Studies On The Technology For Selective Conversion Of Methanol To Propene And Clean Gasoline

Propene mainly comes from steam cracking of naphtha and FCC unit as a by-product. However, with the rapid development of China’s economy, it has been difficult to meet the growing demand of propene with the two traditional approaches mentioned above. Besides, FCC gasoline with high sulfur content accounts for about 76% in the domestic commercial gasoline, which puts great pressure on the gasoline upgrading. Fortunately, our country is rich in methanol, thus developing the technology for selective conversion of methanol to propene and clean gasoline seems to be a potential way to solve the problems.In this study, the reaction rules of methanol conversion over the ZSM-5 catalyst were investigated preliminarily. Results showed that, improving reaction temperature and shortening residence time were beneficial to the production of light olefins such as ethene and propene, but the temperature could not be too high, otherwise the thermal decomposition of methanol would be too serious. Coke could significantly increase the yields of ethene and propene, but it had a weak effect on propene/ethene and could also lower the methanol conversion.Compared with the ZSM-5 catalyst, the ZSM-11 catalyst was more suitable for the reaction of methanol to olefins because it had the smaller HTI index and stronger olefin retention capacity. And the rules of methanol conversion over the ZSM-11 catalyst were investigated in the traditional turbulent/bubbling fluidized bed. Results showed that raising the reaction temperature could significantly improve the methanol conversion and propene yield, but inhibit the production of ethene. In addition, it was propitious to produce light olefins such as propene when shortening residence time or lowering reaction pressure or reducing the catalyst loadings. In the continuous reaction experiments, the regeneration temperature was reduced to cease coke burning. Results indicated that the coke content on the catalyst was just 1.83wt% after 23 hours’ continuous reaction, and the conversion and product distribution changed merely a little, which showed that the catalyst was strongly coke resistant.According to the ZSM-11 catalyst’s reaction characteristics, a novel reactor combined with the advantages of the traditional turbulent/bubbling fluidized bed and the riser reactor was designed. The technology for selective conversion of methanol to propene and clean gasoline was studied in this novel reactor. Results showed that, the stability of the ZSM-11 catalyst was excellent because it’s performance changed little after more than 270 hours’ reaction; Reaction pressure and the water content in the feedstock had a weak effect on the product distribution, but the upper temperature of the settler would affect the yields of light olefins significantly, so the separation of products and catalyst should be carried out as soon as possible in order to reduce the secondary reactions. Besides, different reaction materials and C4 recycle were studied in this paper. It was found that, on one hand, the yield of propene would be lower and the production of COx was promoted when using crude methanol, but the economic advantages, viz., the lower price of crude methanol could not be neglected, on the other hand, C4 recycle could not only reduce the lift medium consumption and the heat load but also improve the yields of propene and gasoline.