Particulate solid catalyst leaching in CaO-catalyzed sunflower oil transesterification: Time-rpm dependent centrifugal separation study

This study investigated the influence of centrifugal separation parameters, specifically rotational speed (revolutions per minute, rpm) and separation time, on reducing leachable calcium from CaO during heterogeneous catalyzed transesterification of sunflower oil for biodiesel production. Consequently, the lowest residual calcium ion concentration in the final product was found to be 3.2 ppm, which was achieved at 4000 rpm for 15 min of centrifugation and is below the international standard limit. In addition, the produced biodiesel at these operating conditions demonstrated acceptable fuel properties, including an acid value of 0.55 mg KOH/g, a saponification value of 108.75 mg KOH/g, a cetane number of 48.33, a cloud point of 5 °C, and a density of 890.6 kg/m³. Moreover, the catalyst’s morphological and surface changes before and after the reaction were analyzed using scanning electron microscopy and Fourier-transform infrared spectroscopy, revealing notable alterations in surface structure and functional groups. Overall, the importance of controlling separation conditions for the removal of dispersed catalyst particles from the intended product, biodiesel, has been covered in this study, which can, in turn, be used as a foundation for spectroscopically monitored, detailed research ahead. • Appropriate separation method improves biodiesel quality. • Centrifugal rpm-time interaction governs catalyst leachability. • 4000 rpm for 15 minutes minimized Ca contamination in biodiesel. • Excess rpm-time interaction risks catalyst dissolution and fuel contamination. • FTIR/SEM confirmed the catalyst’s surface changes.