Soda Pulping of Hardwoods Catalyzed by Anthraquinone and Methyl Substituted Anthraquinones

Abstract

Black liquor gasification (BLG) as well as the recovery of lignin and other organic compounds from pulping black liquor would be aided if an efficient sulfur‐free pulping process could be developed. This has provided new impetus for research on soda pulping with redox catalysts instead of sodium sulfide that is presently used in the kraft process. Soda/anthraquinone (AQ) pulping afforded white birch (Betula papyrifera) and sugar maple (Acer saccharum) pulps with equal if not superior strength to kraft pulps. However, the delignification rate was significantly lower for soda/AQ pulping. When AQ was replaced by 2‐methylanthraquinone (2‐MAQ) a delignification rate only slightly lower than that of kraft pulping was obtained at the same effective alkali (EA). At a kappa number of ∼20, a soda/2‐MAQ pulp was produced from sugar maple at a higher yield (1.2% on chips) than for a kraft pulp. 2‐MAQ was synthesized, as a powder, at 75% yield using an AlCl3–mediated Friedel‐Crafts reaction that is one of the methods used for commercial production of AQ.