CARBON COMPOSITE MEMBRANES - A SOLUTION TO ADVERSE HUMIDITY EFFECTS

While the separation properties of carbon molecular sieving membranes are superior to those of other materials, a significant drawback has b een their vulnerability to adverse effects from exposure to water vapo r. Since significant membrane function is maintained at low levels of exposure, efforts were focused on devising a means to lower the water activity at the carbon surface. This was successfully accomplished wit h the development of carbon composite membranes. These membranes consi st of a hollow fiber carbon membrane coated with a thin layer of certa in unique polymeric materials. The polymers are highly hydrophobic but do not prohibitively reduce the flux of other permeating species, and the resulting composite membranes are much more resistant to water va por effects. The performance of the composite membranes is analyzed in terms of the series resistance model. While small losses in selectivi ty and productivity occur as a result of the resistance added by the p olymer layer, the composite membranes are still very attractive as com pared to conventional polymer membranes. The polymer barrier type and thickness and the resulting degree of protection are variables that ca n be tailored in a controlled manner for specific applications.