Method for catalytic oxidation of cellulose and method for making a cellulose product

Patent metadata

Field	Value
Publication number	US-9969816-B2
Application number	US-201414913513-A
Country	US
Kind code	B2
Filing date	Sep 2, 2014
Priority date	Sep 2, 2013
Publication date	May 15, 2018
Grant date	May 15, 2018

Abstract

A method for catalytic oxidation of cellulose using a heterocyclic nitroxyl radical as catalyst and main oxidant acting as oxygen source comprises, before the catalytic oxidation of the cellulose, pretreatment of the cellulose—in an alkaline pretreatment step, where the cellulose is treated in alkaline solution having hydroxide concentration of above 0.3 M, and—in a washing step, where the cellulose treated in the alkaline solution is washed to lower the pH.

First claim

The invention claimed is:

1. A method for catalytic oxidation of cellulose in fibrous cellulosic material, especially fibers obtained from plant material, using a heterocyclic nitroxyl radical as catalyst and main oxidant acting as oxygen source, characterized in that the method comprises, before the catalytic oxidation of the cellulose, pretreatment of the cellulose
in an alkaline pretreatment step, where the fibrous cellulosic material is treated in alkaline solution having hydroxide concentration of 0.3-2.4 M, and
in a washing step, where the fibrous cellulosic material treated in the alkaline solution is washed to lower the pH.

2. The method according to claim 1 , characterized in that the treatment time of cellulose in the alkaline solution is 30 s-60 min.

3. The method according to claim 1 , characterized in that the alkaline solution is alkali metal hydroxide solution.

4. The method according to claim 1 , characterized in that in the washing step, the pH is lowered to alkaline range.

5. The method according to claim 4 , characterized in that the pH is lowered to the range of 8-12.

6. The method according to claim 4 , characterized in that the pH is lowered to the range of 9-11.

7. The method according to claim 4 , characterized in that the pH is lowered to the range of 9-10.

8. The method according to claim 1 , characterized in that in the pretreatment, the crystalline regions of cellulose remain as cellulose I.

9. The method according to claim 1 , characterized in that in the pretreatment, the DP of the cellulose decreases at the most by 20% compared with the original value.

10. The method according to claim 1 , characterized in that the fibrous cellulosic material comprises hemicellulose, and the hemicellulose content is reduced in the pretreatment.

11. The method according to claim 1 , characterized in that the alkaline solution used in the preteatment is circulated, and if necessary, hemicellulose is removed from the alkaline solution.

12. The method according to claim 1 , characterized in that the reaction time in the catalytic oxidation of the pretreated cellulose is below 1 hour.

13. The method according to claim 1 , characterized in that it comprises a preliminary activation step of the heterocyclic nitroxyl catalyst in the absence of cellulose before the catalytic oxidation of the pretreated cellulose.

14. The method according to claim 1 , characterized in that hypochlorite is used as the main oxidant in the catalytic oxidation of the pretreated cellulose.

15. The method according to claim 1 , characterized in that in the catalytic oxidation of the pretreated cellulose, the pH is 7-10.

16. The method according to claim 1 , characterized in that the pulp initial consistency in the catalytic oxidation of the pretreated cellulose is above 6%.

17. The method according to claim 1 , characterized in that the pretreated cellulose is oxidized in the absence of bromide or iodide.

18. The method according to claim 1 , characterized in that after the catalytic oxidation of the pretreated cellulose, aldehyde groups in the cellulose are oxidized to carboxylic groups in a second, complementary oxidation step.

19. The method according to claim 1 , characterized in that the pretreated cellulose is oxidized to the level of 0.5-1.6 mmol COOH/g pulp.

20. The method according to claim 1 , characterized in that after the catalytic oxidation, the oxidized fibrous raw material is disintegrated.

21. The method according to claim 20 , characterized in that the oxidized fibrous raw material is disintegrated to nanofibrillar cellulose (NFC) having shear-thinning behavior, with zero shear viscosity in the range of 1,000 to 100,000 Pa·s, and with a yield stress in the range of 1 to 50 Pa, determined by rotational rheometer at a consistency of 0.5 wt % in aqueous medium.

22. The method according to claim 21 , characterized in that the nanofibrillar cellulose is essentially crystalline with degree of crystallinity of at least 55%, being preferably made of plant material.

23. The method according to claim 20 , characterized in that the oxidized fibrous raw material is disintegrated to nanofibrillar cellulose (NFC) having shear-thinning behavior, with zero shear viscosity in the range of 5,000 to 50,000 and with a yield stress in the range of 3 to 15 Pa, determined by rotational rheometer at a consistency of 0.5 wt % in aqueous medium.

24. The method of claim 1 , where the fibrous cellulosic material is treated in alkaline solution having hydroxide concentration of 0.5-1.5 M.

25. The method of claim 1 , where the fibrous cellulosic material is treated in alkaline solution having hydroxide concentration of 0.6-1.2 M.

26. The method according to claim 1 , characterized in that the treatment time of cellulose in the alkaline solution is 1-15 min.

27. The method according to claim 1 , characterized in that the alkaline solution is sodium hydroxide (NaOH) solution.

28. The method according to claim 1 , characterized in that in the washing step, the pH is lowered to at the most 12.

29. The method according to claim 1 , characterized in that in the washing step, the pH is lowered to below 12.

30. The method according to claim 1 , characterized in that in the pretreatment, the DP of the cellulose decreases at the most by 10% compared with the original value.

31. The method according to claim 1 , characterized in that in the pretreatment, the DP of the cellulose remains the same compared with the original value.

32. The method according to claim 1 , characterized in that in the catalytic oxidation of the pretreated cellulose, the pH is 8-9.5.

33. The method according to claim 1 , characterized in that the pulp initial consistency in the catalytic oxidation of the pretreated cellulose is above 6% and at the most 12%.

34. The method according to claim 1 , characterized in that the pulp initial consistency in the catalytic oxidation of the pretreated cellulose is in the range of 8-12%.

35. The method according to claim 1 , characterized in that the pretreated cellulose is oxidized to the level of 0.5-1.1 mmol COOH/g pulp.

36. The method according to claim 1 , characterized in that the pretreated cellulose is oxidized to the level of 0.6-0.95 mmol COOH/g pulp.

Assignees

• Upm Kymmene Corp

Inventors

• Nuopponen Markus
• Paakkonen Timo
• Ponni Raili
• Vuorinen Tapani

Classifications

• C08B1/08

  Alkali cellulose · CPC title

• C08B15/02

  Oxycellulose; Hydrocellulose; {Cellulosehydrate, e.g. microcrystalline cellulose} · CPC title

• D21H11/18

  Highly hydrated, swollen or fibrillatable fibres · CPC title

• D21C9/005

  organic compounds · CPC title

• C08B15/04 Primary

  Carboxycellulose, e.g. prepared by oxidation with nitrogen dioxide · CPC title