Catalytic Steam Cracking of a Deasphalted Vacuum Residue Using a Ni/K Ultradispersed Catalyst

Abstract

Catalytic steam cracking (CSC) of heavy hydrocarbons is seen as an alternative for further improvement upon conventional thermal cracking performance. In this work, upgrading of an industrial deasphalted vacuum residue via CSC was assessed in a bench-scale pilot plant resembling a visbreaking unit. The performance of a 400 ppm of Ni and 300 ppm K ultradispersed catalyst (UDC) formulation previously used for CSC of vacuum residue was evaluated for this nonasphaltene containing fraction. Reactivity experiments were conducted at temperatures within 435–445 °C and liquid hourly space velocities (LHSV) of 3–5.5 h–1 and operating pressure of 300 psig. A preliminary reactivity evaluation using isotopic water spanning temperatures between 423 and 445 °C was carried out to determine the conditions at which water splitting was occurring. Finally, lumped kinetic modeling including asphaltenes generation in the process was evaluated, and results were compared with previously reported thermal cracking experiments. Operating variables (T, LHSV) were found to have similar effects on the reactivity, as in thermal cracking for CSC of DAO. Even though water splitting was evidenced at temperatures above 430 °C, no significant improvement in the physical bulk properties of the liquid products was obtained for the catalytic experiments using the current formulation. This is attributed to the high degree of condensation reactions triggered at the range of temperatures evaluated. A global activation energy for the conversion of DAO (560 °C+) of 175 kJ/mol and a modeling error of 4.23% were determined. Asphaltenes generation was evidenced at a similar extent as that of thermal cracking from a kinetic point of view.