Energy requirement for continuous ethanol extraction via pervaporation and/or distillation at low concentrations
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Syngas fermentation, or synthesis gas fermentation, is a microbial process that uses hydrogen, carbon dioxide, and carbon monoxide to produce fuel. The effluent in this process contains low concentration ethanol, which often ranges from 2 to 6 wt% ethanol. To make this ethanol usable, it must be concentrated to >95 wt% to be considered fuel grade ethanol. Most commonly, distillation is used to produce fuel grade ethanol, however this requires too much energy for low concentration ethanol feed streams. Therefore, there exists a need for an energy efficient process for converting low concentration ethanol feed streams to fuel grade ethanol. A model was made for a system that produces an ethanol-water effluent from a syngas fermenter that uses distillation alone to produce 95 wt% ethanol in the distillate. Then, a model was made for a system where the syngas fermentation effluent is first concentrated via a pervaporation module and then distilled. The flow rates in both models was calculated to find the amount of ethanol recovered in grams per hour. Then, the amount of energy required per hour was calculated for both models and an analysis was done to compare the energy required to recover a gram of ethanol for various feed stream concentrations.
dissertation or thesis