Post-functionalized Monolithic Metal-Organic Frameworks for Biodiesel Production: Mechanistic Insights from DFT, Process Optimization via RSM, and Life Cycle Cost and Impact Assessment

Abstract

Despite the green credentials of biofuel development, the cost and ethical concerns surrounding using edible oils for biodiesel production necessitate exploring alternative feedstocks, such as non-edible oils. However, their high free fatty acid content often leads to saponification when using basic catalysts. In this work, we present a novel post-functionalized monolithic zirconiumbased metal-organic framework, monoUiO-66-NH2@SO3H, synthesized by reacting 2aminobenzenedicarboxylic acid with propene-1,3-sultone to generate sulfonic acid groups as the primary acidic sites for one-pot esterification-transesterification reactions. The reaction mechanism was investigated using density functional theory. The monolithic MOF structure enhances the recyclability of the catalyst, as its conformed morphology facilitates simple gravitational separation from the reaction mixture, eliminating the need for complex recovery processes. The optimized catalyst exhibits a total acidity and basicity of 2.78 and 0.22 mmol g - 1 , respectively, as determined by NH3 and CO2 temperature-programmed desorption analysis.Through parameter optimization using a central composite design of response surface 2 methodology, the catalyst efficiently yields used vegetable oil (UVO) into ASTM-compliant biodiesel via a synergistic trans(esterification) process. A maximum biodiesel yield of 97.8 ± 0.2 % was achieved in the initial reaction cycle, with sustained performance across five additional cycles, yielding 89.8 ± 0.3 % in the final cycle. This approach highlights the potential of monolithic MOFs as highly efficient and recyclable solid acid catalysts for sustainable biofuel synthesis.