Effect of Keggin-type heteropolyacids on the hydrocracking of Jatropha oil

Abstract

To investigate the effect of Keggin-type heteropolyacids on the hydrocracking of Jatropha oil, Ni-heteropolyacid/nano-hydroxyapatite (Ni-HPA/nHA) catalysts were prepared with different Keggin-type heteropolyacids loaded: phosphotungstic acid (HPW), phosphomolybdic acid (HPMo), silicotungstic acid (HSiW) and silicomolybdic acid (HSiMo). The catalysts were characterized using N₂ adsorption–desorption, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature programmed desorption of ammonia (NH₃-TPD) and thermogravimetric analysis (TGA). Their acidities at reaction temperature (360 °C) were determined using solid-state ¹H nuclear magnetic resonance (¹H NMR). The acidity order of the catalysts at reaction temperature was as follows: HSiW > HPW > HSiMo > HPMo. The Jatropha oil and hydrocracking product oil were analysed using liquid-state ¹³C nuclear magnetic resonance (¹³C NMR). The hydrocracking conversions of Jatropha oil over these Ni-HPA/nHA catalysts were 100%; the highest iso/n-alkane ratio was 1.64 and the lowest pour point of the product oil was −32 °C at 360 °C, 3 MPa, H₂/oil (v/v) = 600 and LHSV = 2 h⁻¹ over the Ni-HSiW/nHA catalyst. The results demonstrated that Keggin-type heteropolyacids could improve the conversion of Jatropha oil; the isomerization of hydrocracking was affected by the acidity of the heteropolyacids at reaction temperature and stronger acidity could produce more iso-alkanes.