Highly active novel K2CO3 supported on MgFe2O4 magnetic nanocatalyst for low-temperature conversion of waste cooking oil to biodiesel: RSM optimization, kinetic, and thermodynamic studies

Abstract

An innovative K2CO3/MgFe2O4 (KC/MGF) magnetic nanocatalyst for effective biodiesel generation from WCO is demonstrated here. To examine the physiochemical and morphological features of the catalyst, several characterization methods such as XRD, FT-IR, SEM-EDX, HR-TEM, AFM, XPS, BET, CO2-TPD, and VSM are used on the as-synthesized magnetic nanocatalyst. Optimization of K2CO3 loading on MgFe2O4 is achieved and 30KC/MGF was found as the optimum ratio. Response surface methodology (RSM) via central composite design (CCD) is constructed using optimization margins to clarify the optimal parametric conditions; catalyst loading (4–6 wt%), reaction time (90–120 min), and methanol to oil ratio (6:1–9:1) at a fixed low operating reaction temperature (50 ºC). The obtained optimum reaction conditions are 4.4 wt% catalyst loading, 108 min reaction time, 6.6:1 methanol to oil ratio, at 50 ºC achieving ca. 92.9% biodiesel conversion. 30KC/MGF is an energy-conserving magnetic nanocatalyst with excellent basicity that operates at low temperatures, for a markedly short period of time, and with a low methanol-to-oil molar ratio. Kinetics and thermodynamic parameters are estimated i.e., activation energy (Ea), change of enthalpy of activation (ΔH#), and change of entropy of activation (ΔS#) to be 31.5 kJ mol−1, 28.9 kJ mol −1, and −188.8 J mol−1 K−1, respectively. Gibbs free energy (ΔG#) is appraised at 308, 313, and 318 K to be 87.1, 88, and 88.9 kJ mol−1, respectively. Due to K+ leaching, utilizing 30KC/MGF in sequential runs results in a significant activity plummet. The catalyst activity is recovered by re-impregnation with K2CO3 precursor solution, resulting in the same high FAME conversion as fresh 30KC/MGF. Finally, the physicochemical properties of biodiesel are investigated and determined to be compliant with international American and European standards.