Biodiesel production via stearic acid esterification over mesoporous ZrO2/SiO2 catalysts synthesized by surfactant-assisted sol-gel auto-combustion route

Abstract

Biodiesel production from the esterification of stearic acid with ethanol catalyzed by the mesoporous ZrO2/SiO2 catalysts which successfully synthesized by surfactant-assisted sol-gel auto-combustion method. These catalysts were characterized by various physico-chemical techniques such as XRD, BET surface area measurement, HR-TEM and NH3-TPD. The mesoporous catalyst prepared with cationic surfactant (ZrSiOC) showed a maximum BET surface area and pore volume. Interestingly, the ZrSiOC catalyst exhibited the largest acidity value among all catalysts. The results showed that the mesoporous ZrO2/SiO2 catalysts prepared with cationic (ZrSiOC) and non-ionic (ZrSiOT) surfactants demonstrated higher stearic acid conversion than those with anionic (ZrSiOS) or without surfactant (ZrSiO). Significantly, the ZrSiOC and ZrSiOT catalysts exhibited the highest conversion of 69.2% and 63.1% at 120 C after 3 h, respectively. Additionally, it was observed that the conversion increased extremely with increasing the reaction temperature giving a maximum conversion of 76.9% at 125 C by using the most active catalyst (ZrSiOC). Interestingly, the ZrSiOC catalyst displays suitable recycling as it kept performance of 72.5% after five recycle runs without significant lack in performance. Moreover, the kinetic study confirmed that esterification follows pseudo first-order equation