Vapor-liquid equilibriums of the water-ethanol system at low alcohol concentrations

There has been strong interest in the use of renewable energy to reduce the consumption of petroleum fuel. An important consideration in biomass conversion concerns the energy consumption needed to produce alcohol compared to the energy content of the final alcohol product. Hence, there is a special interest in reducing energy consumption In the ethanol recovery step since it consumes a significant portion of the energy of the overall process. In low-energy distillation modeling, the bottom product stream is often assumed to contain no more than 0.02 wt % ethanol ( 7, 2). Thii constraint implies the requirement of efficient stripping. Otherwise, this alcohol loss becomes a significant cost factor when the feed concentration is low. In fact, low alcohol concentrations of 6-8 wt % ethanol are commonly encountered in the fermentation beer stream fed to a distillation system in the manufacture of fuel alcohol. How one can recover alcohol from a very dilute aqueous solution has thus became increasingly important as the interest in fuel alcohol further develops. Approximately 80 reports have appeared in the literature since 1895 on the vapor-liquid equilibrium data of the ethanol-water system (3). However, these investigations have seldom been performed at concentrations lower than 1 wt % ethanol. Specifically, only the report by Dalager (4) contains data at concentrations between 0.01 and 0.1 wt % ethanol (four data points with concentrations between 0.038 and 0.053 wt % ethanol). In this paper, extensive vapor-liquid equilibrium