Esterification of used cooking oil using ZSM-5 and HY zeolite catalysts for low-cost biodiesel feed production

The increasing demand for biodiesel has prompted the investigation of low-quality feedstocks, such as used cooking oil (UCO), as an alternative to refined vegetable oils. Nevertheless, the high free fatty acid (FFA) content, typically indicated by the acid value, in these feedstocks poses challenges in the conventional biodiesel production process using homogeneous alkaline catalysts. This study investigates the use of zeolite-based catalysts, ZSM-5 and HY, for the esterification of UCO to produce biodiesel feed. The catalysts were analyzed through techniques such as X-ray Diffraction (XRD), Brunauer-Emmett-Teller - Barrett-Joyner-Halenda (BET-BJH), and NH3-probed temperature-programmed desorption (NH3-TPD). XRD analysis revealed distinct crystal structures for the catalysts, with ZSM-5 exhibiting an orthorhombic MFI structure and HY displaying a cubic Faujasite structure. N2 physisorption analysis showed the presence of micropores and narrow mesopores in the catalysts, with HY exhibiting a peak at 2.5-5 nm pore sizes and a shoulder at 5-10 nm. NH3-TPD analysis indicated that all catalysts possess weak, moderate, and strong acid sites, with ZSM-5 having a higher acid density compared to HY. The effects of catalyst type, molar ratio, catalyst dosage, and reaction temperature on the esterification process were systematically studied. ZSM-5 demonstrated superior performance with a 61.07% FFA conversion rate, while HY achieved a slightly lower conversion rate of 57.64%. This study highlights the potential of zeolite-based catalysts in the sustainable production of biodiesel from low-grade feedstocks, contributing to the development of cost-effective and environmentally friendly processes.