The effect of solutes on the pervaporation of water‐methanol mixtures through cellophane

The effects on permeation rate and permeate composition of the addition of sodium formate to mixtures of methanol and water pervaporating through cellophane have been examined. In general, the addition of the salt increased the water content of the permeate, but decreased the total rate of pervaporation and that of each of the components. The effect was greater in water‐poor feeds. The effect of the salt on the permeate composition was opposite to the expected effect on the relative volatility of the feed components. The possible causes of this “solute effect” are discussed.