Method for Reducing the Extractives Content of High-Yield Pulps and Method for Producing Bleached High-Yield Pulps

Abstract

The invention relates to a method for reducing the content of extractives of a high-yield pulp in a peroxide bleaching stage, said stage including peroxide bleaching and a subsequent dewatering or washing, said method comprising contacting the pulp in the peroxide bleaching with an organic stabilizer and in or after the peroxide bleaching with a surfactant, and thereafter subjecting the bleached pulp to said dewatering or washing for removing extractives along with the aqueous phase. The invention also relates to a method for producing bleached high-yield pulp.

1 . A method for treating pulp, said method comprising: 
 peroxide bleaching the pulp;    contacting the pulp with an organic stabilizer before or during the peroxide bleaching:    contacting the pulp with a surfactant before, during or after the peroxide bleaching;    said dewatering and/or washing the peroxide bleached pulp containing the organic stabilizer and the surfactant to remove extractives along with the aqueous phase.    
   
   
       2 . The method according to  claim 1  wherein the organic stabilizer and the surfactant are added to the pulp during the peroxide bleaching.  
   
   
       3 . The method according to  claim 1  wherein the organic stabilizer and the surfactant are added to the pulp before the peroxide bleaching.  
   
   
       4 . The method according to  claim 1  wherein the surfactant is added to the pulp after the peroxide bleaching.  
   
   
       5 . The method according to  claim 1  wherein dilution water is added to the pulp between the peroxide bleaching and the dewatering or washing.  
   
   
       6 . The method according to  claim 5  wherein the surfactant is added to the dilution water.  
   
   
       7 . The method according to  claim 1  wherein the organic stabilizer comprises a polymeric stabilizer.  
   
   
       8 . The method according to  claim 1  wherein the amount of the organic stabilizer is from 0.1 kg to 5 kg per ton dry pulp.  
   
   
       9 . The method according to  claim 1  wherein the surfactant comprises an anionic surfactant.  
   
   
       10 . The method according to  claim 1  wherein the amount of the surfactant is from 0.005 kg to 2 kg per ton dry pulp.  
   
   
       11 . A method for producing a bleached having a reduced content of extractives, comprising: 
 bleaching a pulp with a peroxide;    contacting the pulp with an organic, polymeric stabilizer before or during the peroxide bleaching, in an amount of 0.1 kg to 5 kg) per ton dry pulp, wherein the stabilizer comprises a poly-alpha-hydroxyacrylic acid, a salt thereof, the corresponding polylactone, a homopolymer of acrylic acid, a homopolymer of methacrylic acid, a homopolymer of malcic acid, a copolymer of acrylic acid with an unsaturated dicarboxylic acid, a copolymer of methacrylic acid with an unsaturated dicarboxylic acid, or a combination comprising at least one of the foregoing organic stabilizers;    contacting the pulp with an anionic or nonionic surfactant before the peroxide bleaching, during the peroxide bleaching, or after the peroxide bleaching in an amount of 0.1 kg to 5 kg per ton dry pulp, wherein the surfactant comprises naphthalene sulphonate, naphthalene lignosulphonate, an oil-in-water emulsifier, a fatty alcohol ethoxylate, an alkyl phenol ethoxylate, or a combination comprising at least one of the foregoing surfactants; and    dewatering and/or washing the bleached pulp to remove extractives along with the aqueous phase, to produce a bleached pulp having a reduced content of extractives.    
   
   
       12 . The method according to  claim 11  wherein the organic stabilizer and the surfactant are added to the pulp during the peroxide bleaching.  
   
   
       13 . The method according to  claim 11  wherein the organic stabilizer and the surfactant are added to the pulp before the peroxide bleaching.  
   
   
       14 . The method according to  claim 11  wherein the surfactant is added to the pulp after the peroxide bleaching.  
   
   
       15 . The method according to  claim 11  wherein dilution water is added to the pulp between the peroxide bleaching and the dewatering or washing.  
   
   
       16 . The method according to  claim 15  wherein the surfactant is added to the dilution water.  
   
   
       17 . (canceled)  
   
   
       18 . The method according to  claim 11  wherein the amount of the organic stabilizer is from 0.25 kg to 3 kg per ton of dry pulp.  
   
   
       19 . (canceled)  
   
   
       20 . The method according to  claim 11  wherein the amount of the surfactant is from 0.05 kg t o 1 kg per ton dry pulp.  
   
   
       21 . The method according to  claim 1  wherein the organic stabilizer is a poly-alpha-hydroxyacrylic acid, a salt thereof, the corresponding polylactone, a homopolymer of acrylic acid, a homopolymer of methacrylic acid, a homopolymer of maleic acid, a copolymer of acrylic acid with an unsaturated dicarboxylic acid, a copolymer of methacrylic acid with an unsaturated dicarboxylic acid, or a mixture comprising at least one of the foregoing polymers.  
   
   
       22 . The method according to  claim 1  wherein the surfactant comprises naphthalene sulphonate, naphthalene lignosulphonate, an oil-in-water emulsifier, a fatty alcohol ethoxylate, an alkyl phenol ethoxylate, or a combination comprising at least one of the foregoing surfactants.