Combination of ultrasonication and deep eutectic solvent in pretreatment of lignocellulosic biomass for enhanced enzymatic saccharification

Abstract

The synergistic effect of ultrasonication with deep eutectic solvent (DES) on pretreatment of oil palm empty fruit bunch (OPEFB) was investigated. Three different types of DESs, namely choline chloride:lactic acid (ChCl:LA), choline chloride:urea (ChCl:U) and choline chloride:glycerol (ChCl:G) were applied. The performance of the pretreatment was evaluated based on yield of reducing sugars, lignin content, crystallinity index, structural and morphology changes. ChCl:LA pretreated OPEFB attained the highest yield of reducing sugars (36.7%) under the action of ultrasonication for 15 min at sonication power 60% (210 W) and temperature 50 °C, followed by ChCl:U (35.8%) and ChCl:G (35.3%). Under these conditions, ChCl:LA pretreated OPEFB showed significant change in structural and morphology, associated with the lowest crystallinity and lignin content. ChCl:LA promoted the pretreatment process in view of its intrinsic properties of low viscosity and low surface tension. The incorporation of ultrasonication in DES pretreatment significantly increased the reducing sugars yield suggested the synergistic effect of ultrasonication with DES pretreatment. These signifies that ultrasound-assisted DES pretreatment could be a promising alternative pretreatment technique for lignocellulosic biomass.