Novel solid base catalyst for biodiesel production: Mesoporous SBA-15 silica immobilized with 1,3-dicyclohexyl-2-octylguanidine

Heterogeneous transesterification of vegetable oils offers an environmentally more attractive option for biodiesel production compared to the conventional homogeneous processes. In the work, a novel heterogeneous base catalyst was prepared by anchoring 1,3-dicyclohexyl-2-octylguanidine (DCOD) onto the mesoporous SBA-15 silica. The DCOG-functionalized SBA-15 material (SBA-15-pr-DCOG) was demonstrated to be an efficient and recyclable heterogeneous catalyst for the transesterification of soybean oil with methanol. The characterization of the catalyst was carried out using Hammett titration method, X-ray diffraction, Fourier transform infrared spectroscopy, thermo gravimetric and differential thermal analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption-desorption techniques. It was shown that the DCOD was successfully tethered on the SBA-15 silica and ordered mesoporous structure of SBA-15 was largely remained unchanged after the functionalization reaction. The influences of transesterification variables such as the methanol/oil molar ratio, catalyst loading, reaction time, and catalyst reusability on the oil conversion were investigated. By using the methanol/oil molar ratio of 15:1 and catalyst loading of 8 wt.%, the maximum oil conversion of 92.6% was achieved over the solid catalyst at reflux of methanol for 15 h. The heterogeneous base catalyst could be easily recovered and reused for several runs with a negligible loss of activity.