Alkaline peroxide mechanical pulping of non-woody species

• US 6,258,207 B1
• Filed: 04/19/1999
• Issued: 07/10/2001
• Est. Priority Date: 04/17/1998
• Status: Expired due to Fees

• Current Assignee: Alberta Research Council
• Original Assignee: Alberta Research Council Inc. (Alberta Science & Research Authority)
• Inventors: Pan, George X.
• Primary Examiner(s): Nguyen, Dean T.
• Application Number:
  US09/293,810
• Time in Patent Office: 813 Days
• Field of Search: 162/55, 162/76, 162/77, 162/78, 162/80, 162/90, 162/91, 162/96, 162/97, 162/98, 162/99, 162/27
• US Class Current: 162/27
• CPC Class Codes: D21C 1/04 with acid reacting compounds
• CPC Class Codes: D21C 5/00 Other processes for obtaining cellulose, e.g. cooking cotton linters obtaining fibres for spinning D01C; Processes characterised by the choice of cellulose-containing starting materials
• CPC Class Codes: D21C 9/1042 Use of chelating agents
• CPC Class Codes: D21C 9/163 with peroxides

Abstract

High-yield chemimechanical lignocellulosic pulp is produced from non-woody species by cutting and screening the non-woody species, soaking them in an acidic aqueous solution preferably containing a chelating agent, treating the washed non-woody species with an alkaline peroxide solution containing a second chelating agent, and mechanical refining. To further increase the bleaching efficiency the non-woody species are impregnated with ozone or peracetic acid. The resulting pulp has a relatively high brightness while the consumption of peroxide is reduced compared to prior art processes.

Claims

1. A process for preparing lignocellulosic pulp from non-woody species, the process comprising the step of:

(a) impregnating the non-woody species with an alkaline peroxide solution at a temperature and for a time effective to bleach the non-woody species, and (b) mechanically defibrating the impregnated non-woody species to produce pulp, wherein prior to step (a), pretreating the non-woody species with an aqueous acidic solution at a pH from about 2 to about 3, at a temperature and for a time effective to enhance peroxide bleaching efficiency in step (a).

2. A process according to claim 1 wherein said time effective to enhance peroxide bleaching efficiency in step (a) is from about 0.5 to about 2 hours.

3. A process according to claim 1 wherein the temperature in step (a) is below about 80°

C.

4. A process according to claim 3 wherein said temperature in step (a) is between about 50°

C. and about 80°

C.

5. A process according to claim 1 wherein the aqueous acidic solution contains a chelating agent in an amount ranging between 0 to about 1.5 wt. % based on the dry weight of the non-woody species.

6. A process according to claim 5 wherein the amount of said chelating agent in pretreating step is from about 0.3 wt % to about 0.6 wt %.

7. A process according to claim 5 wherein said chelating agent in step (b) is one or more compounds selected from the group consisting of diethylene triaminepenta-acetic acid, hydroxyethylethylenediaminetriacetic acid, nitriloacetic acid, sodium tripolyphosphate and diethylenetriaminepentamethylene-phosphonic acid.

8. A process according to claim 1 wherein prior to said pretreating step the non-woody species are comminuted.

9. A process according to claim 8 wherein said non-woody species comprise at least one of wheat straw and hemp.

10. A process according to claim 9 wherein the non-woody species in step (a) are ether impregnated with at least one of ozone and or peracids.

11. A process according to claim 10 wherein the alkaline peroxide solution, the ozone and the peracid are added separately or sequentially to the non-woody species.

12. A process according to claim 1 wherein said acidic aqueous solution in said pretreating step contains at least one of acetic acid and sulfuric acid.

13. A process according to claim 1 wherein said alkaline peroxide solution contains at least one alkali selected from sodium carbonate and sodium hydroxide.

14. A process according to claim 13 wherein said alkali is present at a concentration between about 1 and 8 wt. % calculated as sodium hydroxide, of the dry weight of said non-woody species before step (b).

15. A process according to claim 13 wherein said alkaline peroxide solution contains hydrogen peroxide.

16. A process according to claim 15 wherein said hydrogen peroxide is present at a concentration between 2 and about 10 wt. % of the dry weight of said non-woody species before step (b).

17. A process according to claim 1 wherein the alkaline peroxide solution contains a chelating agent in an amount ranging between 0 to about 0.5 wt. % based on the dry weight of the non-woody species.

18. A process according to claim 17 wherein said chelating agent in step (a) is selected from diethylene triaminepenta-acetic acid and diethylene triaminepentamethylene phosphonic acid.

19. A process according to claim 17 wherein said chelating agent is present at a concentration between about 0.05 and 0.4 weight percent of the dry weight of said non-woody species before step (b).

20. A process according to claim 17 wherein occurs a loss of weight of the non woody species in step (b), the loss below about 10 wt. %.

21. A process according to claim 20 wherein a loss of weight of a resulting product in step (a) is below about 25 wt. % based on original weight of the non-woody species.