Comment Separation Processes

These highly selective membranes mimic biological ion channels

By Mary Page Bailey |

New membranes developed at Tufts University (Medford, Mass.; can effectively separate similar chemicals based on not only size but on electrostatic charge. “Currently, there are no commercial membranes that are designed to separate organic molecules of similar size but different chemical structure,” explains Ayse Asatekin, a chemical and biological engineering professor at Tufts. The membranes are created by coating a specialty polymer solution — a random copolymer of fluorinated methacrylate and methacrylic acid dissolved in methanol — onto a commercially available porous membrane. The polymer is synthesized in a single step via free-radical polymerization, which is an easily scalable process, explains Asatekin. She believes that this membrane-preparation process could be readily scaled up and adapted for commercial roll-to-roll manufacturing processes, enabling it to be installed into existing production sites with little modification.

What sets these membranes apart is the self-assembly of the polymer in solution to create micelles that form charged nanopores 1–3 nm in size (diagram). This enables a functionalized nanostructure that mimics biological pores, such as the ion channels that regulate the transport of chemicals in cell membranes. “Instead of using complex top-down methods to create these very small pores, we designed a polymer that will create them naturally due to its structure,” says Asatekin. While other membranes have achieved similarly sized functionalized nanopores, the membrane preparation methods were more complex and the resulting membranes suffered from low porosity, making them more challenging to scale up, she adds. Due to the highly functional nanostructure, the team observed extremely high levels of selectivity between similar-sized organic compounds that were differentiated by charge. The applications for such selective separations include purifying pharmaceutical ingredients, such as amino acids and antibiotics, and also biofuels-manufacturing processes that use emerging solvents, such as ionic liquids.

highly selective membranes

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