Synthesis of a KIT-6 mesoporous sulfonic acid catalyst to produce biodiesel from cashew nut oil

In this work, KIT-6 silica functionalized with sulfonic acid by the co-condensation method was prepared and evaluated as a catalyst in the transesterification of Brazilian cashew nut oil (BCNO) with butanol for biodiesel synthesis. The catalyst was characterized by SAXS, TEM, N2 adsorption–desorption measurements, 29Si MAS NMR and 13C CP-MAS NMR to prove the structural integrity of the incorporated organic group and to show the ordered structure, morphology and porosity, respectively. Small-angle XRD confirmed the formation of the mesophase of the synthesized materials. TEM images demonstrated the well-ordered arrangement of the pores and their uniformity throughout the grains, in addition to the highly ordered nature of the cubic mesostructures. The KIT-6 propylsulfonic acid catalyst was able to produce a 70% butyl ester yield, as determined by 1H NMR spectroscopy in 6 h reaction with a BuOH/BCNO molar ratio of 30:1, 140 °C and a 6 wt% of catalyst mass relative to starting oil mass in the reaction. The KIT-6-S catalyst can be reused for two cycles without loss of catalytic activity.