Comparative analysis of deactivation of the catalyst SAPO-34 for methanol conversion to lower olefins was carried out in fixed-bed flow reactors, in fluidized-bed reactors, and slurry reactors with the catalyst dispersed in a polydimethylsiloxane (PDMS) medium. It has been found that the deactivation rate of the catalyst essentially depends on the reactor type. The uniform contact of methanol with the fluidized catalyst makes it possible to increase by one and a half the on-stream stability compared with the fixed bed catalyst. However, the reaction run in the PDMS medium in the slurry reactor leads to significant acceleration of deactivation, which is due to high solubility of olefins and methanol in PDMS and results in an increase in the contact time of the catalyst with the reactants and products. A method has been proposed for measuring the solubility of gases in liquid polymers at high temperatures using mass-spectroscopic detection of effluent gases.