Environmentally-friendly fiberline for producing bleached chemical pulp

Abstract

An environmentally friendly (ECF), yet commercially viable, process produces fully bleached (typically having a brightness of over 89 or 90% ISO) cellulose pulp using a (ZEND) treatment. Typically pulp is produced in an essentially sulphur-free pulping process (such as an soda/AQ process), and is then treated by a D-E O -, D-E P -, or D-E OP -sequence before the (ZEND) treatment. Optional oxygen delignification may also be used, and subsequent elemental-chlorine-free bleaching sequences may also be employed, although normally not necessary since the pulp after the (ZEND) treatment has high brightness and good viscosity (e.g. over 21 cP).

What is claimed is:  
     
         1 . A method of treating a slurry of comminuted cellulosic fibrous material to produce a bleached chemical pulp, comprising: 
 (a) treating the material in a first stage with a gas containing ozone;    (b) treating the material in a second stage with a liquid containing chlorine dioxide;    (c) between (a) and (b) treating the material with an alkaline liquid to raise the pH of the material prior to (b) and so that no washing is performed between (a) and (b).    
     
     
         2 . A method as in  claim 1  wherein (c) is practiced to raise the pH of the material to at least about 6.0.  
     
     
         3 . A method as in  claim 1  further comprising (d), prior to (a), treating the material in an alkaline chemical pulping process, to produce chemical pulp.  
     
     
         4 . A method as in  claim 3  wherein (d) is practiced using an essentially sulfur-free pulping process.  
     
     
         5 . A method as in  claim 4  wherein (d) is practiced using an alkaline chemical pulping process that includes treatment with a strength or yield enhancing additive.  
     
     
         6 . A method as in  claim 5 , wherein (d) is further practiced using an alkaline chemical pulping process includes a bulk delignification stage, and at least one stage prior to or during bulk delignification stage in which a liquid containing a first level of dissolved organic material is removed from the material and replaced with a second liquid having an at least about 50% lower level of dissolved organic material.  
     
     
         7 . A method as in  claim 1  wherein (a) is preceded by (a 1 ) treating the material with a liquid containing chlorine dioxide, followed by (a 2 ) treating the material with an alkaline liquid.  
     
     
         8 . A method as in  claim 7  wherein (a 2 ) includes a treatment with oxygen, a peroxide, or both.  
     
     
         9 . A method as recited in  claim 4  wherein (d) is practiced using a soda pulping process.  
     
     
         10 . A method as recited in  claim 4  wherein (d) is practiced using a soda/AQ pulping process.  
     
     
         11 . A method as recited in  claim 10  wherein (c) is practiced to raise the pH of the material to at least about 7.0  
     
     
         12 . A method as recited in  claim 2  further comprising (d), prior to (a), treating the material in an alkaline chemical pulping process that includes anthraquinone, polysulfide, or their equivalents or derivatives.  
     
     
         13 . A method as in  claim 2  wherein (a) is preceded by (a 1 ) treating the material with a liquid containing chlorine dioxide, followed by (a 2 ) treating the material with an alkaline liquid.  
     
     
         14 . A method as in  claim 13  further comprising (d), prior to (a), treating the material in an alkaline chemical pulping process, to produce chemical pulp.  
     
     
         15 . A method as recited in  claim 14  wherein (d) is practiced using a soda/AQ pulping process.  
     
     
         16 . A method as in  claim 15 , wherein (d) is further practiced using an alkaline chemical pulping process includes a bulk delignification stage, and at least one stage prior to or during bulk delignification stage in which a liquid containing a first level of dissolved organic material is removed from the material and replaced with a second liquid having an at least 50% lower level of dissolved organic material.  
     
     
         17 . A method for producing bleached chemical pulp from comminuted cellulosic fibrous material comprising: 
 (a) treating the material in a chemical pulping process in the presence of chemical additive to produce a chemical pulp containing at least some of the additive;    (b) treating the chemical pulp with at least one elemental-chlorine-free bleaching agent to produce a bleached chemical pulp having at least some discoloration due to the presence of the chemical additive; and    (c) treating the bleached pulp with at least one oxidizing agent to remove the discoloration produced by the presence of the chemical additive.    
     
     
         18 . A method as in  claim 17  wherein (a) is practiced using anthraquinone or its equivalents or derivatives as the chemical additive used in the pulping process.  
     
     
         19 . A method as in  claim 17  wherein (b) is practiced using as the at least one bleaching agent one or more of the following bleaching agents: oxygen, chlorine dioxide, sodium hydroxide, ozone, and hydrogen peroxide.  
     
     
         20 . A method as in  claim 17  wherein (b) is practiced so that the discoloration is characterized by a yellow or orange tinge to the pulp.  
     
     
         21 . A method as in  claim 17  wherein (c) is practiced using as the oxidizing agent at least one of air, oxygen, peroxide, or ozone.  
     
     
         22 . A method as in  claim 18  wherein (c) is practiced using as the oxidizing agent a gas containing ozone; and wherein (a) is a soda/AQ pulping process; and wherein (b) is practiced using as the at least one bleaching agent one or more of the following bleaching agents: oxygen, chlorine dioxide, sodium hydroxide, ozone, and hydrogen peroxide.  
     
     
         23 . A method of ECF treatment of comminuted cellulosic fibrous material comprising the sequence soda/AQ cooking, and then one of D-E p -(ZEND), or D-E o -(ZEND), or D-E op -(ZEND).  
     
     
         24 . A method as in  claim 23  wherein the treatment is practiced to produce pulp with a brightness over 89% ISO.  
     
     
         25 . Pulp produced according to  claim 24 , having a viscosity of over 21 cP.