Alkaline Sulfite-Anthraquinone Pulping of Bagasse

Abstract

Depithed Mexican bagasse was pulped by using the alkaline sulfiteanthraquinone pulping process. The effects of the addition of small amounts of ethanol and varied amounts of AQ as well as different alkali ratios were investigated. 20 minute cooking time results in pulps with good yields, high brightness and excellent strength properties. Despite of the short cooking time, delignification can be performed to extremely low kappa numbers without pulp degradation which provides and easy bleaching. The addition of a small amount of ethanol retards the delignification rate and increases the rejects and the strength properties of the pulp, but after bleaching the improvement in strength is negligble. With respect to yield, reject content and physical properties of the pulp, the optimum alkali ratio (Na_2SO_3: total alkali) is 0.75 and the favourable amount of AQ is 0.05 to 0.1% based on o.d. bagasse. Pulp bleaching can be done in two or three stages with chlorine or hypochlorite yielding high brightness and good pulp strengths.