Optimization of biodiesel production from candlenut oil via simultaneous reaction using a bifunctional CeO2.CaO catalyst

Abstract

The biodiesel synthesis process with a high FFA content can be accomplished in a single stage using solid catalysts that function simultaneously as base and acid catalysts. In this study, CeO₂.CaO was used as a bifunctional catalyst for biodiesel synthesis from candlenut seed oil. CeO2.CaO catalyst with a weight ratio of CeO2: CaO (1:4) was synthesized through a physical mixing process. The effects of t he methanol-to-oil molar ratio, catalyst loading, and reaction temperature on the resulting biodiesel yield were investigated. Biodiesel was synthesized in a three-necked flask with a mole ratio of methanol to oil (8:1, 10:1, 12:1). CeO2.CaO catalyst was added with a concentration of 2% w/w, 4% w/w, and 6% w/w to the weight of candlenut oil. Heating was carried out at 50ºC, 60ºC, and 70ºC with stirring using a magnetic stirrer at 200 rpm for 1 hour. The FTIR analysis shows peaks corresponding to the O-Ca-O and O-Ce-O groups, indicating the formation of the CeO₂.CaO catalyst. BET analysis provides data on the catalyst's surface area (9.536 m²/g), pore diameter (5.876 nm), and pore volume (0.028 cm³/g). SEM-EDX analysis reveals that the catalyst has a mesoporous structure, which is beneficial for transesterification reactions. TPD analysis indicates that the bifunctional CeO₂.CaO catalyst possesses strong acidic and basic properties. The optimum operating conditions to achieve a high FAME yield were a methanol-to-oil molar ratio of 10.3:1, 5.39% w/w catalyst loading, and a reaction temperature of 60°C. Based on the catalyst reusability assessment, the CeO₂.CaO bifunctional catalyst demonstrated favorable stability, retaining catalytic performance over multiple cycles. After four consecutive react ion cycles, the catalyst maintained an overall biodiesel yield exceeding 75%, indicating its potential for repeated use in transesterification processes.