Study On Multi-scale Simulation Of Autothermal Fixed-bed Reactor For Oxidative Dehydrogenation Of Ethane To Ethylene

As a basic organic chemical raw material,ethylene plays an important role in chemical production and national economy.In recent years,with the increase in shale gas production in the United States,China’s ethane imports have continued to expand,and the process of producing ethylene using ethane as a raw material has received widespread attention.The traditional thermal cracking method has inherent disadvantages such as high energy consumption and large amount of carbonacious deposition,and has limited production prospects.The oxidative dehydrogenation of ethane（ODHE）method has become a highly competitive process route due to its advantages of self-heating behavior and lower carbonacious deposition.The development of efficient novel fixed-bed reactor is the key to realize this technical route.The fixed-bed reactor involves multiple chemical technological processes such as fluid flow,heat and mass transfer,homogeneous and heterogeneous chemical reactions,and traditional design methods are difficult to meet the design and development requirements of the novel fixed-bed reactor.In this work,a multi-scale simulation method was used to study the ODHE process based on Pt-based catalysts from micro-kinetics,catalyst particle scale and reactor scale.The knowleages on heat transfer,mass transfer and catalytic reaction kinetics of the ODHE process at different scales were obtained,which laid the foundation for the development and design of industrial reactors.Using kinetic Monte Carlo method（KMC）,the existing ODHE heterogeneous elementary reaction model was simulated and studied,and the different reaction paths were compared and analyzed.The main characteristic reactions were screened out.The reaction network was simplified reasonably.The reaction network before and after the simplification was coupled with the CFD model to predict the distribution of the flow field around the catalyst particles under the same conditions.The results showed that the simplified reaction network model could still more accurately predict the reaction and heat transfer behaviours.The discrete element method（DEM）was used to construct a complex bed structure with randomly stacked particles.Based on the computational fluid dynamics（CFD）method,through coupling the simplified microscopic reaction kinetic network,the homogeneous and heterogeneous catalytic reaction and transfer processes in the ODHE process were coupled and simulated at the catalyst particle scale to achieve quantitative description of the local flow,heat transfer and mass transfer process of fluids in the catalyst bed,and the influences of operating conditions on the local reaction and heat transfer process in the bed were studied.An industrial scale reaction-flow-heat transfer coupling calculation model was established using a porous media model,the characteristics of the ODHE reaction at the macro-reactor scale were studied,and industrial-grade reactor design was carried out according to the above obtained rules.By examining the effect of process conditions on reactor performance,efficient conversion of substances and effective control of reaction temperature were achieved.According to the research results in this work,the fixed-bed reactor with an annual output of 100,000 tons of ethylene was designed.The ODHE reaction was carried out under the conditions of inlet flow rate of 2 m/s,temperature of 783K,pressure of 0.12 MPa,and the feed molar ratio of M_C2H6:M_O2 of3:1.The system would not require an external heating source,could achieve the production with high conversion and high selectivity.