in Wiley InterScience (www.interscience.wiley.com).A novel technique is used to obtain the distribution of particle wetting in trickle-bed reactors for different flow and prewetting conditions. Two prewetting methods were investigated: (1) Levec prewetting, in which the packed catalyst bed is completely flooded and then left to drain before steady state trickle-flow is commenced; (2) Kan prewetting, in which the bed is prewetted by pulsing with the liquid before flow, after which the liquid flow is gradually set back to the required rate. It is shown that the method of prewetting has a major influence on average wetting efficiency and wetting distributions: Average wetting efficiencies differ with as much as 20% between the prewetting modes, and Levec prewetting leads to a considerable fraction of the bed that is not used (up to 7% at the investigated flow conditions), whereas the entire catalyst is used in Kan prewetted beds.It is shown that the particle wetting distributions can influence the modeling of Levec prewetted beds for liquid-and gas-limited conditions.

A novel method for the measurement of wetting efficiency in a trickle-bed reactor under reaction conditions is introduced. The method exploits reaction rate differences of two first-order liquid-limited reactions occurring in parallel, to infer wetting efficiencies without any other knowledge of the reaction kinetics or external mass transfer characteristics. Using the hydrogenation of linear-and isooctenes, wetting efficiency is measured in a 50-mm internal diameter, high-pressure trickle-bed reactor. Liquidsolid mass transfer coefficients are also estimated from the experimental conversion data. Measurements were performed for upflow operation and two literature-defined boundaries of hydrodynamic multiplicity in trickle flow. Hydrodynamic multiplicity in trickle flow gave rise to as much as 10% variation in wetting efficiency, and 10-20% variation in the specific liquid-solid mass transfer coefficient. Conversions for upflow operation were significantly higher in trickle-flow operation, because of complete wetting and better liquid-solid mass transfer characteristics.

The finite element method (FEM) is used to solve the diffusion-reaction equation for spherical particles that are partially wetted by the liquid reagent in a trickle-bed reactor. Boundary conditions are specified using true wetting geometries from photographs of spherical particles that were partially wetted under trickle-flow conditions. Three types of reactions were investigated: completely liquid-limited reactions, completely gaslimited reactions, and reactions that are dependent on both the gas and the liquid reagent, following elementary kinetics. The study is limited to spheres, since wetting geometries were only available for these particles. Both monodispersed and eggshell catalysts were simulated. On the basis of the results, existing models for trickle-bed pellet efficiency factors were verified and models are proposed for the prediction of reaction rates in a partially wetted eggshell and monodispersed catalysts for gas-limited reactions, liquid-limited reactions, and elementary reactions for which both gas-and liquid-reagent concentrations are of importance.

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