Short-sequence ecf bleaching process x/z/d-eop-d or x/d/z-eop-d for kraft wood pulp

Abstract

The present disclosure belongs to the technical field of papermaking, and specifically relates to a short-sequence ECF bleaching process X/Z/D-EOP-D or X/D/Z-EOP-D for kraft wood pulp, comprising the following steps: (1) sequential bleaching (X/Z/D or X/D/Z): subjecting an oxygen delignified wood pulp to X/Z/D1 or X/D1/Z sequential bleaching to prepare a semi-bleached pulp; (2) reinforced alkaline extraction treatment (EOP): performing hydrogen peroxide and oxygen enhanced alkaline extraction treatment on the pulp after sequential bleaching to further dissolve the residual lignin in the pulp; (3) supplemental bleaching (D): performing a chlorine dioxide supplemental bleaching on the pulp after the enhanced alkaline extraction treatment to obtain a fully bleached pulp (88% ISO).

1 . A short-sequence ECF bleaching process for kraft wood pulp, wherein comprising the following steps:
 subjecting an oxygen delignified wood pulp to X/Z/D 1  or X/D 1 /Z bleaching sequence to prepare a semi-bleached pulp;   performing hydrogen peroxide and oxygen reinforced alkaline extraction treatment on the pulp after sequential bleaching;   performing a chlorine dioxide supplemental bleaching D 2  on the pulp after the reinforced alkaline extraction treatment to obtain a fully bleached pulp;   wherein, in the X/Z/D 1  or X/D 1 /Z bleaching sequence, no pulp washing is between X, Z, and D 1  bleaching.   
     
     
         2 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 1 , wherein the oxygen delignified wood pulp is made of natural wood pulp by kraft pulping. 
     
     
         3 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 2 , wherein the natural wood pulp is prepared by washing and screening wood chips after cooked by kraft pulping, the conditions of cooking are as follows: the amount of alkali used is 21%, the liquid ratio is 1:5, the degree of vulcanization is 25%, the cooking temperature is 170° C., a small degassing is performed at 105° C., the heating time is 100 min, and the holding time is 90 min. 
     
     
         4 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 1 , wherein the oxygen delignification is replaced by enhanced oxygen delignification. 
     
     
         5 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 4 , wherein the conditions of oxygen delignification are as follows: the concentration of unbleached kraft pulp is adjusted to 10%, the amount of NaOH is 3%, the amount of MgSO 4  is 0.6%, the oxygen pressure is 0.6 MPa, the temperature is 100° C., and the holding time is 60 min. 
     
     
         6 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 1 , wherein the conditions of xylanase-assisted bleaching X are as follows: the amount of xylanase is 5-20 U/g pulp, the pulp concentration is 10-15%, pH=5-9, the bleaching temperature is 50-80° C., and the bleaching time is 60-120 min. 
     
     
         7 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 1 , wherein the conditions of ozone bleaching Z are as follows: the bleaching temperature is 50-80° C., the pulp concentration is 10-15%, pH=2-4, the bleaching time is 0.5-5 min, the amount of ethylene glycol is 1-3%, and the amount of ozone is 0.2-1.5%. 
     
     
         8 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 1 , wherein the conditions for chlorine dioxide bleaching D 1  are as follows: the amount of ClO 2  is 0.2-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min. 
     
     
         9 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 1 , wherein the pulp washing is performed between the X/Z/D 1  stage or the X/D 1 /Z stage and the E OP  stage and the D 2  stage. 
     
     
         10 . The short-sequence ECF bleaching process for kraft wood pulp according to  claim 1 , wherein the conditions of the E OP  stage are as follows: the amount of H 2 O 2  is 1-3%, the pulp concentration is 10-15%, pH=11-12, the oxygen pressure is 0.4 MPa, the temperature is 80-90° C., and the alkali treatment time is 30-60 min;
 or, the conditions of bleaching process in D 2  stage are as follows: the amount of ClO 2  is 0.5-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min. 
 
     
     
         11 . A fully bleached pulp prepared by the process according to  claim 1 . 
     
     
         12 . Application of the fully bleached pulp according to  claim 11  in the production of paper and cardboard. 
     
     
         13 . The fully bleached pulp according to  claim 11 , wherein the oxygen delignified wood pulp is made of natural wood pulp by kraft pulping. 
     
     
         14 . The fully bleached pulp according to  claim 13 , wherein the natural wood pulp is prepared by washing and screening wood chips after cooked by kraft pulping, the conditions of cooking are as follows: the amount of alkali used is 21%, the liquid ratio is 1:5, the degree of vulcanization is 25%, the cooking temperature is 170° C., a small degassing is performed at 105° C., the heating time is 100 min, and the holding time is 90 min. 
     
     
         15 . The fully bleached pulp according to  claim 11 , wherein the oxygen delignification is replaced by enhanced oxygen delignification. 
     
     
         16 . The fully bleached pulp according to  claim 15 , wherein the conditions of oxygen delignification are as follows: the concentration of unbleached kraft pulp is adjusted to 10%, the amount of NaOH is 3%, the amount of MgSO 4  is 0.6%, the oxygen pressure is 0.6 MPa, the temperature is 100° C., and the holding time is 60 min. 
     
     
         17 . The fully bleached pulp according to  claim 11 , wherein the conditions of xylanase-assisted bleaching X are as follows: the amount of xylanase is 5-20 U/g pulp, the pulp concentration is 10-15%, pH=5-9, the bleaching temperature is 50-80° C., and the bleaching time is 60-120 min. 
     
     
         18 . The fully bleached pulp according to  claim 11 , wherein the conditions of ozone bleaching Z are as follows: the bleaching temperature is 50-80° C., the pulp concentration is 10-15%, pH=2-4, the bleaching time is 0.5-5 min, the amount of ethylene glycol is 1-3%, and the amount of ozone is 0.2-1.5%. 
     
     
         19 . The fully bleached pulp according to  claim 11 , wherein the conditions for chlorine dioxide bleaching D 1  are as follows: the amount of ClO 2  is 0.2-1.0%, the pulp concentration is 10-15%, pH=2-4, the bleaching temperature is 50-80° C., and the bleaching time is 30-180 min. 
     
     
         20 . The fully bleached pulp according to  claim 11 , wherein the pulp washing is performed between the X/Z/D 1  stage or the X/D 1 /Z stage and the E OP  stage and the D 2  stage.