Phosphorus dosing during catalytic n‑butane oxidation in a μ-reactor : a proof of concept

The selective oxidation of n-butane to maleic anhydride over vanadium–phosphorus oxide catalysts is subject to a dynamic change in the catalyst activity. This phenomenon is called phosphorus dynamics and plays a vital role in the prediction of catalytic reaction rates, but to date, no models measured under transport limitation free conditions have been published. This study presents the first investigation of the phosphorus dynamics over extended periods of time (multiple days on stream) under transport limitation free conditions in a μ-fixed-bed reactor. Initially, temperature variation experiments are conducted to investigate whether phosphorus dynamics takes place in a μ-reactor and to determine the onset of phosphorus loss. Then, a setup for dosing of liquid organophosphorous species on the scale of nL min–1 is proposed, and functionality is demonstrated via step test experiments. Results of the temperature variation showed that phosphorus loss occurs in the μ-reactor but starts at temperatures exceeding those of industrial scale reactors by 30–80 K. It was further observed that addition of steam to the feed increases the intensity of the phosphorus dynamics and lowers the onset temperature. Step test results demonstrated the functionality of the dosing setup if a suitable inert material is chosen and the metal surfaces downstream the dosing are treated according to a passivation procedure proposed in this study. The addition of steam appears to be required for appropriate distribution of the dosed organophosphorous species over the catalyst bed.