Effect of inorganic additives and optimisation of the electro-assisted organosolv pretreatment of biomass

The electro-assisted organosolv pretreatment (EAOP) is a biomass pretreatment method which is viable at room temperature. Previously, it was shown that the electrochemically generated hydroxyl radical (OH*) during EAOP is key to the delignification efficiency when 1-butyl-3-methylimidazolium acetate and gamma-valerolactone (10 wt% [Bmim]OAc/GVL) are used as the solvent. However, the effect of additives and biomass loading on this novel pretreatment process have not previously been investigated. In this study, inorganic salts of NaOH, NaCl, FeCl3, with and without added water, were used as additives into [Bmim]OAc/GVL, to determine their effect on OH* formation during EAOP. These inorganic salts were selected as they have been proven effective in the electrochemical conversion of either lignin or cellulose. It was found that [Bmim]OAc/GVL with NaCl/water showed the most rapid and largest amount of OH* formation, being 45% higher than [Bmim]OAc/GVL without additives. The 240-min EAOP with NaCl/water delignified 70.8 wt% of Eucalyptus sawdust and the residual biomass showed 204.4 mg/g total reducing sugar yield. In addition, EAOP with NaCl/water present can be done rapidly (in 30 min) and at high biomass loading (25%). The total reducing sugar (TRS) yield of sawdust from the high-loading rapid EAOP is up to 194.0 mg/g, which is around 10-fold higher than untreated sawdust. The spent solvent from EAOP could be regenerated, with only minor TRS yield decrease (10%) observed after recycling the solvent four times. Synopsis: NaCl and water were added into the electro-assisted organosolv pretreatment as inorganic additives, which enabled EAOP to be completed in 30 min at 25% biomass loading. The residual biomass from EAOP can produce up to 204.4 mg/g reducing sugar (approximately 10-folds higher than untreated biomass) and the regenerated solvent showed only minor decreases (10%) in total reducing sugar yield after four cycles.