Obtaining bio-additives using free and supported ionic liquids: the case study of furfural acetalization with either ethylene glycol or glycerol

This work aims to develop bio-based oxygenated fuel additives through the acetalization of furfural with two polyols — ethylene glycol and glycerol — using an ionic liquid (IL), 1-(4-sulfonic acid) butyl-3-methylimidazolium hydrogen sulfate [C 4 SO 3 Hmim][HSO 4 ], as a homogeneous acid catalyst, as well as two series of heterogeneous catalysts prepared by supporting this IL on silica gel 60 and SBA-15 mesoporous silica at variable loadings (10–50 wt%). All catalysts showed good activity in the formation of the target cyclic ether products: 2-(furan-2-yl)-1,3-dioxolane (I), cis/trans-(2-(furan-2-yl)-1,3-dioxolan-4-yl)methanol (II), and cis/trans-2-(furan-2-yl)-1,3-dioxan-5-ol (III). The supported catalysts outperformed the unsupported IL: the best-performing catalyst, SBAIL30, achieved a cyclic acetal yield of 51%, compared to 40% obtained with the free IL under the same conditions. This sample is characterized by its elevated number of strong acid sites, derived from sulfonic groups within the IL structure, as confirmed by XPS analysis. Furthermore, heterogeneous catalysts significantly altered the stereochemical outcome of the reaction: while the 6-membered ring product (III) predominates in the uncatalyzed reaction, the SILx and SBAILx catalysts favored formation of the 5-membered ring isomer (II), with isomer ratios of up to 64:36 (II:III) for SBAIL30 and > 70% selectivity toward II for SBAIL40.