Pretreatment of cotton stalk with ionic liquids including 2-hydroxy ethyl ammonium formate to enhance biomass digestibility

Cotton stalk was subjected to ionic liquid pretreatment via several ionic liquids; 2-hydroxy ethyl ammonium formate (HEAF), 1-allyl-3-methyl imidazolium chloride (AMIMCl), 1-butyl-3-methyl imidazolium chloride (BMIMCl), 1-ethy1-3-methyl imidazolium chloride (EMIMCl) and 1-ethy1-3-methyl imidazolium acetate (EMIMAc). Ionic liquids readily provided conversion of cotton stalk into fermentable sugars upon enzymatic hydrolysis through reshaping the organized and rigid structure into a less organized and less durable form. The impact of ionic liquid pretreatment was mostly recognized for EMIMAc pretreated cotton stalk, which exhibited a highly deconstructed structure whereas modest changes were detected for those pretreated via other ionic liquids. Biomass digestibility was 65% for EMIMAc pretreated cotton stalk after 72 h of enzymatic hydrolysis, which was 9-fold higher compared to untreated cotton stalk. Despite being incapable of dissolving cellulose. HEAF pretreatment resulted in an enzymatic digestibility of 26%, which was similar to the digestibilities attained by AMIMCl and EMIMCl pretreatments. EMIMAc recycling was also feasible with respect to enzymatic digestibility and structural features including the deconstructed structure and reduced crystallinity for the pretreated samples as analyzed by characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). (C) 2012 Elsevier B.V. All rights reserved.