A new mixing rule developed for cubic equations of state equates the excess Helmholtz free energy at infinite pressure from an equation of state to that from an activity coefficient model. Use of the Helmholtz free energy insures that the second virial coefficient calculated from the equation of state has a quadratic composition dependence, as required by statistical mechanics. Consequently, this mixing rule produces the correct low-and high-density limits without being density-dependent.As a test, the mixing rule is used for ternary mixtures of cyclohexane + benzene + water, ethanol + benzene + water and carbon dioxide + n-propane + water, and all the constituent binaries. The new mixing rule and a simple cubic equation of state can be used for the accurate correlation of vapor-liquid and liquid-liquid equilibria for binary mixtures. Using the parameters obtained from binary systems, the phase behavior of ternary mixtures can be predicted. Also, unlike previous empirical mixing rules, this theoretically based mixing rule is equally applicable and accurate for simple mixtures containing hydrocarbons and inorganic gases and mixtures containing polar, aromatic and associating species over a wide range of pressures. This mixing rule makes it possible to use a single equation of state model with equal accuracy for mixtures usually described by equations of state and for those traditionally described by activity coefficient models. It is the correct bridge between these two classes of models.

Adsorption of carbon dioxide near its critical point on DeGussa IV activated carbon is investigated in this study. A volumetric method was used to measure the adsorption/desorption isotherms at 284, 300, 305, 310, and 314 K over a large pressure range. At subcritical temperatures, adsorption isotherms display a discontinuity at the vapor pressure of carbon dioxide, and desorption hysteresis is observed. However, there is no desorption hysteresis if adsorption is terminated before vapor−liquid transition occurs. At supercritical temperatures, adsorption isotherms display a plateau, and the excess decreases beyond the critical pressure. No hysteresis occurs during the desorption process. The adsorption isotherms can be represented very well by the simplified local density model.

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In this study, the densities of (aminomethanamide + 2-hydroxy-N,N,N-trimethylethanaminium chloride + water) and the solubilities of CO 2 in (aminomethanamide + 2-hydroxy-N,N,N-trimethylethanaminium chloride) with different varying mole fractions of water at temperatures of (303, 308, and 313) K are reported. The common name for (aminomethanamide + 2-hydroxy-N,N,N-trimethylethanaminium chloride) is reline. The densities are linear (AAD % is 0.22 %) with respect to reline mass fraction at each temperature. The logarithms of Henry's law constants were correlated using the two-suffix Margules model as a function of reline mole fraction with an AAD of 3.44 %. The results showed that CO 2 solubility in reline decrease with an increase water content. Hence water can serve as an antisolvent to strip CO 2 dissolved in reline. The absorption of CO 2 in (aminomethanamide + 2-hydroxy-N,N,Ntrimethylethanaminium chloride + water) at low pressures is found to be endothermic at water content. However, the absorption becomes exothermic if the water content increases to a mole fraction greater than 0.769.