In a process for producing ethanol, acetic acid is contacted with hydrogen in a reaction zone in the presence of a hydrogenation catalyst to form a crude ethanol product comprising ethanol, hydrogen and carbon monoxide. At least a portion of the crude ethanol product is separated to yield a vapor stream and a liquid stream, wherein the vapor stream comprises hydrogen and carbon monoxide, and wherein the liquid stream comprises ethanol. At least a portion of the vapor stream is contacted with a methanation catalyst under conditions such that carbon monoxide reacts with hydrogen in the vapor stream portion to produce a treated stream comprising methane, hydrogen and less carbon monoxide than the vapor stream. At least a portion of the treated stream is returned directly or indirectly to the reaction zone and ethanol is recovered from the liquid stream.