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Available onlineKeywords: Agave bagasse Ionic liquid pretreatment Lignocellulosic biofuels Calcium oxalate Characterization a b s t r a c t Previous studies of agave bagasse (AGB-byproduct of tequila industry) presented unidentified crystalline peaks that are not typical from common biofuel feedstocks (e.g. sugarcane bagasse, switchgrass or corn stover) making it an important issue to be addressed for future biorefinery applications. Ionic liquid (IL) pretreatment of AGB was performed using 1-ethyl-3-methylimidazolium acetate ([C 2 mim][OAc]) at 120, 140 and 160 C for 3 h and a mass fraction of 3% in order to identify these peaks. Pretreated samples were analyzed by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electronic microscopy (FE-SEM), thermal analysis (TGA-DSC) and wet chemistry methods. Previous unidentified XRD peaks on AGB at 2q ¼ 15 , 24.5 and 30.5 , were found to correspond to calcium oxalate (CaC 2 O 4 ) in a monohydrated form. IL pretreatment with [C 2 mim][OAc] was observed to remove CaC 2 O 4 and decrease cellulose crystallinity. At 140 C, IL pretreatment significantly enhances enzymatic kinetics and leads to~8 times increase in sugar yield (6.66 kg m À3 ) when compared to the untreated samples (960 g m À3 ). These results indicate that IL pretreatment can effectively process lignocellulosic biomass with high levels of CaC 2 O 4 .

In recent years, Agave has shown its potential as a bioenergy feedstock with a higher land productivity (up to 42 ton/ha year) than traditional feedstocks. Other features are its adaptation mechanism to high temperatures and its resistance to drought. The agronomics of Agave in Mexico are discussed, including total land planted, inputs required, and the harvesting and transport costs. Heating values, mineral concentration, and carbohydrate and lignin content show the potential of the Agave species to compete with current bioenergy crops. Currently, the pre-treatment of Agave is the most widely studied stage in biofuels and value-added products, which include technologies capable of reducing its recalcitrance while removing xylan and/or lignin and reducing cellulose crystallinity, among other effects, to increase the overall yield in saccharifi cation and fermentation, which will be discussed as well. In addition to spirits and fi bers from industrial interests, different liquid (ethanol and n-butanol) and gaseous (methane and hydrogen) biofuels, including certain value-added products (enzymes, lactic acid, and succinic acid), can be obtained from Agave in high yields. The main objective of this review is to address the recent advances in the utilization of Agave as a bioenergy feedstock for biofuels and value-added products within a sustainable biorefi nery scheme.

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