High efficiency fiber bleaching process
AssigneeGPCP IP Holdings LLC
InventorJeffrey A. Lee
Life of this patent
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Abstract
A high efficiency bleaching method for cellulosic pulp includes: (a) providing a charge of aqueous cellulosic pulp to a bleaching vessel at a consistency of from 10% to 30% along with a peroxy bleaching agent and an alkaline agent effective to adjust pH of the charge to 9.5 to 12.5; and (b) bleaching the aqueous cellulosic pulp in the bleaching vessel while maintaining a bleaching temperature of from 110° F. (43° C.) to 135° F. (57° C.) and a pH of the charge from 9.5 to 12.5 for an extended bleaching retention time. The bleaching method is advantageously used to bleach low brightness recycle pulp, and/or as part of a multistage process with bleaching stages of lesser duration, and/or as a high peroxy efficiency, low dose bleaching process or in connection with concurrently storing and bleaching pulp.
Claims20
A high efficiency bleaching method for recycled cellulosic pulp comprising:
- (a) providing a charge of aqueous recycled cellulosic pulp to a bleaching vessel at a consistency of from 10% to 30% along with a peroxy bleaching agent and an alkaline agent effective to adjust pH of the charge to 9.5 to 12.5;
- and
- (b) bleaching the aqueous cellulosic pulp in the bleaching vessel while maintaining a bleaching temperature of from 43° C. to 57° C. and a pH of the charge from 9.5 to 12.5 for a bleaching retention time of at least 10 hours;
- wherein the temperature, retention time, peroxy and alkaline agent levels are controlled such that the brightness gain is at least 8 ISO brightness points/0.295 kg-moles peroxy bleaching agent consumed per dried metric ton of pulp and wherein the aqueous cellulosic pulp is recycle pulp having an ISO brightness of from 40 to 65 prior to bleaching;
- followed by a Y bleaching stage or a P bleaching stage or both, wherein the Y stage comprises bleaching with a reductive bleaching agent, for a retention time of from 5 minutes to 3.5 hours while maintaining a bleaching temperature of from 50° C. to 110° C. and the P stage comprises bleaching with a peroxy bleaching agent, for a retention time of from 5 minutes to 3.5 hours while maintaining a bleaching temperature of from 50° C. to 110° C.
A method for concurrently bleaching and storing cellulosic pulp comprising:
- (a) providing a charge of aqueous pulp to a bleaching vessel at a consistency of from 10% to 30% along with a peroxy bleaching agent and an alkaline agent effective to adjust pH of the charge to 9.5 to 12.5;
- and
- (b) bleaching the pulp in the bleaching vessel while maintaining a bleaching temperature of from 29° C. to 57° C. and a pH of the charge from 9.5 to 12.5 for a bleaching retention time of more than 24 hours,
- wherein the aqueous cellulosic pulp is recycle pulp having an ISO brightness of from 40 to 65 prior to bleaching.
A method for concurrently bleaching and storing cellulosic pulp comprising:
- (a) providing a charge of aqueous pulp to a bleaching vessel at a consistency of from 10% to 30% along with a peroxy bleaching agent and an alkaline agent effective to adjust pH of the charge to 9.5 to 12.5;
- and
- (b) bleaching the pulp in the bleaching vessel while maintaining a bleaching temperature of from 29° C. to 57° C. and a pH of the charge from 9.5 to 12.5 for a bleaching retention time of more than 24 hours, followed by a subsequent bleaching Protocol including one or more bleaching stages of lesser duration, the subsequent bleaching Protocol being selected from Protocols A, B or C, wherein:
- Protocol A is bleaching the aqueous pulp in a reductive bleaching stage of lesser duration with a reductive bleaching agent, for a retention time of from 5 minutes to 3.5 hours while maintaining a lesser duration bleaching temperature of from 50° C. to 110° C.;
- Protocol B is (i) washing the bleached aqueous cellulosic pulp followed by (ii) bleaching the washed cellulosic pulp in a peroxy bleaching stage of lesser duration with a peroxy bleaching agent followed by (iii) washing the aqueous cellulosic pulp;
- followed by (iv) bleaching the aqueous pulp in a reductive bleaching stage of lesser duration with a reductive bleaching agent, wherein the peroxy and reductive bleaching stages of lesser duration have a retention time of from 5 minutes to 3.5 hours and are carried out while maintaining a lesser duration bleaching temperature of from 50° C. to 110° C.;
- and
- Protocol (C) is (1) bleaching the aqueous pulp in a reductive bleaching stage of lesser duration with a reductive bleaching agent;
- followed by (2) bleaching the aqueous cellulosic pulp in a peroxy bleaching stage of lesser duration with a peroxy bleaching agent wherein the reductive and peroxy bleaching stages of lesser duration have a retention time of from 5 minutes to 3.5 hours and are carried out while maintaining a lesser duration bleaching temperature of from 50° C. to 110° C.
Dependencies are inferred from the claim text.