Effects of alkalinity of ionic liquids on the structure of biomass in pretreatment process
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Three basic ionic liquids (BILs), 1,3-dimethyl-imidazole dimethyl phosphate([MMIM][DMP]), 1-butyl-3methylimidazolium acetate([BMIM][Ac]) and 1-ethyl-3-methylimidazolium acetate([EMIM][Ac]), were applied to the pretreatment of eucalyptus biomass under microwave conditions with the decreasing alkalinity order of [EMIM][Ac] > [BMIM][Ac] > [MMIM][DMP]. The results showed that the alkalinity of ionic liquids has great effects on the pretreatment of biomass; the greater the alkalinity is, the more capable are the ionic liquids to dissolve hemicellulose, and [MMIM][DMP] with moderately weak alkalinity has a uniquely stronger ability to remove lignin from biomass. Dissolved lignin could easily be separated by using the acetone/water (1:1, v/v), and [MMIM][DMP] pretreatment can extract 41.8% of the total amount of eucalyptus lignin, of which [BMIM][Ac] and [EMIM][Ac] recovered 18.2% and 10.7% of the total amount of raw lignin, respectively. The untreated and ILs-treated eucalyptus samples were characterized by FTIR, XRD, TGA and SEM. Lower thermal stability and changes in crystal structure were observed after pretreatments.
The authors are grateful for the support of National key R & D project of China (Grant No. 2017YFB0307901) and Natural Science Foundation of China (Grant No. 21476091). The authors also appreciate the financial support from the Science and Technology Planning Project of Guangdong Province (Grant No. 2015A020215009) and the Science and Technology Planning Project of Foshan in Guangdong Province (Grant No. 2015AG10011).
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