Highly efficient tantalum-zirconium oxide catalysts for biodiesel production from higher water and FFA containing soybean oil or yellowgrease feedstocks

Mesoporous tantalum-zirconium oxide (TZ) solid acid catalysts were synthesized by sol-gel method and employed in the biodiesel production from higher water (2.0 and 4.0 wt%) and palmitic acid (20.0 wt%) added soybean oil (SBO) or yellow grease feedstocks. Characterization of TZ catalysts were done by using BET-surface area, XRD, Raman spectroscopy, XPS and NH₃-TPD techniques. Only 35.0% methyl palmitate and 14.0% SBO fatty acid methyl ester (FAME) yield was obtained on bare ZrO₂ at 180 °C. Addition of tantalum to ZrO₂ significantly improved the yield of methyl palmitate (95.0%) and SBO FAME (88.6%) at 180 °C. The greater ester yield on TZ catalysts was associated with improved acidity due to the presence of Ta–O–Ta, Ta[dbnd]O and Zr–O–Ta species which readily interacted with methanol and triglycerides. Further, 20.0 mol.% tantalum loaded zirconium oxide catalyst (20TZ) exhibited consistent biodiesel yield upto two recycles of feed containing 2.0 wt% of added water and 20 wt% PA in SBO. It is noteworthy that, 80.0% yellow grease FAME formation was observed on 20TZ catalyst at 180 °C. The results emphasize, TZ solid acid catalysts are highly efficient compared to polyoxometalates and or sulphated zirconium oxide solid acid catalysts for biodiesel production from higher water and free fatty acid containing feedstocks.