Liquid–solid mass transfer distributions in trickle bed reactors

Abstract

Micro-electrodes with exposed areas ranging from 5 to 30mm2 were placed onto 4.5mm alumina spheres and used for the sub-particle scale quantification of liquid–solid mass transfer. A novel electrochemical technique was applied where the external cathode wetting fraction and liquid–solid mass transfer were simultaneously quantified. Clear bifurcation of the area-specific liquid–solid mass transfer was observed, providing direct evidence of the two-wetted-zone theory previously inferred from tracer response analysis. The lower hysteresis branch (Levec prewetting) exhibited larger fractions of static wetted area compared to the upper branch (Kan prewetting). The static zones were not completely stagnant and the average static mass transfer rate increased with liquid superficial velocity. The spatial position of the static zones varied for a given packing configuration, while no relationship was found between the positioning of static and residual holdup. Static liquid–solid mass transfer coefficients were found to be higher than those obtained from tracer response analyses on porous particles.