Nano-engineered Membranes Might Change Chemical Engineering

Nano-engineered Membranes Might Change Chemical Engineering -- Separation processes, involved in almost all products, will benefit from new "reverse-selective" membranes.

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Research Triangle Park, NC, April 19, 2002 --Scientists have reported new nano-engineered membranes that could enable a new generation of highly efficient, highly selective separation devices for applications in petroleum, chemicals and fuel production, environmental cleanup, and perhaps even biomolecule purification. The new "ultrapermeable, reverse-selective nanocomposite membranes" are reported by RTI, N.C. State University, and industry scientists in Science magazine, 19-April-2002.

The research team found a way to make membranes through which large molecules permeate faster than small molecules do. Researchers achieved this counter-intuitive result by using nanoparticles, about 10 billionths of a meter in diameter, to modify the molecular structure of plastic membranes.

The first applications, already under development, include producing purified hydrogen for uses such as fuel cells, and cleaning pollution-causing chemicals out of fossil fuels.

"Separation processes are an integral part of producing just about any item you go into a store and buy," said Tim Merkel of RTI, first author of the paper. "We have demonstrated a novel way to make one of these processes better, faster, cheaper, and cleaner."

Previous attempts to use particles in industrial gas separation membranes ran up against a Catch-22. If the membrane became more permeable to molecules, then it also became less selective.

Merkel and his colleagues, however, found a way to have their cake and eat it too: they can increase the selectivity of the membrane and at the same time make it more permeable.

"Usually, people add particles to plastics to make them less permeable," Merkel said. "For example, additives in plastic wrap might be used to allow less oxygen through, keeping your food fresh longer. In our case, however, the particles work at a molecular level as 'nanospacers,' opening the membrane and making it more permeable"

Merkel is heading up a basic research project to figure out how to make the particles active.

"Right now, the particles just change the physical structure of the membrane," said Raghubir Gupta, who oversees RTI's energy technology laboratory "But what if we make them chemically active? Then we could fine-tune a membrane to pass or block specific chemicals. The possibilities are mind-boggling. For example, we could use enzymes and selectively separate proteins from mixtures in biochemical processes."

While the basic research on activated particles offers tantalizing possibilities, Merkel and colleagues at RTI emphasize the more immediate promise of a cheaper way to purify hydrogen.

"The existing processes to purify hydrogen are expensive and complicated," he said. "They do have the advantage of being well-established: people at, for example, oil refineries know how to make these processes work. But ours would be so much cheaper and simpler that you could even start to think about recovering hydrogen from hydrocarbon streams that refineries currently just burn as waste."

Cheap hydrogen also could diversify the sources from which the U.S. makes gasoline and diesel fuel.

"Cheap hydrogen, combined with a cost-effective way to remove pollution-causing chemicals, could be the key to a practical way to make motor fuels using coal as the starting point, rather than crude oil," Gupta said.

Merkel's Science paper is based on his Ph.D. dissertation, which he completed at N.C. State University in December 2001, while working part-time at RTI. His faculty advisor and co-author, Benny Freeman, has since moved to the University of Texas at Austin. Merkel and Freeman will continue to work together on the idea of activating the particles in the membrane. The idea for nanocomposite membranes originated in the laboratories of Membrane Technology and Research, Inc., in California, where Merkel worked two years ago on a summer job.

RTI (www.rti.org) is an independent, nonprofit research organization dedicated to conducting research that improves the human condition. With a staff of more than 2,000 people, RTI turns knowledge into practice in health and medicine, environmental protection, technology commercialization, decision support systems, and education and training.

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