The invention relates to a process for the preparation of an olefinic product comprising ethylene and/or propylene from an oxygenate comprising: a) an oxygenate conversion step wherein a gaseous effluent comprising olefins is obtained; b) separation of water from the effluent; c) compression of the effluent; d) acid gas removal from the effluent wherein the water-depleted compressed gaseous effluent is treated with a caustic solution in a caustic tower and a non-aqueous liquid stream comprising one or more aromatic C7+ hydrocarbons is added to the caustic solution to control the formation of red oil; and e) separating the olefinic product from the gaseous effluent treated in step d).