Structural and Hydrolysis Characteristics of Cypress Pretreated by Ionic Liquids in a Microwave Irradiation Environment

Abstract

In the transformation of lignocellulosic biomass into simple sugars that are suitable for microbial fermentation to biofuels, the pretreatment process that increases susceptibility to enzymatic hydrolysis is of the utmost importance. Combination of microwave irradiation as heating mode and ionic liquids (ILs) as solvents was employed in the pretreatment of cypress to figure out the hydrolysis characteristics. Three ILs, namely 1-allyl-methylimidazolium chloride ([Amim]Cl), 1-butyl-3-methylimidazolium bromide ([Bmim]Br), and 1-ethyl-3-methylimidazolium acetate ([Emim]Ac), were used to dissolve wood flour under microwave irradiation, and the cellulosic fractions were regenerated by the addition of alkaline aqueous solution at room temperature. The structural analyses of the regenerated wood were examined offering a scientific understanding into the synergistic effects of microwave irradiation and ILs pretreatment on the efficiencies of cellulase enzymatic hydrolyses. The results showed that [Emim]Ac-regenerated cellulose possessed the highest enzyme saccharification yield (87.1 %) followed by [Amim]Cl (74.9 %) and [Bmim]Br (67.6 %). The highest yield from enzymatic hydrolysis of [Emim]Ac regenerated cellulose was in line with the observations of structural analysis, which indicated a more disrupted and amorphous structure. Results revealed that dissolution of cypress in ILs under the environment of microwave irradiation is a potential alternative method for the pretreatment of lignocellulosic materials. Both microwave irradiation and [Emim]Ac dissolution, which was screened as the best medium for this pretreatment, were found to increase the rate and yield of enzymatic hydrolysis significantly.