Effect of Extrusion Pretreatment on Enzymatic Hydrolysis of Miscanthus for the Purpose of Ethanol Production

Abstract

Lignocellulosic biomass can be converted to energy via several routes. One of them is hydrolysis to sugars with subsequent transformation to fuels and chemicals. Due to the crystalline structure of lignocellulose, pretreatment is a prerequisite to achieving increased enzymatic hydrolysis' rates. The objective of this study was to determine the optimum extrusion operating conditions for glucose and xylose production from Miscanthus. Extrusion was conducted in a high shear extruder (single screw type) with compression ratio 3:1. Barrel temperature and screw speed, along with sample moisture content and particle size were the parameters evaluated using Response surface methodology (RSM). Conversion rate to glucose and xylose was monitored after enzymatic hydrolysis with low enzyme loadings (5 FPU g -1 of cellulase complex and 18 CBU g -1 of β-glucosidase). The optimum conditions for the glucose production (3.63 g L -1 ) were: barrel temperature 150 °C, screw speed 2.5 Hz, moisture content 20% and particle size 2 mm; the optimum conditions for the xylose production (0.78 g L -1 ) were: barrel temperature 150 °C, screw speed 1.67 Hz, moisture content 15% and particle size 2 mm. Hence, under controlled conditions, extrusion resulted in better digestibility of Miscanthus and as such it can be utilized as a source of glucose and xylose in ethanol production.

Sugarcane and Woody Biomass Pretreatments for Ethanol Production

“…The high sugar recovery due to extrusion pretreatment is related to fibrillation, the increase in surface area [79-81, 86, 87] and pore size [103], which facilitate the access of enzymes to cellulose. Some authors have reported that the crystallinity, which confers resistance to enzymatic hydrolysis, was not significantly reduced in extruded biomass [79,102] and therefore was not related to the increase in biomass digestibility.…”

Brazilian biorefineries from second generation biomass: critical insights from industry and future perspectives

“…Briefly, pretreatment by milling aims to reduce the particle size and increase the surface area of the biomass to improve enzymatic saccharification in a later step, 53,54 while extrusion is used to reduce particle size (by the mechanical action of discs combined with temperature) and results in physical and chemical changes in biomass 55 . At industrial scale, biomass should be used as it is received from sugarcane or corn processing mills, without any further milling, to save the prohibitive cost incurred in milling or size reduction.…”

Extrusión húmeda del pasto Kikuyo (Cenchrus clandestinus (Hochst ex Chiov))

“…Ha sido reportado que la extrusión semi-seca genera un aumento significativo en la digestibilidad de DIVMS y DIVFDN del pasto Pheleum pratense L., debido probablemente a que dicho proceso afecta la estructura física y química de esta gramínea (29). Otros autores han encontrado, así mismo, aumentos en la fermentabilidad de otras gramíneas forrajeras luego de su procesamiento mediante diferentes tipos de extrusores, expresada está en el incremento en el rendimiento de diferentes monosacáridos producto de la degradación de la celulosa y hemicelulosa (glucosa, xilosa, arabinosa) (30,31).…”