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. (author)