Beyond Water: Expanding the Spectrum of Efficient Large Scale Separations

Innovations in membrane materials, structures, modules and system design have fundamentally changed the water purification industry over the past four decades. Revolutionary reductions by a full order of magnitude in energy consumption per unit of delivered product were achieved by substituting pressure-driven processes in place of traditional thermally-driven separation systems. Scalability has also been achieved, with state-of-the-art membrane plants delivering over 50 million gal/day of pure water. More recently, this revolution has begun to spread beyond water to more difficult-to-separate gaseous species differing by 0.5Å or less between permeated and rejected components. Oxygen-nitrogen separation, hydrogen and natural gas purification and monomer capture and recycle typify these extensions. Besides more demanding size discrimination than needed for water purification, more aggressive feeds must also be treated in these nonaqueous cases. Realistically expanding the separation spectrum, therefore, requires a new generation of nanostructured materials ranging from pure inorganics to metals and carbons, rather than conventional organic polymers favored for aqueous systems. Revolutionary materials alone are not enough, since evolution of module manufacturing platforms and seamless integration of these more efficient devices into existing systems via process modeling must also occur. Besides membranes, other low energy intensity approaches like sorbents will also be considered to illustrate options for orderly transition paths to a healthy lower energy intensity chemical industry based on conventional and alternative feedstocks.