1. Introduction
With energy crisis and environmental issues, biodiesel, the environmentally sound renewable resource, has attracted an increasing amount of attention in recent years. Because biodiesel is made from natural, renewable sources such as new and used vegetable oils and animal fats In addition, compared with fossil fuels, it leads to much less emission of greenhouse gases, such as particulates, nitrogen oxides, sulphur, and volatile organic compounds Biodiesel is produced from plants oils or animal fats through a transesterification reaction with methanol or alcohol The conventional catalysts applied in the transesterification reaction are homogeneous catalysts, such as strong acids and strong bases However, acidic catalysts (such as H2SO4) will corrode the
equipment and the reaction rates are relatively slow [11].Alkaline catalysts (such as NaOH, KOH, and NaOCH3) are generally sensitive to water and free fatty acid of oils Both of them are very difficult to separate from the reaction mixture and must be neutralized and washed at the end of reaction, which cannot be recycled As heterogeneous catalysts can be easily removed from the liquid products and avoid producing large amount
of wastewater contributing to polluting the environment, they have an exciting potential for improving the economics of biodiesel production Peterson and Scarrah reported that alkalineearth metal oxides, notably calcium oxide, were used as heterogeneous catalysts for the production of biodiesel. Among the reported heterogeneous catalysts, CaO shows an active catalytic performance in transesterification reaction Moreover, it shows potential in biodiesel production from the economic point of view. Because CaO can be obtained from the wastes consisting of CaCO3 such as waste eggshell oyster shell shrimp shell mud crab shell mollusk shell and fish scale which is a kind of innovation involved in making utilization of wastes, saving resources, and improving economic efficiency.
In northern China, heating groundwater (such as well water and springs) containing some minerals can produce waste water scale. The derivatives of waste water scale are composite metal oxide with the main content CaO. In this work, we present a novel waste
water scale-derived catalyst by calcining method to enhance the basic strength in tandem with the surface properties of the catalyst. The waste water scale and its derivatives used as heterogeneous catalysts for biodiesel production were investigated via transesterification of soybean oil with methanol. Furthermore, the possible mechanism of transesterification was proposed.