Multi-Scale Modeling For Oxidative Dehydrogenation Of Butene To Butadiene In Fixed Bed Reactor

Since the technology of oxidative dehydrogenation (ODH) of butene has been considered an effective method for producing raw material of rubber-butadiene-in industry, it is extremely important to explore ODH of butene process for rubber industry. ODH of butene in fixed bed reactor is a typical gas-solid catalytic reaction process and its multi-scale interaction can affect the performance of fixed bed reactor. In order to understand the action mechanism among differnet scales in detail and instruct expeditiously the optimization of fixed bed, a multi-scale gas-solid model was developed to calculate the multi-scale effect in ODH of butene fixed bed reactor. Moreover, this work also built a monolith reactor model. Basing on above two model, the reactor performance between monolith reactor and fixed bed reactor were compared.First of all, a single particle model was establish and then it can be validated by comparing the experimental data. After validation, the model successfully investigated the diffusion phenomena inside particle, which the simulation results show an obvious intraparticle transfer exists and reacion process within particle is mainly restricted by particle diffusion. In addition, the time of unstable state within particle is so short that it can be neglected in industry. Intraparticle transfer resistance has a significant effect on intraparticle species concentrations but a minimal effect on pressure and temperature inside catalyst. The model also can be used to predict the influence of parameters such as particle diameter, operating pressure and operating temperature to intraparticle diffusion. It reveal that increasing diameter can increase the intraparticle transfer resistance yet cannot change the external transfer resistance and the intraparticle transfer resistance can be regarded as zero at dp<0.5mm. Besides, the particle transfer resistance is not affected by changing operating pressure. Although the higher operating temperature leads to the larger intraparticle transfer resistance and particle surface temperature, it can not change particle surface species concentrations and pressure. At the end of this chapter, the single particle model is able to be simplify at the base of front simulation.Secondly, using the mechanism of parameter passing, a multi-scale model for ODH of butene fixed bed reactor was developed via coupling the simplified single particle model with the porous medium model. The model was validated after the simulated result was compared with Ergun equation and experiment data. Subsequently, the advanced model can compute the diffusion effect and the influence of parameters to flow field in reactor. The computations certify the particle diffusion effect has a great influence on species mass fraction and temperature field. Because of the self-stability of fixed bed reactor, there are three typical oxidative dehydrogenation operating zones along the axial direction in the fixed-bed, namely, the bottom of transport-controlled, the middle intermediate transition and the top of reaction-controlled zones. The diffusion effect can be ignored at the top of reaction-controlled zone. Particle diameter, space velocity, and wall temperature will change the distribution of flow field in reactor, but catalyst diameter make no difference to temperature field. Moreover, particle diameter, space velocity, and wall temperature will have an effect on the conversion of butadiene.Finally, this text simulated a monolith reactor model for ODH of butene. Basing on the monolith reactor model and the above multi-scale model, the performance of the monolith reactor and conventional fixed bed were compared by model simulation. The compared results reveal that the monolith reactor has the higher efficiency and it can improve the selectivity of butadiene. However, the internal temperature of monolith reactor is uncontrolled due to the poor heat transfer property.