4. Conclusions
A novel waste water scale-derived catalyst (CaO–MgO–Fe2O3–Al2O3–SiO2) was successfully prepared by calcination for transesterification to biodiesel production. The results indicated that the catalyst calcined at 1000 C had shown excellent catalytic performances with a biodiesel yield of about 93% at a 1.0% catalyst to soybean oil weight ratio, a methanol/oil ratio of 12:1, a temperature of 70 C, and a reaction time of 5 h. In addition, the biodiesel production was effectively accelerated by activation of the catalyst, and the composite metal oxide had many surface adsorption sites and reactive sites, which brought about the high catalytic activity for transesterification reaction. More importantly than all of that, this catalyst is good for biodiesel production from the economic point of view, which makes waste profitable, reduces cost, saves resources, and protects the environment. We anticipate that the research could provide promising potential for remarkably improving the present chemical process for biodiesel production.