2.2. Catalyst preparation
The mussel shells were cleaned and washed thoroughly with warm water several times. The cleaned and washed mussel shells were calcined at 1000 oC with heating rate of 10 oC /min for 1 h. The solid
powder was crushed and sieved with 63 μm. This resulted solid is as known as non-impregnated catalyst. The impregnated catalyst was prepared by the impregnation process using potassium hydroxide. A typical calcium oxide was suspended in ammonia solution (5 wt%), and 50 mL aqueous potassium hydroxide was added. The solution was heated at 80 oC for 2 h. The precipitate was collected, washed and calcined at 400 oC for 12 h.