Investigation Of The Coupled Reaction Of Methyl Acetate And N-Hexane Over HZSM-5

At present,steam cracking was one of the most important processes for light olefins and aromatics production in petrochemical industry.Light alkanes and naphtha were widely used as raw feedstocks in steam cracking.After decades of development,steam cracking had become a very proven technique.However,steam cracking was an endothermic reaction operated at very high temperature?about 650 ^oC?.Very large amount of energy consumption was still the main problem.If we couple strong exothermic reaction with strong endothermic reaction will present another route to solve the high temperature of thw steaming cracking.The research idea of this thesis could be devided into the following two aspects:Firstly,coupled reaction of methyl acetate and n-hexane was carried out over HZSM-5 catalyst in fixed bed reactor.Combining the strongly exothermic methyl acetate conversion with the strongly endothermic cracking reaction of n-hexane resulted in the coupling of heating.Second,methyl acetate had a carbon-oxygen double bonds and was a"hydrogen-deficient"compound.While n-hexane,as a"hydrogen-rich"compound,had a large amount of hydrogen.The reaction of these two reactants,besides the thermal coupling effect,must have some form of elemental coupling effect.The main research contents and conclusions were summarized as follows:The systematical changes of product distribution in the coupled system were observed.Under most reaction conditions,Olefins and C₅₊selectivity were remarkably improved while alkanes,H₂,CO and CO₂ selectivity decreased.These results indicate chemical coupling effect was presented in the reaction system.And these changes of selectivity were consistent with the"hydrogen deficiency"characteristics of methyl acetate and the"hydrogen rich"characteristics of n-hexane.On the Si/Al=19 HZSM-5 molecular sieve,the initial n-hexane conversion of the coupled system reached 100%at 300 ^oC.At this time,the initial conversion of n-hexane in the individual system was only 58.9%.The TPSR was used to investigate the trend of n-hexane in two reaction systems.It was found that the addition of methyl acetate significantly decreased the initial cracking temperature of n-hexane,which in turn promoted the conversion of n-hexane,and at the same time exacerbated the aromatization of n-hexane.The extremely high activity of methyl acetate resulted in rapid deactivation of the catalyst,while the deactivation was alleviated after addition of n-hexane.By GC-MS analysis of the carbonaceous species,we found that the addition of n-hexane changed the precursor of carbon deposits formed on the molecular sieve by methyl acetate,which also provided evidence for the study of the reaction mechanism of the coupled system.Combining the product distribution of methyl acetate at lowtemperature and in-situ IR analysis of three reaction systems,we proposed a possible reaction mechanism of coupling of n-hexane and methyl acetate on the HZSM-5.