Wetting Efficiency in Tubular Reactors with Solid Foam Packings

In the recent years, the performance of gas-liquid-solid fixed bed reactors with structured catalysts instead of catalyst particles has been intensively discussed. Structured catalysts based on solid foams with an open cell structure are in particular very promising. Such porous structures combine high specific surface area up to 2000 m²/m³, low single-phase and two-phase pressure drop due to bed porosities between 75 and 95 %, and interconnected pores for enhanced heat and mass transfer (Stemmet et al., 2005; Grosse and Kind, 2011). The performance of fixed bed reactors with structured catalysts depends heavily on the gas-liquid-solid contacting pattern. For a broad range of flow conditions, the liquid phase does not cover the solid surface homogeneously, which is known as partial wetting. The externally wetted fraction, which is defined as fraction of the external solid foam area covered by the liquid phase to the total external solid foam area, is directly linked to the liquid-solid and gas-solid mass transfer and thus, to the overall rate of reaction. The wetting fraction is a function of the superficial gas and liquid velocity and depends also on the physical properties of the liquid phase as well as catalyst shape, surface, porosity, etc. (Nigam and Larachi, 2005). However, studies on the wetting efficiency in trickle bed reactors also indicated the impact of the pre-wetting mode (Joubert and Nicol, 2012).
The aim of this work was to adopt an electrochemical method for: (a) measuring the wetting fraction in tubular reactors with solid foam packings and (b) to study the effect of pre-wetting.