Abstract
Four types of green alkali modified clinoptilolite (K, Na, Ca, and Mg) were prepared using green tea extracts as novel types of eco-friendly heterogeneous basic catalysts in the transesterification of commercial waste cooking oil into biodiesel. The modified products displayed significant enhancement in the total basicity, surface area, ion exchange capacity, and the morphological properties. The modified samples of K/clinoptilolite (K/Clino), Na/clinoptilolite (Na/Clino), Ca/clinoptilolite (Ca/Clino), and Mg/clinoptilolite (Mg/Clino) showed promising catalytic activities achieving biodiesel yields of 93.6%, 95.2%, 96.4%, and 98.7%, respectively. The best yields were recognized using 4 wt, % as catalysts loading, 16:1 as methanol-to waste oil molar ratio, and at 70 °C as temperature. The best transesterification intervals were identified at 120 min, 120 min, 180 min, and 150 min for K/Clino, Na/Clino, Ca/Clino, and Mg/Clino, respectively. The modified products also demonstrated high reusability properties and the resulted biodiesel in their transesterification systems are of technical properties within the accepted limits of EN 14214 and ASTM D-6751 standards.
[Display omitted]
•Green alkali modified clinoptilolite samples were prepared as promising basic catalysts.•The products displayed enhancement in the surface area, basicity, and ion exchange properties.•They were applied in the transesterification of waste cooking oil with yields higher than 93%.•The best catalytic activities were reported in order for Mg/Clino > Ca/Clino > Na/Clino > K/Clino.•The technical qualifications of the biodiesel samples close to the international standards.