Location: Bioenergy ResearchTitle: Effect of particle size on enzymatic hydrolysis of pretreated Miscanthus Author
Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2012
Publication Date: 12/15/2012
Citation: Khullar, E., Dien, B.S., Rausch, K.D., Tumbleson, M.E., Singh, V. 2013. Effect of particle size on enzymatic hydrolysis of pretreated Miscanthus. Industrial Crops and Products. 44:11-17. Interpretive Summary: Miscanthus giganteus is being investigated as a bioenery crop for production the Midwest because of its high production and carbohydrate yields. The majority of carbohydrates are contained in the plant cell wall, whereby these carbohydrates are converted to free sugars by enzymes such as cellulases. Efficient enzymatic conversion requires that the biomass be first pretreated thermo-chemically to open up the plant cell wall structure. While biomass is typically milled prior to pretreatment there has not been a systematic investigation as to what role size reduction plays in pretreatment for Miscanthus. In this study, several different size fractions of Miscanthus were generated, treated with various pretreatment reactions, and evaluated for enzymatic conversion to sugars. The results herein demonstrated that milling to finer particle sizes promoted enzymatic conversion. This result will be useful for cellulosic ethanol companies considering perennial bioenergy crops as one of their feedstocks.
Technical Abstract: 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.