Process for the manufacture of dissolving grade pulp

Claim 2

A process for producing a highly polymerized dissolving-grade pulp from vegetable matter in a yield of at least about 45 percent by weight, based upon the dry weight of said vegetable matter, by removing lignin and hemicellulose from said vegetable matter, said process comprising, in combination, the steps of: a. subjecting said vegetable matter to acid prehydrolysis; b. pretreating said vegetable matter to obtain a refined vegetable matter in a yield of about 64 percent to about 100 percent by weight, based upon the dry weight of said vegetable matter; c. water washing said refined vegetable matter; d. reacting said washed vegetable matter wIth about eight-fifteenths of at least about 1 percent to about 15 percent of a chlorine dioxide lignin reaction agent, based upon the total weight of dry fibrous material fed to said pretreating stage until said agent is substantially consumed; e. water washing said treated vegetable matter; f. treating said washed vegetable matter with approximately 4 percent by weight water-soluble caustic material based on the dry weight of said vegetable matter entering step (f) for at least about one-half hour at a temperature of from about 50* C. to about 75* C., said treating being carried out at from about 5 percent to about 50 percent pulp consistency; g. water washing said treated vegetable matter; h. reacting said washed vegetable matter with about one-half the amount of chlorine dioxide lignin reaction agent used in step (d) for about 30 minutes to about 4 hours at a temperature of from about 40* C. to about 60* C. i. water washing said vegetable matter; j. treating said washed vegetable matter with approximately 4 percent by weight water-soluble caustic material based upon the dry weight of said vegetable matter entering step (j) for at least about one-half hour at a temperature of from about 50* C. to about 75* C., said treating being carried out at from about 5 percent to about 50 percent pulp consistency; k. water washing said vegetable matter; l. reacting said washed vegetable matter with about one-half the amount of chlorine dioxide lignin reaction agent used in step (h) for about 2 to about 6 hours at a temperature of from about 40* C. to about 80* C. m. water washing said vegetable matter; n. treating said vegetable matter with a water-soluble caustic material in aqueous solution at a pulp consistency of about 10 percent for about 1 hour at room temperature, said solution containing from about 50 to about 60 grams of alkali per liter. o. press-washing said vegetable matter; p. reacting said refined vegetable matter with about one-half the amount of chlorine dioxide lignin reaction agent used in step (l) for about 2 hours to about 6 hours at a temperature of from about 40* C. to about 80* C.; and q. water washing said vegetable matter.

Claim 3

The process of claim 3 wherein said chlorine dioxide lignin reaction agent is selected from the group consisting of chlorine dioxide, a solution of chlorine dioxide and water, a mixture of chlorine dioxide and chlorine gas, and a solution of chlorine dioxide, chlorine, and water.

Claim 4

The process of claim 4 wherein said water-soluble caustic material is sodium hydroxide.

Claim 5

The process of claim 4 wherein the pretreatment is substantially a mechanical pretreatment.

Claim 6

The process of claim 4 wherein said prehydrolysis is conducted for from about 10 to about 180 minutes at from about 300* to about 380* F.

Claim 7

The process of claim 4 wherein said pretreating is a chemical prepulping selected from the group consisting of alkafide prepulping, acid sulfite prepulping, cold soda prepulping, soda prepulping, sodium xylene sulfonate prepulping, polysulfide prepulping, bisulfite prepulping, kraft prepulping, nitric acid prepulping, and neutral sulfite prepulping.

Claim 8

The process of claim 8 wherein said neutral sulfite prepulping comprises contacting said vegetable matter with from about 5 percent to about 30 percent sodium sulfite by weight and from about 3 percent to about 25 percent sodium carbonate by weight, both percentages being based upon the dry weight of said vegetable matter.

Claim 9

The process of claim 1 wherein said vegetable matter is subjected to an acid prehydrolysis prior to said pretreatment.

Claim 10

The process of claim 10 wherein said prehydrolysis is condUcted for from about 10 to about 180 minutes at from about 300* to about 380* F.

Claim 11

The process of claim 1 wherein the alkali is sodium hydroxide.

Claim 12

The process of claim 1 wherein said lignin reaction agent is a mixture of chlorine dioxide and chlorine and said chlorine is less than about 30 percent by weight of the total chlorine dioxide requirement on an equivalent oxidant basis.

Claim 13

The process of claim 1 wherein the pretreatment is substantially a mechanical pretreatment.

Claim 14

The process of claim 2 wherein said neutral sulfite prepulping comprises contacting said vegetable matter with from about 5 percent to about 30 percent sodium sulfite by weight and from about 3 percent to about 25 percent sodium carbonate by weight, both percentages being based upon the dry weight of said vegetable matter.

Claim 15

The process of claim 1 wherein the pretreatment is followed, sequentially, by water washing, chlorine dioxide treatment, water washing, dilute sodium hydroxide extraction, water washing, chlorine dioxide treatment, water washing, dilute sodium hydroxide extraction, water washing, chlorine dioxide treatment, water washing, strong sodium hydroxide extraction, press-wash treatment, chlorine dioxide treatment, final washing.