Process for preparing C2- to C4- olefins from a feed stream comprising oxygenates and steam

Process for the preparation of C2- to C4-olefins from a feed stream comprising vapor-form oxygenates and steam and having a temperature of from 280 to 480° C., which is passed through at least one fixed-bed zone (3) arranged in a reactor (2) and formed from a bed of granular, shape-selective zeolite catalyst of the pentasil type, and the oxygenates are converted catalytically into olefins with high selectivity for lower olefins at a reaction temperature of from 350 to 550° C. and the reaction mixture exiting the reactor is separated into a first product stream comprising C2- to C3-olefins and inert gas components, at least one further, second product stream comprising C4+-olefins, and a third product stream consisting of aqueous phase, characterized in that a reaction pressure of from 1.0 to 3.0 bara prevails at the entry of the feed stream into the fixed-bed zone (3) and a reaction pressure of from 0.5 to 2.0 bara prevails at the exit of the reaction mixture from the fixed-bed zone, and the temperature of the catalytic reaction is regulated in accordance with a target temperature value in the range from 440 to 520° C. specified for the reaction mixture exiting the fixed-bed zone by means of a supplementary stream comprising C4+ olefins and inert gas components fed into the feed stream, wherein the target temperature value for the reaction mixture exiting the reactor is measured by means of a temperature sensor beneath the catalyst fixed bed and the temperature of the feed stream entering the reactor and flowing through the catalyst fixed bed is measured by means of a temperature sensor arranged above the catalyst mixed bed.