| Propylene is the main chemical component of a range of chemicals and plastics in modern chemistry,and the level of a country's chemical industry is usually measured by the amount of propylene produced.In recent years,with the rapid growth of the demand for propylene and the increasing demand for propylene derivatives in the industrial market,the shortage of propylene is obvious and the supply and demand relationship is very tense.In the traditional process,propylene production is mainly based on petroleum through steam cracking and catalytic cracking.This has to do with a lot of energy consumption and a lot of carbon dioxide emissions,and these production routes are too dependent on dwindling fossil resources to meet the growing demand for propylene.Therefore,with the increasing shortage of oil resources and the oppression of the global energy crisis,the search for alternative energy and the development of non-oil-based propylene production technology is extremely urgent.With the increase of natural gas exploitation and proved reserves,many researchers are also engaged in the study of natural gas as raw material for propylene production.Among them,the two-step methane-to-propylene reaction using platform molecules of halomethane is an ideal non-petroleum route for propylene production.The key of this route is the chloromethane to propylene reaction.Based on the similarity between the reaction of propylene from methyl chloride(CMTP)and propylene from methanol(MTP),we believe that zsm-11 with excellent MTP catalytic performance should also have good catalytic performance in the CMTP reaction.Therefore,this paper takes the preparation of propylene from chloromethane as the target reaction,ZSM-11 as the basic material,attempts to improve its catalytic performance through modification.The effect of modification on the structure and properties of ZSM-11 was investigated by various characterization methods,and the structure-activity correlation was established.The results show that H-ZSM-11 is partially dealuminized by F modification.Dealumination did not change the crystallinity and structural properties,but made the grains become irregular and smaller.In addition,the reduction of Si-(OH)-Al bridge bond resulted in a significant decrease of the amount of strong B acid in H-ZSM-11.The reduction of strong B acid sites inhibited the hydrogen transfer reaction,reduced the selectivity of alkane and high carbon products,and thus increased the selectivity of propylene.When the modified concentration of F is 0.04 M,the catalyst had the best reaction performance.When the modified concentration of F is 0.04 M,the catalyst show the best reaction performance.The conversion rate of methane chloride,the selectivity and yield of propylene are 92.1%,43% and 39.6%,respectively.However,dealumination reduces the stability of the catalyst and shortens its catalytic life.In order to inhibit catalyst deactivation and improve reaction life,we further adopted alkali solution treatment on the basis of F modification.Further alkali solution treatment can make the partially exhaled aluminum species re-enter the skeleton and form new acid sites.However,this acid site is relatively weak compared with the unmodified acid site and cannot be used as the active center of hydrogen transfer reaction,so it can still maintain high propylene selectivity.The structure of the catalyst is stabilized and the life of the catalyst is restored because of the re-entry of non-skeleton aluminum into the skeleton.When the concentration of alkali treatment is 0.05 M,H-ZSM-11 molecular sieve catalytic performance is best,the conversion rate of methane chloride,the selectivity and yield of propylene are 94.0%,46.2% and 39.1%,respectively.With the progress of reaction time,chloride methane conversion rate has been above unmodified molecular sieve and F modified molecular sieve,chloride methane conversion rate decline more slowly,After 10 h of reaction,the conversion rate of chloromethane is 86%. |
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