Biodiesel production through the esterification of palm oil effluent using sulfonated MIL-101(Cr) catalyst using linkers derived from PET plastic waste

Abstract

Palm oil fatty acid distillate (PFAD), a byproduct of crude palm oil refining, has gained interest as a biodiesel feedstock. Concurrently, the growing accumulation of PET waste poses serious environmental challenges. In this study, sulfonated metal-organic frameworks (MOF) using linkers derived from PET waste were employed as catalysts for PFAD esterification using various alcohols. When methanol was employed as the solvent, high free fatty acid (FFA) conversions (∼100 %) were consistently observed within the temperature range of 60–120 °C. In contrast, FFA conversion increased significantly with ethanol and isopropanol at elevated temperatures, reaching 99.4 % and 99.7 % at 90 °C and 120 °C, respectively, due to enhanced molecular interactions. This enhancement is attributed to improved solvation effects and increased molecular mobility, which facilitate esterification at higher temperatures. Higher alcohol chain length negatively impacted esterification efficiency due to increased activation energy. A greater catalyst-to-feedstock (C/F) ratio also improved conversion. The sulfonic acid group (SO₃H) content in MOFs played a crucial role: the MCS30 catalyst (30 % SO₃H linker) yielded the highest FFA conversions with methanol, ethanol and isopropyl alcohol, followed by the 20 % and 10 % counterparts. This is attributed to the abundance of Brønsted acid sites facilitating proton donation during the reaction. MCS30 Catalyst also exhibited excellent reusability, with the FFA conversion dropping only slightly from 99.7 % to 95.2 % over four cycles. Overall, this approach offers a dual environmental benefit: mitigating PET plastic waste and enabling sustainable biodiesel production via PFAD esterification.