Effect of H-Bonding on Brønsted Acid Ionic Liquids Catalyzed in Situ Transesterification of Wet Algae

Brønsted acid ionic liquids (BAILs) are effective to biodiesel production of in situ transesterification of wet algae due to their dual role as both solvents of cellulose and catalysts of transesterification. The cellulose solubilities of BAILs are depending on H-bonding of BAILs-cellulose in varied solvent conditions, which subsequently affect the biodiesel productions. For this reason, the effects of H-bonding between BAILs including [Bmim][H₂PO₄], [Bmim]₂[HPO₄], [Bmim][HSO₄], and cellulose under different methanol and water conditions on cellulose extractions are experimentally and theoretically investigated. The cellulose extractions in BAILs are decreasing as [Bmim][H₂PO₄] > [Bmim]₂[HPO₄] > [Bmim][HSO₄], contrary to the variation of their thermal stabilities and crystallinities caused by varied H-bonding of BAILs-cellulose. Increasing methanol is positive to cellulose extractions in [Bmim][HSO₄], while negative to those in [Bmim][H₂PO₄] and [Bmim]₂[HPO₄], due to the solvent effect of methanol confirmed by cyclic voltammetry (CV) measurements. The effect of water on H-bonding of BAILs-cellobiose is contrary to the effect of methanol. It is confirmed via the bonding interaction of BAILs-cellobiose through the density functional theory (DFT) computational method. However, the biodiesel yields are varied differently due to the competition of H-bonding of BAILs-cellobiose and deprotonation of BAILs under different methanol and water conditions. This study might pave the way to neutralize the negative effect of water on in situ transesterification via enhancing the cellulose extractions of BAILs.