Catalytic hydroprocessing of fatty acid methyl esters to renewable alkane fuels over Ni/HZSM-5 catalyst

A series of Ni/HZSM-5 catalysts with different Ni loading and Si/Al ratios were prepared by incipient wetness impregnation. The physicochemical properties of the catalysts were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N 2 -adsorption, temperature-programmed desorption of ammonia (NH 3 -TPD), and thermogravimetric (TG) analysis. Moreover, their catalytic performance was investigated for the hydroprocessing of long-chain unsaturated fatty acid methyl esters (FAMEs) to renewable alkane fuels using a high-pressure fixed bed reactor system with a facility for online analysis. The different Ni loading and Si/Al ratios of the catalysts, as well as the influence of reaction conditions such as temperature, pressure, H 2 /oil molar ratio, and liquid hourly space velocity (LHSV), were studied in detail. The NiO aggregates dispersed on the surface of the support clearly increased the acidity after H 2 reduction, thus significantly affecting the catalytic performance. Temperature and pressure played crucial roles in the conversion of FAMEs and selectivity for gasoline or jet or diesel alkane. Hydroprocessing over 10   wt% Ni/HZSM-5 (Si/Al   =   25) at 280   °C, a H 2 pressure of 0.8   MPa, an LHSV of 4   h −1 , and with a highly purified H 2 /oil molar ratio of 15 led to a high selectivity of 88.2% for C 5 –C 18 liquid alkanes, which includes 8% of gasoline alkane, 32.5% of jet alkane and 47.7% of diesel alkane, along with appropriate isomerization selectivity of 27.0%, while the conversion of FAME reached 85.1%. To demonstrate the potential of this catalyst for practical applications, its stability in the hydroprocessing of FAMEs was also investigated. The conversion of FAMEs decreased to 30.1% over 10   wt% Ni/HZSM-5 (Si/Al   =   25) after operation for 80   h. Catalyst deactivation was predominantly caused by the deposition of carbon which causes blockage of the pores for FAMEs as evidence from TG analysis.