The synthesis of maleic anhydride (MSA) is an important industrial process with an annual production of approx. 2.8 million tons. MSA is produced by the selective catalytic oxidation of n-butane with air in the presence of vanadium-phosphorus oxide (VPO) catalysts at temperatures between 390 and 420°C. The heat of reaction released is used in the industrially widespread production of maleic anhydride. The heat of reaction released causes pronounced hotspots to form in the salt-bath-cooled shell-and-tube reactors widely used in industry, with the associated risks with regard to the stability and safety of the process. This effect is intensified by the phosphorus dynamics of the catalyst, which leads to a gradual increase in the activity of the catalyst with a simultaneous reduction in selectivity and yield. Precise control of the reaction process is therefore essential for economical and safe operation of the reactor.

The aim of current research work is a mathematical description of the process, including the phosphorus dynamics, in order to enable model-based optimization of the process. This requires both precise reaction kinetics, which can be used to describe the conversion of n-butane to the target product and the various by-products, as well as separate kinetics to describe the change in activity of the VPO catalyst.

To investigate the phosphorus dynamics, systematic experiments are to be carried out under varying reaction conditions, such as temperature, water content of the supplied gas mixture or addition of phosphorus-containing species. It is also planned to experimentally verify recently published reaction kinetics. The targeted addition of catalyst poisons, for example, is conceivable for this purpose. Corresponding addition procedures must be developed and implemented.

A salt bath tempered millistructured fixed bed reactor specially developed at the ICVT is used for all these experiments. Due to its almost isothermal behavior, it offers ideal conditions for the kinetic investigation of highly exothermic reactions.