Microwave irradiation-assisted ionic liquid or deep eutectic solvent pretreatment for effective bioconversion of sugarcane bagasse to bioethanol

Abstract

Ionic liquids (ILs), and deep eutectic solvents (DESs), the eco-friendly solubilizing agents for processing of lignocellulosic feedstock, facilitate effective delignification and enhanced carbohydrates accessibility to hydrolytic enzymes for proficient bioconversion. Furthermore, the efficacy of these solvents may be increased by combinative application of microwave irradiation. In the present report, a novel and intensified strategy were developed for sugarcane bagasse (SCB) biomass pretreatment by using combined application of microwave irradiation and IL (1-butyl-3 methylimidazolium chloride, [Bmim]Cl) or DES (choline chloride, ChCl)/glycerol). The in-house enzyme preparation developed from Aspergillus assiutensis VS34 was employed for the saccharification of the pretreated SCB. The maximum sugar was released by combined microwave-[Bmim]Cl + PEG-8000 pretreatment (327.76 ± 1.8 mg/g biomass) followed by microwave + [Bmim]Cl (308.1 ± 2.4 mg/g biomass), and microwave-choline chloride/glycerol (297.36 ± 2.4 mg/g biomass) after 7 min of microwave irradiation. The analysis of combinatorially pretreated biomass by physicochemical techniques such as ¹H NMR, FT-IR, XRD, and SEM showed that combined pretreatment induced severe biomass structural deformities, which facilitated the enzymatic hydrolysis and hence, improved the yield of reducing sugars. Fermentation of the sugar hydrolysate yielded an ethanol content of 146.96 ± 1.9 mg/g biomass (bioconversion efficiency, 44.39%). The results of the current study substantiate the effectiveness of microwave-aided combinatorial pretreatment approach with DESs/ILs for an efficient biomass conversion. Comprehensive physicochemical analysis of suitably pretreated SCB biomass may help unraveling the underlying functional processes of combinatorial pretreatment, and for developing biomass specific designer pretreatments for efficient conversion.

Keywords

Deep eutectic solvents / Ionic liquids / Microwave / Sugarcane bagasse / Pretreatment

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Funding

Department of Science and Technology, Ministry of Science and Technology