Pulpability and Bleachability of Xylan-Depleted Eucalyptus Wood Chips

Abstract

Wood autohydrolysis for xylan removal prior to kraft pulping and the consequences of this practice downstream in a kraft pulp mill has been investigated. Chip autohydrolysis for 60 min at 165 °C removed 61% of the xylans, but subsequent kraft cooking produced a 9.4% lower yield than reference. Pulp from 60-min autohydrolyzed chips showed 75% efficiency in oxygen delignification compared to 43.6% from the reference, resulting in a subsequent ECF bleaching cost reduction of 36% and significant effluent improvement. The chip autohydrolysis process resulted in a pulp of higher bulk, lower beatability and strength in relation to the reference, and an acid hydrolysate of low xylan concentration. Pulp cellulose and xylan derived from autohydrolyzed chips are less stable during kraft pulping because of their low molecular weight and high polydispersity. Xylan−lignin and cellulose−lignin complexes from kraft pulps derived from autohydrolyzed chips contain lignin of higher molecular weight than that of regular kraft pulp.