Ethanol Production from Eucalyptus Sawdust Following Sequential Alkaline Thermochemical Pretreatment with Recovery of Extractives

Abstract

Eucalyptus sawdust is a forest residue that, through a biorefinery approach, can be used to manufacture value-added products in the pulp and paper industries as well as to produce a biofuel. This study examines the suitability of a sequential thermochemical pretreatment that uses processes and reagents commonly utilized in the pulp and paper industry to separate valuable biomass components from eucalyptus sawdust and increase its enzymatic digestibility for ethanol production. The research strategy was based on a forest biorefinery that can be integrated into an existing industrial plant for the production of cellulose pulp. A combination of alkaline solutions was evaluated to obtain an extract rich in tannins and intended to be used in the formulation of wood adhesives. A second alkaline treatment was used to recover lignin and hemicellulose components and improve cellulose digestibility. The cellulose fraction was fermented using three commercial Saccharomyces cerevisiae yeasts (Thermosacc®, PE-2, and CAT). Different process configurations (separate hydrolysis and fermentation (SHF), pre-saccharification followed by simultaneous saccharification and fermentation (PSSF), and simultaneous saccharification and fermentation (SSF)) at 16% (w/v) solid loading by Thermosacc® yeast were also studied. Thermosacc® yeast enabled higher ethanol production than the other strains but resulted in similar productivity. The two-stage alkaline pretreatment of eucalyptus sawdust was successful in recovering 34 g of tannins, 56 g of xylo-saccharides, 16 g of acetic acid, and 90 g of lignin and produced 152 g of ethanol from 1 kg of dry eucalyptus sawdust.