Hydrotreating of fast pyrolysis oil: A comparison of carbons and carbon-covered alumina as supports for Ni2P

Abstract

Nickel phosphide is a promising material for substitution of metal nobles and sulfides catalysts in fast pyrolysis oil hydrotreating. In this study, we compared the effects of three different carbon supports for Ni2P on the catalyst activity and selectivity in hydrodeoxygenation (HDO) reactions. It was also evaluated the impacts of temperature and pressure on the quality of hydrotreated bio-oils. The experiments were carried out in a batch reactor at 150 °C and 250 °C while the pressure ranged from 50 to 100 bar. The results showed that Ni2P on activated carbon (AC) performed better at 150 °C than Ni2P on carbon covered alumina (CCA) and mineral charcoal (MC), producing bio-oils with lower oxygen content and higher heating value. At 250 °C, best results were obtained with Ni2P/CCA catalyst, giving bio-oils with lower O/C molar ratio and higher H/C molar ratio. Overall, hydrogenation reactions were favored at the higher temperature in all catalytic systems. TGA analysis indicated that coking tendency of hydrotreated bio-oils was influenced by their chemical composition and reaction temperature. In addition, catalyst characterization before and after reactions, revealed that carbon supported materials were more affected at 250 °C by pore blocking. XRD results also showed the presence of different Ni-phases after reaction, such as Ni12P5 and Ni, probably due to the loss of P by oxidation and/or formation of PH3.