Sulfonation of pulp produced by alkali pulping process

Abstract

This invention relates to the delignification of lignocellulosic pulp. More particularly, the invention relates to sulfonation and bleaching of the alkali pulping produced by Kraft pulp processes or produced through combination of alkali pulping processes and extended delignification stages.

What is claimed is: 
     
         1 . A method of making pulp comprising:
 sulfonating an alkali pulp at a pH less than 7 prior to, during, or after at least one bleaching sequence.   
     
     
         2 . The method of  claim 1  wherein the sulfonating of the alkali pulp followed by a washing stage. 
     
     
         3 . The method of  claim 1  wherein the sulfonating of the alkali pulp is performed during a bleaching sequence. 
     
     
         4 . The method of  claim 3  wherein the bleaching sequence is prior or during extended delignification stage. 
     
     
         5 . The method of  claim 3  wherein the bleaching sequence comprises an oxygen delignification stage. 
     
     
         6 . The method of  claim 3  wherein the bleaching sequence comprises an ozone delignification stage. 
     
     
         7 . The method of  claim 3  wherein the bleaching sequence comprises a chlorine-based bleaching agents. 
     
     
         8 . The method of  claim 1  wherein the alkali pulping process is a Kraft pulping process. 
     
     
         9 . The method of  claim 1  comprising a bleaching sequence selected from the group of the formula: D*D 0 , D 0 D*, D*D 0 Eop, D*D 0 Ep, OD*(ZD)EpD 1 , OD*D 0 EpD 1 . 
     
     
         10 . The method of  claim 1  wherein the sulfonating of the alkali pulp is performed by a sulfonating agent 
     
     
         11 . The method of  claim 10  wherein the sulfonating of the alkali pulp selected from the group consisting of sulfur dioxide (SO 2 ) or sulfur trioxide (SO 3 ) or sulfurous acid (H 2 SO 3 ), sodium metabisulfite (Na 2 S 2 O 5 ), bi-sulfite (MHSO 3 ) or sulfite (M 2 SO 3 ) where M can be Na, Ca, H, K, Mg or any combination of two or more thereof. 
     
     
         12 . The method of  claim 1  wherein the pulp pH is from about 2.0 to about 4.0. 
     
     
         13 . The method of  claim 1  wherein the pulp consistency in the D* stage is from about 8% to about 14%. 
     
     
         14 . The method of  claim 1  wherein the retention time is from about 60 min. to about 120 min. 
     
     
         15 . The method of  claim 1  wherein the temperature is from about 70° C. to about 120° C. 
     
     
         16 . The method of  claim 1  wherein the pulp washing stage after the sulfonation stage removes substantially the entire residual sulfonating agent. 
     
     
         17 . The method of  claim 1  wherein 35% less bleaching agent is used in the bleaching sequence as compared to the same or substantially the same bleaching sequences not sulfonating the alkali pulp to obtain the same or substantially the same level of pulp brightness after bleaching. 
     
     
         18 . The method of  claim 1  wherein pulp brightness after bleaching sequences is at least 3 ISO points greater than the brightness of a pulp by the same or substantially the same bleaching sequences not sulfonating the pulp. 
     
     
         19 . A sulfonated and fully bleached pulp comprising a composition of cellulose, hemicelluloses wherein the amount of cellulose contained in the pulp is from about 55% to about 75% by dry weight of the pulp and the amount hemicellulose contained in the pulp is from about 25% to about 45% by dry weight of the pulp. 
     
     
         20 . A paper or paperboard comprising a sulfonated and bleached pulp wherein the amount of cellulose contained in the pulp is from about 55% to about 75% by dry weight of the pulp and the amount hemicellulose contained in the pulp is from about 25% to about 45% by dry weight of the pulp.