Sustainable alternative transportation fuels are in high demand
and are of interest as second-generation biofuels. One such biofuel
is ethanol produced from non-food biomass. Ethanol production consists of four principal
steps: (1) chemical and physicochemical pretreatment, (2) enzymatic
hydrolysis, (3) microbial fermentation (often using Saccharomyces
cerevisiae), and (4) separation and concentration of ethanol. To decrease the energy required
for the final separation process and to commercialize lignocellulosic
ethanol technology, it is necessary to increase the ethanol
concentration of the product after fermentation. Concentrating enzymatic hydrolyzates
(glucose and xylose) using membrane separation process, nanofiltration,
with molecular weight cutoffs between ultrafiltration and
reverse osmosis, is attractive because nanofiltration is a widelyused
technique in biorefineries due to its low energy consumption
and unique separation properties.