Dihydrolevoglucosenone (Cyrene™) as a versatile biobased solvent for lignin fractionation, processing, and chemistry

Abstract

The solubility of technical lignins is a complex issue that depends on many parameters, such as the lignin structure governed by the botanical origin and the extraction process. Only polar aprotic solvents, such as dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMAc), are able to fully dissolve a large range of technical lignins. However, DMF and DMAc are fossil-based and present serious toxicity issues. In this study, we evaluated the potential of a biobased, non-cytotoxic and non-mutagenic solvent, dihydrolevoglucosenone (Cyrene™) as an alternative polar aprotic solvent for lignins. The solubility of Kraft (KL), soda and organosolv lignins was first evaluated. It appeared that full solubility could be achieved in Cyrene–water mixtures, between 60 and 80–90 vol% Cyrene, probably because of the peculiar property of Cyrene to form a geminal diol upon water addition. Cyrene and water could then be used as solvent and non-solvent to refine KL by fractional precipitation, leading to the recovery of fractions of controlled molar masses. Finally, after ensuring that it was inert to lignin, Cyrene was shown to be a suitable solvent for the chemical modification of different lignins. Three common reactions were tested as proof-of-concept: esterification with an acyl chloride or a cyclic anhydride, and formation of urethane linkages with an isocyanate. This study thus shows that Cyrene is a promising and versatile green solvent for lignin fractionation, processing and chemistry, to ensure greener processes when solvents are mandatory.