significant as the p-value < 0.05. There was two insignificant value which was higher than p-value > 0.05, quadratic term temperature (AB) and temperature-catalyst loading (BC). This shows the model could be used to predict the biodiesel yield.
Three-dimensional surface plots of the predicted yield of the biodiesel production are given in Figs. 2–4. The figures show the yield of oil increases with the increase of mixing, temperature and catalyst loading. The results were in agreement with the literature