Study On The Coupling Aromatization Reaction Of Methanol And N-Hexane

In recent years,the global methanol industry is in overall surplus,and the situation that supply exceeds demand is difficult to change.Therefore,It is urgent to develop methanol downstream routes to drive the harmonious development of the methanol industry.At the same time,there are many low value-added light resources produced by our country’s oil refineries（such as aromatics raffinate,reformed topping oil,hydrogenated coking naphtha,etc.）are difficult to be rationally utilized because of their low saturated vapor pressure and octane number.At the same time,some enterprises are experiencing a shortage of aromatic raw materials,resulting in low installation load and affecting economic benefits.The co-aromatization technology of methanol and light hydrocarbon can not only alleviate the current situation of overproduction of methanol,but also solve the problem that it is difficult to make full use of light hydrocarbon resources in China,so as to realize the rational utilization of resources,and provide technical support for the industrial layout optimization and product structure upgrading of methanol industrial chain upgrading enterprises.In this paper,HZSM-5 zeolite was used as the carrier to systematically study the coupling aromatization of low-carbon alkanes with methanol.The effects of different light hydrocarbons and different feed ratios on the performance of co-aromatization were investigated.After selecting the appropriate ratio of low-carbon alkanes to feed,HZSM-5zeolite was modified to obtain the coupling aromatization catalyst with better performance.The stability of the catalyst was investigated and the existing reaction mechanism was supplemented.Using methanol and different alkanes（n-pentane,n-hexane,cyclohexane,n-heptane）as raw materials,under the conditions of 400℃,0.25 MPa,2 h^-1,it was found that the conversion of methanol was not affected by the type of alkanes,and remained at about 99%,while the conversion of alkanes decreased with the increase of intermolecular bond energy of alkanes,and the selectivity of aromatic products increased with the increase of intermolecular bond energy of alkanes.The co-aromatization of methanol and n-hexane with different ratios was studied.At 400℃,0.25 MPa,2 h^-1compared with MTA,the addition of n-hexane does not affect the conversion of methanol,and can effectively inhibit the self decomposition of methanol and increase the selectivity of aromatics;compared with pure n-hexane aromatization,the feed forward reaction greatly reduces the selectivity of gases products,and improves the yield of oil phase products and the selectivity of aromatics.When the mass ratio of methanol to n-hexane was 7:3,the aromatics selectivity was the highest,which was 30.56%.Toluene and xylene were the main aromatics with the selectivity of 9.92%and 12.01%,respectively.HZSM-5 zeolite was used as the support,and the effects of Zn loading and the type of second metals（Mo,Cr,La,Ce,Ga）on the co-aromatization were further investigated.When Zn loading was 2%,the conversions of methanol and n-hexane was 99.19%,79.93%,respectively.Aromatics selectivity was 37.03%with toluene selectivity 9.10%and xylene selectivity 17.16%.When the optimum loading of Ga is 0.5%,the aromatics selectivity increases to 43.35%with selectivity of toluene and xylene 12.88%and 18.60%,respectively.The results showed that the optimum reaction condition is at 420℃,0.5 MPa,2 h^-1.In this case,the conversion of methanol and n-hexane was 99.30%and 89.3%,respectively.The selectivity of aromatics was 46.46%with the selectivity to benzene,toluene and xylene 1.57%,13.60%and 21.14%,respectively.Although the catalyst has good co-aromatization performance,its stability needs to be further optimized.