Enzymatic treatment of pulp for lyocell manufacture

Abstract

Bleached and unbleached pulps are treated with an enzyme in one or more stages of the bleaching process to yield a low DP pulp suitable for lyocell manufacture. This allows higher throughput of fiber an economy of manufacture.

1 . A method for making a lyocell pulp comprising the steps of
 providing an unbleached pulp;   wherein said pulp has a IV of from 10 to 5 dl/g;   contacting said pulp in a bleaching sequence;   wherein said bleach sequence has at least one stage of an enzyme treatment;   wherein said bleach sequence having at least one enzyme treatment reduces said pulp by 8 to 2 IV units;   and wherein said bleached pulp is suitable for lyocell manufacture.   
     
     
         2 . The method of  claim 1  wherein the enzyme treatment is immediately after the oxygen delignification stage. 
     
     
         3 . The method of  claim 1  wherein the enzyme treatment is after the last bleaching stage. 
     
     
         4 . The method of  claim 1  wherein the enzyme treatment is immediately after the oxygen delignification stage and after the last bleaching stage. 
     
     
         5 . The method of  claim 1  wherein the enzyme is added at 0.045 to 4.5 kg/MT pulp. 
     
     
         6 . The method of  claim 1  wherein the enzyme is added at 0.136 to 3.27 kg/MT pulp. 
     
     
         7 . The method of  claim 1  wherein the enzyme is added at 0.227 to 1.3 kg/MT pulp. 
     
     
         8 . The method of  claim 1  wherein the IV is reduced to 2 to 4 IV units 
     
     
         9 . The method of  claim 1  wherein the IV is reduced to 2.5 to 3.5 IV units. 
     
     
         10 . The method of  claim 1  wherein the pH is adjusted after the oxygen delignification stage and before the bleaching stage. 
     
     
         11 . The method of  claim 10  wherein the pH is adjusted in the range of a pH of 3 to a pH of 10. 
     
     
         12 . The method of  claim 1  wherein the pH is adjusted after the last bleaching stage. 
     
     
         13 . The method of  claim 12  wherein the pH is adjusted in the range from a pH of 3 to a pH of 10. 
     
     
         14 . The method as in any one of  claims 10  or  12  wherein the pH is adjusted with carbon dioxide. 
     
     
         15 . The method as in any one of  claims 10  or  12  wherein the pH is adjusted with a mineral acid. 
     
     
         16 . The method as in any one of  claims 10  or  12  wherein the pH is adjusted with an organic acid. 
     
     
         17 . The method of  claim 1  wherein the enzyme is selected from the group consisting of xylanases, cellulases, hemicellulases, peroxidases, mannases, laccases, lipases and combinations thereof.