Modeling and optimization of transesterification of rubber seed oil using sulfonated CaO derived from giant African land snail (Achatina fulica) catalyst by response surface methodology

Rubber seed oil (RSO) is an abundance of low-cost non-edible vegetable oil and an attractive resource for biodiesel production through transesterification. The study aims to model and optimize the transesterification of RSO to biodiesel using sulfonated CaO derived from snail shells as a bifunctional heterogeneous catalyst. We prepared the raw snail shell (RSS) catalyst by calcination and sulfonated it to produce an acid-activated snail shell (AASS) catalyst. We used the central composite design (CCD) of the response surface methodology (RSM) to model and optimize the transesterification process. The X-ray fluorescence (XRF), Scanning Electron Microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), and Brunauer-Emmett-Teller method (BET) were used to characterize RSS and AASS catalysts. The results show that CaO (95.6%) is the major component of RSS. The maximum biodiesel yield of 97.6% was obtained at a 12:1 methanol to oil molar ratio, 80 °C reaction temperature, 2.5 h reaction time, and 2.5 wt% catalyst loading with a quadratic regression model. The recyclability of the catalyst shows six runs without an appreciable decrease in biodiesel yield. The AASS catalyst can perform excellently as a bifunctional solid acid heterogeneous catalyst, and the fuel properties of the biodiesel produced compare favorably with American society for testing and materials (ASTM D6751) and European standard methods (EN 14214) standards.