Partial oxidation of o‐xylene in melts containing vanadium pentoxide

Abstract

o-Xylene vapor in nitrogen was partially oxidized by bubbling it through a melt of the 39 wt. % vanadium pentoxide-potassium sulfate eutectic a t temperatures from 528" to 598°C. The principal product was o-tolualdehyde; some benzene and traces of phthalide were formed but no organic acids. These products are similar t o those found in o-xylene oxidation over a solid vanadium oxide catalyst, except for the absence of acid products but are far different from the product distribution found from homogeneous oxidation with air. The rate of reaction per unit of gas-melt interface was approximately equal to that reported for oxidation of o-xylene in air on an unsupported fused vanadium oxide catalyst. With o-xylene-air mixtures bubbled through either a vanadium pentoxide-potussium sulfate eutectic melt or vanadium pentoxidepotassium pyrorulfate melt, homogeneous reaction obscured any contribution from heterogeneous processes.In present chemical technology, catalyzed gas-phase reactions are usually carried out in either fixed-or fluidized-bed reactors. With highly exothermic or endothermic reactions, isothermal operation is difficult to achieve in a fixed-bed reactor because of the poor radial heat transfer. In a fluidized bed essentially isothermal operation can be achieved, but the flow patterns and residence times of solids and gas are understood poorly. The purpose of this work was to explore a different contacting method, that of passing the reactant gas in the form of bubbles up through a vessel containing a melt which would act as an oxidizing agent or as a catalyst. In addition to providing a more nearly isothermal operation than the fixed-bed reactor, a melt reactor system may permit new methods of carrying out a catalytic reaction. For example, in a catalytic oxidation it may be possible to achieve more selective reaction and minimize overoxidation by not allowing the reactant to come in contact with the primary oxidant. By proper choice of a suitable melt, the reactants may be oxidized by the melt in one reactor, and the reduced melt reoxidized by a second gas stream, such as air in a second reactor, and then be recirculated to the first. The high catalytic activity of many metal oxides has been attributed to the ease with which they may alternate between two oxidation states. That of a solid vanadium pentoxide catalyst in o-xylene oxidation, for example, has been ascribed to a V,O,-V,O,, oxidation-reduction system (18).

Viscosity of the Vanadium Pentoxide-Potassium Sulfate Eutectic.

“…The VISCOSITY of the 37 mole % VA-63 mole % K,S04 eutectic mixture (1) was determined as a function of temperature in the range of 460°to 600°C. In an associated investigation, possible catalytic effects of this melt system for the gas phase partial oxidation of o-xylene (7) were studied in a bubble reactor. For interpretation of the rsults of that study, it was important to have a knowledge of the viscosity of the melt at various reaction temperatures.…”