Research On The Reaction Condition Optimization For Ethene Oligomerization To Synthesize Gasoline Components Over ZSM-5 Catalyst In Methanol Synthesis Gasoline

At present,in our country,the industrialization of methanol synthetic ethylene or propylene(MTP and MTO)from domestic coal chemical industry is already in the leading position in the world.Particularly,catalytic oligomerization is more relevant in processes that upgrades light olefinic gases into hydrocarbons in the gasoline(C5-C10)and diesel(C10-C20)ranges,such as the MOGD process(mobile olefin to gasoline and distillate).Olefins oligomerization is a significant process with impact in many chemical and petrochemical processes such as methanol to gasoline(MTG)and Fischer-Tropsch synthesis which base on chemical processing of coal to synthesize liquid fuel.It is different from the traditional petrochemical industry of naphtha cracking to liquid fuel which the components from large molecules to small molecules.In this paper,the process optimization,reaction mechanism and reaction kinetics of olefin oligomerization system on ZSM-5 zeolite catalyst were studied.The main research contents include two aspects.In the first part,ethylene feed alone,the optimization of olefin oligomerization process in MTG condition are performed in the isothermal fixed bed reactor with an internal diameter of 0.08 m and a total length of 0.4 m.There are three different kinds of xZSM-5 catalyst with Si/Al ratio of 46,81,150 are used,x indicate the ratio of Si/Al.The catalyst,with particle size of 60-80 meshes to avoid heat transport limitations and eliminate the effects of internal diffusion,located in the isothermal part of the reactor.The upper and lower part of reactor was filled with quartz sand to get a plug flow of the feed.The experimental data was obtained under the following conditions:temperature,between 250-550?;space time is designed for each different ZSM-5 to avoid too high or too low ethylene conversion.The experimental results show that the high conversion of ethylene and high selectivity of gasoline components obtained over the 46ZSM-5.However,there are a large amount of strong acid site on the ZSM-5 with lower Si/Al ratio,hydrogen transfer reaction is stronger and high selectivity of alkane obtained.Increasing with reaction time,a part of acid site on the catalyst surface covered by coke,the catalytic activity of the catalyst and the conversion of ethylene decreased,catalyst deactivation.Hydrogen transfer is inhibited the selectivity of propene and butene increased.With increasing space time,the contact time between ethylene and catalyst extended,the conversion of ethylene increased,the products distribution towards high carbon number.But,the secondary reactions intensified and the content of low-carbon alkanes in the product increased.Due to the effects of thermodynamics and kinetics,under low temperature(<573K),the reaction rate is slow,and the conversion of ethylene is difficult to improve.With the increase of temperature,ethylene conversion increases first then decreases,which indicates that ethylene oligomerization has an optimum reaction temperature.The effect of pressure on the conversion of ethylene is very significant.With increase of pressure,ethylene conversion and aromatics yield increased,but the yield of alkanes are also greatly increased.At high temperature,low pressure,appropriate space velocity,high conversion of ethylene obtained,secondary reactions inhibited,improve the content of gasoline components in the product.In the second part,ethylene oligomerization was used as model reaction for discussing the kinetic modeling of olefin oligomerization in MTG.The experiments performed in the isothermal fixed bed reactor and the experiments data for kinetic modeling are obtained.The 46ZSM-5 catalyst was used.The kinetic data was obtained under the following conditions:temperature,between 320? and 550?;pressure,latm;partial pressure of the feed,18.4 kPa;space time,0.03-0.133 h,35 groups of experimental kinetic data were measured.According to the change of ethylene conversion and the yield of each product,the reaction mechanism and pathway of upgrades light olefinic gases into gasoline components are explored.On the basis of the reaction pathway,nine reaction rate equations which describe the pathway of light olefins oligomerization summarized.Based on the simple lumped reaction pathway,the reaction model of light olefins oligomerization was established with group of isomers.Total 11 reaction rate constants were calculated through kinetic experimental data.The kinetic modeling can reproduced the experimental results.