A larch biorefinery: Influence of washing and PS charge on pre-extraction PSAQ pulping

Abstract

This study deals with a biorefinery concept based on larch wood. Wood chips of Siberian larch (Larix sibirica Lebed.) were treated with water before pulping at the optimal pre-extraction (PE) condition of 150 °C and 90 minutes. Through PE, about 12.4% of the wood mass is dissolved, mainly from the arabinogalactan hemicellulose component. Fermentation of the hemicellulose-rich larch extract with Bacillus coagulans resulted in consumption of all C6 and C5 sugars and produced lactic acid in high yield. PE before pulping resulted in lower (4 to 5%) pulp yield than for control kraft pulps. However, the pulp yield loss may be reduced by addition of polysulfide (PS) and anthraquinone (AQ). The present study focuses on the effect of the degree of washing of the extracted chips and that of the PS charge in PSAQ pulping on the final properties of the pulp. Three different levels of washing and three different PS charges were tested. The characteristics of the extract, wash water, pulp, and black liquor samples were determined. The amount of sugars in the combined stream of collected extract and wash water obtained by mild washing was 10.2% on o.d. wood.