Trickle bed reactors: Effect of liquid flow modulation on catalytic activity

The effect of slow ON-OFF liquid flow modulation on the oxidation of aqueous solutions of ethanol using a 0.5% Pd/Al2O3 commercial egg-shell catalyst was investigated in a laboratory trickle bed reactor (TBR). In this mode of operation. the catalyst was cyclically exposed to oxidative and reductive environments. The study was carried out under different gas and liquid flow rates, cycle periods and splits. Cycling results have been compared with the steady-state experiments performed at the corresponding average liquid flow rate. Significant improvements over the continuous operation were obtained when the catalyst was exposed to a short surplus of oxygen (to minimize deactivation by overoxidation in the kinetic regime) after a longer time of working in the mass transfer limited regime. According to the results presented here, it is recommended to work with high liquid flow rates and moderate gas flow rates to ensure complete wetting of the catalyst during the ON cycle and to minimize the overoxidation process during the OFF cycle. (C) 2008 Elsevier Ltd. All rights reserved.