Highly active CaO catalyst was prepared by the calcination–
hydration–dehydration treatment of egg shells. Egg shells were
washed thoroughly in tap water to remove any unwanted
material adhered on its surface, and rinsed twice with distilled
water. The washed egg shells were then dried in hot air oven at
105 C for 24 h. The dried egg shells were reduced to small
pieces and calcined in a muffle furnace under static air conditions
at 900 C for 2.5 h to transform the calcium species in the
shell into CaO particle (denoted as Egg shell-CaO-900). Then
the CaO derived from the egg shell was refluxed in water at
60 C for 6 h and the solid particle was filtered and dried in
hot air oven at 120 C overnight [27]. The solid product was
dehydrated by performing calcination at 600 C for 3 h to
change the hydroxide form to oxide form. Thus the egg shells
subjected to the calcination–hydration–dehydration treatment
generate a highly active CaO (denoted as Egg shell-CaO-
900-600).
2.