Production of Fermentable Sugars from Energy Cane Bagasse

Abstract

Lignocellulosic biomass contains cellulose and hemicellulose which are composed of hexose and pentose sugars. These sugars can be used in the sustainable production of fuels and chemicals. However, the recalcitrant nature of lignocellulosic biomass makes this conversion a challenging process. An effective pretreatment can remove lignin, solubilize the hemicellulose, decrease cellulose crystallinity, and prepare the biomass for enzymatic hydrolysis and conversion into green renewable chemicals. The research study presented in this dissertation addressed some of the challenges associated with the conversion of lignocellulosic biomass into green fuels and chemicals. This study was divided into three main goals. The first goal was to optimize a liquid ammonium hydroxide pretreatment for energy cane bagasse for maximum sugar yields via Response Surface Methodology (RSM). Optimum pretreatment conditions for maximum glucose yield were 208°C, for 36 min and ammonium hydroxide to biomass ratio of 0.4:1. A yield of 30.77 g glucose and 3.99 g xylose was predicted per 100 g of untreated biomass (dry weight). The quadratic models were found reliable within the design space. The second goal of this study was to evaluate the interaction effect of cellulase (Cellic® CTec2), xylanase (Cellic® HTec2), and laccase along with a non-ionic surfactant (Tween® 80) on the cellulose digestibility of unwashed and post-washed pretreated substrate. Highest cellulose digestibilities observed were 84.30% and 97.10% for values set within the design range for the unwashed and washed biomass, respectively. Optimum enzymatic hydrolysis conditions for unwashed substrate were 19.39% CTec2, 12.04% HTec2, 46.32 IU/g laccase, and 10.15% Tween® 80; and for washed substrate were 16.90% CTec2, 14.17% HTec2, 34.64 IU/g laccase, and 14.86%Tween® 80. The third and last goal of this research study involved assessing six hydrophobic imidazolium-based ionic liquids in the liquid-liquid extraction and recovery of non-sugar compounds (i.e., phenolic compounds, organic acids, and furans) from enzymatically hydrolyzed dilute ammonia pretreated energy cane bagasse hydrolysates. Phenolic compounds were considerably removed from the hydrolysates by all six ionic liquids, followed by furfural and 5-HMF; however, formic acid and acetic acid failed to partition. No more than two regenerations of these ionic liquids are recommended.