Eco-friendly CaO catalyst from waste blood cockle shells activated by citric acid for efficient biodiesel production from used palm oil

The abundant availability of cockle shell waste and the potentially hazardous reuse of used palm oil highlight the need to develop more sustainable and value-added alternatives. This study aims to determine the optimal catalytic activity of a bifunctional catalyst in a one-pot reaction for converting used palm oil into biodiesel. The bifunctional catalysts were prepared by synthesizing CaO base catalysts derived from blood clam shell waste (Anadara granosa), followed by modification with citric acid using the impregnation method, resulting in an environmentally friendly CKS–CA catalyst. The CKS–CA catalyst had a surface area of 8.15 m2/g. SEM–EDX analysis showed aggregate morphology with increased porosity. NH₃-TPD and CO₂-TPD analyses revealed total acidity and basicity of 11.63 and 3.39 mmol/g, respectively. The highest biodiesel yield obtained was 80.10% under the conditions of 10 wt% catalyst loading, a reaction temperature of 65 °C, an oil-to-methanol molar ratio of 1:15, and a reaction time of 5 h. GC–MS analysis showed that the main components of the biodiesel were methyl palmitate and methyl oleate. 1H NMR analysis indicated a biodiesel conversion of 88.69%. The reusability test of the CKS–CA catalyst after four cycles resulted in a biodiesel yield of 42.74%.