Recoverable and reusable aluminium solvated species used as a homogeneous catalyst for biodiesel production from brown grease

tHomogeneous aluminium species, obtained by dissolving AlCl3·6H2O into methanol, were characterisedand tested as catalysts into the direct esterification of free fatty acids with methanol. The nature andthe role of this catalyst was further investigated through ESI-MS and FTIR spectroscopy, by revealingan immediate exchange reaction between methanol and the water molecules originally bounded to thealuminium, producing a final mixed methanol-aquo-complex whose reactivity was found to be compa-rable to that of a methanolic solution of hydrogen chloride. Reaction conditions were optimised using thedesirability function applied on the response surface methodology analysis of a Box-Behnken factorialdesign of experiments. By carrying out the reaction at 72oC for 120 min and using a catalyst amount of1.5% (mol of Al respect to fatty acids), almost 94% of the starting acids were converted. At the end of thereaction, a biphasic system was obtained in which the upper methanolic phase, which contained mostof the starting catalyst, was separated from the heaviest phase, mainly composed of fatty acid methylesters. Such a distribution not only allowed the biodiesel to be easily separated, but also the catalystswere efficiently recovered and reused for at least four times, determining a total TON greater than 200,without revealing any loss of its activity.