Redox kinetics of VOPO4 with butane and oxygen using the TAP reactor system

The reaction kinetics for the selective oxidation of n-butane (n-C-4) to ma leic anhydride (MAN) over delta-VOPO4, and gamma-VOPO4, catalysts were inve stigated by a transient response method using the Temporal Analysis of Prod ucts(R) (TAP) reactor system. These catalyst phases are contained in select ive mixed-phase vanadium-phosphorus oxide (VPO) catalysts for n-C-4 to MAN processes that are based upon multi-tubular fixed-beds, fluidized-beds, or circulating-solids reactors. In the latter reactor type, the catalyst is ex posed to alternating zones of hydrocarbon-rich and oxygen-rich reaction gas es so the reactor operation can be classified as a type of forced unsteady- state process. Previous kinetic models for n-C-4 oxidation to MAN that are based upon steady-state experiments with oxygen-rich feeds are not directly applicable to this operating mode. TAP reactor step response experiments w here n-C-4 and O-2 are cycled over 380-420 degrees C and atmospheric pressu re were used to generate transient responses for n-C-4, O-2, CO2, and MAN. It is shown that a kinetic model that combines surface kinetics and solid-s tate diffusion of oxygen in the lattice is able to predict the transient re sponse data for oxidation and reduction of the VOPO4 catalysts over a reaso nable range of reaction temperature and inlet mole fractions of the reactan ts. (C) 1999 Elsevier Science Ltd. All rights reserved.