In situ H-ZSM-5 zeolite deactivation study in dimethyl ether to hydrocarbons transformation reaction

Today, catalytic processes for the synthetic fuel components production are of considerable interest for both scientific and industrial area. The transformation of dimethyl ether into hydrocarbons is one of the possible solutions for the development of a closed hydrocarbon cycle, in connection with which a wide study of this process is an important task of modern catalysis. The transformation of dimethyl ether into hydrocarbons occurs with the formation of heavy polyaromatic hydrocarbons, which are deposited on the surface of active centers, which in turn prevents the further occurrence of chemical processes on their surface. This article presents a study of the deactivation of zeolite H-ZSM-5 by the thermogravimetric method in situ. The results of experiments carried out in the temperature range from to 300 to 400 °C are presented. The accumulation of carbon deposits in the first hour of operation indicates the presence of an induction period due to the formation of the first layer of carbon deposits. Linear decontamination occurs when the first five weight percent of carbon deposits accumulate. Further accumulation of carbon deposits up to eight weight percent leads to a sharp decrease in the rate of conversion of dimethyl ether into hydrocarbons to 0.08 kg (DME) / (kg (Cat) h). In the first hour of operation, aromatic hydrocarbons predominate in the reaction medium; with increasing time, the concentration of aromatic hydrocarbons decreases, and the concentration of light olefins and alkanes increases due to carbonization of the catalyst surface. The concentration of heavy aromatic hydrocarbons with a number of carbon atoms equal to or greater than eleven has a maximum after 240 minutes of reaction. The decrease in the content of heavy aromatic hydrocarbons after 240 minutes of reaction can be explained by the sharp loss of surface acidity due to carbonation.