Rising oil prices and uncertainty over the security of existing fossil fuel reserves, combined with concerns over global climate change, have created the need for new transportation fuels and bioproducts to substitute for fossil carbon-based materials. Ethanol is considered to be the next generation transportation fuel with the most potential, and significant quantities of ethanol are currently being produced from corn and sugar cane via a fermentation process. Utilizing lignocellulosic biomass as a feedstock is seen as the next step towards significantly expanding ethanol production. The biological conversion of cellulosic biomass into bioethanol is based on the breakdown of biomass into aqueous sugars using chemical and biological means, including the use of hydrolotic enzymes. From that point, the fermentable sugars can be further processed into ethanol or other advanced biofuels. Therefore, pretreatment is required to increase the surface accessibility of carbohydrate polymers to hydrolytic enzymes. This paper reviews recent developments of several widely used pretreatment technologies, including alkali, hotwater, acid and inorganic salt (ionic liquid and Lewis acid) pretreatments. Recent advancements in the pretreatment field include: 1) application of novel chemicals or processes on biomass fractionation; 2) the use of new enzyme mixtures such as combinations of purified xylan related enzymes, appreciation of soluble inhibitors of cellulases, and especially the evaluation of pretreated biomass at varying cellulase loading; 3) application of a wide variety of sophisticated techniques for analyzing native and pretreated biomass solids, especially microscopic techniques and methods for measuring surface area; and 4) greater efforts at scale up and commercialization of biomass processes for biofuels and chemicals.
Last date updated on July, 2014