Process for preparing ethylene and propylene

The present invention provides aprocess for preparing ethylene and/or propylene, comprising the steps of a)contacting a stream comprising C4+ olefins with a zeolite-comprising catalyst at a temperature in the range of from 350 to 1000 DEG C and retrieving an olefinic product stream comprising: ethylene and/or propylene, and a C4+ hydrocarbon fraction, comprising paraffins, normal olefins and iso-olefins; b) subjecting at least part of the C4+ hydrocarbon fraction to an etherification process with methanol and/or ethano lwherein at least part of the iso-olefins are converted with methanol and/or ethanol to an tert-alkyl ether, and retrieving an etherification product stream; c) separating at least part of the etherification product stream into at least an ether-enriched stream and an iso-olefin-depleted C4+ hydrocarbon stream; d )withdrawing part of the iso-olefin-depleted C4+ hydrocarbon stream from the process to purge part of the paraffinic C4+ hydrocarbons; e) recycling another part of the iso-olefin-deple