Mathematical modeling of regeneration of coked Cr-Mg catalyst in fixed bed reactors

Kinetics and percolation: coke in heterogeneous catalysts

“…In the context of the experimental and theoretical studies (briefly reviewed in section 2), the current simulations of the coke removal are most interesting, because in the earlier studies this process was described by employing the first-order model [22,30] or other phenomenological analytical models based on the assumption that initially the coke distribution in a pellet is uniform or that all the porous space is fully filled by coke [36,37]. These models are not applicable in the cases when the main reaction inducing the coke formation is influenced or limited by reactant diffusion so that the final coke distribution is not uniform (section 3), and accordingly the initial coke distribution in the process of catalyst regeneration is not uniform either (section 4).…”

“…In industrial reactors, both these processes depend on the spatio-temporal interplay of reaction itself, reactant diffusion, and coke formation or removal on all the length scales mentioned above, and the complete analysis of the kinetics of these processes should be done at the level of a whole reactor. The corresponding calculations are now available only for models with highly simplified reactant transport (see, e.g., [22,30]). For more complex models, as usual, one should first clarify what may happen inside a porous pellet provided the reactant concentrations at the external pellet-gas interface are fixed.…”

“…In fact, the latter models are now highly simplified. For example, the analysis of decoking process in reactors is often based on the analysis of O 2 transport in reactor including diffusion and coke removal in pellets, and the latter is described by using the reaction-diffusion equation with the first-order expression for the burn-off reaction rate and constant (coke-independent) D eff [22,30].…”

“…It may occur via poisoning of CNPs by adsorption of impurities from the feed stream [9], sintering or, more specifically, Ostwald ripening and/or agglomeration of CNPs [9,20], or actual loss of catalytic species [9]. In reactions occurring with participation of hydrocarbons, the catalyst deactivation is often related to the formation of coke which not only reduces the activity of CNPs but also blocks the reactant supply via pores [9,21], so that many catalysts need regeneration by burning off coke via reaction with oxygen [22]. The coke formation and removal are complex processes representing interesting examples of the already mentioned interplay between kinetics and percolation, or, more specifically, between reaction and percolation.…”

Simulation of catalytic toluene alkylation with methanol in fixed‐bed reactors

“…Philipp et al 18 proposed a pseudo-homogeneous continuous model, which fully investigated the distribution of 2D flow, heat, and materials in a fixed bed with the change of stoichiometry, highlighting the importance of fully coupling fluid flow and chemical reaction. Reshetnikov et al 19 established a 2D model to study the regeneration process of coking catalysts in adiabatic reactors. Liang et al 20 established a 3D toluene combustion reactor model to optimize the traditional countercurrent reactor.…”