Catalytic Performance Of Modified Zeolite For Methanol To Aromatics

As a widely used basic chemical,aromatics are mainly produced through catalytic reforming of petroleum resources.Due to the shortage of domestic oil resources,combined with the energy structure framework of"poor oil,less gas and relatively rich coal",it is of great strategic significance to carry out the research on the production of aromatics from coal-based methanol.As an important technical route of coal chemical industry,coal based methanol to aromatics has attracted extensive attention.However,because the reaction process is affected by side reactions such as hydrogen transfer,the effective utilization rate of carbon atoms is generally low,which greatly affects the development of coal based methanol to aromatics technology.In order to solve the above bottleneck problems,this paper puts forward two ideas that can promote the aromatization of coal based methanol,carries out detailed research,and makes the following progress:（1）The one-step reaction of methanol to aromatics is decomposed into two-step reactions of methanol to light olefins and light olefins to aromatics,and SAPO-34 and Zn/ZSM-5 are designed as matching catalysts for the above two-step reactions.Through the investigation of the loading methods and loading ratios of the two catalysts,it is found that when SAPO-34 and Zn/ZSM-5 are loaded up and down in a ratio of 1:9,the aromatization process is promoted by the low-carbon olefins produced by SAPO-34 in the upper layer on Zn/ZSM-5 in the lower layer,and some low-carbon alkanes are also converted to aromatics.Finally,the aromatics selectivity of the two-step reaction can reach 80.0%,It is much higher than 64.9%when Zn/ZSM-5 is filled alone.Moreover,since the light olefins of the upper catalyst entering the lower catalytic bed can promote the"olefin cycle"and inhibit the generation of C₉+in the"aromatics cycle",the selectivity of BTX in the two-step reaction reaches 56.7%,which is much higher than 32.0%when Zn/ZSM-5 is filled alone.（2）CO₂ is used as the hydrogen atom acceptor in the process of coal based methanol to aromatics,which is fed together with methanol to reduce the probability of hydrogen transfer reaction and improve the selectivity of aromatics.Combined with various characterization methods,the effects of ZSM-5 with different Zn introduction methods on the aromatization properties of methanol coupled CO₂ co feedstock were studied.It is found that Zn/ZSM-5obtained by different Zn introduction methods can improve the selectivity of aromatics.It is proposed that the aromatics selectivity is affected not only by aromatization ability,but also by CO₂ adsorption and activation ability in the reaction of methanol coupling CO₂ co feed to aromatics.It is proved that on Zn/ZSM-5,Zn O is the active center for activation and conversion of CO₂,and Zn OH⁺is the active center for aromatization.By optimizing the proportion of the above two active centers,the final aromatics selectivity can reach 85.2%,which is much higher than 71.4%when methanol is fed alone.