Kinetics of SO2-ethanol-water pulping of spruce 10th EWLP, Stockholm, Sweden, August 25–28, 2008

Abstract

Abstract SO2-ethanol-water (SEW) pulping is a promising fractionation process for lignocellulosics to produce pulp and value-added chemicals as a contribution to the concept of forest biorefinery. The presence of SO2 leads to dissolution of hemicelluloses in high yield mostly as monomeric sugars, while lignin becomes soluble through sulfonation. After lignin removal, the dissolved sugars may be used as feedstock for fermentation to ethanol or butanol. SEW pulping may be considered a hybrid between solvent pulping (organosolv pulping by solvolysis) and acid sulfite pulping. Absence of an inorganic base leads to simplification of the recovery cycle. Furthermore, alcohol increases the impregnation rate of dissolved SO2 into wood, so that a separate impregnation phase is not necessary. Also, the presence of SO2 allows cooking of softwoods, while ethanol pulping is limited to hardwoods. Thus, SEW pulping may be applied to a wide variety of lignocellulosics at lower temperatures and similar cooking times than those used in kraft pulping. In the present study, SEW pulping experiments were performed on spruce chips at cooking temperatures of 135–165°C with a 12% SO2 solution at a liquor-to-wood ratio of 6:1 l kg-1. The effect of cooking temperature and time on kappa number, yield, and intrinsic viscosity of the pulp was determined. Based on these results, the kinetics of delignification, hemicelluloses removal, and cellulose hydrolytic destruction were established.