| Propylene is one of the basic raw materials of petrochemical industry,and it can be produced many kinds of organic chemical products.However,the propylene which produced by steam cracking and catalytic cracking naphtha has been in short supply,and the catalytic dehydrogenation of propane technology has become a hot research in the present.Pt based catalyst has been widely applied in the propane dehydrogenation for its high activity and selectivity,and the coke formed on Pt catalysts affects the propane dehydrogenation performance and service life of catalyst.Therefore,this article mainly studied the nature of coke on Pt-based catalysts,kinetics of coke formation and regeneration performance for the propane dehydrogenation.Fristly,Pt3Sn/Al2O3,PtSn/Al2O3,PtSn2/Al2O3 and PtSn3/Al2O3 catalysts with different Sn addition amount were prepared in this work.The results of BET and TEM characterization showed that Pt3Sn/Al2O3 catalyst has the largest specific surface area,the highest dispersion degree and the smallest average particle size.Next,the influence of different Sn addition on dehydrogenation performance of the catalyst has been studied,and with considering various factors,the Pt3Sn/Al2O3 catalyst was selected as the studying object.This article also studied The effect of different reaction conditions on Pt3Sn/Al2O3catalyst in propane dehydrogenation,and selected reaction temperature for 600°C,hydrogen atmosphere,H/C for 1:4,propane WHSV for 4 h-1 as the best reaction conditions.The initial conversion rate of Pt3Sn/Al2O3 catalyst under this condition was40.05%.At the same time,Four propane dehydrogenation reaction models were deduced based on Langmuir-Hinshelwood mechanism for heterogeneous catalytic surface reactions,the kinetic parameters of the model were obtained by fitting the equation?II?with experimental data,the results showed that the model?II?had the best fitting effect,in the end,the multiple correlation coefficients?2 and F-distribution were used to check the model?II?,and the results showed that the F>10F0.05,?2>0.90,it also showed that the model is credible in the 95%confidence level.Then the coke properties of the catalyst were researched with different Sn addition,reaction conditions and metal particle diameters.This study found that the carbon graphitization degree of the catalyst increased continuously with the increase of Sn addition,the decrease of content of H2 in raw materials and the propane WHSV,and also the decrease of the metal particles size.The carbon kinetics of Pt3Sn/Al2O3 catalyst with different reaction temperature and different propane WHSV was studied by power law model.This study has shown that for the carbon deposition on the catalyst under different temperature process,with the increase of temperature and propane WHSV,the carbon amount on catalyst and the initial carbon deposition rate are increased,and the deactivation constants are in an irregular change trend,this may be due to the deactivation caused by different reasons.Finally,the influence on the catalyst activity with different regeneration conditions were investigated.By observing the Pt3Sn/Al2O3 catalyst activity after regeneration at different regeneration conditions,and the regeneration temperature for 520°C,air WHSV for 4 h-1 and regeneration time for 2 h were selected as the best regeneration conditions.Also,the influence of regeneration cycles on catalyst activity were investigated.It is found that the activity of dehydrogenation catalysts is reduced through the characterization of regenerated catalyst,but the selectivity of propylene increased with the increase of regenerative cycles. |
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