Effects of Consecutive Oxidation on the Production of Maleic Anhydride in Butane Oxidation over Four Kinds of Well-Characterized Vanadyl Pyrophosphates

Article abstract of DOI:10.1021/j100129a023

Factors determining the selectivity of butane oxidation at high conversion levels have been examined by using four kinds of well-characterized vanadyl pyrophosphate catalysts (C-1 - C-4) in kinetic experiments.The catalysts were carefully characterized by scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and infrared spectroscopy and were made of a single crystalline phase of vanadyl pyrophosphate, (VO)2P2O7.C-1 was prepared by reduction with NH2OH*HCl and consisted of large particles (5 μm) and small particles (0.2 μm).The particles of C-2 obtained from V2O4 had a size of 2 μm.C-3, which was obtained by an organic solvent method, showed a rose-like structure.C-4 from VOPO4*2H2O had a large plate-like structure (5 μm).While all of the catalysts exhibited similar selectivities for the formation of maleic anhydride (63-72 percent) at low conversion levels, the extend of selecticity decreases with an increase in the conversion and strongly depends on the catalysts.It also correlates oppositely with the catalytic activity for the oxidation of maleic anhydride, measured separately.This indicates that the consecutive oxidation of product maleic anhydride is a crucial factor for the selectivity at high conversions.A simulation using a model that includes the consecutive oxidation of maleic anhydride, in which the experimental rate constants for the oxidation of butane and maleic anhydride have been used, reproduced the selectivity-conversion curves experimentally observed.