Biodiesel production by transesterification using tetraalkylammonium hydroxides immobilized onto SBA-15 as a solid catalyst

• Solid catalysts were prepared and employed for soybean oil transesterification.
• The catalysts were characterized by using various techniques.
• The catalytic activity and stability of the catalyst were investigated.

The main aim of this work was to develop an efficient and stable solid base catalyst for the production of biodiesel. To this purpose, the tetraalkylammonium hydroxide-functionalized SBA-15 materials (SBA-15-pr-NR3OH) have been prepared by anchoring dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium hydroxides onto the surface of mesoporous SBA-15 silica, and then the catalytic activity was tested in the transesterification of soybean oil with methanol. Characterization of the solid catalyst was carried out by using Hammett titration, Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption, and X-ray photoelectron spectroscopy (XPS) techniques. The catalytic activity of the catalysts for the transesterification reaction is found to be owing to their basic properties. By using this catalyst, an eco-friendly more benign process for the transesterification of soybean oil in a heterogeneous manner is developed. Under the suitable transesterification conditions (methanol/oil molar ratio 12:1, catalyst loading 2.5 wt.%, reaction time 30 min, and at reflux of methanol), a good yield to methyl esters of 99.4% could be achieved over the solid catalyst. The obtained SBA-15-pr-NR3OH catalyst could be recovered and reused for several recycle runs with a negligible loss of activity.