br Materials and methods br Results and discussion br Conclu

Materials and methods
Results and discussion
Conclusions The centre composite design of response surface methodology was successfully used in optimising the reaction conditions for biodiesel production from waste vegetable oil in the presence of Biotin-tyramide heterogeneous catalyst prepared from eggshell. Optimal reaction conditions obtained were methanol-to-oil molar ratio of 22.5:1, catalyst loading of 3.5 wt% and temperature of 65 °C. The catalyst, characterised with high surface area (30.9 m2/g) and large pore size (91.2 Å), had excellent activity in mediating the transesterification of waste oil containing 9% FFA, to biodiesel production. This was used in sufficient amount with respect to oil in order to shift the reaction toward the formation of methyl ester. The reusability of the catalyst preparation over 10 cycles of transesterification reaction has the potential to reduce cost of biodiesel production. The empirical value of yield obtained from RSM (89.6%) was comparable to that obtained experimentally (91%). The relationship between the predicted and experimental yield indicated that the values were in reasonable agreement and the data fit well with the model by giving a good estimate of response for the system in the range studied. Results indicated that a second order quadratic model was the best fit for the experiments conducted. The model can be considered statistically significant at 95% confidence, with all three independent variables having an effect on the yield and R2 of the model was found to be 0.9908. Properties of the biodiesel produced from waste vegetable oil using egg shell as the catalyst were within the biodiesel standard specifications.
Acknowledgments The authors would like to acknowledge the Cape Peninsula University of Technology for the financial support to undertake veins project.