Rapid dissolution of switchgrass in 1-butyl-3-methylimidazolium chloride by ultrasonication

Abstract

The utilization of ultrasonics to rapidly dissolve switchgrass in ionic liquid, 1-butyl-3-methylimidazolium chloride ([Bmim][Cl]) was evaluated in this work. The objective of the study focused on determining the effects of various ultrasonic conditions on the recovery of carbohydrate from biomass, lignin removal, and enzymatic hydrolysis. Dried ground switchgrass was added to ionic liquid, then sonicated at a frequency of 20kHz. The experiments were conducted using a catenoidal horn at varying amplitudes of 96μm, 128μm, and 160μm and sonication times of 2, 3, and 4min. Similarly, ground switchgrass was dissolved in ionic liquid assisted by conventional heat treatment at 130°C for 12 and 24h. The results showed good delignification results of 53% for the 24h heat pretreated samples and of 50.8% for ultrasonic assisted samples at 160μm amplitude and 4min. Even in the presence of lignin in the recovered biopolymer, both of heat treated and ultrasonicated samples obtained 100% glucan digestibility after only 3h of enzymatic hydrolysis. Heat pretreated samples exhibited 44–59% lower xylan digestibility compared to ultrasonic pretreated samples (160μm amplitude and 4min sonication time). Scanning electron microscope images displayed significant changes in biomass structure from intact and crystalline of the untreated biomass to disintegrated and amorphous of the treated biomass (heat treated and ultrasonicated). With increasing ultrasonic amplitude the carbohydrate recovery decreased. Also, more than 50% of the hemicellulose fraction was lost during biomass recovery. Overall, it was concluded that ultrasonication was a promising technology to enhance dissolution of lignocellulose in ionic liquid.