Acid-Base Bifunctional Monolithic MOF Catalyst for Biodiesel Production

Abstract

The adoption of biofuel at scale is compromised by the cost and ethics of using edible oils in its production. However, the high free fatty acid content of inedible oils means these undergo saponification with current basic catalysts. Circumventing this issue with multi-step processing is commercially unattractive. In contrast, acid-base bifunctional catalysts offering one-pot biofuel production and straightforward product separation have emerged as a compelling technology. We report a novel monolithic (conformed) acid-base bifunctional zirconium-based MOF, monoUiO-66-NH2-SO3H-30. To achieve this, 2-aminobenzenedicarboxylic acid is reacted with Zr(IV), harnessing mercaptoacetic acid as a dual steric modulator and source of sulfonic acid sites when intermediate monoUiO-66-NH2-SH-30 is oxidized. The optimized bifunctional catalyst achieves a biodiesel yield of 97.3±0.5%, compared to 93.5±0.2% for its powdered analogue, under methanol-to-oil molar ratio 21.7:1, catalyst loading 6.3 wt%, reaction temperature 92 °C, and time 1.6 h. Data establish that catalyst bifunctionality enables simultaneous esterification and transesterification for transformation of inedible Jatropha curcas oil into ASTM compliant biodiesel.