Loblolly pine pretreatment by ionic liquid-glycerol mixtures

Glycerol was used as a cosolvent with the two ionic liquids 1-ethyl-3-methylimidazolium formate ([C2mim][O2CH]) and 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) to pretreat loblolly pine at 140 °C. Enzymatic hydrolysis was then performed on raw and pretreated pines to establish pretreatment efficacy. With pretreatment, glucose yield from enzymatic hydrolysis was improved from 2 % for raw pine up to 43 %, while yields of mannose/xylose combined improved from 4 % up to 77 %. Pine pretreated with a 50 % [C2mim][O2CH]-50 % glycerol mixture exhibited a pulp-like structure, likely formed from removal of the lignin that binds cell walls together. Using this 50 % mixture of [C2mim][O2CH] and glycerol for pretreatment gave a slightly lower glucose yield than a 75 % mixture of [C2mim][O2CH] and glycerol but gave a mannose/xylose yield twice as high. Klason lignin and Fourier transform infrared spectroscopy (FTIR) analysis indicated that [C2mim][O2CH]-glycerol pretreatment preferentially dissolves lignin. FTIR analysis also suggested increased amorphous cellulose content with this pretreatment. Using the anti-solvent ethanol, a lignin-rich substance was precipitated from the solvent mixtures.