Maleic anhydride from mixtures of n-butenes and n-butane:: Simulation of a production-scale nonisothermal fixed-bed reactor

The partial selective oxidation of mixtures of n-butenes and n-butane in an industrial-scale fixed-bed reactor has been simulated to find suitable operation conditions and to give a rough estimate of the performance of such a reactor. A two-dimensional homogeneous reactor model has been used in combination with a kinetic model based on experimental results. Since the pressure drop along the reactor tubes was assumed to be 1-1.5 bar, the gas phase in the reactor tubes had to be treated as a compressible fluid. The operation conditions of the reactor were found by repeated simulation and continuous improvement. The simulations resulted in a conversion level of 90% and a yield of maleic anhydride of 48% for a synthetic raffinate II mixture containing only n-butenes and n-butane. A typical real raffinate II mixture which also contains isobutane would result in a yield of maleic anhydride of approximate to 42%. Production capacities of 17 100 and 22 5000 t/y where achieved with allowed pressure drops of 1.0 and 1.5 bar, respectively.