Fischer-Tropsch kinetic studies with cobalt-manganese oxide catalysts

An investigation was undertaken to establish the reaction mechanism for the Fischer-Tropsch reaction, in the presence of the water-gas shift reaction, over a cobalt-manganese oxide catalyst under conditions favoring the formation of gaseous, liquid, and solid (waxes) hydrocarbons (210-250 degrees C and 6-26 bar). A micro-fixed-bed reactor was used with a cobalt-manganese oxide catalyst prepared by a coprecipitation method. An integral reactor model involving both Fischer-Tropsch and water-gas shift reaction kinetics was used to describe the overall performance. Reaction rate equations based on Langmuir-Hinshelwood-Hougen-Watson models for the Fischer-Tropsch reaction (hydrocarbon forming) and empirical reaction rate equations for the water-gas shift reaction from the literature were tested. Different combinations of the reaction rate equation were evaluated with the aid of a nonlinear regression procedure. It was found that a reaction rate equation for the Fischer-Tropsch reaction based on the enolic theory performed slightly better than a reaction rate equation based on the carbide theory. Reaction rate constants for the cobalt-manganese oxide catalyst are reported, and it is concluded that this catalyst also behaves very much like iron-based catalysts.