Fischer−Tropsch Kinetic Studies with Cobalt−Manganese Oxide Catalysts

Abstract

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 °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.