The conversion of mixtures of n-butane and n-butenes to maleic anhydride over an industrial vanadium-phosphorus oxide (VPO) catalyst was experimentally investigated. Specifically, the conversion of a synthetic raffinate II mixture was studied. The reaction kinetics were modeled on the basis of a reaction network consisting of eight individual reactions and by using hyperbolic rate equations. Calculations and experimental results are shown for a temperature range from 400 to 450 °C and for molar fractions of the synthetic raffinate II in the feed that were varied from 1% to 2%. The kinetic model shows good agreement with the experimental results. The value of the maximum yield of maleic anhydride is insensitive to changes in temperature and hydrocarbon feed fractions and amounts to ∼48%. Increases in temperature, however, reduce the amount of catalyst required to reach the maximum yield. The conversions of pure 1-butene and pure n-butane lead to maximum yields of ∼53% and 56%, respectively. The efficiency of a maleic anhydride process will, therefore, strongly depend on the choice of feedstock and, in particular, on the availability of n-butane at the designated production site.

The partial selective oxidation of mixtures of n-butenes and n-butane in an industrial-scale fixed-bed reactor has been simulated to find suitable operation conditions and to give a rough estimate of the performance of such a reactor. A two-dimensional homogeneous reactor model has been used in combination with a kinetic model based on experimental results. Since the pressure drop along the reactor tubes was assumed to be 1−1.5 bar, the gas phase in the reactor tubes had to be treated as a compressible fluid. The operation conditions of the reactor were found by repeated simulation and continuous improvement. The simulations resulted in a conversion level of 90% and a yield of maleic anhydride of 48% for a synthetic raffinate II mixture containing only n-butenes and n-butane. A typical real raffinate II mixture which also contains isobutane would result in a yield of maleic anhydride of ≈42%. Production capacities of 17 100 and 22 5000 t/y where achieved with allowed pressure drops of 1.0 and 1.5 bar, respectively.

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charakterisiert, gefunden (s. Abb.). Die LII-Ergebnisse waren unabhängig von der Aggregatstruktur. Das LII-System erwies sich als einfach und robust in der Anwendung und stellt u. a. aufgrund der schnellen Detektionsfrequenz von mindestens 1 Hz ein sehr gutes Werkzeug zur direkten Prozesskontrolle ohne Zeitverzug dar. Abbildung.Korrelation Partikelgröûe aus LII und CTAB-Absorptionszahl.