As syngas fermentation leads to lower ethanol concentrations than corn fermentations, the energy and cost to separate the ethanol from water is proportionally higher. To reduce this differential, Coskata has exclusively licensed membrane separation technology to reduce the energy requirements by over 50%.
The vapor permeation process is amenable to separating ethanol from biofermentation broth because of the very low solids content of the broth relative to other fermentation processes.
The membrane separation strategy is clever because it uses so much less energy and cooling water than does distillation, but I see no mention of throughput rates or large scaleups yet...but it sure is worth watching.