Microwave-assisted biodiesel synthesis from waste cooking oil: Exploring the potential of carob pod-derived solid base catalyst

Abstract

This work examined the potency of carob (Ceratonia siliqua) pod as a heterogeneous base catalyst for converting waste cooking oil (WCO) into biodiesel via a microwave irradiation system. The optimal calcination for the catalyst synthesis was achieved at 500 °C for 4 h. Various analytical techniques were employed to investigate the properties of the developed catalyst. The results indicate that the catalyst primarily consists of mesoporous particles abundant in potassium, with medium to strong basic sites, which are crucial for its catalytic function. WCO underwent pretreatment with H₂SO₄ before being converted to biodiesel. Optimum conditions for the biodiesel production were a methanol-to-WCO molar ratio of 9.87, 1.00 wt% catalyst dosage, 3.03 min reaction time, 450 rpm stirring speed, and 600 W microwave power, yielding 98.20 ± 0.81 wt% biodiesel. The low specific energy consumption value of 0.91 kWh/kg and specific CO₂ emission of 0.73 kg/kg of biodiesel suggest the effective utilization of microwave energy in driving the transesterification reaction and in promoting a reduction in carbon footprint, respectively. The synthesized catalyst remained effective up to the 5th production cycle and the biodiesel produced met established specifications. The results of this study show that carob pod is a suitable candidate to be included in the database of biobased catalysts currently being developed for heterogeneous catalysis of cost-effective biodiesel production.