Catalytic combustion of carbon particulate at high values of the carbon/catalyst mass ratio

Abstract

The oxidation of diesel soot and amorphous carbon black, in the presence, of a copper-vanadium-potassium catalyst supported on α-alumina, was studied to investigate the influence of the carbon/catalyst initial mass ratio, R m , on the carbon reactivity. A differential flow reactor was employed to perform kinetic tests. The progress of the catalytic combustion process was followed measuring the concentrations of carbon oxides in the product stream at the reactor outlet with on-line NDIR analyzers. Experimental results conform to those obtained while operating at relatively low values, of R m for what concerns the influence of oxygen partial pressure and temperature. Furthermore, burn-off temperatures in the presence of the catalyst were lowered by ca. 300 K, and correspondingly, the apparent activation energy for the catalytic oxidation was found to be less than half with respect to the uncatalyzed combustion. A strong influence of R m on the evolution with time of the combustion process was experienced. Specifically, time profiles of reactivity obtained when R m was higher than 0.1 show a maximum whose amplitude increases as R m increases. This behavior was related to the segregation of a more-or-less large fraction of the total carbon. Following such findings, a kinetic model for carbon catalytic oxidation was proposed. It is based on the assumption that different carbon portions enter the reaction zone at different times. Model parameters were estimated by a numerical code properly adapted. A good agreement between model predictions and experimental results was found for all R m values.