Process for treating a cellulose-lignin pulp

Abstract

A process of treating a cellulose-lignin pulp. In an ozone stage, the pulp is contacted with ozone to bleach and delignify the pulp. The ozone stage is conducted without the addition of a peroxide bleaching agent. A chelant is introduced into the ozone stage to improve selectivity of the delignification.

1 . A process of treating a cellulose-lignin pulp comprising: 
 in an ozone stage, contacting the pulp with ozone to bleach and delignify the pulp, without the addition of a peroxide bleaching agent; and    introducing a chelant into the ozone stage to improve selectivity of the delignification.    
   
   
       2 . The process of  claim 1  wherein the ozone stage produces hydrogen peroxide, and the introduction of the chelant reduces decomposition of the hydrogen peroxide.  
   
   
       3 . The process of  claim 1  wherein the pulp comprises a suspension of a cellulose-lignin material in water, and the pulp further comprises trace metals, and the chelant ties up the trace metals.  
   
   
       4 . The process of  claim 3  comprising the additional steps, before the ozone stage, of determining the species of trace metal and/or the amount of trace metal in the pulp, and then selecting the chelant type and/or chelant dose to match the trace metal based on the trace metal determination.  
   
   
       5 . The process of  claim 1  wherein the selectivity of the delignification is improved by at least about 10% compared to the same process without the chelant.  
   
   
       6 . The process of  claim 1  wherein the pulp is a wood pulp.  
   
   
       7 . The process of  claim 6  wherein the wood pulp is a chemical pulp or a recycle pulp.  
   
   
       8 . The process of  claim 1  wherein the chelant is a phosphonate.  
   
   
       9 . The process of  claim 1  wherein the pulp comprises a suspension of a cellulose-lignin material in water, and the pulp has a consistency within a range of from about 0.2% to about 50% cellulose-lignin material by weight of the pulp.  
   
   
       10 . The process of  claim 1  wherein the pulp comprises a suspension of a cellulose-lignin material in water, and wherein the chelant is introduced into the pulp in an amount within a range of from about 1 to about 100 times the total trace metals.  
   
   
       11 . The process of  claim 10  wherein the chelant is introduced in an amount within a range of from about 20 to about 50 times the total trace metals.  
   
   
       12 . The process of  claim 1  wherein the pulp is reacted with the ozone for a time within a range of from about 1 second to about 5 hours.  
   
   
       13 . The process of  claim 12  wherein the reaction time is within a range of from about 10 seconds to about 10 minutes.  
   
   
       14 . The process of claim I wherein the pulp is reacted with the ozone at a temperature within a range of from about 20° C. to about 90° C.  
   
   
       15 . The process of  claim 14  wherein the reaction temperature is within a range of from about 20° C. to about 35° C.  
   
   
       16 . The process of  claim 1  wherein the pulp is reacted with the ozone at a pH within a range of from 1 to about 7.  
   
   
       17 . The process of  claim 16  wherein the pH of the reaction is within a range of from about 2 to about 6.  
   
   
       18 . The process of  claim 1  wherein the bleaching and delignification is conducted with the ozone as the only bleaching/delignification agent.  
   
   
       19 . The process of  claim 1  wherein the ozone stage is conducted without the use of cyanamide or cyanamide salt.  
   
   
       20 . A process of treating a wood pulp comprising: 
 in an ozone stage, contacting the pulp with ozone to bleach and delignify the pulp, the ozone stage producing hydrogen peroxide; and    introducing a chelant into the ozone stage to tie up trace metals in the pulp and reduce decomposition of the hydrogen peroxide, thereby improving selectivity of the delignification.    
   
   
       21 . The process of  claim 20  wherein the wood pulp is a chemical pulp or a recycle pulp.  
   
   
       22 . A process of treating a cellulose-lignin pulp in which, in an ozone stage, the pulp is contacted with ozone to bleach and delignify the pulp, the ozone stage producing hydrogen peroxide which decomposes to produce first free radicals, and the first free radicals activating decomposition of the ozone to produce second free radicals, the first and second free radicals causing degradation of the cellulose; 
 the improvement comprising introducing a chelant into the ozone stage to reduce decomposition of the hydrogen peroxide, thereby reducing production of the first free radicals, thereby reducing activation of the decomposition of the ozone and production of the second free radicals, and thereby reducing the degradation of the cellulose to improve selectivity of the delignification.    
   
   
       23 . The process of  claim 22  wherein the pulp is a wood pulp.