Supporting Tungsten Oxide on Zirconia by Hydrothermal and Impregnation Methods and Its Use as a Catalyst To Reduce the Viscosity of Heavy Crude Oil

Abstract

Tungsten oxide was supported on zirconia via hydrothermal and conventional impregnation methods and used as a catalyst to reduce the viscosity of heavy crude oil without the addition of water. Their properties and viscosity reduction activity were compared. X-ray diffraction and the Rietveld method were used to characterize the crystal structure and determine the phase composition. The properties of catalysts were also measured by N2 adsorption–desorption, differential scanning calorimetry, a Hammett indicator, and ammonia temperature-programmed desorption. Compared with the impregnation method, the hydrothermal method facilitates the formation of strong tungsten–zirconia interaction and promotes the diffusion of tungstate on zirconia, hence leading to better-dispersed tungsten oxide, as well as more tetragonal zirconia and acid sites. Under the reaction conditions of 220 °C, 6 h, and 2 MPa, the catalysts prepared via the hydrothermal method exhibit higher viscosity reduction activity than those prepared by impregnation. It is found the catalytic activity mainly depends on the acidity of the catalyst. The catalyst containing 20 wt % tungsten prepared by the hydrothermal method can attain a viscosity reduction ratio of 82.2% and reduce the viscosity of oil from 5.74 Pa s (50 °C) to 1.02 Pa s. Different from the widely used aquathermolysis technique, the presence of water is not required and the viscosity of the treated oil will not regress, even over long periods of time.