Intensification of enzymatic hydrolysis of cellulose to glucose by high frequency ultrasound: Optimization of process parameters and effects on enzyme stability

The conversion of lignocellulosic biomass for biofuels and biorefinery applications is limited due to the cost of pretreatment to separate or access the biomass’s three main components, cellulose, hemicelluloses, and lignin. Ultrasound and cavitation-assisted technologies are green techniques that have the potential to enhance the separation and hydrolysis of lignocellulosic materials for use in biofuel production and biorefineries, through physical and/or chemical mechanisms. We have studied the enzymatic hydrolysis of cellulose using a novel multifrequency ultrasonic reactor, and optimized glucose yield at 50°C and 5.2 pH. The best cellulose hydrolysis was observed at 611 kHz and 104 W. The effects of ultrasound and enzyme on the surface and structure of the cellulose were studied using BET, SEM, X-Ray Diffraction (XRD) and Scanning Helium Ion Microscopy (SHIM). The effect of ultrasound on the enzymes (cellulase + cellobiase) was also preliminarily observed from High Pressure Liquid Chromatography (HPLC) and FTIR analyses. It appeared that ultrasound did not affect the specific activity of the complex structure of the enzyme macromolecules at the treatment conditions reported in this study. Up to 70 % glucose yield was obtained with prolonged time (40 – 50 h). A synopsis of our current research projects and some results of work on cavitation-enhanced intensification and optimization of the conversion of cellulose to glucose will be discussed. An overview of studies of ultrasound effects on enzyme stability and future research work will also be presented.