Biofuels produced from various lignocellulosic materials, such as wood, agricultural, or forest residues, have
the potential to be a valuable substitute for, or complement to, gasoline. Many physicochemical structural
and compositional factors hinder the hydrolysis of cellulose present in biomass to sugars and other organic
compounds that can later be converted to fuels. The goal of pretreatment is to make the cellulose accessible
to hydrolysis for conversion to fuels. Various pretreatment techniques change the physical and chemical
structure of the lignocellulosic biomass and improve hydrolysis rates. During the past few years a large number
of pretreatment methods have been developed, including alkali treatment, ammonia explosion, and others.
Many methods have been shown to result in high sugar yields, above 90% of the theoretical yield for
lignocellulosic biomasses such as woods, grasses, corn, and so on. In this review, we discuss the various
pretreatment process methods and the recent literature that has reported on the use of these technologies for
pretreatment of various lignocellulosic biomasses.