Concentration effects on the selective extraction of ethanol from aqueous solution using silicalite-1 and decanol isomers

The high-energy requirement to separate ethanol from fermentation broths by distillation is a major hurdle for the economical use of bio-renewable ethanol in a wide variety of chemical applications. Three-phase Gibbs ensemble Monte Carlo simulations have been employed to assess the performance of two promising alternatives: adsorptive separation using silicalite-1, a hydrophobic zeolite, and liquid-liquid extraction using two high-molecular-weight alcohols, namely decan-1-ol and decan-4-ol. These simulations show that in both separation processes the selectivity for ethanol over water is significantly higher at low concentrations though this trend is more pronounced in the zeolite system. The vapor-to-sorbent partition coefficient is significantly higher at low concentrations, while the organic solvent systems show only a weak dependence of the vapor-to-solvent partition coefficient on concentration. This behavior can be rationalized by the different ethanol/water aggregates (in terms of size and architecture) formed in these two environments. A key factor in these differences is the spatial confinement of the hydrogen-bonded aggregates by the alkyl tails of the solvent or by the rigid zeolite structure.