Biomass-derived hydrophobic metal-organic frameworks solid acid for green efficient catalytic esterification of oleic acid at low temperatures

Biodiesel, of great significance, is a promising kind of non-polluting renewable energy that can meet world energy needs. However, the by-product water of esterification reaction used for biodiesel production is not conducive to the positive reaction, and even destroys the activity and structure of the used catalyst. In this study, a renewable solid acid catalyst FDCA/SA-Hf with a degree of hydrophobicity was simply prepared by a solvent-free assembly manner using biomass-based materials. FDCA/SA-Hf was found to be efficient for producing biodiesel from the abundant free fatty acid and nonedible raw oils at a low temperature, and its reaction mechanism was also studied. FDCA/SA-Hf showed stable structural properties and excellent hydrophobic network (131.5°), wherein the chemical grafting of stearic acid improved its Lewis acidity and promoted the adsorption of free fatty acid and the desorption of water. Importantly, as promoted by FDCA/SA-Hf in esterification, a high biodiesel yield reached 98.6% (49 °C, 4.1 wt%, 19.5:1 and 9.5 h). After being easily reused, biodiesel yield still achieved 90% even in the presence of 6 wt% water or after six cycles, which was due to the high hydrophobicity and stability. FDCA/SA-Hf shows great potential in heterogeneous acid-mediated catalytic fields, especially for biodiesel production.