PROCESS AND A DISSOLVING PULP MANUFACTURED BY THE PROCESS

• US 20150136346A1
• Filed: 05/28/2013
• Published: 05/21/2015
• Est. Priority Date: 05/28/2012
• Status: Active Grant

• Current Assignee: Lenzing AG (B & C Privatstiftung), Sodra Skogsagarna Ekonomisk Forening Co.
• Original Assignee: Lenzing AG (B & C Privatstiftung), Sodra Cell AB
• Inventors: Bogren, Johannes, Borgards, Andrea, Parks, Jim, Schild, Gabriele
• Granted Patent: US 10,023,995 B2
• Time in Patent Office: Days
• US Class Current: 162/41
• CPC Class Codes: C08B 9/00 Cellulose xanthate; Viscose formation of films C08J5/18; formation of fibres D01F; rendering cellulose suitable for esterification C08B1/02
• CPC Class Codes: C08H 8/00 Macromolecular compounds derived from lignocellulosic materials pretreatment thereof B27N
• CPC Class Codes: D21C 11/0007 Recovery of by-products, i.e. compounds other than those necessary for pulping, for multiple uses or not otherwise provided for volatile compounds obtained by decomposition of spent liquors in order to regenerate them D21C11/125; compounds obtained by fractionating the liquors in order to regenerate them D21C11/0042
• CPC Class Codes: D21C 11/0057 Oxidation of liquors, e.g. in order to reduce the losses of sulfur compounds, followed by evaporation or combustion if the liquor in question is a black liquor deodorisation of gases D21C11/08; combustion D21C11/12, D21C11/14
• CPC Class Codes: D21C 3/02 with inorganic bases or alkaline reacting compounds, e.g. sulfate processes
• CPC Class Codes: D21C 3/022 in presence of S-containing compounds
• CPC Class Codes: D21C 3/045 in presence of O2 or O3
• CPC Class Codes: D21C 9/004 inorganic compounds
• CPC Class Codes: D21C 9/02 Washing ; Displacing cooking or pulp-treating liquors contained in the pulp by fluids, e.g. wash water or other pulp-treating agents
• CPC Class Codes: D21C 9/18 De-watering de-watering in general F26B; Elimination of cooking or pulp-treating liquors from the pulpD21C9/002, D21C9/02 take precedence; paper-making machines D21F; strainers in digesters D21C7/00; presses in general B30B
• CPC Class Codes: D21H 11/04 Kraft or sulfate pulp
• CPC Class Codes: Y02W 30/64 Paper recycling

Abstract

The invention relates to processes for manufacturing pulp and more specifically to improved processes for manufacturing dissolving pulp. The processes have primarily been developed to be used in connection with large scale kraft processes, i.e. they have been designed to be incorporated into a plant. A liquor derivable from the process and comprising xylan, lignin, alkali and water is also disclosed as well as a dissolving pulp produced by the process.

Claims

1. A process for manufacturing dissolving pulp comprising the steps of:

a) selecting a wood based raw material, said wood based raw material having a xylan content of from 12 weight % or more;

b) adding a cooking liquor comprising white and/or black liquor to the wood based raw material;

c) digesting the wood based raw material composition obtained from step b) in a kraft cooking process;

d) oxygen delignifying the pulp obtained from step c);

e) adding industrial white liquor with high ionic strength to the pulp obtained from step d) wherein said pulp has a xylan content of 8 weight % or more and wherein the temperature is lowered and kept at 65°

C. or lower for 5 minutes or more and wherein the alkali concentration in the liquid phase of the obtained pulp suspension is in the range of 70 g/l to 100 g/l; and

f) removing 90% or more of the alkali and dissolved xylan as a liquor flow from the pulp obtained from step e) by dewatering the pulp; and

g) subjecting the pulp to washing and pressing in a washing press device 1-5 times.

2. The process according to claim 1, wherein said white liquor comprises Na₂CO₃, NaHS and NaOH.

3. The process according to claim 1, wherein said white liquor added in step e) has a suspended solids content of 20 mg/l or less.

4. The process according to claim 1, wherein said white liquor has a combined Na⁺ and K⁺ concentration of from 3 to 5 mol/l, OH concentration of from 2.25 to 3.5 mol/l, HS⁻

concentration of from 0.2 to 1.0 mol/l, and a CO₃²⁻

concentration of from 0.10 to 0.60 mol/l.

5. The process according to claim 1, wherein the pulp obtained from step g) is filtered in a wash filter.

6. The process according to claim 1, wherein the temperature in step e) is 60°

C. or lower.

7. The process according to claim 1, wherein the alkali concentration in step e) is in the range of from 85 to 100 g/l.

8. The process according to claim 1, wherein said process comprises a washing step between step d) and step e), said washing step comprising washing the pulp obtained from step d) in a washing device.

9. The process according to claim 1, wherein xylan and alkali removed in step f) are recirculated as a liquor flow and used as an alkali source in step e) and/or wherein xylan and alkali are removed as a liquor flow and used as an alkali/xylan source in another process for manufacturing pulp.

10. The process according to claim 1, wherein xylan and alkali removed in step f) are recirculated as a liquor flow and used as an alkali source in step d).

11. The process according to claim 10, wherein said liquor flow is oxidized before being used in step d).

12. The process according to claim 9, wherein the alkali concentration of said liquor flow is in the range of from 60 to 90 g/l without any supplementary addition of alkali.

13. The process according to claim 12, wherein said liquor flow is used as an alkali source in another process for manufacturing pulp.

14. The process according to claim 1, wherein said process comprises a step before step b), which step comprises activation of the wood based raw material by using steam until a P-factor of from 0 to 200 has been reached.

15. The process according to claim 1, wherein said process comprises a step after step g), which step is a combined depolymerization and bleaching step.

16. The process according to claim 15, wherein said combined depolymerization and bleaching step is performed by adding ozone, or by adding hypochlorite or by adding chlorine dioxide and sulfuric acid.

17. The process according to claim 15, wherein said combined depolymerization and bleaching step is performed at a temperature of from 80 to 99°

C. and at an effective acid charge of from 5 to 20 kg H₂SO₄/air dried tons.

18. The process according to claim 15, wherein the obtained pulp after the combined bleaching and depolymerization step comprises 6 weight % or less xylan.

19. A liquor obtained from the process of claim 1, wherein the liquor comprises xylan, water, lignin and alkali, wherein the xylan/lignin ratio is from 2:

1 to 20;

1.

20. The liquor according to claim 19, wherein said liquid comprises xylan having a weight average molecular weight (M_w) of from 15 to 40 kg/mol.

21. A pulp obtained from the process for producing dissolving pulp according to the process of claim 1.

22. A pulp according to claim 21, wherein said pulp has a kink of from 1.3 to 2.0 kinks/mm and a shape factor of from 70 to 82%.

23. The pulp according to claim 21, wherein said pulp has a cellulose II content of from 7 to 50 weight % based on the total amount of cellulose and a lateral fibril aggregate dimension of from 16 to 40 nm.

24. A pulp according to claim 21, wherein the pulp is present in a cellulosic product.