Catalysis Science and Engineering, Invited Lecture
Modelling the Phosphorous Dynamics of Vanadyl Pyrophosphate Catalysts
G. Mestl1, S. Böcklein1, D. Lesser1, T. Turek2
1Clariant Produkte (Deutschland) GmbH, Waldheimerstr. 13, 83052 Heufeld, Deutschland, 2Institut für Chemische Verfahrenstechnik, TU Clausthal, Leibnizstr. 17, 38678 Clausthal-Zellerfeld, Deutschland
Maleic anhydride (MA) is an important intermediate in chemical industry. It is produced by heterogeneous catalytic oxidation of n-butane in air. Mainly tubular fixed bed reactors are used for this strong exothermal reaction. The catalyst consists of vanadium phosphorous oxides (VPO) and is employed as pelletized full-body shapes. Even after many years of investigation, reaction mechanism and nature of the active sites are not fully understood. An important subject is the slow loss of phosphorous shifting conversion and MA-selectivity in commercially unattractive regions. In order to prevent this phosphorous loss, it is industrial practice adding several ppm of an organic phosphorous compound together with water to the reactor feed [1]. Dynamic experiments in an industrial-scale pilot reactor showed various partially opposed effects on different time scales. From these experiments a kinetic model was derived that accounts for any observed interactions between TMP and water on the VPO surface. The kinetic model was integrated in a two-dimensional, heterogeneous reactor model (gPROMS) which could be successfully applied describing well the temperature profiles and product compositions up to 500 h time on stream.
[1] J. R. Ebner, Monsanto, WO1993016027A1 (1993)