Membrane processes are receiving increasing attention in the scientific community and in industry because in many cases they offer a favorable alternative to processes that are not easy to achieve by conventional routes. In this context, membranes made with perfluorinated polymers are of particular interest because of the unique features demonstrated by these materials. Both highly hydrophobic and hydrophilic membranes have been developed from appropriate perfluoropolymers that were, in turn, obtained by copolymerizing TFE with special monomers available on an industrial scale. Highly hydrophobic membranes obtained from the glassy copolymers of TFE and 2,2,4-trifluoro-5 trifluoromethoxy-1,3 dioxole (Hyflon AD) exhibit properties that make them particularly well suited for use in optical applications, in the field of gas separation, and in gas-liquid contactors. Conditions for preparing membranes that are adequate for use in various applications are exemplified. Hydrophylic highly conductive proton exchange membranes obtained from the copolymer of TFE and a short-side-chain (SSC) perfluorosulfonylfluoridevinylether (Hyflon Ion) find interesting application in the field of fuel cells, especially in view of the current tendency to move to high temperature operation. The advantages offered by these hydrophobic and hydrophylic perfluorinated materials for use in membrane technology are discussed. Comparison of membrane properties and performance is made with other membranes available on the market.

The transient response of the enriching section of a packed distillation column to a step change in the reflux ratio was investigated. The solution in the case of a straight-line equilibrium curve was adapted to the real case ( w i t h a nonlinear equilibrium curve). This solution gives the liquid concentration, x, at any height of column, z, after the step change in the reflux ratio, in the form of a series of exponential functions of the time, f :where the S,'S are negative constants which depend only on the parameters characteristic of the final steady state, but not on the magnitude of the step disturbance, and.the coefficients C,'s depend on z only. A series of exponential terms is a convenient form of the solution for computing transfer functions,