Fermentable sugars from pyrolysis oil : extraction and hydrolysis of levoglucosan

Fermentable sugar obtained from lignocellulosic material exhibits great potential as a renewable feedstock for the production of bio-ethanol. One potentially viable source of fermentable sugars is pyrolysis oil, also commonly called bio-oil. Depending on the type of lignocellulosic material used and the operating conditions for the process of pyrolysis, bio-oil can contain up to 33 wt% (Li and Zhang, 2004) of 1,6-anhydro-β-D-glucopyranose (levoglucosan, LG), an anhydrosugar that can be readily hydrolyzed to glucose. This research investigated and improved the extraction of levoglucosan from bio-oil via phase separation, the acid-hydrolysis of the. levoglucosan once in the aqueous phase into glucose, and the subsequent fermentation of the glucose into ethanol using a Saccharomyces cerevisiae yeast strain, T2. Maximum levoglucosan extraction (7.8 wt% of the initial bio-oil) occurred when minimal amounts of water were used; optimally, at the point of phase separation. For the bio-oil used in this study, phase separation occurred when the total water in the solution equalled 41 wt% of the bio-oil. Extraction was improved when the temperature of the bio-oil was raised (34°C) and effective mixing was applied. Hydrolysis yields greater than 100% (based on levoglucosan) occurred at high temperatures (130°C), strong sulphuric acid concentrations (0.5M) and short reactions times (20 minutes). Temperature exhibited the most significant effect on the yield; yet a strong interactive effect between temperature and time due to sugar degradation at temperatures at or above 130°C prohibits the use of higher temperatures. The initial levoglucosan concentration in the aqueous phase also demonstrated a significant effect on the hydrolysis yield. As is, the hydrolysate was too toxic for yeast growth and fermentation due to the presence of inhibitory compounds such as organic acids and sugar degradation products. However, theoretical fermentation yields were made possible for hydrolysate fractions of up to 20% by using micro-aerophilic conditions and high yeast inoculums (1 g/L in vial). Fermentation rates of 0.40 g/L hr were observed under these conditions.