Optimization of conversion of waste rapeseed oil with high FFA to biodiesel using response surface methodology

In the present study, waste rapeseed oil with high free fatty acids (FFA) was used as feedstock for producing biodiesel. In the pretreatment step, FFA was reduced by distillation refining method. Then, biodiesel was produced by alkaline-catalyzed transesterification process, which was designed according to the 24 full-factorial central composite design. The response surface methodology (RSM) was used to optimize the conditions for the maximum conversion to biodiesel and understand the significance and interaction of the factors affecting the biodiesel production. The results showed that catalyst concentration and reaction time were the limiting conditions and little variation in their value would alter the conversion. At the same time, there was a significant mutual interaction between catalyst concentration and reaction time.The biodiesel produced in the present experiment was analyzed by gas chromatography/mass spectrometry (GC/MS), which showed that it mainly contained six fatty acid methyl esters. In addition, the diesel indexes analysis showed that most of the fuel properties were in reasonable agreement with the 0# diesel standard of China (GB252-2000) and the biodiesel standard of America (ASTM D6751).