Enhanced low-temperature production of biodiesel from waste cooking oil: aluminum industrial waste as a precursor of efficient CaO/Al2O3 nano-catalyst

Abstract

The objective of the current study is to employ aluminum industrial waste (AIW) as a precursor for the preparation of a novel environmentally benign CaO/Al2O3 nano-catalyst for efficient biodiesel production from waste cooking oil (WCO) at a low optimizing reaction temperature. Physico-chemical characterizations of the as-prepared CaO/Al2O3 nano-catalysts are performed under various conditions via diverse analytical techniques such as TGA, XRD, XPS, BET, SEM - EDX, TEM, and AFM. The calcination temperature influence along with the ratio of CaO to Al2O3 on the catalyst activity toward biodiesel conversion have been investigated and optimized. Furthermore, the optimization process of the four variable parameters of the transesterification reaction (i.e., catalyst loading, reaction temperature and time, and M:O molar ratio) are investigated. The optimum reaction conditions for biodiesel production (≈ 95% conversion) are catalyst loading of 3 wt.% operating at 45 °C for 180 min with a methanol to oil ratio of 7:1. These conditions are superior to comparable catalysts reported in the literature. The kinetic and thermodynamic parameter's values, i.e., activation energy (Ea), activation enthalpy (ΔH#), and activation entropy (ΔS#) are 39 kJ mol−1, +36.38 kJ mol−1, and ─161.75 J mol−1 K−1, respectively. The as-prepared nano-catalyst retains its catalytic activity for five consecutive cycles. Physico-chemical characteristics of the produced biodiesel are congruent with the ASTM D − 6751 and EN − 14,214 standards. Therefore, it may be thought of as a potential catalyst for renewable producers of biodiesel production.