Issues concerning the use of renewable Ca-based solids as transesterification catalysts

The purpose of this work is to discuss some relevant issues that affect the catalytic performance of renewable-based CaCO3/CaO solids in the transesterification of triglycerides for producing biodiesel. Particularly, this study analyses the catalytic performance of the renewable catalysts obtained from calcined eggshells focusing on the calcination step, handling of the activated catalysts, and on the ageing when exposed to the atmosphere. Only severe calcination conditions ensure a complete decomposition of CaCO3 based precursors into CaO, which, on the other hand, result in quite uniform catalyst properties. Neither the source of the eggshells nor the preparation procedure before calcination influenced the catalytic performance of the calcined solids, which remained essentially unaltered through five reaction/recovery cycles. Exposure to atmospheric air negatively affects the catalytic performance of the solids, causing a significant loss of activity in samples aged for 30 days, though most of their initial fresh catalytic activity could be recovered by washing them with methanol.