Semi-industrial studies of Tungsten-based catalyst for hydroisomerization/hydrocracking of n-hexane and n-heptane

Abstract

WO3/TiO2(WTi) composite was prepared via an environmentally friendly, fast and facile wet impregnation method using distilled water as the solvent. The catalyst composite was investigated by in-situ XPS-UPS and ex-situ BET and XRD characterization techniques before and after the activation under hydrogen flow. The activation of the composite resulted in the formation of metallic and acidic catalytic sites in the form of WO3-x(OH)y on the surface of the WTi composite. The distribution of these sites depends on the activation temperature. XPS results show the formation of a different oxidation state of tungsten after its activation. The formation of WO3-x with metallic properties was confirmed by an examination of the density of states in the valence band region. On the other hand, the Brønsted acidic sites were attributed to the OH group observed in the XPS peak fitting of the O1 s peak at 531.4 eV. The catalytic activity was evaluated for the hydroisomerization/hydrocracking of n-hexane and n-heptane using 15 cm3 WTi in a large-scale reactor at different experimental parameters. At a reaction temperature of 598 K, the catalytic activity was 97.1% in the case of n-heptane in favor of β-scission (C3-iC4, 78.4%), compared to 76.1% activity in favor of the isomerization products (84.6%) in the case of n-hexane after the composite activation at 673 K. The research octane number (RON) was improved from 24.8 for n-hexane to the 70–80 range for hexane isomers and from zero in the case of n-heptane to cracking products with a high octane number. Upon increasing the activation temperature to 773 K, the hydrogenolysis of n-heptane was the dominant catalytic reaction.