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Arthur T Knackerbracket has found the following story:

A research team from the Georgia Institute of Technology and ExxonMobil has demonstrated a new carbon-based molecular sieve membrane that could dramatically reduce the energy required to separate a class of hydrocarbon molecules known as alkyl aromatics.

The new material is based on polymer hollow fibers treated to retain their structure -- and pore sizes -- as they are converted to carbon through pyrolysis. The carbon membranes are then used in a new "organic solvent reverse osmosis" (OSRO) process in which pressure is applied to effect the separation without requiring a phase change in the chemical mixture.

The hollow carbon fibers, bundled together into modules, can separate molecules whose sizes differ by a fraction of a nanometer while providing processing rates superior to those of existing molecular sieve zeolites. Because it uses a commercial polymer precursor, the researchers believe the new membrane has potential for commercialization and integration into industrial chemical separation processes. The research will be reported in the August 19 issue of the journal Science.

Separation is currently achieved through refining processes such as crystallization and adsorption with distillation, which are energy-intensive. Globally, the amount of energy used in conventional separation processes for alkyl aromatics is equal to that produced by about 20 average-sized power plants.

"We see this as a potentially disruptive technology in the way we separate xylenes and similar organic compounds," said Benjamin McCool, one of the paper's co-authors and an advanced research associate at ExxonMobil Corporate Strategic Research in Annandale, N.J. "If we can make this work on an industrial scale, it could dramatically reduce the energy required by these separation processes."

Fabrication of the new membrane material begins with hollow polymer fibers approximately 200 microns [0.2 mm] in diameter, slightly thicker than the average human hair. The fibers have pore sizes of less than one nanometer, and are treated via cross-linking before they are converted to carbon through a pyrolysis process. The pore sizes of the fibers can be adjusted during the fabrication process.

[...] Though the membrane has demonstrated promising results, it still faces a number of challenges. The membranes will have to be tested with more difficult separations before they can be considered for commercialization and scale-up. Industrial mixtures normally contain multiple different organic compounds, and they may include materials that can foul membrane systems. The researchers will also have to learn to make the material consistently and demonstrate that it can withstand long-term industrial use.

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