Electro-Assisted Pretreatment of Lignocellulosic Materials in Ionic Liquid-Promoted Organic Solvents

Organosolv pretreatment is highly effective for delignification of lignocellulosic materials (LCMs), but the requirement for high operation temperature has economically hindered the industrial use of this process. Although it is accepted that organosolv pretreatment using thermo energy can have a high delignification effectiveness, the effect of using electric energy as an alternative to thermal energy has not been investigated. In this study, we have investigated different solvents and applied potentials to refine the electro-assisted organosolv pretreatment (EAOP) process, aiming at the delignification of LCMs at ambient temperature. The solvents used for EAOP are referred to as ionic liquid-promoted organic solvent (IL/O), which consisted of an ionic liquid (IL) and an organic solvent (O), with combinations of three ILs and four organic solvents. Selected physicochemical and electrochemical properties of these IL/O were initially characterized to identify the promising solvent compositions, such as those that support OH* formation. The three promising IL/O solvents were then used in the EAOP and assessed for their performance toward the delignification of Eucalyptus sawdust, rice straw, and wheat straw at ambient temperature (25 °C). The best delignification condition using EAOP was the IL/O of 10 wt % 1-butyl-3-methylimidazolium acetate in γ-valerolactone, with 2.0 V applied for 4 h. Under these conditions, 73 wt % delignification of Eucalyptus sawdust was achieved, with 70.5 and 86.1 wt % of cellulose and hemicellulose retained in the residual biomass, respectively. Overall, the results support that EAOP is a viable delignification method at ambient temperature compared to conventional organosolv pretreatment and that further optimization of the process configuration and reaction conditions is warranted.