Coupled Aromatization Of Methanol/C₅-C₇ Alkanes Over HZSM-5 Catalyst

In our country,oil refineries aromatic hydrocarbon raffinate oil,reforming head oil,hydrogenated coking naphtha and and other low value-added light hydrocarbon resources.It was difficult for this kind of light to get a reasonable use,because their saturated vapor pressure is high and octane number is low,could not be used directly as the reconciliation of commercial gasoline.If made these low-octane light hydrocarbons a certain feaction,and mixed methanol to the reaction,finally obtained aromatics.The methanol coupled with light hydrocarbons to aromatics reaction could alleviate the status of excess methanol and broaden the source of aromatics production.At the same time,There were two different heating effect in the reaction of light hydrocarbons modification and methanol to aromatics,Light hydrocarbons modification reaction was a strong endothermic reaction,while methanol to aromatics reaction is a strong exothermic reaction.If the two reaction were coupled,which was beneficial to the heat complementarity and decreas energy consumption,and ultimately improve the economic efficiency of enterprises.In this paper,the effects of methanol coupled with light hydrocarbons reaction was investigated by using n-pentane,n-hexane and n-heptane as probes.And the effects of molar ratio of Si/Al catalyst on methanol coupling with light hydrocarbons was investigated.The effects of different metal oxides modified ZSM-5 on the reaction were investigated by using different metal oxides.Last,above parameters were determined,and then optimizated the process conditions.Firstly,the different molar ratio of Si/Al HZSM-5 catalyst（38,50,120,200 and 300）were investigated in the coupling reaction of menthanol/lighthydrocarbons in this paper.The study found that it was suitable for coupling to olefin reactions,but the conversion rate of n-hexane is low when Si/Al ratio is 200;the catalyst of Si/Al ratio was 50 suitable for coupling to aromatics reaction,the conversion rate of n-hexane was high.Selected Si/Al ratio was 50 catalyst to coupled aromatization reaction of methanol/n-hexane,the selectivity of gasoline and aromatics,the conversion rate of n-hexane were went up when reaction pressure from atmospheric pressure increased to 0.5MPa.Methanol could couple with pentane,n-hexane,n-heptane and cyclohexane to aromatics,the alkane conversion sequence was: n-heptane > n-hexane >cyclohexane > pentane.Secondly,four metal oxides（e.g.,ZnO,NiO,CuO and CoO）were loaded to modified HZSM-5 zeolite,all mass fraction of metal oxides was 2%.After modification with Zn O and CuO,HZSM-5 zeolite weak acid and mid-strong acid were increased,strong acid was reduced.And after modification with NiO and CoO,HZSM-5 zeolite weak acid and strong acid were reduced,mid-strong acid was increased.The HZSM-5 zeolite modified by Zn O showed a higher selectivity of C⁵⁺ and aromatics,and a better aromatization stability.Then the mass fraction of ZnO-loading was investigated,found that with the increase of mass fraction of ZnO-loading,HZSM-5 zeolite weak acid and mid-strong acid were increased,strong acid was reduced.When the mass fraction of ZnO-loading was 3%,the C⁵⁺ and aromatics had a higher selectivity and a better aromatization stability.Finally,In order to obtain a higher aromatics selectivity,the optimization of process conditions for coupled aromatization conversion of methanol/n-hexane over 3% ZnO/HZSM-5 catalyst were: 420℃ for reaction temperature,0.6 MPa for reaction pressure,1.0 h^-1 for WHSV,the n-hexane proportion in feedstock was 30%.After the deactivated catalyst regeneration,main performance could recovery to the state of fresh catalyst.The main reason for the deactivation of the catalyst was the formation of carbon deposition in the pores,leading to the clogging of the pores and the decrease of the acid concentration of the catalyst.