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

Abstract

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.

Assessment of the SM12, SM8, and SMD Solvation Models for Predicting Limiting Activity Coefficients at 298.15 K

“…Brouwer and Schuur [73] recently conducted a comparative study of eight predictive methods to compute ln γ ∞ i,j at 298.15 K. Of the methods evaluated, the solubility parameter method MOSCED was the top performer. This strong performance of MOSCED is consistent with the findings of the 2005 re-parameterization [20,74] and our recent work [8,75]. MOSCED was therefore selected as an additional comparison alongside UNIFAC.…”

Assessment of the SM12, SM8, and SMD Solvation Models for Predicting Limiting Activity Coefficients at 298.15 K

“…Brouwer and Schuur [72] recently conducted a comparative study of eight predictive methods to compute ln γ ∞ i,j at 298.15 K. Of the methods evaluated, the solubility parameter method MOSCED was the top performer. This strong performance of MOSCED is consistent with the findings of the 2005 re-parameterization [20,73] and our recent work [8,74]. MOSCED was therefore selected as an additional comparison alongside UNIFAC.…”

“…Note that for water, we adopted the revised MOSCED parameters from ref. 74 The Minnesota Solvation Database, DECHEMA, and Yaws' reference databases were constrained to match the compound availability provided by the two models, UNIFAC and MOSCED. In comparison to the Minnesota Solvation Database, UNIFAC was able to make predictions for 1065 (of 1140) systems with 99 unique solutes and 68 unique solvents.…”

“…MOSCED in both cases was the highest performer, yet modeled the lowest number of systems due to its limited compound inventory. We additionally note that the MOSCED parameters for water were optimized using limiting activity coefficients from "Yaws' Handbook of Properties for Aqueous Systems" [74]. Overall, all models seem to have more difficulty predicting ln γ ∞ i,j when water is the solute.…”

“…MOSCED can only be used to model binary systems for which the the molar volume and five molecular descriptors are available for each component. At present, MOSCED parameters are available for 130 organic solvents and water [20,74]. Efforts have been made to use electronic structure calculations to predict missing MOSCED parameters, including the use of solvation free energy calculations with the SMx universal solvent models [42,[79][80][81][82][83].…”