Effects Of Methanol Cofeeding On Reaction And Deactivation Performances For Light Olefin Production From Butene

Light olefins,such as ethene and propene,are key building blocks of morden chemical industry.With the rapid growth of market demands and the depletion of petroleum resources,it is imperative to develop new technologies and broaden the sources for light olefin production.On the other hand,with the continuous expansion of petroleum refining and steam cracking and the completion of the 'West-East Gas Transmission' project,the utilization of C4 hydrocarbon has become one of the hot spots in the petrochemical industry,and the importance of light olefin production from C4 hydrocarbon becomes increasingly prominent.Butene cracking is the key to the light olefin production from C4 hydrocarbon cracking,which follows the "dimerization-cracking" mechanism.C8 dimers were first formed through butene dimerization,then cracked into light olefins.To improve the selectivity of light olefins,catalysts with weak acidity were usually adopted in butene cracking,leading to general problems such as insufficient butene conversion activity and easy catalyst deactivation for C4 hydrocarbon cracking technology.The 'coupled methanol and hydrocarbon cracking' reaction of butene and methanol neutralized the reaction heat of butene cracking and methanol to olefin reaction.C5+ intermediates were first formed in the cofeeding reaction through methylation reactions of butene with methanol in the cofeeding reaction of butene and methanol,then cracked into light olefins,providing another pathway for butene conversion,which was a potential way to optimize the light olefin production from C4 hydrocarbon cracking from the mechanism level.The research in this thesis focused on the effect of methanol cofeeding on reaction and deactivation performances of light olefin production from butene cracking on ZSM-5 zeolite catalyst,aiming at improving the conversion activity of butene and prolonging the catalyst life.The main contents were as follows.1.Effects of methanol cofeeding on the reaction performances of butene.The effects of methanol cofeeding on conversion of butene and selectivity of the products were studied,along with the kinetics of butene conversion in butene cracking and cofeeding reaction of 1-butene and methanol.The mechanism of the enhanced performances caused by methanol cofeeding for light olefin production from butene was discussed.The results showed that significant improvements on the conversion of butene and production of light olefins were obtained when methanol was cofeeded.The cofeeding reaction could be divided into two stages along the catalyst bed.The methylation reaction in the first stage of the reaction which methanol joined the reaction was the primary cause for the enhancement.2.Correlation between the improvements caused by methanol cofeeding and the catalyst structure.The enhanced performances caused by methanol cofeeding for light olefin production from butene on NKF-5 zeolites with different silica-alumina ratios and NKF-5 zeolites modified by phosphorus and alkaline earth metals were studied.The relationship between the enhancement caused by methanol cofeeding and the acidity and pore structural properties of the catalyst was discussed.The results showed that the enhancement caused by methanol cofeeding was closely related to the structure of the zeolite catalyst,and the enhancement caused by methanol cofeeding was more obvious on catalysts with weak acidity or low micropore area and volume.3.Effects of methanol cofeeding on coking deactivation of the catalyst.The coking deactivation process of the catalyst and the influence of coking on the catalyst structure were studied.The mechanism of the catalyst deactivation deferring caused by methanol cofeeding was discussed.The results showed that methanol cofeeding slowed down the loss of strong acid sites during the coking deactivation process of the catalyst and prolonged the catalyst life.The property of regional coking in cofeedinge reaction was the primary cause for the slowing of coking deactivation.4.Effects of catalyst hydrothermal deactivation on reaction performances of cofeeding reaction.The effects of steam treatment on the structural properties of zeolites were studied,along with the reaction performances of butene cracking and cofeeding reaction on steam treated catalysts.The enhancement caused by methanol cofeeding on steam treated catalyst was discussed.The results showed that methanol cofeeding improved the activity of butene conversion and the yield of light olefins on hydrothermal dealuminated catalysts.The reaction performance of cofeeding reaction was much better than butene cracking on hydrothermal dealuminated catalysts.