KINETICS AND FIXED-BED REACTOR MODELING OF BUTANE OXIDATION TO MALEIC-ANHYDRIDE

Selective oxidation kinetics of n-butane to maleic anhydride in air were studied over a commercial, fixed-bed vanadium-phosphor oxide catalyst. The temperature range was 573-653 K with butane concentrations up to 3 mol % in the feed, which is within flammability limits but below ignition temperatures. The rate data were modeled using power law kinetics with product inhibition and included total oxidation and decomposition reactions. Kinetic parameters were estimated using a multiresponse, nonlinear regression algorithm showing intercorrelation effects. The kinetics were combined with independent measurements of catalyst diffusivity and reactor heat transfer using a one-dimensional heterogeneous reactor model. Model predictions and observed temperatures and concentrations from non-isothermal pilot plants were compared up to 115 days on stream. Agreement was acceptable with inlet butane concentrations up to 2.7 mol%. For example, runaway was predicted at a salt temperature 3 K higher than observed. Effectiveness factors around the hot spot were estimated at 0.6 with the catalyst surface temperature 2-3 K higher than the average gas temperature.