Butane Oxidation to Maleic Anhydride: Kinetic Modeling and Byproducts

Reactor technology for maleic anhydride continues its evolution. New processes achieve higher yields with lower investment by operating in a net reducing environment where the oxygen concentration is lower than that required stoichiometrically to react all of the butane. In this paper, we examined a wide range of operating conditions to quantify the effect of a reducing environment on maleic anhydride selectivity, byproduct acid productivity, and reaction rates. The experiments were carried out with a vanadium phosphorus oxide catalyst in a fluidized-bed reactor and a novel feed gas manifold. Oxygen, carbon monoxide, butane, and acid concentrations were measured online at a frequency of about 1 Hz. Acetic and acrylic acids were the predominant byproduct acids, but fumaric, methacrylic, and phthalic acids were also detected. Under reducing conditions, carbon adsorbed on the catalyst surface, byproduct acid yields increased, and both the selectivity and reaction rates decreased. A redox kinetic model was developed to account for the experimental observations and included both V5+ and V4+ oxidation states and a "VC4" complex, which represented carbon adsorption.