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 ove r 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 cata lyst and result in reactor performance different from that obtained under s teady-state conditions. The effect of key parameters such as extent of gas/ liquid limitation, total cycle period, cycle split, and liquid mass velocit y were investigated experimentally to demonstrate the cause-effect relation ships in periodic operation. Performance enhancement was observed for a wid e range of operating conditions under gas reactant limitation. It was stron gly dependent upon the extent of catalyst wetting under liquid-limited cond itions. 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 b y periodic operation. Moreover, performance enhancement is dependent upon t he induced flow modulation frequency and this is discussed in relation to t he natural frequency of the governing process. (C) 1999 Elsevier Science Lt d. All rights reserved.