Catalytic oxidation of carbon black - I. Activity of catalysts and classification of oxidation profiles

The oxidation of carbon black in the presence of catalytically active compounds has been studied under isothermal conditions in a flow reactor. In the presence of metal oxides, oxidation rates of the carbon black are found to be up to a few hundred times higher compared with the non-catalysed oxidation. Alkali metal carbonates increase this oxidation rate even up to a factor of over 100 000. The combustion curves (reaction rate as a function of carbon conversion) of isothermal, catalytic oxidation of carbon black can be classified in four distinct profile types. From these combustion curves, it can be concluded that a relative ranking of catalysts depends on the carbon conversion level and on the catalyst-to-carbon black ratio. The contact between catalyst and carbon black is an essential parameter in the catalysed oxidation of carbon black. When this contact is poor, the catalytic effect of the metal oxides and alkali metal carbonates is low or even absent. For alkali carbonate catalysts, the very high reaction rates were attributed to redistribution of the catalyst during reaction. Also for some of the metal oxides (i.e., Ag(2)O, CuO, MoO(3), PbO, Sb(2)O(3)) it is suggested that mobility of the catalyst can increase the contact between the catalyst and the carbon black, resulting in higher oxidation rates. (C) 1998 Elsevier Science Ltd.