Optimization of Biomass Pretreatment with Deep Eutectic Solvent

Waste biomasses from agro-food industry may be adopted as cellulose rich feedstock for biorefinery [1]. Effective biomass pretreatment must be developed to overcome some issues related with conventional mechanical and chemical-physical pretreatments. Environmental and economic issues related with the use of solvents and with the energy demand for biomass pretreatment should be addressed. The use of green solvents for lignin extraction from biomass is a promising strategy, among these Deep Eutectic Solvents (DESs) have been proposed [2]. DES is a fluid made by two or three ionic compounds that forms eutectic mixture. DESs have physicochemical properties similar to ionic liquids and in addition, they are much environmental friendly and cheaper than ILs. The present contribution reports on part of the study included in the research project Waste2Fuels funded by the European Horizon 2020 work program. The biomass pretreatment with DES was optimized by testing two solvent compositions (CholineChloride-Glycerol and CholineChloride-Ethylenglycole) on four agro-food wastes: potato peels, apple residues, brewery spent grains, coffee silverskin. The adopted biomass to solvent ratio and the temperature were varied between 1:8 - 1:32 and 60-150°C, respectively. The pretreated biomass was hydrolyzed using a commercial cellulase cocktail, then samples were characterized in terms of residual lignin, cellulose and hemicellulose content, concentrations of sugars and of inhibitors in the hydrolysate. Hydrolysis glucose yields (percentage of the glucan content in the raw biomass) was about 90% after ChCl-Gly pretreatment at 150°C of all the agro-food wastes. Fermentation inhibitors in the hydrolyzate were negligible. Furthermore, structural changes of the pretreated biomass were characterized by X-Ray Diffraction and Scanning Electron Microscopy.