Decomposition of different lignocellulosic biomasses by microwave-assisted pretreatment with various aqueous solutions of deep eutectic solvents
Dawid Mikulski, Grzegorz Kłosowski, Santhosh Pillai
Abstract
Effective pretreatment of lignocellulosic biomass is of key importance for the preparation and use of this raw material in biological synthesis processes such as the production of bioethanol. The aim present study was to determine the impact of the integrated use of microwave radiation and selected aqueous solutions of deep eutectic solvents (DES) on changes in lignocellulose structure and composition, and their influence on the efficiency of enzymatic hydrolysis. Effective delignification was enabled by an aqueous solution of DES containing a mixture of choline chloride and imidazole. The use of this solvent in the molar ratio of 1:4, at 0.54 MPa pressure, enabled an 84 % lignin content reduction in the oat hull biomass and a 77 % lignin content reduction in the brewer’s spent grain biomass. Significant changes in lignocellulose composition were also caused by the use of a mixture of choline chloride and ethylene glycol. Pretreatment using selected aqueous solutions of DES also contributed to an increase in the efficiency of cellulose hydrolysis in the pretreated biomass. The hydrolysis of oat hull biomass after pretreatment involving a mixture of choline chloride and ethylene glycol in the molar ratio of 1:4 at 0.27 MPa pressure, the generated glucose concentration was 838 mg/g of biomass with a hydrolysis efficiency was 94.9 %. The suggested pretreatment using aqueous solutions of DES and microwave radiation allows the acquired lignocellulosic biomass to be highly susceptible to enzymatic hydrolysis, which can be used for the production of second-generation bioethanol or the preparation of substrate for other microbiological syntheses.