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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 .

Occurrence of calcium oxalate (CaC 2 O-CaOX) crystals has been observed in more than 215 plant families. However, very little is known about the effects of calcium oxalate on biomass pretreatment and saccharification. Agave bagasse (AGB) was used as a model material due to its natural high levels of CaOX. To understand the physicochemical changes in function of biomass pretreatment, both raw AGB and CaOX-extracted agave bagasse (EAB) were subjected to ionic liquid (IL) with 1-Butyl-3-methylimidazolium chloride [C 4 C 1 Im][Cl] and alkaline hydrogen peroxide (AHP) pretreatments. Physicochemical changes were monitored by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and wet chemistry methods. Results show that free CaOX crystals affected negatively (by ca 39%) the saccharification of AHPpretreated EAB compared to AGB. On the other hand, IL pretreatment achieved higher sugar yield (7.8 g dm-3) and lower crystallinity (14%) with EAB than for AHP (5.4 g dm-3 and 29%, respectively).

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