Membranes for the removal of fermentation inhibitors from biofuel production

Decreasing world fossil fuel reserves combined with increasing greenhouse gas emissions have led to significant interest in developing alternative renewable energy resources. Lignocellulosic biomass represents one of the largest renewable energy resources. Production of biofuels from lignocellulosic biomass is particularly attractive because competition between food and energy crops is eliminated. Lignocellulosic biomass is highly recalcitrant to hydrolysis and requires several steps before the product biofuel is produced. These pretreatment steps lead to the production of inhibitory compounds that adversely affect subsequent fermentation steps. Consequently, biomass detoxification or conditioning is needed to remove these inhibitory compounds before fermentation. Here, a number of potential membrane-based processes are described for the removal of inhibitory compounds. Because of the large number and variety of inhibitory compounds that could be present, it is likely that the actual unit operations used will depend on the specific hydrolysate and pretreatment conditions employed in a particular process. When more than one unit operation is required, membrane-based processes offer the promise of process intensification in which two unit operations can be combined into one.