Transesterification of poultry fat with methanol using Mg–Al hydrotalcite derived catalysts

Abstract

The synthesis of biodiesel from poultry fats provides a way to convert the by-product of a renewable resource to a very important value-added biofuel. In this work, the use of heterogeneous base catalysts derived from Mg–Al hydrotalcite was investigated for the conversion of poultry lipids to biodiesel. This solid base showed high activity for triglyceride (TG) transesterification with methanol without signs of catalyst leaching. Catalytic performance was significantly affected by pretreatment and operating conditions. Calcination at optimum temperature was key in obtaining the highest catalyst activities. Rehydration of the calcined catalyst before reaction using wet nitrogen decreased catalytic activity for the transesterification of poultry fat, opposite to what has been reported for condensation reactions. Also, methanol had to be contacted with the catalyst before reaction; otherwise, catalyst activity was seriously impaired by strong adsorption of triglycerides on the active sites. Both temperature (60–120 °C) and methanol-to-lipid molar ratio (6:1–60:1) affected the reaction rate in a positive manner. The use of a co-solvent (hexane, toluene, THF), however, gave rise to a change in TG conversion profile which cannot be explained solely by a dilution effect. The catalyst underwent significant deactivation during the first reaction cycle probably due to deactivation of the strongest base sites. Subsequent reaction cycles showed stable activity. By re-calcination in air, complete catalyst regeneration was achieved.