Separation of olefin vapor from liquid fraction to reduce fouling

A process for separating an olefin stream produced from an oxygenate feed into a vapor and liquid fractions, comprising:

• contacting the oxygenate feed with a molecular sieve catalyst to form an olefin stream;
• condensing a portion of the olefin stream to form an olefin vapor and a condensed liquid, wherein the liquid comprises water and molecular sieve catalyst particles;
• separating the olefin from the condensed liquid;
• adding hydrocarbon to at least a portion of the condensed liquid to effect separation of the condensed liquid fraction into at least an upper fraction and a lower fraction so the lower fraction contains a majority of the water and the molecular sieve catalyst particles present in the condensed liquid;
• and
• separating the upper fraction from the lower fraction.