Effect of low dose xylanase on pulp in prebleach treatment process

Abstract

A prebleach treatment of pulp with xylanase enzyme prior to chemical bleaching is disclosed. A process of making pulp comprises treating a pulp with xylanase in an amount of less than 50 g of xylanase per ton of pulp. The treating step is carried while buffering the pulp and xylanase with a buffering agent to a pH of from about 6.5 to about 7.5 prior to at least one bleaching stage to form a treated pulp.

1 . A process of making pulp comprising:
 treating a pulp with xylanase in an amount of less than 50 g of xylanase per ton of pulp, wherein the treating step is carried while buffering the pulp and xylanase with a buffering agent to a pH of from about 6.5 to about 7.5 prior to at least one bleaching stage to form a treated pulp.   
     
     
         2 . The process of  claim 1  wherein the pulp is unbleached. 
     
     
         3 . The process of  claim 1  wherein the xylanase is luminase enzyme. 
     
     
         4 . The process of  claim 1  wherein the luminase is endo-β-1,4-xylanase. 
     
     
         5 . The process of  claim 1  wherein the pulp is treated with the xylanase in an amount from about 10 g to about 50 g per ton of pulp. 
     
     
         6 . The process of  claim 3  wherein the pulp is treated with the xylanase in an amount from about 30 g to about 50 g per ton of pulp. 
     
     
         7 . The process of  claim 1  wherein the buffering agent is selected from a group of carbon dioxide (CO 2 ) and H 2 SO 4 . 
     
     
         8 . The process of  claim 1  wherein the pulp is subjected to a first bleaching stage (D o ) after the treating step. 
     
     
         9 . The process of  claim 8  wherein the treated pulp causes 10 to 30% reduction of bleaching chemicals in first bleaching stage (D o ) without causing an increase in pulp yield loss and bleached filtrate Chemical Oxygen Demand (COD) loading as compared with a pulp not being treated in accordance to  claim 1 . 
     
     
         10 . The process of  claim 8  wherein the treated pulp after the first bleaching stage step (D o ) is subjected to an Eop bleaching stage. 
     
     
         11 . The process of  claim 10  wherein the treated pulp permits a reduction of pH by 2 units in the subsequent Eop bleaching stage to minimize the filtrate Chemical Oxygen Demand (COD) filtration as compared with a pulp not being treated in accordance to  claim 1 . 
     
     
         12 . The process of  claim 11  wherein the pH of treated pulp in Eop bleaching stage is from about 9 to about 11. 
     
     
         13 . The process of  claim 10  wherein the treated pulp permits a reduction of temperature by 15° C. in the Eop bleaching stage as compared with a pulp not being treated in accordance to  claim 1 . 
     
     
         14 . The process of  claim 13  wherein the temperature in the Eop bleaching stage is from about 55° C. to about 85° C. 
     
     
         15 . The process of  claim 1  wherein the xylanase is added to the pulp at and/or after the pulp is washed. 
     
     
         16 . The process of  claim 1  wherein the buffering agent is added to the pulp simultaneously with, prior to, or after the xylanase is added to the pulp. 
     
     
         17 . The process of  claim 1  wherein the retention time for the treating step of the pulp is from about 15 min. to about 240 min. 
     
     
         18 . The process of  claim 1  wherein the temperature for the treating step of the pulp is from about 40° C. to about 70° C. 
     
     
         19 . The process of  claim 1  wherein the consistency for the treating step is from about 2% to about 15%. 
     
     
         20 . The process of  claim 1  wherein the treated pulp ISO brightness is at least about 2 to 5% greater than the brightness of the pulp made by the same or substantially the same bleaching processes without the pulp being treated in accordance to  claim 1 . 
     
     
         21 . The process of  claim 1  wherein treating the pulp with xylanase in an amount from 10 g to of 50 g of xylanase per ton of pulp and wherein the treating step is carried while buffering the pulp and xylanase with a buffering agent to a pH of from about 6.5 to about 7.5 prior to at least one bleaching stage. 
     
     
         22 . The process of  claim 21  wherein treating the pulp with xylanase in an amount from 10 g to of 15 g of xylanase per ton of pulp and wherein the treating step is carried while buffering the pulp and xylanase with a buffering agent to a pH of from about 6.8 to about 7.2 prior to at least one bleaching stage. 
     
     
         23 . The process of  claim 1  further comprising a step of recycling unused enzyme from a prewasher and added to an outlet of a washer for pH control. 
     
     
         24 . In a pulp bleaching system comprising at least one Do stage and at least one Eop bleaching stage, a prebleach treatment stage which comprises:
 pulp;   xylanase in an amount of less than 50 g of xylanase per ton of pulp; and   a buffering agent being used buffering the pulp and xylanase to provide a pH in the prebleach treatment stage from about 6.5 to about 7.5.