Valorization of used cooking oil into bio-based surfactant: modeling and optimization using response surface methodology

Bio-based surfactants are emerging specialty chemicals for the industrial market. The production of this type of surfactant is still a green area as there are very few synthetic routes. Further, the demand for sustainability in the financial and energy sector may be augmented if domestic carbon sources are utilized. In this study, we report the synthesis of bio-based surfactant, i.e., methyl ester sulfonates (MES) from used cooking oil. The optimization was performed using response surface methodology via Box-Behnken design (BBD). The optimized parameters included the fatty acid methyl ester (FAME)/chlorosulfonic acid molar ratio, reaction temperature, and reaction time. These reaction variables were examined to study their effect on the sulfonation reaction. Furthermore, the synthesized MES was characterized using various analytical techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), thermogravimetric analyzer (TGA), and surface tension measurements. The maximum yield of MES, 91.12%, was achieved at a molar ratio of 1:3, a reaction temperature of 60 °C, and a reaction time of 3 h. The value of the regression coefficient (R²) was 0.9798, indicating that the model was appropriate. This work can motivate the research communities to synthesize environment friendly surfactant from the renewable feedstocks that can replace the fossil-fuel based surfactant.