Gas phase oxidation of furfural to maleic anhydride on V2O5/γ-Al2O3 catalysts: Reaction conditions to slow down the deactivation

Abstract

An alumina-supported vanadium oxide catalyst (13.9wt.% vanadium oxide) has been characterized by different techniques and tested in the gas phase oxidation of furfural. These studies have shown that the catalyst unavoidably deactivates by deposition of maleates and resins over the surface. Full regeneration is accomplished by burning off these deposits at 773K. The studies have also demonstrated that if the primary contact occurs at temperatures at which furfural conversion is low and then the temperature is increased in a low- to high-temperature mode, intense deposition of maleates and resins takes place and the catalyst is rapidly deactivated. The increase of the temperature does not result in removal of deposits but accelerates the deposition. Under this protocol, the yield of maleic anhydride never exceeded 30%, irrespective of the reaction conditions (temperature and O2/furfural mole ratio). In contrast, if the catalyst first contacts the reaction mixture at high oxidizing potential, then the rate of maleate and resin deposition is much slower, and so is the deactivation rate, and the catalyst can display a higher yield of maleic anhydride for a longer period of time. A high oxidizing potential can be attained at a high reaction temperature (close to full conversion). A higher oxidizing potential at a given high temperature can be accomplished by increasing the O2/furfural mole ratio. Thus, for example, first contacting the catalyst at 593K (full conversion), 1vol.% of furfural, and O2/furfural mole ratio=10, obtained an initial maleic anhydride yield of 68%, and the yield was still greater than 50% after 15h on stream. On contacting at 573K with 1vol.% furfural and 20vol.% O2, the maleic anhydride yield was initially close to 75% and was above 60% after 15h.