Computational modelling approach of an inclined rotating fixed bed reactor

In the last decades several research groups investigated the dynamic operation of trickle bed reactors to intensify mass transfer-limited multiphase reactions. This process intensification strategy is realized via a cyclic flow rate modulation of the liquid phase, which results in a spatial and time-dependent liquid holdup in the catalytic fixed bed. Here, the variation of the liquid holdup causes an enhanced accessibility of the limited components to the catalyst, whereby a higher overall reaction rate is achieved. Although promising enhancements of the overall reaction rate in lab-scale trickle bed reactors were proved, the forced liquid cycling suffers from pulse attenuation along the reactor, thus the beneficial flow conditions mitigate at lower axial reactor positions (Atta et al., 2014).
Recently, an inclined rotating fixed bed reactor was developed, which ensures a permanent wetting intermittency of the catalyst within the stratified flow. The latter is caused by the reactor inclination. A twofold increase of the conversion for the α-methylstyrene hydrogenation was obtained, compared to the trickle bed operation, which highlights the potential of the new reactor concept (Härting et al., 2015).
In this contribution, a feasible hybrid model approach for the prediction of the space-time yield is proposed. The model consists of a three-dimensional two-phase Eulerian-Eulerian model and a heterogeneous continuum model to describe the hydrodynamics and the mass transfer and reaction phenomena, respectively. In this hybrid framework, the Eulerian-Eulerian model provides information about the wetting intermittency in terms of the dynamic holdup, which is incorporated in the heterogeneous continuum model by time-dependent boundary conditions at the particle scale.
The hydrodynamic model is based on a recently modified permeability approach with permeability coefficients of the gas phase depending on the flow pattern to approximate the solid-gas interactions of the phases (Subramanian et al., 2016). In this contribution different reactor geometries are studied and operated with α-methylstyrene, cumene and hydrogen. Additionally, the influence of the interfacial area density and the drag coefficient in the gas-liquid closure is examined via simulation studies.
The heterogeneous continuum model consists of a stationary reactor model considering the Danckwerts boundary conditions and of a transient particle model accounting for the intraparticle concentration gradients.
Eventually, the implemented hybrid model approach is applied for simulation studies to extend the knowledge of the new reactor concept and to support the optimal design and operation.