3-18: Solvent selection and recovery for liquid-liquid extraction of acetic acid and water

The removal of acetic acid from biomass hydrolysate is crucial to increase the yield of ethanol during fermentation.  Acetic acid is a well-known inhibitor and is present in all biomass in its native form as an acetyl group.  The acetyl groups are released from the biomass during hydrolysis as acetic acid.  Hydrolysis is a processing step in which the long-chain sugars in the biomass are broken into smaller chains that can be consumed by the yeast to form ethanol.  The acetic acid released during hydrolysis works to slow down the fermentation and significantly decrease the yield of ethanol.  The overall goal of this project is to explore the removal of acetic acid from the hydrolysate using liquid-liquid extraction (LLE).

The work performed for this study was to use Aspen Plus to determine a reasonable solvent to recover Acetic Acid from water.  A list of solvents was identified based on the tertiary-phase diagram with acetic acid and water.  Next, the solvents available in the Aspen Plus data bank were simulated to remove acetic acid from water.  The aim was to identify a solvent that has great affinity to acetic acid and low solubility in water, and also required the least extreme operating conditions as far as temperature and pH were concerned.  Once the solvent was identified, the next step was to determine the best type of membrane.  Based on the molecular size of the solvent and acetic acid and also their hydrophobicity differences, molecular sieve or zeolite-based membrane systems were tested.