Pseudo-homogeneous fixed-bed reactor

In the ideal CSTR and PFR reactors in homogeneous phase, the reactants and products constitute a single phase. The homogeneous reaction takes place in a liqnid or gas phase whose concentration varies throughont the PFR, while in the CSTR reactor the concentration is instantaneous. 

In a specific case, when the reaction takes place on the catalyst present on the internal wall of the tube and the flow is uniform, the behavior is equal to a reaction in homogeneous phase. 

If the catalyst consists of particles, one has a fixed or mobile stationary particles reactor. The flow is no longer nniform and the reaction is considered heterophasic. In this case, the catalyst consists of solid particles, but the reactants and products are gas or liquid and may flow through the particle bed in the concurrent or counter current direction. The reaction may be catalytic or noncatalytic and takes place on the particle surface and/or within the pores of the catalyst. In this case, the system is heterophasic and may be solid-gas type, solid-liquid, or solid-liquid-gas taking place in the respective reactors fixed or mobile-bed, trickle bed, and slurry bed. 

These reactors exhibit complex fluid dynamics. The velocity profile in a cross section is not uniform due to the influence of the wall and the porosity of the catalytic bed, causing the nonideality of the continuons reactor. 

The solid particles have high specific snrface areas due to high porosity (pore volume). Convection phenomena occur in fixed or mobile-bed reactor due to three 

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