Process for preparing ethylene and propylene

A process 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° C. and retrieving an olefinic product stream comprising:
• ethylene and/or propylene, and
• a C4+ hydrocarbon fraction, comprising paraffins, normal olefins and iso-olefins;
• a1) dividing the C4+ hydrocarbon fraction into a first part and a second part;
• b) recycling a first part of the C4+ hydrocarbon fraction to step (a);
• c) subjecting a second part of the C4+ hydrocarbon fraction to an etherification process with methanol and/or ethanol wherein 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;
• d) separating at least part of the etherification product stream into at least an ether-enriched stream and an iso-olefin-depleted C4+ hydrocarbon stream;
• e) withdrawing at least part of the iso-olefin-depleted C4+ hydrocarbon stream from the process to purge part of the paraffinic C4+ hydrocarbons;
• f) converting at least part of the tert-alkyl ether in the ether-enriched stream to ethylene and/or propylene by contacting at least part of the ether-enriched stream with a molecular sieve-comprising catalyst at a temperature in the range of from 350 to 1000° C.