Fabrication of ionic liquids-functionalized PVA catalytic composite membranes to enhance esterification by pervaporation

A novel ionic liquids (ILs)-functionalized catalytic composite membrane (CCM), poly(vinyl alcohol)-g-poly(ionic liquids)/poly(vinyl alcohol)-glutaraldehyde (PVA-g-PILs/PVA-GA), was proposed for enhancing the esterification between ethanol and acetic acid in a pervaporation catalytic membrane reactor (PVCMR). The ILs-functionalized catalytic layer was prepared by free radical polymerization reaction between PVA and 1-vinyl-imidazole acidic ILs monomer. Covalent bonds between ILs and PVA were formed, and there were –SO₃H groups in PVA-g-PILs copolymer chain after graft polymerization, thus improving the stability of immobilized ILs and ensuring high catalytic activity. The PVA-g-PILs copolymer was investigated by ¹H nuclear magnetic resonance, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The morphology of ILs-functionalized CCM was characterized by scanning electron microscopy. The separation performance of ILs-functionalized CCM was measured by dehydration of ethanol by pervaporation, and the catalytic performance of ILs-functionalized CCM was evaluated via batch experiments and pervaporation coupling esterification experiments. The result of esterification between acetic acid and ethanol showed that acid conversion reached 93% in 12 h at 75 °C with ILs-functionalized CCM in PVCMR; a conversion enhancement of approximately 19% was achieved, compared to that of an equilibrium conversion in a batch reactor under the same conditions. Moreover, the ILs-functionalized CCM exhibited good reusability and catalytic stability owing to the graft polymerization between PVA and acidic ILs.