Process for producing a pulp

Patent metadata

Field	Value
Publication number	US-10648129-B2
Application number	US-201715856996-A
Country	US
Kind code	B2
Filing date	Dec 28, 2017
Priority date	May 10, 2006
Publication date	May 12, 2020
Grant date	May 12, 2020

Abstract

The invention relates to a process for producing a dissolving pulp from a cellulosic starting material using the kraft process, comprising the step of cooking the starting material with a cooking liquor. The process according to the invention characterized in that the starting material is exposed to a steam treatment prior to cooking and that the pulp obtained by cooking is subjected to cold caustic extraction (CCE) in the course of further processing.

First claim

What is claimed is:

1. A process for producing a lyocell fiber from a dissolving pulp, comprising the step of cooking a cellulosic starting material with a cooking liquor in a kraft process to obtain the dissolving pulp, wherein the cellulosic starting material is exposed to a steam treatment prior to cooking, wherein the steam treatment consists of applying a temperature of 120° C. or more and a P-factor of 50 or less, wherein the dissolving pulp obtained by cooking is subjected to cold caustic extraction (CCE) in the course of further processing whereby a CCE treated dissolving pulp is formed, and wherein the lyocell fiber having a content H of hemicellulose of more than 3.5% by weight and less than 5% by weight is produced from the CCE treated dissolving pulp.

2. The process according to claim 1 , further comprising treating the dissolving pulp obtained by cooking to adjust the degree of polymerization (DP).

3. The process according to claim 1 , wherein, for the steam treatment, the cellulosic starting material is treated with medium-pressure steam at a temperature of from 150 to 180° C.

4. The process according to claim 1 , wherein the cellulosic starting material is subjected to an impregnation prior to cooking.

5. The process according to claim 1 , wherein the cooking, the steam treatment and optionally an impregnation of the cellulosic starting material are carried out in the same cooker.

6. The process according to claim 1 , wherein the cooking is carried out in a form of continuous batch cooking (CBC).

7. The process according to claim 1 , wherein at least a portion of a press liquor formed in the cold caustic extraction is purified using a membrane separation process.

8. The process according to claim 7 , wherein the membrane separation process is nanofiltration.

9. The process according to claim 7 , wherein the membrane separation process is an ultrafiltration.

10. The process according to claim 1 , wherein at least one of a portion of a press liquor formed in the cold caustic extraction and a portion of a retentate of a membrane separation process performed on the press liquor is supplied to the cooking liquor of a linked cooking process carried out for the production of paper pulp.

11. The process according to claim 1 , further comprising bleaching the pulp obtained by cooking.

12. The process according to claim 1 , wherein the cooking step of the pulp is carried out in two stages, and wherein, in a first stage, a delignification using a first cooking liquor to a kappa number of from 35 to 70 in case of softwoods as the cellulosic starting material and to a kappa number of from 30 to 60 in case of hardwoods as the cellulosic starting material is carried out and, in a second stage, the cooking is continued to the desired degree of purity of the pulp, using a second cooking liquor.

Assignees

• Chemiefaser Lenzing Ag

Inventors

• Sixta Herbert
• Promberger Andrea
• Borgards Andrea
• Möslinger Roland

Classifications

• D21C3/02

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

• C08B37/14

  Hemicellulose; Derivatives thereof (not used) · CPC title

• D21C9/001

  Modification of pulp properties (purification D21C9/08) · CPC title

• D21C1/02 Primary

  with water or steam · CPC title

• D21C9/004 Primary

  inorganic compounds · CPC title