product having a xylose content of at least 55% on DS. The dissolving pulp obtained from the process can be used for example for the production of viscose.

First claim

The invention claimed is:

1. A process for the production of xylose and dissolving pulp from a hardwood biomass, which has a xylan content of 10 to 35%, calculated on the dry substance (DS) of the biomass,
comprising the steps of:
(a) prehydrolyzing the hardwood biomass in a digester with a solution containing sulphur dioxide in a concentration of 0.1 to 2.5% based on the total liquid weight of the prehydrolysis liquid, at a temperature of 120-150° C., a liquid-to-biomass ratio of less than 6, and with a reaction time of 0.3 to 1 h, to provide (1) a dissolved hemicellulose hydrolyzate, wherein the xylose content is 25 to 55% of the dissolved solids of the hydrolyzate, the ratio of xylose to xylo-oligomers is more than 2 and the xylose yield is 30 to 80% on xylan in the biomass, and (2) a non-dissolved prehydrolyzed biomass,
(b) separating the dissolved hemicellulose hydrolyzate from the non-dissolved prehydrolyzed biomass,
(c) subjecting the dissolved hemicellulose hydrolyzate to chromatographic fractionation, nanofiltration or precipitation crystallization to obtain a xylose product having a xylose content of at least 55% on DS, and
(d) subjecting the non-dissolved prehydrolyzed biomass to sulphate cooking in a digester to obtain a dissolving pulp with a viscosity of more than 600 ml/g.

2. A process as claimed in claim 1 , wherein the concentration of sulphur dioxide in the prehydrolysis is 0.1 to 2.0%.

3. A process as claimed in claim 1 , wherein sulphur dioxide is added as a water solution or in a liquid or gas form.

4. A process as claimed in claim 1 , wherein sulphur dioxide is impregnated into the hardwood biomass.

5. A process as claimed in claim 1 , wherein the spent sulphur dioxide is recovered and returned to the prehydrolysis.

6. A process as claimed in claim 1 , wherein sulphur dioxide is returned to the prehydrolysis by dissolving into water after having been liberated from the digester.

7. A process as claimed in claim 1 , wherein the liquid/biomass ratio in the prehydrolysis is in the range of 1 to 6.

8. A process as claimed in claim 1 , wherein 15 to 40% of the dry substance of the hardwood biomass is dissolved in the prehydrolysis.

9. A process as claimed in claim 1 , wherein the prehydrolysis also comprises heating with direct steam.

10. A process as claimed in claim 1 , wherein the content of xylose in the dissolved hemicellulose hydrolyzate is 35 to 55% on DS.

11. A process as claimed in claim 1 , wherein the concentration of oligosaccharides in the dissolved hemicellulose hydrolyzate is less than 10% based on DS.

12. A process as claimed in claim 1 , wherein the content of monosaccharides in the dissolved hemicellulose hydrolyzate is more than 35% based on DS.

13. A process as claimed in claim 1 , wherein the content of xylose in the dissolved hemicellulose hydrolyzate is more than 65% based on total monosaccharides.

14. A process as claimed in claim 1 , wherein the ratio of xylose to xylo-oligomers in the dissolved hemicellulose hydrolyzate is more than 10.

15. A process as claimed in claim 1 , wherein the hemicellulose hydrolyzate has a dry substance content of more than 7% by weight.

16. A process as claimed in claim 1 , wherein the process also comprises evaporation of the prehydrolyzate after step (a), wherein acetic acid is partially removed from the prehydrolyzate by evaporation.

17. A process as claimed in claim 1 , wherein the process also comprises post-hydrolysis after step (a).

18. A process as claimed in claim 17 , wherein the post-hydrolysis is selected from enzymatic post-hydrolysis and hydrolysis with a hydrolyzing agent selected from sulphuric acid and sulphur dioxide.

19. A process as claimed in claim 1 , wherein the separation step (b) is carried out by washing selected from displacement wash, pressing and filtration.

20. A process as claimed in claim 19 , wherein the displacement wash is carried out in the digester with a liquid selected from water, a condensate, white liquor, chromatographic separation residue fraction and a nanofiltration retentate.

21. A process as claimed in claim 19 , wherein the yield of monomeric xylose dissolved from the biomass in the wash is 50 to 95%.

22. A process as claimed in claim 1 , wherein the process also comprises pH adjustment before step (c).

23. A process as claimed in claim 1 , wherein step (c) is carried out by chromatographic fractionation using an ion exchange resin as the column filling material.

24. A process as claimed in claim 23 , wherein the ion exchange resin is a cation exchange resin.

25. A process as claimed in claim 24 , wherein the cation exchange resin is a strongly acid cation exchange resin.

26. A process as claimed in claim 25 , wherein the cation exchange resin is in a monovalent metal cation form.

27. A process as claimed in claim 1 , wherein step (c) is carried out by nanofiltration, whereby the xylose product is recovered as the nanofiltration permeate.

28. A process as claimed in claim 1 , wherein the xylose product recovered from step (e) is subjected to crystallization to obtain crystalline xylose.

29. A process as claimed in claim 1 , wherein in step (d) dissolving pulp with a viscosity of more than 700 ml/g is obtained.

30. A process as claimed in claim 1 , wherein in step (d) dissolving pulp is obtained with a yield of greater than 35% on dry biomass.

31. A process as claimed in claim 30 , wherein in step (d) dissolving pulp is obtained with a yield of 76% or greater on dry biomass.

Assignees

• Heikkila Heikki
• Lewandowski Jari
• Lindroos Mirja
• Saari Pia
• Dupont Nutrition Biosci Aps

Inventors

• Heikkila Heikki
• Lewandowski Jari
• Lindroos Mirja
• Saari Pia

Classifications

• Y02E50/10

  Biofuels, e.g. bio-diesel · CPC title

• C13B20/148

  for fractionating, adsorption or ion exclusion processes combined with elution or desorption of a sugar fraction · CPC title

• C13K1/04

  Purifying · CPC title

• D21C1/04

  with acid reacting compounds · CPC title

• D21C3/02

  with inorganic bases or alkaline reacting compounds, e.g. sulfate processes · CPC title