Liquid-liquid extraction using hydrophobic extraction solvents is a technology well-suited to the removal of certain hydrogen-bonding organics from water or brine. Even when distillation is technically feasible, extraction might allow a significant reduction in energy consumption depending on the specific application. Various methods are available for estimating the partition ratio (K) to assess technical feasibility; however, these methods often provide only rough approximations because of the complexity of hydrogen-bonding interactions in solution. To better understand the application of the MOSCED and standard UNIFAC activity-coefficient prediction methods for screening extraction solvents, calculations were compared with K data for the extraction of propylene glycol n-propyl ether (PnP), a model hydrogen-bonding compound. Estimates of limiting activity coefficients for PnP dissolved in the organic phase (γ ∞ PnP,organic ) obtained using MOSCED and UNIFAC are shown to be highly correlated with K data for a variety of hydrophobic organic solvents, including various alcohols, ketones, ethers, chlorinated hydrocarbons, aromatics, and aliphatic hydrocarbons. This example demonstrates how MOSCED or UNIFAC can be used to quickly rank candidate solvents for this class of compounds. The methodology facilitates process synthesis and design efforts by reducing the number of experiments required to identify suitable solvents.
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