Here is a "dewatering" membrane which appears to be in prototype production now - useful as an alternative to distillation, for enriching alcohol:
http://wwww.vaperma.com/industrial_applications/ethanol.php?lang=en ... this type of membrane should work even better for enriching butanol than ethanol, since that alcohol molecule is significantly larger. A Canadian plant using this technique is scheduled to open this year. Butanol, as mentioned many time here, is far superior to ethanol. Fortunately, the manufacturing infrastructure is almost completely interchangeable, even "hot swappable" to borrow a phrase. Bio-butanol from non-food biomass like cellulose is looking more and more like the sustainable and carbon-neutral transportation fuel of the future. Until then, we are stuck with ethanol.
