a process to prepare an olefin from its corresponding alcohol is improved by reacting , under reaction conditions including a first temperature , an aliphatic alcohol and , optionally , diluent water , to form a reaction product including at least a dialkyl ether . the product is then reacted again , under higher temperature to complete the dehydration of the dialkyl ether to the desired olefin . this process is particularly suitable to prepare ethene from ethyl alcohol . the stepped temperature scheme serves to reduce the formation of byproduct aldehydes , which in turn reduces coke formation , fouling , and the need to handle large amounts of water , thereby lowering energy and capital costs .