: Effect of liquid flow modulation on the stability of noble metal catalysts for alcohol oxidation

AYUDE, MARÍA ALEJANDRA; CASSANELLO, MIRYAN C.; MARTÍNEZ, OSVALDO MIGUEL; HAURE, PATRICIA M.

Buenos Aires, Argentina

Congreso; V Congreso Argentino de Ingenieria Quimica y XXII Congreso Interamericano de Ingeniería Química; 2006

Asociación Argentina de Ingenieros Químicos (AAIQ) y Confederación Interamericana de Ingenieros Químicos (CIIQ)

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 scale Trickle Bed Reactor (TBR). The behavior of noble metal catalysts used in alcohol oxidation strongly depends on the degree of exposure to oxygen. At low oxygen concentration, the reaction rate is low and the catalyst may deactivate by adsorption of carbonaceous deposits, while under rich oxygen concentration, the catalyst deactivates due to over-oxidation. So, ON-OFF modulation of the liquid flow was implemented with the aim of increasing the conversion and/or reaction rate. In this mode of operation, the catalyst was cyclically exposed to oxidative and reductive environments, therefore the TBR behaved as a redox cycle reactor. Experiments were conducted at differentliquid flow rates, cycle periods and splits. Significant improvements over the steady state operation were obtained when the catalyst was exposed to a short surplus of oxygen after a longer time of working in the mass transfer limited regime. Proper selection of cycle duration and an adequate start-up protocol are crucial to maintain long term catalytic activity.