Effect of particle size on enzymatic hydrolysis of pretreated Miscanthus

Particle size reduction is a crucial factor in transportation logistics as well as cellulosic conversion. The effect of particle size on enzymatic hydrolysis of pretreated Miscanthus x giganteus was determined. Miscanthus was ground using a hammer mill equipped with screens having 0.08, 2.0 or 6.0 mm sieve openings. Particle size distribution and geometric mean diameters were determined for all samples. Ground samples were subjected to hot water, dilute acid or dilute ammonium hydroxide pretreatment. Enzyme hydrolysis was conducted on washed pretreated solids; sugar generation was used as a measure for pretreatment efficiency. Glucose and xylose concentrations were monitored using HPLC. Glucose and xylose profiles were generated and hydrolysis rates estimated. Glucose, xylose and total conversion yields were determined by comparing final sugar concentrations obtained to amounts present in pretreated biomass. Geometric mean diameters were the smallest from 0.08 mm sieve screen (56 μm) followed by 2.0 mm (301 μm) and 6.0 mm (695 μm) screens. An increasing trend in percent total conversion was observed with decreasing mean particle size. Across all pretreatments, biomass ground using 0.08 mm screens resulted in highest total conversion. Enzyme hydrolysis of unpretreated biomass samples also resulted in increased total conversions as particle size decreased, although mean conversions (10–20%) were much lower than for pretreated biomass samples (53–94%), indicating the need for chemical pretreatments in biomass conversion.

► Decreased particle size increased total polysaccharide conversion for hot water, dilute acid and dilute ammonium hydroxide pretreatments. ► Effect of decreased particle size on enzyme hydrolysis of unpretreated biomass resulted in increased total polysaccharide conversion. ► Polysaccharide conversions were 43–74% lower than when chemical pretreatments were employed prior to enzyme hydrolysis.