US 3,985,674 A · Stabilized sodium dithionite solutions

Abstract

Sodium dithionite bleaching solutions for groundwood pulps which require no additional chemicals for pH adjustment prior to direct application to the pulps, based on zinc-derived or formate-derived sodium dithionite and containing small percentages of at least four additives selected from the following: a chelating agent, zinc dithionite, zinc sulfate, sodium carbonate, sodium hydroxide, sodium tripolyphosphate, sodium phosphate, and sodium metaborate. Tested chelating agents are nitrilotriacetic acid (NTA) trisodium salt and ethylenediaminetetraacetic acid (EDTA) tetrasodium salt. The solutions are cool-stable (50.degree.F. or 10.degree.C) for at least 5 days with less than 5% decomposition of the sodium dithionite, and several exhibit similar stability at storage temperatures of 70.degree.-75.degree.F. (21.degree.-24.degree.C.) A method of preparation of the solutions is also provided. Bleaching performance was proved in laboratory and field trials to be comparable to the performance of solutions prepared from dry, commercially available sodium dithionite blends or commercial zinc dithionite when compared on a basis of pounds of bleaching agent per ton of pulp per point brightness gain.

Claims15

Dependent claims

A storage-stabilized aqueous sodium dithionite bleaching solution, comprising:

A. a chelating agent which is selected from the group consisting of ethylenediaminetetraacetic acid tetrasodium salt and nitrilotriacetic acid trisodium salt, said nitrilotriacetic acid trisodium salt being at a concentration in said solution of 0.3-1.0% by weight;
B. a source of zinc ion which is selected from the group consisting of zinc sulfate and zinc dithionite at a concentration in said solution of 0.1-0.5% by weight;
C. a complex former which comprises sodium tripolyphosphate at a concentration of 0.6-3.0% by weight;
D. a source of hydroxyl ion which comprises sodium carbonate at a concentration in said solution of 1.0-4.0% by weight;
and
E. sodium dithionite at a concentration by weight of at least 12%, said sodium dithionite being zinc derived.

3 more elements

A storage stabilized aqueous bleaching solution that undergoes less than 5% decomposition during anaerobic storage for 5 days at 50.degree. F and is substantially free of fines, floc, and turbidity, said solution being based on sodium dithionite and comprising at least two additives selected from the group consisting of a chelator, a source of soluble zinc ion, a complex former, and a source of hydroxylation, wherein:

A. said sodium dithionite is at a concentration of at least 12% by weight of said solution;
B. said source of soluble zinc ion is zinc dithionite at a concentration of at least about 0.2% by weight of said solution;
and
C. said chelator is selected from the group consisting of ethylenediaminetetraacetic acid tetrasodium salt and nitrilotriacetic acid trisodium salt.

1 more element

Dependencies are inferred from the claim text.

Stabilized sodium dithionite solutions

Life of this patent

Stabilized sodium dithionite solutions

Life of this patent

Abstract

Claims15