Design and synthesis of novel amphipathic ionic liquids for biodiesel production from soapberry oil

Biodiesel produced from non-edible oils has received intensive attention in recent years. Herein, a series of novel amphipathic ionic liquids (ILs) based on the 4-dimethylaminopyridine (DMAP) were prepared for the transesterification of soapberry oil and methanol. The structures of the prepared ILs were systematically characterized by both Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR, 1 H NMR and 13 C NMR). In addition, the effects of side-chain length of cation and the number of active site (H + ) of ILs on the biodiesel yield were investigated, and the results suggested that 1-dodecyl-(4-dimethylammonium)-pyridinium bisulfate ([C12-DMAPH][HSO 4 ] 2 ) exhibited the highest catalytic efficiency. Meanwhile, [C12-DMAPH][HSO 4 ] 2 was proven to be amphipathic, and the corresponding catalytic mechanism was proposed. Under the catalysis of [C12-DMAPH][HSO 4 ] 2 , the optimum operating conditions of transesterification of soapberry oil and methanol were explored via the combination of single factor experiment and response surface methodology , obtaining the high biodiesel yield of (98.02 ± 0.36)% under the optimum operating conditions. Importantly, [C12-DMAPH][HSO 4 ] 2 exhibited high stability in the transesterification of soapberry oil and methanol in five consecutive runs. Furthermore, the catalytic activities of [C12-DMAPH][HSO 4 ] 2 towards other transesterification of non-edible oils and lower alcohols were also investigated, which indicated a general applicability of the prepared IL.