Assessment and Revision of the MOSCED Parameters for Water: Application to Limiting Activity Coefficients and Binary Liquid–Liquid Equilibrium

Modified Separation of Cohesive Energy Density (MOSCED) is an attractive method for modeling phase-equilibria because it both can make quantitative predictions and give insight into the system’s underlying molecular-level interactions. While MOSCED predicts satisfactory values of limiting activity coefficients of organics in water, we find that predicted limiting activity coefficients for water (here the solute) in organic solvents shows a much greater disparity with reference data. Moreover, the error is systematic and increases as the value of the limiting activity coefficient increases. After detailed assessment of the MOSCED parameters for water, we find this is not a limitation of the model but results from how the parameters were regressed. As a consequence, in the present study we reregress MOSCED parameters for water which greatly improves the accuracy with which MOSCED may predict limiting activity coefficients of water in organic solvents, with the average absolute error decreasing from 3056.2% to 63.2%. The improvement is systematic, increasing as the value of the limiting activity coefficient increases. We additionally demonstrate the ability of the revised parameters to make improved binary liquid–liquid equilibrium calculations in aqueous systems.