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Energy Efficient Hybrid Vapor Stripping-Vapor Permeation Process for Ethanol Recovery ad Dehydration
Citation:
VANE, L. M., F. R. ALVAREZ, Y. Huang, AND R. Baker. Energy Efficient Hybrid Vapor Stripping-Vapor Permeation Process for Ethanol Recovery ad Dehydration. Presented at 2008 Annual Meeting of the American Institute of Chemical Engineers, Philadelphia, PA, November 16 - 21, 2008.
Impact/Purpose:
To inform the public
Description:
Distillation combined with molecular sieve dehydration is the current state of the art for fuel grade ethanol production from fermentation broths. To improve the sustainability of bioethanol production, energy efficient separation alternatives are needed, particularly for lower fermented ethanol concentrations and small scale systems. A process, termed Membrane Assisted Vapor Stripping (MAVS), integrating steam stripping with a vapor compression step and a vapor permeation membrane separation step is proposed. The stripping column provides high ethanol recoveries and low effluent concentrations; the vapor compression-vapor permeation membrane component enables the efficient recovery of latent and sensible heat from both the ethanol-enriched retentate and water-enriched permeate streams from the membrane system. Based on computer simulations, recovery of 1 kg of fuel grad3e ethanol (0.5 wt% water) from a 1 wt% ethanol feed stream can be achieved using 8.9 MJ of fuel-equivalent energy. For 5 wt% relative to standard distillation producing azeotropic ethanol 7 wt% water). To produce a 99.5 wt% ethanol product from a broth containing 11.5 wt% ethanol, a conventional distillation/mol sieve system is expected to use 5.5 MJ-fuel equiv/kg-ethanol; the MAVS process would require as little as 2.2 MJ-fuel equiv/kg-ethanol. Overall costs are also estimate to be lower for a MAVS system. The energy saving of the MAVS approach was confirmed through experiments. The experimental system consisted o a vapor stripping column with six (6) stages of vapor-liquid equilibria, a vapor compressor, and a water-selective vapor permeation membrane module. The membrane was prepared with a solvent resistant perfluoro coating. Energy savings of over 50% were measured for recovery of ethanol from feed streams containing 1.5 and 5.5 wt% ethanol. Experiments with an actual fermentation broth will also be reported.
