Unlock the Compact Structure of Lignocellulosic Biomass by Mild Ball Milling for Ethylene Glycol Production

Ball milling pretreatment was found to be an efficient method to promote the catalytic conversion of lignocellulosic biomass to ethylene glycol (EG). After 3–6 h ball milling of Miscanthus at 450 rpm, the EG yield reached about 52%, which is comparable to the result of pure cellulose conversion. The reasons of the promotion effect were investigated by characterizing the structure of biomass and the reaction residuals with X-ray diffraction, scanning electron microscopy, particle size distribution analyzer, contact angle measurement, thermogravimetric analysis-differential scanning calorimetry, and Fourier-transform infrared spectroscopy. The mild ball milling liberated (hemi)cellulose from the compact plant tissues without affecting the crystallinity of cellulose. It reduced the size of biomass to 30 μm and improved the accessibility of (hemi)cellulose, leading to a hydrophilic surface and high energy state of biomass for catalytic conversion. During the catalytic conversion, the mass transfer between sugar intermediates and heterogeneous hydrogenation catalysts were improved. Correspondingly, the self-reaction of sugar intermediates, and the reactions between sugar intermediates and lignin fractions were suppressed, resulting in the high EG yield.