Microwave-Driven Sugar Beet Pulp Liquefaction in Polyhydric Alcohols

Liquefaction of sugar beet pulp (SBP) was carried out using microwave irradiation as the heating source, ethylene glycol/glycerol at a ratio of 80/20 (w/w) as the liquefaction solvent and sulfuric acid as the catalyst at 160 °C. The effects of different liquefaction conditions, including two particle size ranges of SBP, liquefying solvent-to-SBP solids (LS/S) ratio and reaction time on the liquefaction yield, viscosity of the liquefaction products, chemical characteristics and morphology of residues were studied using viscometry, Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electronic microscopy (SEM). The efficiency of liquefaction of SBP was found to depend on its particle size of SBP raw material and the LS/S ratio. The smaller SBP particles improved liquefaction efficiency and reduced the amount of solvent required. The crystallinity index of liquefaction residues indicated that crystalline cellulose was no longer the rate limiting factor of liquefaction process when the particle size of SBP was small (75–177 μm). A rugged and deformed surface of the liquefaction residue (observed through SEM) indicated that severe damage in the native fiber structure occurred during the liquefaction.