(611a) Biosep: a New Ethanol Recovery Technology for Small Scale Rural Production of Ethanol from Biomass

Research activities on bioethanol have increased substantially as a result of the current concerns with energy security. Inexpensive biomass including forest residues, mill residues, agricultural residues, urban wood wastes and dedicated energy corps that exists in abundance across the entire United States could be harvested for ethanol production. However, efforts to exploit this resource have been limited due to the high cost of collecting and transporting distributed biomass to a central processing plant required by the current ethanol production technology of two-step distillation followed by molecular sieve drying.

MTR, together with the USEPA, is developing a new ethanol recovery technology called BioSep that combines a proven membrane technology (pervaporation) with an innovative condensation technology (dephlegmation). In simple pervaporation, a multicomponent liquid stream is passed across a selective membrane that preferentially permeates one or more of the components as vapor. Pervaporation is inherently energy-efficient because only the small fraction of the feed liquid that passes through the membrane must be vaporized. Alternatives such as distillation require vaporization of a much larger fraction of the feed to achieve the separation. A dephlegmation process consists of partial condensation with countercurrent flow of rising vapor and falling condensate. With the dephlegmator, better separation can be achieved and only vapor condensing at the top of the column must be cooled to the lowest temperature. Therefore, the BioSep process is cost-effective and energy efficient in recovering ethanol from biomass that will allow distributed and small-scale production of bioethanol across rural America.

The BioSep process includes two includes two membrane pervaporation steps, one upstream pervaporation step with ethanol permeable membrane is used to provide an ethanol enriched feed to the dephlegmator, and a second pervaporation dehydration step with water permeable membrane is used to treat the overhead ethanol product from the dephlegmator. In the latter step, the last 10 wt% of water in the alcohol vapor is removed to produce 99.5 wt% dry alcohols.

In this paper, the progress of this BioSep project will be reviewed with the focus on the discussion of the pervaporation membranes developed.