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US researchers have made Molecular Sieve fibers that open up new possibilities for large scale chemical separations that use much less energy than conventional distillation methods. Sankar Nair and his Georgia Institute of Technology team have shown their metal–organic framework (MOF)-lined fibers can perform similarly to distillation in separating propylene and propane. That’s the same post-cracking raw mixture that the majority of the 77 million tons of propylene produced in 2011 was distilled from. ‘The degree of separation by the membrane is comparable, but uses vastly less energy,’ Nair says.
Though scientists recognize MOF membranes’ separation potential, they’ve mostly been fabricated on large tubes, whose surface area-to-volume ratio is too low for producing cheap separation modules. Micron-scale fibers would be better, but inside them conditions for successful membrane formation change significantly, Nair explains. ‘The amount of reactant present in the fiber is miniscule, and molecular transport and reaction processes are quite different,’ he says.
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