Investigation of the Unsteady-State Oxidation of n-Butane to Maleic Anhydride in Fixed-Bed Reactors

The periodic operation performance of n-butane selective oxidation to maleic anhydride over a VPO catalyst in fixed-bed reactors was investigated. A temperature-programmed oxidation experiment demonstrated that reoxidation sufficient to activate the catalyst could only be carried out at a temperature higher than that of butane oxidation step. A periodic operation scheme, simultaneous modulation of both composition and temperature, was proposed and examined in a fixed-bed microreactor filled with 0.6 g of crushed catalyst and in a tubular fixed-bed reactor packed with 30 g of catalyst. In both reactors, feed composition modulation enhanced selectivity to maleic anhydride, but the conversion of butane and the yield of maleic anhydride dropped. With a 1:0.4 cycle split and period of 4 min, reoxidation of the catalyst at 530°C, and selective oxidation at 405°C, the yield of maleic anhydride by both composition and temperature modulation was improved by 11.4% over that obtained for operation under steady-state conditions with the same time-average flow of n-butane, which indicated that the higher reoxidation temperature was effective in improving reactor performance.