The invention provides a process for preparing an olefin, comprising: (a) reacting an oxygenate, in a reaction zone in the presence of a molecular sieve catalyst, at a temperature from 350 to 1000° C., to produce a effluent stream, comprising at least oxygenate, olefin, water and acidic by-products; (b) cooling the reaction effluent stream by an indirect heat exchange to a temperature greater than the dew point temperature of effluent stream; (c) further rapidly cooling the effluent stream to a temperature lower than the dew point temperature of the effluent stream by direct injection of an aqueous liquid into the effluent stream, to form a quench effluent stream; and (d) passing the quench effluent stream into a quench tower and contacting the quench effluent stream with a second aqueous liquid in the presence of at least one set of internals, to produce a quench tower gaseous stream comprising the olefin.