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.

内聚能密度修正分离法（Modified Separation of Cohesive Energy Density, MOSCED）是一种极具应用价值的相平衡建模方法，其既可实现定量预测，又能揭示体系内在的分子级相互作用。尽管MOSCED对水中有机物的极限活度系数预测效果较为理想，但我们发现，以水为溶质、在有机溶剂中的极限活度系数预测值与参考数据间的偏差却显著更大。且该误差具有系统性，随极限活度系数数值的升高而不断增大。在对水的MOSCED参数进行详细评估后，我们发现该问题并非源于模型本身的局限，而是由参数的回归方式所导致。据此，本研究重新对水的MOSCED参数进行了回归，这大幅提升了MOSCED预测有机溶剂中水的极限活度系数的精度，平均绝对误差从3056.2%降至63.2%。该改进同样具有系统性，且随极限活度系数数值的升高而愈加显著。此外，我们还验证了修正后的参数可优化水相体系中的二元液液平衡计算。