An oxygenate to olefins (OTO) process, comprising the steps of: (i) purifying an oxygenate feedstream comprising one or more ionic contaminants by contacting the feedstream with a membrane, resulting in the formation of a retentate and a permeate separated by the membrane, which permeate is a purified oxygenate stream which contains a lower ionic contaminant concentration than the original oxygenate feedstream; (ii) introducing the purified oxygenate stream into an oxygenate to olefins reaction zone; and (iii) contacting the purified oxygenate stream with a molecular sieve catalyst in the oxygenate to olefins reaction zone to form a product stream comprising olefins.