Cubic Two-State Equation of State for Associating Fluids

Abstract

The Kontogeorgis' approach (CPA; Ind. Eng. Chem. Res. 1996, 35, 4310) was employed for the extension of the Soave-Redlich-Kwong (SRK) equation to associating systems. The two-state association model (TSAM) of Cerdeirin ˜a et al. (J. Chem. Phys. 2004, 120, 6648) was modified and employed for describing the association contribution. The modification of TSAM consisted of developing an expression for the association contribution for the Helmholtz free energy as an explicit function of temperature and density, on the basis of the two-state approach. Similar to the CPA equation, the resulting cubic two-state (CTS) equation of state (EoS) has five parameters, three of them related to the nonspecific (physical) contribution and the other two related to the association. The CTS EoS is polynomial in volume and preserves the shape of a cubic equation in the region of positive volumes greater than the covolume, having one or three roots in this zone. For pure substances the equation is quartic, and it has analytical solution. The equation was fit to experimental vapor pressure and liquid density data of water, alcohols, and phenols, with very low deviations. The model was also employed to predict second virial coefficients of pure compounds, and phase equilibria of alcohol-alkane mixtures, using conventional mixing rules and one binary parameter, with very good agreement with experimental data.

Thermodynamic modeling of solubility of hydrogen sulfide in ionic liquids using Peng Robinson-Two State equation of state

“…Also, in this work, for reduction of the adjustable parameters of pure ionic liquids, the association energy parameter for pure ionic liquids is fixed to 2600 K and therefore four parameters are adjusted for PR-TS model. This value is obtained from the correlated results using the five-parameter PR-TS EoS that show the association energy parameter is very close to 2600 K, which is consistent with the typical value of association energy parameter reported in the literature [3,38].…”

Correlation of water-chlorohydrocarbon mutual solubilities using a modified non-quadratic mixing rule and the Cubic-Two-State equation of state

“…The CTS (Cubic Two-State) equation is derived from a combination of two contributions to the Helmholtz energy of a system: a physical part given by the Soave-Redlich-Kwong EoS and a molecular associative term obtained from the Two-State Association model [13]. Its pressure-explicit form is:…”

“…Values for Tci, pci and ωi were taken from the Aspen Plus V8.8 database. For self-associating substances, such as water, the physical and association parameters were taken from Medeiros and Téllez-Arredondo [13], who obtained them by fitting the CTS model to measured pressures and densities at saturation conditions. They also showed that the parameters a0i and bi have a similar interpretation to the van der Waals' parameters for non-polar molecules, with a0i being related to intermolecular dispersion energy and bi to the molecular volume.…”

“…Molecules with easily accessible association sites have a higher vij. The complete development of the model from statistical thermodynamics can be seen elsewhere [13]. The CTS EoS can be transformed into a compressibility polynomial that can be solved by robust methods such as Laguerre's, which was used in this work.…”

Hydrate Equilibrium Modelling with the Cubic two-state Equation of State

“…Recently, Medeiros and Téllez-Arredondo have presented an EoS that can deal with the association of substances, namely, the cubic two-state (CTS) EoS [10]. Its basis is the combination of the Soave-Redlich-Kwong (SRK) EoS, representing the physical part, and the two-state association model for the hydrogen bonding contribution.…”