| abstract |
A liquid mixture of water and a small percentage of an alcohol, for example a cellulosic fermentation broth, is converted into a mixture of vapours. The vapour mixture includes an increased percentage of alcohol vapour relative to the liquid mixture but is mostly water vapour. Water vapour is removed from the vapour mixture by permeation through a vapour separation membrane unit. Retained vapour has an increased alcohol content, optionally to the level of a fuel grade alcohol. Heat energy in permeate or product vapours or both may be recovered, for example by us as heating steam or by flow through a heat exchanger. The membrane unit may have two or more stages. Permeate from a stage may be condensed and used for example as fermentation make up water, compressed and fed to the permeate from an upstream stage or heating steam, or fed to another membrane stage for further dewatering. |