Maleic anhydride production

A process for producing maleic anhydride from n-butane which comprises:

• (a) feeding n-butane and air to a reactor;
• (b) contacting the butane and air in the reactor with a crystalline vanadium and phosphorus mixed oxide catalyst at reaction conditions including a temperature between 550.degree. F. and 1000.degree. F. so as to convert 15 to 28% of the butane per pass and obtain a reactor effluent containing maleic anhydride, unreacted butane, nitrogen, and oxygen, said catalyst consisting essentially of pentavalent phosphorus, vanadium and oxygen, said vanadium having an average valence in the range from about +3.9 to +4.6, said catalyst moreover having a phosphorus-to-vanadium atomic ratio in the range from about 0.9-1.8 to 1;
• (c) removing maleic anhydride from the reactor effluent to obtain maleic anhydride-lean effluent;
• (d) recycling a portion of the maleic anhydride-lean effluent to the reactor so as to maintain in the reactor an oxygen content of about 6-12 volume %;
• (e) removing butane from the other portion of maleic anhydride-lean effluent;
• and
• (f) recycling the removed butane to the reactor.