Refining of vegetable matter and delignification of the refined matter with chlorine dioxide

Abstract

.[.A process for the delignification of chips of vegetable matter by pretreating the chips to obtain at least 64 percent by weight refined vegetable matter, and delignifying the refine vegetable matter with chlorine dioxide. A pulp produced in high yield by the process which refines easier, dries more readily on a paper machine, exhibits higher on-machine filler retention, and possesses greater strength than conventionally bleached kraft pulp made from the same wood mixture. A paper produced from said pulp which has higher tensile, tear, burst, fold, pick and delamination strengths and greater brightness stability that paper produced from conventionally bleached kraft pulp made from the same wood mixture..]. .Iadd.A process of delignifying lignocellulosic vegetable matter wherein the vegetable matter is pretreated to obtain a refined vegetable matter which is thereafter delignified by reacting it in at least two stages with chlorine dioxide, each successive stage using less chlorine dioxide than the preceding stage and the total chlorine dioxide used being from about 1% to about 15% based upon the dry weight of the vegetable matter, and wherein the vegetable matter is extracted between successive chlorine dioxide stages with a caustic material, pulp produced from said process and paper prepared from said pulp..Iaddend.

What is claimed is: 
     
       1. A process for the delignification of .Iadd.lignocellulosic .Iaddend.vegetable matter comprising, in combination, the steps of: (a) pretreating said vegetable matter to obtain a refined vegetable matter in a yield of about 64% to about 100% by weight, based upon the dry weight of said vegetable matter,   (b) .Iadd.delignifying .Iaddend. .[.reacting.]. said refined vegetable matter .Iadd.by reacting it in at least two stages .Iaddend.with .[.at least about 2% to about 15%.]. .Iadd.preformed .Iaddend.chlorine dioxide.Iadd. , each successive stage using less chlorine dioxide than its preceding stage, and the total chlorine dioxide used being from about 1% to about 15% based upon said dry weight.Iaddend.; .Iadd.and .Iaddend.   (c) .[.treating.]. .Iadd.extracting .Iaddend.said vegetable matter .Iadd.between successive chlorine dioxide stages .Iaddend.with a water-soluble caustic material at a temperature of from about 50° C. to about 75° C; wherein said water soluble material is an alkali metal hydroxide, alkali metal carbonate, ammonium hydroxide or ammonia gas.[.; and   (d) reacting said vegetable matter with chlorine dioxide.]..   
     
     
       2. The process of claim 1 wherein said reacting following said pretreatment comprises, sequentially, chlorine dioxide treatment, water wash, caustic extraction, water wash, chlorine dioxide treatment, water wash, caustic extraction, water wash, chlorine dioxide treatment, and water wash. 
     
     
       3. The process of claim 2 wherein said water-soluble caustic material is sodium hydroxide or sodium carbonate. 
     
     
       4. The process of claim 2 wherein said caustic material is sodium hyroxide in aqueous solution. 
     
     
       5. The process of claim 2 wherein said pretreating is substantially a mechanical operation. 
     
     
       6. The process of claim 2 wherein said pretreating is a chemical prepulping treatment selected from the group consisting of sodium sulfide prepulping, acid sulfite prepulping, cold soda prepulping, soda prepulping, sodium xylene sulfonate prepulping, bisulfite prepulping, kraft prepulping, .Iadd.neutral sulfite prepulping .Iaddend.and nitric acid prepulping. 
     
     
       7. The process of claim 2 wherein said pretreating includes, in combination, the steps of: (i) prepulping prepared vegetable matter chips by a kraft, nitric acid, bisulfite, or neutral sulfite process;   (ii) refining said prepulped vegetable matter;   (ii) washing said prepulped vegetable matter; and   (iv) dewatering said prepulped vegetable matter.   
     
     
       8. The process of claim 7 wherein said chips of vegetable matter are prepulped by a process comprising contacting said vegetable matter with from about 5% to about 30% sodium sulfite by weight and from about 5% to about 25% sodium carbonate by weight, both percentages being based upon the dry weight of said vegetable matter. 
     
     
       9. The process of claim 2 wherein the pH of the mixture of vegetable matter and chlorine dioxide of step (b) varies up to about 8.0. 
     
     
       10. The process of claim 2 wherein said vegetable matter is treated with about 4% of said water-soluble caustic material and the total .[.concentration.]. .Iadd.amount .Iaddend.of chlorine dioxide used is from about .[.1.]. .Iadd.2.Iaddend.% to about .[.15.]. .Iadd.13.Iaddend.% by weight, all percentages being based on the total dry weight of said vegetable matter fed to the pretreating stage. 
     
     
       11. The process of claim 1 wherein the temperature of the mixture of said vegetable matter and said chlorine dioxide of step (d) is adjusted to from about 40° C. to about 60° C. 
     
     
       12. The process of claim 2 wherein fresh water is fed only to the last water washing step and then circulated countercurrently to the flow of said vegetable matter to the next to last water washing, to the next preceding washing, and finally to the first water washing. 
     
     
       13. The process of claim 2 wherein said chlorine dioxide .[.is a mixture of chlorine dioxide and.]. .Iadd.contains .Iaddend.chlorine .[.wherein.]. .Iadd.and .Iaddend.said chlorine is less than about 30% .[.by weight.]. of the total chlorine dioxide requirement on equivalent oxidant basis. 
     
     
       14. A process for the delignification of vegetable matter comprising, in combination, the steps of: (a) pretreating said vegetable matter to obtain a refined vegetable matter in a yield of about 64% to about 95% by weight, based upon the dry weight of said vegetable matter, said pretreating comprising, in combination, the steps of: (i) prepulping prepared vegetable matter chips by kraft, nitric acid, bisulfite, or neutral sulfite process,   (ii) refining said prepulped vegetable matter,   (iii) washing said prepulped vegetable matter;     (b) reacting said refined vegetable matter with from about 2% to about 7% chlorine dioxide, based upon the total weight of dry fibrous material fed to said pretreating step until all of said chlorine dioxide is substantially consumed;   (c) water washing said reacted vegetable matter;   (d) treating said washed vegetable matter with an aqueous solution of sodium hydroxide for at least about one-half hour at a temperature of from about 50° C. to about 75° C.;   (e) water washing said treated vegetable matter;   (f) reacting said washed vegetable matter with about one-half the amount of chlorine dioxide used in step (b) at a temperature of from about 40° C. to about 60° C. for about 30 minutes to about 4 hours;   (g) water washing said reacted vegetable matter;   (h) treating said washed vegetable matter with sodium hydroxide in aqueous solution for at least about one-half hour at a temperature of from about 50° C. to about 75° C.;   (i) water washing said caustic treated vegetable matter;   (j) reacting said washed vegetable matter with about one-half the amount of chlorine dioxide used in step (f) for a period of from about 2 hours to about 6 hours at a temperature of from about 40° C. to about 80° C.; and   (k) water washing said reacted vegetable matter.   
     
     
       15. The process of claim 14 wherein said chips of vegetable matter are prepulped by a process comprising contacting said vegetable matter with from about 5% to about 30% sodium sulfite by weight and from about 3% to about 25% sodium carbonate by weight, both percentages being based upon the dry weight of said vegetable matter. 
     
     
       16. The process of claim 15 wherein said washed vegetable matter is treated with about 4% of said watersoluble caustic material and the total concentration of said chlorine dioxide used is from about 1% to about 15% by weight, all percentages being based on the total dry weight of said vegetable matter fed to the pretreating stage. 
     
     
       17. The process of claim 16 wherein the pH of said mixture of vegetable matter and chlorine dioxide of step (b) varies up to about 8.0. 
     
     
       18. The process of claim 17 wherein the pH of said mixture of vegetable matter and chlorine dioxide of step (f) varies from about 4.0 to about 8.0 at the beginning of the reaction and is about 2.0 upon consumption of said chlorine dioxide. 
     
     
       19. A pulp produced by the process of claim 1. 
     
     
       20. A paper prepared from the pulp of claim 19. 
     
     
       21. A paper made predominantly from softwood pulp produced by the process of claim 14 wherein the grease-proofness is greater than 500, the tensile strength is greater than 120%, the bursting strength is greater than 160%, the tear resistance is greater than 320%, and the folding endurance is greater than 1000. 
     
     
       22. A paper made prodominantly from hardwood pulp produced by the process of claim 14 wherein the grease-proofness is greater than 500, the tensile strength is greater than 80%, the bursting strength is greater than 140%, the tear resistance is greater than 160%, and the folding endurance is greater than 500. .Iadd. 23. The process of claim 1 in which the delignification with chlorine dioxide is effected in at least three 
     
     
        chlorine dioxide reaction stages. .Iaddend..Iadd. 24.  A process for the delignification of wood chips comprising, in combination, the steps of: (a) pretreating said chips to obtain a refined vegetable matter in a yield of about 64% to about 100% by weight, based upon the dry weight of said chips;   (b) delignifying said refined vegetable matter by reacting it in three stages with preformed chlorine dioxide, each successive stage using less chlorine dioxide than its preceding stage, and the total chlorine dioxide used being from about 2% to about 13% based upon said dry weight; and   (c) extracting said vegetable matter after the first two of the three chlorine dioxide stages with a water solution of caustic material at a temperature of from about 50°C. to about 75°C; wherein said caustic material is an alkali metal hydroxide, alkali metal carbonate, ammonium hydroxide or ammonia gas. .Iaddend..Iadd. 25. The process of claim 24 wherein the pretreating is a chemical prepulping treatment followed by a refining treatment, the chemical prepulping treatment being selected from the group consisting of sodium sulfide prepulping, acid sulfite prepulping, cold soda prepulping, soda prepulping, sodium xylene sulfonate prepulping, bisulfite prepulping, kraft prepulping, neutral sulfite prepulping and nitric acid prepulping. .Iaddend..Iadd. 26. The process of claim 25 in which the chemical prepulping treatment is a Kraft or neutral sulfite prepulping and the total amount of chlorine dioxide used is not more than 9% based on the dry weight of the chips. .Iaddend. .Iadd. 27. The process of claim 25 in which the caustic material is caustic soda. .Iaddend..Iadd. 28. The process of claim 27 in which the first chlorine dioxide treating stage is conducted so that its pH begins at from about 4.0 to about 8.0 and ends at a pH of about 0.5 to about 3.0, and the second chlorine dioxide treating stage is conducted so that its pH begins at a pH of about 4.0 to about 8.0 and ends at a pH of about 2.0. .Iaddend..Iadd. 29. A pulp produced by the process of claim 25. .Iaddend..Iadd. 30. A paper prepared from the pulp of claim 29. .Iaddend.