Overcoming biomass recalcitrance to enhance platform chemical production from soft wood by organosolvolysis coupled with fast pyrolysis

Softwood is an abundantly available lignocelloluse feedstock which can be converted into chemical and liquid fuels via sugar-based platform molecules. However, cost-effective release of pyrolytic sugars from softwood is considerably hindered by the biomass recalcitrance related to its compositions and structures as well as the catalytic effect of alkali and alkaline earth metals. In order to address these challenges, a novel biorefinery based on H2SO4 assisted organosolvolysis of softwood (e.g. pine wood) in high boiling organic solvents coupled with subsequent fast pyrolysis is proposed. The experimental results demonstrated that H2SO4 assisted organosolvolysis could effectively deconstruct pine wood into pentose, organosolv lignin, cellulose-rich fraction, and simutaneously transfer alkali and alkaline earth metals to solutions, thus improving the yields of platform chemcials (levoglucosan and phenols) in subsequent fast pyrolysis. Moreover, different high boiling solvents showed obviously distinct performance for the deconstruction of pine wood and removal of alkali and alkaline earth metals, thus resulting in different yields of platform chemcials in the subsequent fast pyrolysis. The rank order of these solvents which are beneficial for improving the yield of pyrolytic sugars from pine wood was ethylene glycol > glycerin + ethylene glycol (mass ratio of 1:1) > glycerin > gamma-valerolactone. The yield of levoglucosan increased drastically from 3.53 wt% of raw pine wood to 27.19 wt% of cellulose-rich fraction pretreated by ethylene glycol with 1 wt% H2SO4. It was found that the yield of levoglucosan from fast pyrolysis of feedstocks was subjecetd to the mutual effect of normalized total alkali and alkaline earth metals' valencies and severity of delignification. These findings help to provide a simple and efficient process to selective production of platform chemicals from highly recalcitrant biomass