Abstract: Temperature-programmed methanol conversion was performed in a microscale fluidized-bed reactor and the deposited coke species formed during the reaction at different temperature ranges was analyzed. By combining effluent detection and measurements of confined coke species evolution with thermal analysis and GC/MS, a particular phenomenon that appeared in the methanol conversion was explained. Among the coke products, besides aromatic coke species, a new kind of coke compounds, multi-ringed alkanes, mainly composed of methyladamantane hydrocarbons were found in the low temperature range. The generation and accommodation of these adamantane hydrocarbons on the SAPO-34 catalyst suppressed the successive formation of hydrocarbon pool species, polymethylbenzenes, as the reaction center of methanol conversion, and caused the low activity of the SAPO-34 catalyst at low reaction temperature. In the temperature range of 300–350 ^oC, methylbenzenes and methyladamantanes were the main coke materials and they were transformed to methylnaphthalenes and polycyclic aromatics at higher temperature. The evolution of the confined coke compounds corresponded to the initial reactivity enhancement of the catalyst at 300–325 ^oC, the lowered activity at 325–350 ^oC, and recovered methanol conversion at 350–400 ^oC. Based on the coke analysis and catalytic performance tests, a new deactivation mechanism was proposed for the methanol conversion with the consideration of the abundant formation of adamantane hydrocarbons as the confined materials at low temperature.

Key words: methanol conversion, coke deposition, temperature-programmed reaction, hydrocarbon pool mechanism, deactivation, adamantane hydrocarbon