Parametric study of unsteady-state flow modulation in trickle-bed reactors

Unsteady-state liquid flow modulation (periodic operation) was investigated for hydrogenation of alpha-methylstyrene to cumene in a hexane solvent over 0.5% Pd on alumina spheres. This test reaction was run under both gas and liquid reactant-limited conditions. It is shown that periodic liquid flow modulation can alter the supply of liquid and gaseous reactants to the catalyst and result in reactor performance different from that obtained under steady-state conditions. The effect of key parameters such as extent of gas/liquid limitation, total cycle period, cycle split, and liquid mass velocity were investigated experimentally to demonstrate the cause-effect relationships in periodic operation. Performance enhancement was observed for a wide range of operating conditions under gas reactant limitation. It was strongly dependent upon the extent of catalyst wetting under liquid-limited conditions. The feasibility of achieving improved reactor performance is shown to depend on the extent of reactant limitation, the cycle period and split, mean liquid mass velocity, and the improvement of liquid maldistribution by periodic operation. Moreover, performance enhancement is dependent upon the induced flow modulation frequency and this is discussed in relation to the natural frequency of the governing process. (C) 1999 Elsevier Science Ltd. All rights reserved.