Analysis of the Selective Oxidative Dehydrogenation of Ethane over a NiO-SnO2 Catalyst in an Industrial Packed-Bed Reactor: Heterogeneous Reactor Modelling

Ethylene, the largest-scale (petro)chemical intermediate, is mainly produced by thermal cracking. This process presents several drawbacks from an environmental and energetic point of view. To overcome these downsides, alternative production routes have been proposed over the years. Among all these alternatives, oxidative dehydrogenation of ethane (ODH-C₂) is the most promising one. Its industrial-scale implementation faces two challenges: the development of a highly selective catalyst and the design of a corresponding industrial reactor. In the present work, we model the ODH-C₂ performance over a highly selective NiO-SnO₂ catalyst in a wall-cooled industrial-scale multitubular packed-bed reactor. A pseudo-heterogeneous model accounting for fluid dynamics was used to elucidate the effect of the operating conditions on the reactor performance. To capture the pure effect of the velocity profile on temperature and concentrations profiles, a comparison of the simulations considering either fluid dynamics or plug flow for varying reaction bath temperatures (T_b) was made (Figure 1). The heat transfer was improved when the fluid dynamics was considered; this effect was most pronounced at higher reaction bath temperatures. When considering a velocity profile in the bed, an overestimation of the hot spots by 10 °C and 20 °C at bath temperatures of 440 °C and 480 °C, respectively, was avoided. The effect of the inlet ethane and oxygen concentration on the product spectrum was similar, more severe conditions led to higher hot spot temperatures and reactant conversion. The danger of overoxidation evidently became more pronounced at higher oxygen concentrations. The higher ethylene yield was obtained at the lower Rep albeit that caution was required as hot spots up to 27 °C were obtained.

Figure 1. Effect of the velocity profile on the industrial-scale reactor predictions for different T_b. a)Void fraction and velocity profiles,b) gas phase temperature, (c) ethane conversion and (d) oxygen conversion.