BACKGROUND: Energy efficient alternatives to distillation for alcohol recovery from dilute solution are needed to improve biofuel sustainability. A process integrating steam stripping with a vapor compression step and a vapor permeation membrane separation step is proposed. The objective of this work is to estimate the energy and process costs required to make a fuel grade ethanol (0.5 wt% water) from 1 and 5 wt% ethanol aqueous streams using the proposed process.

BACKGROUND: Fermentative production of butanol is limited to low concentrations, typically less than 2 wt% solvent, due to product inhibition. The result is high separation energy demand by conventional distillation approaches, despite favorable vapor-liquid equilibrium and partial miscibility with water. In previous work, a process integrating steam stripping, vapor compression, and vapor permeation separation was proposed for separating ethanol from water. Such a membrane assisted vapor stripping (MAVS) process is considered in this work for 1-butanol/water and acetone/butanol/ethanol/water (ABE/water) separation.RESULTS: Using process simulations, the earlier MAVS design was estimated to require 6.2 MJ-fuel kg −1 -butanol to produce 99.5 wt% 1-butanol from a 1 wt% 1-butanol feed, representing an energy savings of 63% relative to a benchmark distillation/decanter system. Adding a fractional condensation step to the original MAVS design is predicted to reduce energy demand to only 4.8 MJ-fuel kg −1 -butanol and reduce membrane area by 65%. CONCLUSION: In the hybrid distillation/membrane MAVS systems, the stripping column provides high butanol recovery and low effluent concentration while the vapor compression and membrane steps enable the efficient recovery of latent and sensibleheat from both the retentate and permeate streams from the membrane system. Addition of the dephlegmator condenser reduces both compressor size and membrane area. . c 2-phase azeotrope: upper phase = 30.8 wt% water, lower phase = 92.1 wt% water 34 d 2-phase azeotrope: upper phase = 15.0 wt% water, lower phase = 91.3 wt% water 50

BACKGROUND: The energy demand of distillation-based systems for ethanol recovery and dehydration can be significant, particularly for dilute solutions. An alternative separation process integrating vapor stripping with a vapor compression step and a vapor permeation membrane separation step, termed membrane assisted vapor stripping (MAVS), has been proposed. The hydrophilic membrane separates the ethanol-water vapor into water-rich permeate and ethanol-enriched retentate vapor streams from which latent and sensible heat can be recovered. The objective of this work was to demonstrate experimentally the performance of a MAVS system and to compare the observed performance with chemical process simulation results using a 5 wt% ethanol aqueous feed stream as the benchmark.

For all experiments, the concentrations of ethanol in the feed liquid, bottoms liquid, and permeate vapor condensate were determined using a gas chromatograph (GC, Agilent 6890) equipped with a Flame Ionization Detector (FID) with DI water dilution, as necessary, for the concentration to be in the calibrated range. Ethanol and water were quantitated in the feed vapor and retentate vapor condensates using a thermal conductivity detector (TCD) on the same GC using anhydrous 1-propanol (Sigma Aldrich) as a diluent. For experiments with the fermentation broth, all five samples were subjected to an additional set of analytical procedures to measure the concentration of the target analytes. Based on earlier scoping experiments and analyses with a

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