The energy demand of distillation-molecular sieve systems for ethanol recovery/dehydration can be significant, particularly for dilute solutions. An alternative hybrid process integrating vapor stripping (like a beer still) with vapor compression and a vapor permeation membrane separation step has been proposed [1-2]. The water-selective membrane in the vapor permeation step produces water-rich and ethanol-enriched vapor streams from which latent/sensible heat can be recovered into the stripping step. In this work, the performance of such an integrated system with surrogate and actual fermentation broths was demonstrated and the fate of secondary fermentation products in the system was assessed. The experimental apparatus was equipped with a membrane module provided by Membrane Technology and Research, Inc., through a cooperative R&D agreement.
For a simple ethanol-water mixture containing 5wt% ethanol, the integrated system used only 2.2MJ of fuel per kg of ethanol, a 63% reduction in the energy requirement relative to a distillation/molecular sieve system. Ethanol purity, which ranged from 75-95wt%, was limited by the membrane area in the experimental unit. Increasing ethanol purity to 99.5wt% is easily achieved with additional membrane area and only marginally more energy.
Secondary fermentation products, such as alcohols, esters, and organic acids, displayed varying degrees of recovery in the stripping and membrane steps based on the relative vapor-liquid partitioning of the compounds and rejection by the membrane.
**This abstract of a proposed presentation does not necessarily reflect USEPA policy.
 Vane & Alvarez, JChemTechnolBiotechnol, 83 (2008) 1275.
 Vane, Alvarez, Huang, & Baker, JChemTechnolBiotechnol, 85 (2010) 502.