Catalytic Performance and Coking Behavior of a Submicron HZSM‐5 Zeolite in Ethanol Dehydration

The catalytic performance and coking behavior of a submicron ZSM‐5 zeolite in dehydration of ethanol to ethylene were investigated by means of low temperature nitrogen adsorption, thermal gravimetric analysis, and nuclear magnetic resonance. The submicron catalyst showed higher activity than the micron one due to more mesopores and more strong acid sites. As the reaction temperature increased, ethanol conversion increased over the submicron catalyst, while ethylene selectivity went through a maximum. The selectivities of propylene and butylene increased with increasing reaction temperature, and they decreased with time on stream at constant temperature. The coke deposits can be divided into coke precursor and hard coke, which were attributed to polyalkylbenzene and polycyclic aromatic hydrocarbons, respectively; and increasing reaction temperature can accelerate the transformation of coke precursor into hard coke. A precoking pretreatment method was verified very effective for improving the catalyst stability.