A bifunctional catalyst from waste eggshells and its application in biodiesel synthesis from waste cooking oil

Improvement in biofuel synthesis technology could facilitate widespread utilization of biodiesel, and an efficient operation in terms of cost. Catalyst enhancement through mineralization of waste biogenic material is vital for biodiesel production. In this study, biodiesel production was from waste cooking oil (WCO) using a bifunctional catalyst synthesized from waste eggshells and ferric sulfate. The CaO precursor developed from calcined eggshell at 800 °C for 3 h was impregnated with ferric sulfate at a ratio of 1:1. The Bifunctional catalyst synthesized was characterized using an X-ray diffractometer, scanning electron microscopy, Fourier transform infrared spectroscopy and energy-dispersive X-ray analysis. The bifunctional catalyst was applied in a one-pot reaction of WCO and methanol to produce biodiesel. The reaction was modeled using the Taguchi orthogonal array design to maximize biodiesel production. The heterogeneous catalyst contained Ca (20.7 %), Fe (18.5 %), S (4.5 %), and O (54.8 %). The identified crystalline phases are CaSO4/Fe2O3 and CaSO4.0.5H2O/Fe2O3. A maximum biodiesel yield of 89.94 wt% was observed under the operating conditions of methanol/oil molar of 5:1, time of 45 min, temperature of 70 °C, and catalyst amount of 4 wt%. The reusability of the catalyst was established for (four) 4 cycles without further treatment. The synthesized biodiesel met the standard specifications. Hence, the synthesized catalyst proved effective in the transesterification of oil with a moderately high free fatty acid, thereby the bifunctional catalyst could expedite biodiesel production from waste cooking oil, and this biofuel could serve as fuel in powering diesel engines.