A Bleaching Process

Abstract

A bleaching process of pulp is disclosed comprising performing a delignification of the pulp by carrying out in a following sequence: an enzymatic treatment step comprising contacting the pulp with a glycoside hydrolase family GH11 xylanase enzyme at a pH of at least 9.5 and a temperature of at least 85° C., an oxidation step wherein a bleaching agent is added, an alkaline extraction step wherein an alkaline agent is added, and recovering bleached pulp, wherein the GH11 xylanase enzyme has an ability to cause at least 20% reduction in viscosity of a xylan-containing mixture at 90° C. and pH 10.5, compared to the same mixture without any xylanase enzyme.

1 . A bleaching process comprising:
 providing pulp;   performing a delignification of the pulp by carrying out in the following sequence:
 a) an enzymatic treatment step (X) comprising contacting the pulp with a glycoside hydrolase family GH11 xylanase enzyme at a pH of at least 9.5 and a temperature of at least 85° C.; 
 b) an oxidation step (D), wherein a bleaching agent is added; 
 c) an alkaline extraction step (E), wherein an alkaline agent is added; and 
 d) recovering bleached pulp; 
   wherein the GH11 xylanase enzyme has an ability to cause at least 20% reduction in viscosity of a xylan-containing mixture at 90° C., pH 10.5 and at a concentration of 3.0 μg or less of the GH11 xylanase enzyme protein per gram of said xylan-containing mixture, when compared to the xylan-containing mixture without any xylanase enzyme, wherein the xylan-containing mixture comprises 0.07 g/ml or less of xylan.   
     
     
         2 . The process of  claim 1 , wherein the GH11 xylanase enzyme has an ability to cause at least 25% reduction in viscosity of the xylan-containing mixture, compared to the same mixture without any xylanase enzyme. 
     
     
         3 . The process of  claim 1 , wherein the xylan-containing mixture comprises: not more than 0.07 g xylan per ml of said mixture, and not more than 3.0 μg of the GH11 xylanase enzyme protein per gram of said mixture; and wherein the reduction in viscosity takes place within 20 minutes. 
     
     
         4 . The process of  claim 1 , wherein the step X comprises contacting the pulp with the GH11 xylanase enzyme at a pH 9.5-11.5 and a temperature of 85-100° C. 
     
     
         5 . The process of  claim 1 , wherein at least 0.01 g of the GH11 xylanase enzyme protein is added per 1000 kg of dry matter pulp at the step X. 
     
     
         6 . The process of  claim 1 , the delignification further comprising an oxygen-delignification step (O) before the oxidation step D, wherein oxygen is added at the step O; and wherein the step X is before or after the step O. 
     
     
         7 . The process of  claim 1 , wherein the bleaching agent at the oxidation step D comprises an oxygen-containing oxidizing agent. 
     
     
         8 . The process of  claim 1 , wherein the bleaching agent used is H 2 O 2 , a metal chelation step (Q) for removal of metals is performed prior to the oxidation step D, and the GH11 xylanase enzyme is added to the pulp before, during or after the chelation step Q. 
     
     
         9 . The process of  claim 1 , wherein the alkaline agent of the alkaline extraction step E is selected from NaOH, MgO, or combinations thereof. 
     
     
         10 . The process of  claim 1 , wherein the GH11 xylanase enzyme originates from bacteria. 
     
     
         11 . The process of  claim 1 , wherein the GH11 xylanase enzyme has a molecular mass of 19-40 kDa calculated from its amino acid sequence without glycosylation. 
     
     
         12 . The process of  claim 1 , wherein the GH11 xylanase enzyme is a polypeptide comprising an amino acid sequence having amino acids corresponding to the amino acids 3-180 of SEQ ID NO: 2, or functional fragments thereof; the GH11 xylanase enzyme having at least one disulfide bridge between two cysteine residues of the polypeptide. 
     
     
         13 . The process of  claim 1 , wherein the GH11 xylanase enzyme is a polypeptide comprising an amino acid sequence having at least 79% amino acid sequence identity with the amino acids 3-180 of SEQ ID NO: 2, or functional fragments thereof. 
     
     
         14 . The process of  claim 1 , wherein the GH11 xylanase enzyme is a polypeptide comprising an amino acid sequence having at least 79% amino acid sequence identity with the amino acids 3-180 of SEQ ID NO: 2, or functional fragments thereof, wherein the amino acid sequence has at least one disulfide bridge between two cysteine residues of the polypeptide. 
     
     
         15 . A pulp composition comprising:
 (a) pulp having a pH of at least 9.5; and   (b) 0.01-200 g of a glycoside hydrolase family GH11 xylanase enzyme protein per 1000 kg of dry matter pulp;   wherein the GH11 xylanase enzyme protein has:
 xylanase activity, and 
 an ability to cause within 20 minutes at least 20% reduction in viscosity of a xylan-containing mixture at 90° C., pH 10.5 and at a concentration of 3.0 μg or less of the GH11 xylanase enzyme protein per gram of said xylan-containing mixture, when compared to the xylan-containing mixture without any xylanase enzyme, wherein the xylan-containing mixture comprises 0.07 g/ml or less of xylan. 
   
     
     
         16 . The pulp composition of  claim 15 , wherein the GH11 xylanase enzyme is a polypeptide comprising an amino acid sequence having at least 79% amino acid sequence identity with the amino acids 3-180 of SEQ ID NO: 2, or functional fragments thereof. 
     
     
         17 . The pulp composition of  claim 15 , wherein the pulp is cellulosic pulp. 
     
     
         18 . The process of  claim 1 , wherein the pulp is cellulosic pulp.