Multi-Stage Fluidized Bed for Methanol to Aromatics

The conversion of methanol to aromatics (MTA) was expected as an alternative route to meet the increasing demand of aromatics in China. It is of importance since the technical route is crucial to China, which lack oil but was rich in coal. MTA process involves a series of consecutive reactions according to the hydrocarbon pool dual cycle concept. But, all of these reactions are mutually interactive and fully coupled in a single reactor. Apartment from aromatics, MTA process could producelarge amounts of olefinic intermediates and paraffinic by-products, especially with the reduction of catalyst acidity in reaction-regeneration cycles. The further conversion of non-aromatics products could improve the total aromatics yield. However, their conversion characteristic varied and depended on reaction temperature and acidic sites over zeolite. The characteristics of secondary conversion of MTA products with time was crucial to design reaction process and was investigated in a wide temperature range. It was clarified that the possible path of secondary conversion process of intermediates products depended on temperature and acidity. Corresponding products from different processes were determined. Based on these results and considering the variation of the temperature and acidity of catalyst during the fluidized bed reaction-regeneration cycle, the multi-stage fluidized bed process was proposed for three-step conversion of methanol for high-yield aromatic production. In this concept, the fresh catalyst characterized by high temperature and strong acidity from regeneration reactor flowed into the second stage of fluidized bed for the conversion of olefins and alkanes at high temperature of 550 ^oC. The partial deactivation of catalyst from the second stage overflowed into the first stage of fluidized for MTA at 470 ^oC. The spent catalyst with medium acidity from the first stage was lift into the third stage for deep conversion of olefins at 470 ^oC. The fresh and mold Zn/ZSM-5 was used in this study and packing with each stage for simulate the proposed concept. The experimental results suggested that the yield of aromatics reached as high as 66% and its increase was about 10% in comparison of the result in the first stage.The undesired propane decreased obviously as is hoped by controlling the hydrogen transfer reaction and enhancing the dehydrogenation of alkanes.