Hierarchically interconnected porous (IL-HPMo)x/MOF@PloyHIPEs catalysts for microwave-assisted biodiesel production from low-quality oils

Developing efficient catalysts for biodiesel production from low-quality oils remains a critical challenge in sustainable energy research. In this study, a hierarchically porous MOF@PolyHIPE composite was synthesized using a Pickering high internal phase emulsion (HIPE) template stabilized by NH2-UiO-66 nanoparticles, followed by functionalization with phosphomolybdic acid (HPMo) and a glycine-derived ionic liquid ([Gly-H][OTs]) through the co-impregnation method. The resulting structured (IL-HPMo)X/MOF@PolyHIPEs catalyst exhibited high catalytic activity in the microwave-assisted transesterification of soybean oil when the mass ratio of [Gly-H][OTs] to HPMo was 1:1. Structural and acidity characterization revealed that the (IL-HPMo)1.0/MOF@PolyHIPEs catalyst possessed a hierarchical macro/mesoporous structure with a high density of Lewis/Brønsted acid active sites. A maximum oil conversion of 96.5 % was attained on this catalyst within 30 min at a catalyst loading of 6 wt%, a reaction temperature of 120 °C, a methanol-oil molar ratio of 30:1, and microwave power of 600 W. Notably, the catalyst concurrently facilitated transesterification of oil and esterification of free fatty acids (FFAs), achieving 96.5 % oil conversion and complete FFAs conversion in one-pot. It also demonstrated strong tolerance toward FFAs and water, and the catalyst maintained 76.3 % oil conversion after 5 consecutive cycles. Kinetic studies indicated that the transesterification follows pseudo-first-order kinetics, with an apparent activation energy (Ea) of 64.21 kJ/mol. Furthermore, the thermodynamic parameters (ΔH = 61.07 kJ/mol, and ΔS = −110.05 J/mol/K) strongly confirmed that the transesterification process is both non-spontaneous and endothermic under the studied reaction conditions. This work successfully integrates the hierarchical porous (IL-HPMo)1.0/MOF@PolyHIPEs heterogeneous acid catalyst with microwave irradiation to enable rapid, high-yield biodiesel production with broad alcohol adaptability. The estimated production cost for biodiesel from waste cooking oil is $0.88 per kg, emphasizing high commercial viability.