Mitigating Deactivation Effects through Rational Design of Hierarchically Structured Catalysts: Application to Hydrodemetalation

The broad pore network of a hierarchically structured hydrodemetalation catalyst, containing both nano- and macropores, is mathematically optimized to maximize the conversion of nickel metalloporphyrins in crude oil residue. A random spheres model (RSM) describing the nanoporous catalyst at the mesoscale is combined with a two-dimensional continuum approach to model the entire catalyst at the macroscale. Catalysts with a spatially uniform as well as a nonuniform macroporosity distribution are optimized. The macroporosity profiles of the optimal nonuniform catalysts fluctuate about the optimal uniform value, while the spatially and temporally integrated reaction rates from both types of optimized catalysts are almost the same. Moreover, the integrated reaction rate of the optimal hierarchically structured catalysts are almost 8 times higher than the yield obtained from a purely nanoporous catalyst. For a time on stream of 1 year, approximately 21% less catalytic material is required in the optimal hierarch...