Method for producing pulp having low lignin content from lignocellulosic material

Abstract

A method for the production of cellulose having a low lignin content characterized by a combination of the measures that a) a lignocellulosic material is treated with an aqueous solution comprising a C 1-6 -alcohol and having a pH from 10 to 14 at a temperature of below 100° C., whereupon the aqueous solution, in which lignin split off from the lignocellulose is present in dissolved form, is separated from the solid which represents a material enriched with cellulose and hemicellulose, b) hemicellulose is removed from the material of a) enriched with cellulose and hemicellulose, c) the material obtained in b), which is hemicellulose depleted, is treated with an alkali sulfite, an alkaline earth sulfite or ammonium sulfite, in particular Na 2 SO 3 and/or with oxygen in aqueous alkaline solution, whereby lignin dissolves and cellulose having a low lignin content is obtained; as well as cellulose which can be produced by the method.

1 . A method for the production of cellulose having a low lignin content, comprising:
 a) treating a lignocellulosic material with an aqueous solution comprising a C 1-6 -alcohol and having a pH from 10 to 14 at a temperature of below 100° C., whereupon the aqueous solution, in which lignin split off from the lignocellulose is present in dissolved form, is separated from a solid which represents a material enriched with cellulose and hemicellulose,   b) removing hemicellulose from the material of a) enriched with cellulose and hemicellulose to yield a hemicellulose depleted material,   c) treating the material obtained in b) with an alkali sulfite, an alkaline earth sulphite, or ammonium sulfite and/or with oxygen in aqueous alkaline solution, whereby lignin dissolves and cellulose having a low lignin content is obtained.   
     
     
         2 . Method according to  claim 1 , wherein in b) hemicellulose is solubilized from the material of a) enriched with cellulose and hemicellulose by treatment with at least one carbohydrate-cleaving enzyme. 
     
     
         3 . Method according to  claim 1 , wherein in b) hemicellulose is solubilized from the material of a) enriched with cellulose and hemicellulose by treatment with an aqueous alkaline solution at a temperature from 20° C. to 50° C. 
     
     
         4 . Method according to  claim 1 , wherein in b), hemicellulose is solubilized from the material of a) enriched with cellulose and hemicellulose both by treatment with an aqueous alkaline solution at a temperature from 20° C. to 50° C. and by treatment with at least one carbohydrate-cleaving enzyme. 
     
     
         5 . Method according to  claim 1 , wherein in c) a temperature from 90° C. to 150° C. is applied if alkali sulfite, an alkaline earth sulphite, or ammonium sulfite is used. 
     
     
         6 . Method according to  claim 1 , wherein in c) a temperature from 60° C. to 130° C. is applied if oxygen is used. 
     
     
         7 . Method according to  claim 1  wherein straw, bagasse, energy grasses are used as a lignocellulosic material. 
     
     
         8 . Method according to  claim 1  wherein the lignocellulosic material is provided in the aqueous solution at a consistency of from 3 to 30% by weight, based on the dry matter. 
     
     
         9 . Method according to  claim 1  wherein in c) an anthraquinone derivative is added as a mediator in an amount from 0.05 to 5% by weight based on the dry matter. 
     
     
         10 . Cellulose produced according to  claim 1 . 
     
     
         11 . Method according to  claim 1 , wherein the material obtained in b) is treated with Na 2 SO 3 . 
     
     
         12 . Method according to  claim 3 , wherein the temperature is from 25° C. to 35° C. 
     
     
         13 . Method according to  claim 4 , wherein the temperature is from 25° C. to 35° C. 
     
     
         14 . Method according to  claim 5 , wherein the temperature is from 120° C. to 140° C. 
     
     
         15 . Method according to  claim 6 , wherein the temperature is from 80° C. to 100° C. 
     
     
         16 . Method according to  claim 7 , wherein elephant grass, switch grass, and/or husks are used as the lignocellulosic material. 
     
     
         17 . Method according to  claim 16 , wherein lemmas are used as the lignocellulosic material. 
     
     
         18 . Method according to  claim 9 , wherein the anthraquinone derivative is sodium anthraquinone-2-sulfonate. 
     
     
         19 . Method according to  claim 9 , wherein the anthraquinone derivative is added in an amount from 0.1 to 1% by weight based on the dry matter. 
     
     
         20 . Method according to  claim 9 , wherein the anthraquinone derivative is added in an amount of 0.5% by weight based on the dry matter.