Vaporizing acetic acid in the presence of hydrogen to provide a vapor feed stream for a hydrogenation process that produces ethanol. The vaporizer forms a vapor feed stream and a blowdown stream having a weight ratio of the vapor feed stream to the blowdown stream of at least 2:1. The acetic acid may vaporized at a temperature below acetic acid's boiling point at the operating pressure of the reactor. The hydrogenation process produces a crude ethanol product and ethanol is separated from the crude product. In addition, at least one recycle stream comprising acetic acid and less than 1.0 wt. % compounds having a boiling point higher than acetic acid, may also be separated. The recycle streams may be introduced to the vaporizer along with acetic acid to form the vapor feed stream.