(218b) Separation of Ethanol and Water: Molecular-Level Insights On Extraction and Adsorption Systems

The high energy cost of producing ethanol from fermentation broths is one of the biggest obstacles to the economical use of bio-renewable fuels for transportation and other applications. The separation of ethanol from a concentrated aqueous solution, usually by distillation, is one of the most energy intensive steps, motivating the development of more efficient alternatives, including liquid-liquid solvent extraction and adsorption in zeolites.  Coupled-decoupled configurational-bias Monte Carlo (CBMC) simulations in the isobaric-isothermal version of the Gibbs ensemble (GE) using the TraPPE (transferable potentials for phase equilibria) force field have been performed to screen a series of long-chain alcohols and diols for their ethanol capacity and for their selectivity for ethanol over water.  The distribution of hydrogen-bonded aggregates has been analyzed and used to identify several key features of these aggregates that promote high selectivity or capacity, as well as characteristics of the extraction solvent that enhance the formation of these favorable types of aggregates.  The CBMC-GE methodology is also applied to investigate the selective adsorption of ethanol in zeolites from aqueous solutions over a wide range of composition and two temperatures.