3.2.3. Reusability of eggshell waste-derived catalysts
We also investigated the reusability of the catalyst. The results indicated that the eggshell-derived catalyst can be repeated use for 13 times with no apparent loss of activity. After being used for more than 13 times, eggshell-derived catalyst lost activity gradually. The eggshell-derived catalyst was completely deactivated after being used more than 17 times. The deactivation of eggshell-derived catalyst may be ascribed to its structure change. The XRD patterns of the eggshell-derived catalyst used more than 17 times were characteristic of Ca(OH)2, while fresh eggshell-derived catalyst displayed diffraction reflections characteristic of CaO. This showed that the major phase of catalyst has changed from CaO (fresh catalyst, Fig. 1) to Ca(OH)2 (catalyst used more than 17 times). The structure change of catalyst could result from the reaction between H2O and CaO, because the reactants (soybean oil and methanol) contain a little amount of water. However, the catalyst can be regenerated just by simple calcination. Therefore, eggshell-derived catalyst can be reused and regenerated.