Investigation of NaCl-Modified Graphitic Carbon Nitride for Efficient Biodiesel Production from Waste Oil via Transesterification: A Box-Behnken Design Approach

NaCl-modified graphitic carbon nitrides (GCN) were applied in the base-catalyzed transesterification of recovered oil. GCN has been seen as a prospective heterogeneous catalyst for transesterification, but pristine-GCN has a narrow range of applications because of its weak basic sites and small surface area. To overcome these defects, NaCl-modified GCN was prepared through the co-thermal polymerization of NaCl with urea. The doping of NaCl generated C=N and Na-N species, which enhanced the basicity of the catalyst. Meanwhile, with the assistance of NaCl, GCN was decomposed and produced a large number of small pores of hundreds of nanometers, which contributed to the increase in specific surface area. In addition, the effects of transesterification parameters and their interactions on biodiesel yields were investigated by using Box-Behnken design, and the reaction conditions were optimized. A high biodiesel yield of 93.05% was achieved under the optimal conditions.