Esterification of oleic acid with methanol by a sulfonated carbon-based solid acid microspheres (SCMs)

A carbon-based solid acid microspheres rich of sulfonated groups (-SO3H) was prepared by simple hydrothermal and sulfonation method using cheap glucose as raw material. The green, non-corrosive, renewable and environmental friendly carbon material was used as heterogeneous catalysts for the esterification of oleic acid with methanol for biodiesel production. The structure and properties of the carbon microsphere were characterized by using Field-Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Thermo Gravimetric Analysis (TGA) and Differential Scanning Calorimeter (DSC), elemental analysis, N2 adsorption–desorption test and acid-base titration. It is found that the carbon microspheres prepared under the optimal reaction conditions showed smooth surfaces, uniform particle sizes and good dispersion. The sulfonated carbon-based solid acid microspheres showed high acidity and comparable activities to sulfuric acid for the esterification reaction of oleic acid with methanol. Reaction parameters including methanol/oleic acid mass ratio and catalyst usage amount were studied to get optimal esterification reaction conditions. The catalysts showed high reusability although there is some loss in acidity due to the leaching of active sites, the sulfonated groups.