|Authors: (Bo Zhang, School of Chemical Engineering and Pharmacy, Wuhan Institute of Technology, Hubei, China, and others)
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 chapter reviews recent developments of several widely used pretreatment
technologies, including alkali, hot-water, 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.