3.2. Catalytic activity
Catalytic activities of the waste scale derived catalysts were shown in Fig. 5. Reaction conditions were as follows: n (methanol):n (soybean oil) = 12:1, dosage of catalyst = 1.0 wt.%, reaction temperature = 70 C, and reaction time = 5 h. From the results, it could be seen that the activity of the waste scale-derived catalysts calcined at 700 C had a saltation, and the catalyst calcined at 1000 C was the most active catalyst with a biodiesel yield of about 93%. The biodiesel yield of the catalysts obtained by calcining in The reason is that a solid base CaO–MgO–Fe2O3–Al2O3–SiO2 with higher catalytic activity is formed. Similar result was obtained by Yan et al the range of 700–1000 C was better than that of CaO obtained after calcination of CaCO3 of analytical grade at 1000 C for 2.5 h(a biodiesel yield of 88.7%)namely, the combination of CaO and MgO showed a higher catalytic activity than pure CaO. The waste scale-derived catalysts calcined below 700 C were mostly inactive in biodiesel production, because the main content of waste water scale is neutral CaCO3. The fact that CaO is active in catalyzing the transesterification, but CaCO3 is not has been shown in previous study which can demonstrate the above results.