Synthesis, characterization and applications of carbon-based calcium catalysts deriving from avocado seeds for biodiesel production from waste cooking oil

In this work, avocado seeds were successfully used as precursors to produce carbon-based calcium catalysts for biodiesel production. The catalysts were synthetized via precipitation method, by loading different amounts of calcium nitrate on carbonized supports obtained by pyrolysis under nitrogen flow of dried biomass. The effect of Ca loaded on the structure and the activity of the catalysts for biodiesel synthesis from sunflower oil with methanol was investigated. Results showed that supported catalyst loaded with 20%wt of Ca, efficiently promote the trans-esterification process (FAMEs content >80%) with the catalyst that was easily recovered and reused. Reaction conditions were then optimised using the desirability function applied on the response surface methodology analysis of a Box–Behnken factorial design of experiments. Finally, the optimized conditions were adopted on several non-edible oils with Free Fatty Acids content range between 1 and 15 mg KOH/g. In all cases, a FAMEs content >95% was in any case obtained.