Sugars and lignosulphonates recovery from eucalyptus spent sulphite liquor by membrane processes

Thin spent sulphite liquor (SSL) generated in pulp and paper mills is a biomass resource that is usually concentrated and burnt in steam boilers. The general aim of this work was to investigate the application of membrane processes to filter the SSL produced by Eucalyptus globulus sulphite pulping, namely for the separation of the lignosulphonates (LS) from the sugars, LS fractionation to produce valuable products, and sugars concentration. Laboratory experiments were conducted in total recirculation, natural pH and 25 °C with ultrafiltration, nanofiltration, and reverse osmosis membranes from Alfa Laval, Dow Filmtec, and Microdyn-Nadir. Microdyn-Nadir UP010 membrane displayed the widest gap between the retentions of lignosulphonates (68%) and sugars (3%), i.e., it separated the high molecular weight LS from the low-medium molecular weight LS and sugars. For its high retentions with respect to glucose (96%) and xylose (93%), Alfa Laval RO99 membrane is the most promising membrane to concentrate the sugars (after the total separation of LS by an integrated process of Ultrafiltration coupled to Ion Exchange, for instance).