Study On The Catalysts For Catalytic Conversion Of Methanol To Propene And Gasoline Components In Fixed-Bed Reactor

In recent years,with the growing shortage and inferior quality of global oil resources,coutinuing research and development efforts focused on finding non-oil route for hydrocarbon production have received more and more attention.Among different alternative techniques being developed,Methanol-to-Hydrocarbon?MTH?route offers a desired solution,since the feed methanol for MTH can be readily manufactured from synthesis gas,which is easily produced by steam reforming of nature gas or gasification of coal or biomass.Generally speaking,this reaction is in accordance with characteristics of our energy structure of“rich in coal,poor in oil and less in gas”,which can effectively relieve the situation of shortage of oil resources;in addition,it can complete the process of low value-added methanol to high value-added propene or gasoline,which fundamentally relieve the pressure of supply of propene and gasoline.Therefore,it is of great significance to study and develop the coal-based technology of Methanol-to-Propene?MTP?with gasoline components as by-products.It is well known that MTP reaction is an acid-catalyzed and shape-selective reaction,methanol conversion,product distribution and catalyst regeneration depend strongly on the acidity and pore structure of the catalyst.The key factor of MTP reaction exists in how to effectively restrain secondary reactions like hydrogen transfer,polymerization and aromatization,realizing efficient utilization of CH₂ in methanol.However,the study of the nature of the catalyst used for MTP reaction is still not perfect.Thus,the effect of aluminum content on the catalytic performance ZSM-5 zeolite in MTP reaction was investigated preliminarily in this study.The results showed that with the reduction of aluminum content,both the amount of weak and strong acid sites decrease dramatically,and the peaks of weak and strong acid sites of the samples shift to higher temperatures,manifesting that decreasing the content of aluminum leads to a decrease in the acid strength of ZSM-5 zeolite.With the weaker acid strength of silanol nests in Silicalite-1 than that of the bridging hydroxyl groups in ZSM-5 zeolite,the secondary reactions like hydrogen transfer and aromatization are effectively inhibited,so as to make the higher propene selectivityand better catalyst stability.The catalytic performance of Silicalite-1 zeolite in MTP reaction was investigated in a fixed-bed reactor.The experimental results showed that increasing reaction temperature or weight hourly space velocity is beneficial to the production of ethene and propene,but the yield of gasoline is decreased.It is worth noting that the temperature could not be too high,otherwise the thermal decomposition of methanol would be too serious;likewise,the weight hourly space velocity could not be too high,otherwise the conversion of methanol could not be ideal.For the conversion reaction of methanol to propene with gasoline components as by-products,the optimum operational conditions are as follows:reaction temperature of450?,weight hourly space velocity of 9.6 h^-1,and at that time,methanol conversion was100 wt%and the yield of propene was 13.9 wt%.To prepare the fixed-bed Silicalite-1 catalyst,the nature of the support has a significant influence on the textural and catalytic properties of the catalyst.The influence of introduction of kaoline on methanol conversion and product distribution is minimal,and the mechanical strength of the S-1/Kaoline catalyst is enough,thus making kaoline the best one for catalyst shaping.A series of Ce-modified Silicalite-1 catalysts were prepared by incipient wetness impregnation method and characterized by XRD,N₂ absorption/desorption,FTIR and NH₃-TPD techniques.Their catalytic performance for the conversion reaction of methanol was tested in a continuous flow fixed-bed reactor at reaction temperature of 450?,weight hourly space velocity of 9.6 h^–1 and carrier gas flow rate of 20 mL?min^-1 under atmospheric pressure.The results showed that the introduction of Ce can effectively adjust the acid properties and pore structure of Silicalite-1 zeolite.An appropriate concentration of Ce modification can decrease the amount of strong acid sites on Silicalite-1,as well as its specific surface area and pore volume,hence making an increase in propene selectivity and catalytic stability from 31.9 wt%and 51 h to 38.2 wt%and 72 h,respectively.But the introduction of kaolin has failed to significantly improve its catalytic behavior in MTP reaction.