Wrong-way behavior in packed-bed reactors with "large-pore" catalysts

The effect of intraparticle convection on the wrong-way behavior of a non-isothermal packed-bed reactor is analyzed. Transient one-dimensional heterogeneous models were used to calculate the dynamic responses of the system: the HTdc model, which takes into account both internal convective and diffusive fluxes and the HTd model, that includes only diffusional resistances inside the particle. The o-xylene oxidation to phthalic anhydride, described by a single first-order irreversible exothermic reaction was used as an example. For a sudden decrease in the feed temperature (T-o), the HTdc model predicts an inverse temperature response along it wide range of inlet concentrations, which becomes more significant for rising C-o values. Wrong-way behavior is also reported by the HTd model, for more severe operating conditions (high values of C-o and T-o), where the temperature excursion can exhibit a sharp transient increase. It is also shown that, for the same operating conditions, the dynamic behavior of the packed-bed reactor depends on the intraparticle Peclet number, lambda(m), that accounts for the competition between convection and diffusion inside the catalyst particle.