Regeneration of a P [sbnd]V [sbnd]O [sbnd]Zn butane oxidation catalyst using chlorine containing hydrocarbons

Abstract

A fresh V P O Zn (vanadyl phosphate) catalyst has a maximum molar yield of maleic anhydride of 52% (at 450°C) which eventually becomes a spent catalyst having a maximum yield of 44% (at 400°C). This catalyst can be regenerated by passing carbon tetrachloride (in an air or nitrogen carrier gas) over its surface at 300–450°C. The products in the effluent of the reactor are consistent with the decomposition of CCl 4, (CO, CO 2, VCl 4, unknown chlorine compounds) and with part of the catalyst surface being “stripped” off (VCl 4, O 2, unknown phosphorus containing compounds). Twenty-four hours after the CCl 4 regeneration, the catalytic properties of the regenerated and fresh catalysts are identical i.e. the conversion, selectivities, yields (as a function of temperature) as well as other physical properties - surface areas, XRD patterns, and bulk P/V ratios. The experimental data is consistent with the CCl 4 selectively reacting with the poisoned sites and removing the vanadium from them by forming VCl 4. A regenerated catalyst gives a XRD pattern consisting of a mixture of the catalyst precursor and the fresh catalyst indicating a bulk rearrangement (presumably topotactic). The regeneration procedure can be practiced a large number of times without a detrimental effect on the catalytic performance.