The Microkinetic Analysis Of Acetylene Hydrogenation Over PdAg/Al₂O₃ Catalyst

Selective hydrogenation of acetylene in ethylene-rich streams is an important process for the purification of ethylene product.Micro-kinetic method is helpful for building kinetic models applicable in a wide range of operation conditions with high accuracy.The modeling results can be used for designing and optimizing the hydrogenation reactor and process and the understanding of reaction mechanism.In this thesis,a micro-kinetic model of selective hydrogenation of acetylene over a commercial PdAg/Al₂O₃ catalyst was established based on DFT calculation results reported in the literatures.After adjusting the kinetic parameters according to the experimental data,the model can predict the kinetic behaviors quiet well.The micro-kinetic modeling results show that the most abundant surface species is C₂H₄*,the second abundant surface species is C₂H₂*and the rate determining step is the hydrogenation of vinyl group to form ethylene.A power-law kinetic equation is directly built from micro-kinetic analysis.Further,the effect of Ag on kinetic behaviors is studied through the micro-kinetic analysis.The result show that addition of Ag in the catalyst decreases the activation energy of hydrogen desorption,and then change the surface coverage of surface species and,therefore,the kinetic characteristic of acetylene hydrogenation reaction.With the increase of Ag addition,the reaction order to acetylene increases and reaction order to hydrogen decreases.