High Flux Carbon Membranes for Water Desalination

Freshwater flux and energy consumption are two important benchmarks for the membrane desalination process. In this talk we show that a nanoporous carbon composite membranes, comprising a layer of porous carbon fiber structures grown on a porous ceramic substrate, can exhibit 100% desalination effect with 3 to 20 times higher freshwater flux compared to existing polymeric membranes. Thermal accounting experiments found the carbon composite membrane to save over 80% of latent heat consumption. Theoretical calculations combined with molecular dynamics simulations revealed the unique microscopic process in the membrane. When the salt solution is stopped at the openings to the nanoscale porous channels and forms a meniscus, the vapor can fast transport across the narrow gap to condense on the permeate side, driven by the chemical potential gradient and aided by the unique smoothness of the carbon surface. The high thermal conductivity of the carbon composite membrane insures that most of the latent heat is recovered.