Process of bleaching softwood pulps in a D1 or D2 stage in a presence of a weak base
AssigneeInternational Paper Company
InventorsCaifang Yin, Kent Witherspoon
Life of this patent
Estimating the term…
Abstract
This invention relates to an improved bleaching process for bleaching pulp comprising at least one bleaching stage which comprises treating a softwood pulp with a bleaching agent comprising ClO2 in the presence of a weak base such as, for example, Mg(OH)2 preferably at pH from about 3.5 to about 6.5. The invention is also relates a bleaching process for bleaching pulp having two or more bleaching stages, at least one of which and preferably two of which comprises treating a softwood pulp with a bleaching agent comprising ClO2 in the presence of a weak base such as, for example, Mg(OH)2 preferably at pH from about 3.5 to about 6.5.
Claims20
An improved bleaching process for bleaching pulp comprising:
- at least one D1 or D2 bleaching stage which comprises treating a softwood pulp solely with a bleaching agent which is selected from the group consisting of chlorine dioxide and chlorine dioxide with less than about 1.5% elemental chlorine in the presence of a weak base which is selected from the group consisting of NaH2PO3 and NH4OH at a pH of from about 3.5 to about 6.5.
An improved bleaching process for bleaching pulp comprising:
- at least one extraction stage and at least one bleaching stage wherein the least one D1 or D2 bleaching stage comprises bleaching a softwood pulp solely with a bleaching agent which is selected from the group consisting of chlorine dioxide and chlorine dioxide with less than about 1.5% elemental chlorine in the presence of a weak base which is selected from the group consisting of NaH2PO3 and NH4OH at a pH of from about 3.5 to about 6.5.
An improved bleaching process for bleaching pulp having two or more bleaching stages, at least one of which is a D1 or D2 bleaching stage which comprises treating a softwood pulp solely with a bleaching agent which is selected from the group consisting of chlorine dioxide and chlorine dioxide with less than about 1.5% elemental chlorine in the presence of a weak base which is selected from the group consisting of NaH2PO3 and NH4OH at a pH of from about 3.5 to about 6.5.
An improved bleaching process for bleaching pulp comprising:
- at least one D1 or D2 bleaching stage which comprises treating a softwood pulp solely with a bleaching agent comprising chlorine dioxide in the presence of a weak base at a pH of from about 3 to about 5, wherein the amount of chlorine dioxide used in the at least one bleaching stage is from about 0.1% to about 0.5% and wherein the weak base is NH4OH.
An improved bleaching process for bleaching pulp comprising:
- at least one D1 or D2 bleaching stage which comprises treating, in the absence of oxygen, a softwood pulp with a bleaching agent which is selected from the group consisting of chlorine dioxide and chlorine dioxide with less than about 1.5% elemental chlorine in the presence of a weak base which is selected from the group consisting of NaH2PO3 and NH4OH at a pH of from about 3.5 to about 6.5.
Dependencies are inferred from the claim text.