(701a) Ultrasonically Assisted Conversion of Lignocellulosic Biomass to Ethanol

Lignocellulosic biomass can be converted to ethanol by hydrolysis and subsequent fermentation of sugars. The enzymatic saccharification lignocellulosic biomass is of low efficiency due to many reasons summarized as the substrate and enzyme factors. A pretreatment step that softens the lignocellulosic material is needed in order to increase the yield of hydrolysis. Current pretreatment processes are mostly chemically catalyzed [1]. In order to improve the hydrolyzability of lignocellulosic materials in an environmentally friendly manner, we choose to use the ultrasonic energy. Thus, the sonication was employed in a two steps concept process: ultrasonically pretreatment and ultrasonically assisted hydrolysis of biomass. The ultrasonically assisted pretreatment do not seek to actually hydrolyze the biomass to soluble sugars, but rather to generate a pretreated substrate that is more easily hydrolyzed via increasing enzyme accessible surface area and affect the crystallinity [2]. The efficiency of enzymatic hydrolysis was evaluated to determine the optimal conditions of ultrasonic exposure for the pretreatment of lignocellulosic biomass as well as of the ongoing hydrolysis. We employed various type of ultrasonic devices in order to optimize the ultrasonic parameters of biomass exposure to the ultrasounds. Our results show that a direct exposure of the lignocellulosic substrate to the 20 kHz high power ultrasound is in the main benefit of both pretreatment and ongoing hydrolysis. Thus, the highest yield of glucose was obtained with a horn type sonicator (Homogeniser, Bransonic Model 250/450 Sonifer) when the sonication was performed by using a special designed glass vessel that facilitate an ultrasonically promoted propelling of the biomass (Fig.1). This enhancement effect is a consequence of the cavitational shock intensity that is higher at lower frequencies [3] As a result of ultrasonic pretreatment the size of substrate particle was significantly decreased and the extraction of lignin and hemicellulose was achievable. Furthermore, when the microcrystalline cellulose was used as standard substrate the crystallinity of the substrate was decreased. We also demonstrated that a gain in efficiency of cellulose hydrolysis due to the ultrasound exposure is possible by employing ultrasound for the promotion of the ongoing hydrolysis. Thus, the benefit of ultrasonic energy for biomass conversion is significant when the ultrasonic energy is delivered directly to the lignocellulosic substrate. References [1] C. N. Hamelinck, G.. van Hooijdonk, A. P. C. Faaij, Biomass and Bioenergy 28, 384 (2005). [2] D. N.-S. Hon, N. Shiraishi, Wood and Cellulosic Chemistry (Marcel Dekker, Inc., NY, 2001), p. 83. [3] T. J. Mason. Sonochemistry: (Oxford University Press, Inc., New York 1999), p.65. Fig.1 Direct Sonication of Lignocellulosic Biomass sonication