Effects of alkalinity of ionic liquids on the structure of biomass in pretreatment process

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.