Hoechst Celanese Corporation

Virginia Chemicals Inc.

Mark A Schroeder

James C Robinson

S Allen Grimsley

Leonard L Diaddario, Jr

An aqueous sulfuric acid anolyte solution is circulated through the anode compartment of an electrolytic cell, and an aqueous NaHSO.sub.3 catholyte solution is circulated through its cathode compartment, while maintaining an anolyte and catholyte temperature range of 20.degree.-25.degree. C., a catholyte pH range of 4.6 to 5.8, and a reduction potential of -1.25 to -1.50 V versus Ag.degree./AgCl, to produce an aqueous solution of Na.sub.2 S.sub.2 O.sub.4. Optimum pH is maintained by small additions of an alkali to the catholyte solution for electrolysis and solution stability.

Electrosynthesis of sodium dithionite

Compositions and a method are disclosed for minimizing brightness reversion of chromophore-containing wood pulps, especially low-cellulose wood pulps, such as groundwood and thermomechanical pulps, which have been reductively bleached or bleached with hydrogen peroxide. Ascorbic acid and palmitoyl ascorbate are particularly effective for preventing such reversion at low levels.

Enhanced dithionite bleaching

A method is described for increasing the brightness of reductively bleached high yield pulps, comprising bleaching the pulps with a reductive bleaching solution under anaerobic conditions and maintaining the bleached pulps under anaerobic conditions during all handling steps subsequent to bleaching, including paper formation, wet pressing, and drying of the paper formed therefrom. The bleached paper has higher brightness than the same paper produced under aerobic conditions, and the bleaching and handling-derived portion of this higher brightness is retained after storage of the finished paper.

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Norfolk, VA, United States of America

Mark A Schroeder