Carbocation scavenger pretreatment to mitigate lignin self-condensation in a semi-industrial steam explosion process

Abstract

Softwood bark is a potential resource for biorefineries, abundantly available in the Nordic countries. Meanwhile, carbocation scavenger pretreatment has been suggested as a biorefinery technology beneficial to the enzymatic conversion of softwood. This study aimed to evaluate the effect of 2-naphthol addition for monosaccharide production during enzymatic hydrolysis at high solid loadings of pilot-scale steam-exploded bark mimicking industrial conditions. Multiple linear regression analysis showed that 2-naphthol added as a dry powder with a 5 % dose reduced the hexose hydrolysis recoveries by 0.7 and 0.2 % for glucose and mannose, respectively, while increasing the acid-insoluble and acid-soluble lignin content. The main factors affecting saccharide conversions were reactor temperature and enzyme loading, while acetic acid addition and bark pre-drying had no or little effect. In general, carbocation scavenger addition in the form of 2-naphthol was detrimental to sugar hydrolysis yields, contradicting earlier literature findings.