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.

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Ordered mesoporous MCM-48 membranes with cubic pore structure were prepared by the solution growth method on symmetric R-alumina supports using cetyltrimethylammonium bromide as a surfactant. The surfactant was removed by Soxhlet extraction using an ethanol/HCl mixture to synthesize defect-free MCM-48 membranes as confirmed by N 2 unsteady-state permeation. MCM-48 membranes and powders were successfully modified with a polymer, polyethyleneimine (PEI) containing amino groups as confirmed by N 2 adsorption-desorption data, X-ray diffraction, Thermo gravimetric analysis (TGA), and N 2 unsteady-state permeation experiments. The PEI/MCM-48 membranes were permeable to N 2 after pore modification, suggesting incomplete filling of MCM-48 pores by PEI, which was confirmed by the N 2 adsorption-desorption experiments on the bulk PEI/MCM-48 powder. The PEI-modified MCM-48 membranes were highly selective to N 2 permeation from N 2 /CO 2 mixtures at room temperature in the presence of ∼2.6% water vapor. Binarygas N 2 /CO 2 permeation data for the PEI-modified MCM-48 membranes showed much-higher N 2 permeance as compared to CO 2 permeance in the presence of water vapor. The selectivities increased with CO 2 concentration in the feed, and selectivities greater than 80 were observed. The N 2 /CO 2 selectivities diminished significantly at 363 K for the PEI/MCM-48 membranes.