a system using membranes for separating a desired component from a liquid or gas mixture to obtain a high - concentration organic solvent , such as in a plant for fermenting a biomass feedstock to produce ethanol . a module for removing water from the ethanol / water mixture comprises multiple vessels or elements connected together in series and supported by a frame . each element includes a number of flow tubes concentrically enclosing a tubular membrane leaving an annular space between the membrane &# 39 ; s outer wall and the flow tube &# 39 ; s inner wall . the preferred membrane is a hollow ceramic tube . an ethanol / water vapor is passed through the space between the tube walls , and a vacuum is pulled on the membrane &# 39 ; s hollow core . water molecules selectively move through the membrane . multiple passes through a series of elements having the concentric tubes and membranes gradually reduces the water content of the ethanol .