(689e) Simultaneous Transesterification and Esterification to Biodiesel Using Zinc-Based Catalyst
Biodiesel is a mixture of fatty acid esters which can be produced from vegetable oils or animal fats with methanol. Recently, many researchers focus on using waste or unrefined oils as feedstock to decrease the production cost of biodiesel. A two-step method was reported, which firstly esterified free fatty acids (FFA) with methanol in the presence of H2SO4, then transesterified oil with methanol in the presence of NaOH. This production process is long and highly corrosive. In this study, a single-step method was developed for biodiesel production using waste or unrefined oils as feedstock based on a series of heterogeneous zinc and lanthanum mixed oxides. Oil transesterification and FFA esterification reactions simultaneously took place in one reactor. In this study, effects of catalyst structure, metal oxide molar ratio, FFA and water contents in feedstock, reaction temperature and oil concentration on the yield of biodiesel were investigated. The zinc and lanthanum catalysts were prepared by a homogeneous coprecipitation method using urea as precipitant, and characterized by XRD, XPS and EDS measurements. Results indicated that there was a strong interaction between Zn and La species which varied with the molar ratio of Zn to La. At a high ratio of Zn to La, La acted as a diluent of the matrix, promoting ZnO particle distribution, increasing the surface basic and acid sites, and enhancing activity of transesterification and esterification. At a low ratio of Zn to La, destruction of ZnO crystal structure by La species was observed and the catalytic activity was decreased. A reaction temperature window was found in 170 ~ 220 oC for biodiesel formation. At the optimal reaction conditions, 42:1 molar ratio of methanol to oil, 2.3 (wt) % catalyst and an agitation rate of 400 rpm, a high yield (95 %) of biodiesel was obtained within 3 hours using some kinds of waste or unrefined oils as feedstock. This class of zinc and lanthanum mixed oxides catalysts are very promising to lower the overall production cost of biodiesel.