Method of making pulp having high hemicellulose content

Abstract

Bleached, Kraft chemical pulp having increased hemicellulose content compared to conventional Kraft chemical pulps. In one embodiment, the pulp has a hemicellulose content greater than about 17 weight percent as measured by the 18% caustic solubility test. In another aspect, a method for making wood cellulose pulp having increased hemicellulose content compared to conventional Kraft chemical pulps. In the method, a lignocellulosic material is pulped in caustic sulfide to provide a first brownstock, which is treated with oxygen to provide a second brownstock, which is then bleached to provide the pulp product.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:  
     
         1 . A method for making a chemical pulp, comprising: 
 (a) pulping a lignocellulosic material in caustic sulfide to provide a first brownstock, wherein the caustic sulfide comprises polysulfide and anthraquinone;    (b) treating the first brownstock with oxygen to provide a second brownstock; and    (c) bleaching the second brownstock to provide a bleached pulp.    
     
     
         2 . The method of  claim 1 , wherein the polysulfide is present in an amount from about 4 to about 9 g/L in the white liquor.  
     
     
         3 . The method of  claim 1 , wherein the anthraquinone is present in an amount from about 0.03 to about 0.1 percent by weight based on the weight of lignocellulosic material.  
     
     
         4 . The method of  claim 1 , wherein the kappa number after pulping is in the range from about 20 to about 65.  
     
     
         5 . The method of  claim 1 , wherein the kappa number after pulping is in the range from about 36 to about 43.  
     
     
         6 . The method of  claim 1 , wherein treating the first brownstock with oxygen comprises treating with oxygen at a pressure between about 80 and about 120 psi and at a temperature from about 90 to about 130° C.  
     
     
         7 . The method of  claim 1 , wherein the kappa number after treating with oxygen is in the range from about 8 to about 35.  
     
     
         8 . The method of  claim 1 , wherein bleaching comprises bleaching without elemental chlorine.  
     
     
         9 . The method of  claim 1 , wherein bleaching comprises bleaching with chlorine dioxide.  
     
     
         10 . The method of  claim 1 , wherein bleaching comprises at least two chlorine dioxide bleaching stages.  
     
     
         11 . The method of  claim 1 , wherein bleaching comprises an alkali extraction stage.  
     
     
         12 . The method of  claim 1 , wherein bleaching comprises bleaching without chlorine.  
     
     
         13 . The method of  claim 1 , wherein bleached pulp has a hemicellulose content greater than about 17 weight percent as measured by the 18% caustic solubility test (TAPPI T-235 CM-00).  
     
     
         14 . A method for making a chemical pulp, comprising: 
 (a) pulping a lignocellulosic material in caustic sulfide to provide a first brownstock, wherein the kappa number after pulping is in the range from about 20 to about 65;    (b) treating the first brownstock with oxygen to provide a second brownstock; and    (c) bleaching the second brownstock to provide a bleached pulp.    
     
     
         15 . A method for making a chemical pulp, comprising: 
 (a) pulping a lignocellulosic material in caustic sulfide to provide a first brownstock;    (b) treating the first brownstock with oxygen to provide a second brownstock; and    (c) bleaching the second brownstock to provide a bleached pulp, wherein bleached pulp has a hemicellulose content greater than about 17 weight percent as measured by the 18% caustic solubility test (TAPPI T-235 CM-00).