On the importance of by-products in the kinetics of n-butane oxidation to maleic anhydride

Abstract

The kinetics of n-butane oxidation to maleic anhydride (MA) is investigated under industry-related conditions using an almost isothermal millistructured fixed-bed reactor. In addition to the influence of reaction conditions and feed composition, in particular, the influence of the reaction products is investigated. Besides water and MA, the main focus is on the by-products acetic and acrylic acid, which are usually neglected in the literature. In this context, it can be demonstrated that acetic and acrylic acid play an important role in the formation of CO and CO2, and therefore should be considered in the kinetics. On the other hand, direct oxidation of n-butane to CO and CO2 seems to be rather unlikely. The result is a reaction network with at least nine reactions. All of these reactions are inhibited by water and show an apparent reaction order smaller than one concerning their carbon source. Furthermore, a complex pattern of inhibitions is observed, which, in most cases, can be well explained by a redox mechanism. In summary, a large amount of data is collected that can be used for the development of improved kinetics, including the often neglected by-products acetic and acrylic acid.