Effects of binders on internal reaction process of single particle catalyst in methanol to olefin
Objective Heterogeneous catalytic reactions,such as Methanol to olefins(MTO),play an important role in the modern chemical industry.The study of reaction kinetics,mass and heat transfer of single-particle catalyst in the MTO process is helpful to under-standing catalytic reaction mechanism,optimizing catalyst design and realizing process upgrading.Methods The particle model,reaction kinetics model and mass and heat transfer model of single-particle catalyst were estab-lished.COMSOL Multiphysics 6.0 software was used to simulate the MTO reaction process,and the SAPO-34 zeolite catalyst particle model was established with silica,alumina and kaolin as binders,respectively.The methanol diffusion and temperature conduction processes within the catalyst particles were analyzed.The influences of binders on the concentration distribution of acid sites,polymethylbenzene and polymethylnaphthalene were studied,and the heat and mass transfer in catalyst particles were coupled with the chemical reaction.Results and Discussion The methanol quickly diffuses into the catalyst particles at the initial stage,and the methanol concentra-tion decreases from the edge of the particle to the middle and core of the particle at 100 seconds(s)due to the large concentra-tion difference between inside and outside the catalyst particles,during the diffusion process of methanol molecules into the cata-lyst particles.The highest methanol concentration is foundinside the particles with silica as a binder,so the binder silica has the greatest influence on the diffusion of methanol in the catalyst particles.During the MTO reaction process,the thermodynamic temperature distribution inside the three kinds of particles decreases from the center to the edge.The reaction temperature in particles with silica as the binder is the highest,and the thermodynamic temperature within the particles reaches the highest val-ues at 100 s,which are 656 K at the center and 627 K at the edge of the particles,respectively.The usage of silica as the binder for catalyst particles is more conducive to promoting the reaction within the particles.With the increase of MTO reaction time,the average acidic sites concentration of the three catalyst particles gradually decreases,and the particles with silica as the binder have the fastest decreasing rate,and the acidic sites concentration at the edge of the catalyst particles decreases the most.The average polymethylbenzene concentration of the three catalyst particles increases gradually,with the lowest average polymethyl-benzene concentration in the particles used silica-based binder and the fastest polymethylbenzene concentration at the edge.The concentration of polymethylnaphthalene within the three catalyst particles increases gradually,and the distribution of polymethyl-naphthalene within the particles is more uniform using silica as the binder.Conclusion Conclusion The mass and heat transfer processes inside catalyst particles formed by three kinds of binders and the influence of their chemical reaction processes are studied by numerical simulation.It is found that the MTO reaction in silica particles is more fully carried out,which exhibits more utilization efficiency of acid sites and more uniform carbon deposition distribution,compared with other particles.
methanol to olefinbindersingle particle catalystreaction kineticsmass transferheat transfer
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