Efficient sulfated high silica ZSM-5 nanocatalyst for esterification of oleic for acid with methanol

The high silica ZSM-5 nanocatalyst was synthesized by hydrothermal technique and modified through the sulfation process. The nanocatalysts were applied in the esterification of free fatty acids (FFA) in the presence of methanol to produce biodiesel. The effect of different levels of sulfation and operating conditions were investigated. XRD, FT-IR, BET, FE-SEM, ICP-OES, TEM, and NH3-TPD techniques characterized the structure and acidity of the nanocatalysts. The loading of SO42- decreases the specific surface area and pore volume slightly. FESEM results represented spherical particles for both of the parent and modified nanocatalysts but the surface of the sulfated nanocatalyst was rough. The NH3-TPD pattern showed that the sulfation process slowly decreased the concentration of the acid sites. The sulfation with acid to catalyst ratio of 1 resulted in the best nanocatalyst. The optimum reaction conditions were 5 wt% of the nanocatalyst, methanol/oleic acid molar ratio of 20:1, T = 190 degrees C, the stirring rate of 700 rpm, and reaction time of 8 h, leading to the highest FFA conversion (97%). The nanocatalyst had the high stability and reusability in which FFA conversion dropped only 9% after the five sequence cycles. The results confirmed the high potential of the developed nanocatalyst for biodiesel production.