Solid ionic liquids with macro–microporous structure for efficient heterogeneous catalysis of biodiesel

Abstract

By anchoring ionic–liquid moiety (MIMS·MSA) on the ligands of the metal–organic framework (MOF) via covalent bond, a new solid acidic ionic liquid Macro-UiO-67-ILs was achieved and used as an acid catalyst for biodiesel esterification. Template and reticular chemistry synthesis using H₂BPDC-MIMS ligand (3-(1-((4,4′-dicarboxy-[1,1′-biphenyl]-2-yl)methyl)-1H-imidazol-3-ium-3-yl)propane-1-sulfonate) as ligands obtained porous Macro-UiO-67-MIMS. Such solid acidic ionic liquids (ILs) feature hierarchical pore structures including the instinct micropores (∼1 nm) of MOF and the artificial macropores (∼110 nm) etched via template polystyrene pellets. By incorporating methylsulfonic acid (MSA) and Brønsted acid-zwitterion buffer, solid Macro-UiO-67-ILs bearing micropore and acidic ILs moiety (MIMS·MSA) on the channel wall of the framework was obtained and displayed 99% esterification of fatty acid in a short time. This conversion is double that of its counterpart without the macroporous structure as well as higher than that of liquid super acid MSA.