Mutual solubilities of water and hydrocarbons from the Cubic plus Association equation of state: A new mixing rule for the correlation of observed minimum hydrocarbon solubilities

• A new mixing rule for CPA EoS to correlate water–hydrocarbon mutual solubilities is presented.
• The new mixing rule has only one additional binary parameter.
• The binary parameters were determined for alkanes, cycloalkanes and aromatics.
• The CPA EoS with the new mixing rule is able to describe the minimum HC solubility vs temperature curves.
• The new mixing rule was successfully employed for multicomponent mixtures.

The cubic plus association (CPA) equation of state was employed to correlate the mutual solubilities of water and hydrocarbons (n-alkanes, cycloalkanes and aromatics). In order to reproduce the minimums observed in concentration vs. temperature curves, a new mixing rule is proposed based on Kabadi and Danner's idea, whereby the water–water dispersive term is corrected to include the hydrophobic hydration effect. With this correction, correlated hydrocarbon solubilities curves have observable curvature at low temperatures. Two binary interaction parameters are required for saturated hydrocarbons and three for aromatics, which is just one more than the original CPA formulation. Using parameters determined from binary data, this improved mixing rule was employed for multicomponent water–hydrocarbon systems, with no further regression, producing better predictions when compared to the conventional van der Waals’ rules.