Chemical and Biological Engineering 5-22-2009 Proceedings of the 38 th Annual Biochemical Engineering Symposium

Brian Carter, Todd J. Menkbaus, and Patrick C. Gilcrease Department of Chemical and Biological Engineering South Dakota School of Mines and Technology Rapid City, SD 5770 l Furfural, 5-hydroxymethylfurfural, and acetic acid are formed during the high temperature acidic pretreatment of cellulosic biomass (10); such pretreatments are used to increase the yield of fermentable sugars for the production of ethanol or other biorenewable products. These compounds inhibit ethanol fermentation by Saccharomyces cerevisiae at relatively low concentrations (e.g. furfural :::: l giL). Effective removal of these inhibitory compounds would allow the use of more severe pretreatment methods to improve sugar yields, leading to more efficient fermentations; if recovered and purified, these inhibitors could also be sold as valuable by-products. This study investigated the separation of inhibitory compounds from fermentable sugars by using polyethyleneimene (PEl), a soluble cationic polyelectrolyte flocculant. Due to the secondary amine structure of PEl, it participates in the Mannich reaction with aldehydes such as furfural and hydroxymethylfurfural. Experiments were performed on simple solutions and Pine slurry hydrolysates. The removal of inhibitory compounds from actual hydrolysates was evaluated as a function of wood particulate loading and enzyme concentration. Simple acetate solutions were evaluated as a function of sulfate concentration and solution pH. PEl added to simple solutions at a ratio of one mole of imine functional group to one mole inhibitor, removed up to 8.7, 59.0, and 64.5 wt% of acetic acid, 5-hydroxymethylfurfural, and furfural, respectively. The inclusion of wood particulates, or low pH conditions decreased the furfural and HMF removal. Furfural and 5-hydroxymethylfurfural were recovered after removal by washing the flocculant with an acid solution. Recoveries up to 81.0 and 97.0 wt% were achieved for furfural and 5-hydroxymethylfurfural, respectively. Results have shown that by choosing the appropriate conditions (pH 5, solids removed), the inhibitory aldehydes can be selectively removed with minimal (<3 wt. % glucose loss) fermentable sugar losses. The selective removal of inhibitory compounds may improve ethanol productivity and the specific growth rate of Saccharomyces cerevisiae, and may also provide a means to recover valuable co products. Introduction The world's continually increasing demands for energy and the limited supply of energy derived from fossil fuels have led to an increasing interest in alternative sources of energy (l, 4, 11). In recent years, ethanol fermentation from biomass feedstocks has gained attention. Sustainability, local availability, and low substrate cost are some of the advantages of using biomass (7). Another advantage is that fuel derived from biomass is not in direct competition with food production, as is the case with fuel derived from com. Although ethanol production from biomass has been greatly improved, there are still areas that need further investigation including pretreatment, hydrolysis, solid-liquid clarification, and fermentation for the wide variety of feedstocks.