Soap removal from crude biodiesel using industrial polyols

In this study, polyols were introduced as effective industrial solvents for soap removal from crude biodiesel using liquid-liquid extraction technique. Crude biodiesel was prepared using potassium hydroxide (KOH) and sodium hydroxide (NaOH) as alkaline catalysts. This study used different types of industrial polyols such as glycerol (GLY), triethylene glycol (TEG), ethylene glycol (EG), and diethylene glycol (DEG). A Conductor-like screening model for real solvents (COSMO-RS) screening was performed to evaluate the most effective polyols for soap removal. Various parameters such as the extraction duration, biodiesel-to-polyol volume ratio, mixing speed, temperature and solvent recyclability were optimized. The COSMO-RS results show that TEG is the most effective polyols for soap removal. Experimental findings corroborated the COSMO-RS screening, highlighting the TEG's superior performance. TEG emerges as the most efficient solvent, reducing the soap content in KOH-based biodiesel from 3400 ppm to 16.3 ppm (99.52 % efficiency) and in NaOH-based biodiesel from 5530 ppm to 126.8 ppm (97.71 % efficiency). The optimal conditions for soap removal are a mixing speed of 250 rpm, biodiesel-to-TEG volume ratio of 1:1, and extraction time of 15 min at room temperature. However, only the KOH-based biodiesel refined with TEG meets the international standards for soap content. The soap removal follows the first-order kinetic model with a rate constant of 0.428 and 0.375 min ⁻¹ for KOH-based biodiesel and NaOH-based biodiesel respectively. This study suggests that polyols could potentially reduce the generation of wastewater from the biodiesel industry and serve as an alternative to the water washing method.