Effect of catalyst wettability on ON-OFF liquid flow modulation of a Trickle Bed Reactor

M.ALEJANDRA AYUDE; PAOLA MASSA; FRANK STUBER; ROSA J. FENOGLIO; PATRICIA M. HAURE

Braga

Congreso; GLS10 Gas-Liquid and Gas-Liquid-Solid reactor Engineering congress; 2011

Catalytic Wet Air Oxidation processes can be carried out in Trickle Bed Reactors (TBRs) in which the transport resistance provided by the liquid film reduces the reaction rate, thereby decreasing conversion. Additionally this scenario is complicated by the presence of a variety of catalyst wetting conditions induced by two-phase flow. For a gas-limited reaction, higher reaction rates can be obtained for lower wetting efficiencies, where the gas can access the particle directly from the surface. Therefore, TBRs are candidates for Process Intensification since a decrease in the wetting efficiency may improve the supply of the gas reactant to the particle. Wettability changes can be accomplished by means of spatial or temporal segregation of the phases. Spatial segregation can be attained using other reactor configurations or (for the case of oxygenations or hydrogenations in aqueous media) carrying the reaction over hydrophobic catalysts. On the other hand, temporal segregation can be achieved operating the TBR with forced ON-OFF liquid flow modulation (LFM) The impact of periodic operation on the performance of catalyst with different degrees of wettability has not been reported yet. Therefore, the aim of the present work is to study the oxidation of phenol aqueous solutions at 413 K and 7 atm oxygen pressure over hydrophilic and wet-proofed CuO/γ-Al2O3 catalysts in a TBR operated at steady state and with slow ON-OFF LFM (periods 3 – 10 min, splits 1/2, 1/3 y 1/6). Steady state results obtained with both catalysts are similar. Moreover, under the conditions investigated, LFM does not improve reactor performance. Observed experimental trends are explained through a dynamic model aimed at the particle scale that accounts for the mass transport-reaction steps involved for the case of completely hydrophobic, hydrophobized and hydrophilic particles. Kinetic parameters are evaluated from experimental data obtained in steady state operation with the hydrophilic catalysts, considering the external partial wetting of the catalyst. The effect of the hydrophobic coating width on reaction rate is analyzed and the behavior of hydrophobic catalysts is also outlined. Finally, the model allows the evaluation of the results attained under liquid flow modulation.