Transient Behavior And Kinetics Studies Of The Bulk Phase Lattice-Oxygen In The Catalyst Used For Ammoxidation Of Propylene

Abstract: Ammoxidation catalyst MB-98 is used to produce Acrylonitrile. The activity would decrease when the catalyst is in the low oxygen zone because of the loss of lattice oxygen. The partial reduced catalyst needs to be regenerated continually in order to keep its activity. Therefore, to investigate the re-oxidation kinetics is significative for the improvement of the regeneration efficiency.firstly, An experimental set-up was built for splitting up of the overall reaction to two steps, selective reduction and re-oxidation of deoxidized catalyst . Partial reduced catalyst can be prepared in a fixed bed reactor. The as-prepared catalyst was then put into a thermo-analyzer with an air flow. The thermal re-oxidation behavior of the catalyst can be studied by measuring the mass variety under different heating rates. The reaction kinetics was investigated according to the thermal analysis data and a most suitable reaction mechanism model was obtained.The experimental results showed that there are two stages in the oxidation process. The first stage is about the Fe being oxidized and the second one is relative to the oxidation of some molybdenum oxides in a lower valent. According to the industrial conditions we know that the first stage is the main process which should be paid more attention to.The reaction rate increases as the heating rate increases and the total oxidation mass increase of the catalyst turn to be the highest value when the heating rate is 10 K.min. The reaction temperature with no heating rate influence is obtained using approximate extrapolate method.Several methods for estimating the kinetic parameters and identifying the mechanism of the reaction were used to treat the non-isothermal kinetic data. The results obtained suggest that the re-oxidation process of the catalyst obeys the contracted core model controlled by the Phase border. The reaction rate equation can be expressed as dα/dt =Aexp(-E/RT)*3(1-α), where the activation energy E=110 kJ/mol, the frequency factor A=1．79*10min...