Temperature-independent Binary Interaction Parameter Research Articles

Water/Hydrocarbon Phase Equilibria Using the Thermodynamic Perturbation Theory

Two equations of state, the cubic plus association (CPA) and the statistical associating fluid theory (SAFT), which account explicitly for the effect of hydrogen bonding on the thermodynamic properties of associating fluids using the perturbation theory of Wertheim (J. Stat. Phys. 1986, 42, 459, 477), are applied to predict the phase equilibrium of pure water, n-alkanes, and 1-alkenes as well as the low- and high-pressure phase equilibrium of water/hydrocarbon mixtures. The pure compound parameters for the two equations are estimated by fitting experimental vapor pressure and saturated liquid density data that cover a very wide temperature range from approximately the triple point to very close to the critical point. One temperature-independent binary interaction parameter is calculated for each of the mixtures examined. The analysis of the results shows that the increased complexity of SAFT over CPA does not offer any improvement in modeling highly nonideal fluid behavior, at least for the systems examined here.

Modelling of high-pressure phase equilibria using the Sako–Wu–Prausnitz equation of state: I. Pure-components and heavy n-alkane solutions

A cubic equation of state (EOS) proposed by Sako, Wu and Prausnitz (SWP) [T. Sako, A.H. Wu, J.M. Prausnitz, J. Appl. Polym. Sci. 38 (1989) 1839–1858.] is used to correlate phase equilibria in systems containing small and large molecules. Two pure-component parameters are fitted to vapour pressures (volatile molecules) and to liquid density data (non-volatile molecules and polymers), respectively. New pure-component parameters for nitrogen and a series of 1-alkenes are reported. The parameter estimation procedure for polymers and polymer-like substances such as heavy n-alkanes is refined. For this purpose, the repulsion parameter b is refitted to describe the correct slope of the PV-isotherms. This was found to be necessary to improve the phase-equilibrium calculations of binary polymer systems. Binary systems of ethylene with heavy alkanes or alkenes and one ternary system (ethylene/eicosane/tetracontane) are investigated. It is shown that one temperature-independent binary interaction parameter is sufficient to describe the phase equilibrium in these binary systems. The accuracy of the correlation in systems containing a heavy alkane is comparable or better than the results obtained from the Peng–Robinson (PR) EOS.

Saturated liquid densities and bubble point pressures of the ternary HCFC-22/HFC-152a/HCFC-142b system

Maezawa, Y., Widiatmo, J.V., Sato, H. and Watanabe, K., 1991. Saturated liquid densities and bubble point pressures of the ternary HCFC-22/HFC-152a/HCFC-142b system. Fluid Phase Equilibria, 67: 203-212. Seventy-one data points for the saturated liquid density and bubble point pressure of the ternary system HCFC-22/HFC-152a/HCFC-142b were measured by a magnetic densimeter coupled with a variable-volume cell. The results of six different compositions of 20/20/60, 20/40/40, 20/60/20, 40/20/40, 40/40/20 and 60/20/20 wt.% cover a range of temperatures from 280 to 390 K. The experimental uncertainties in temperature, pressure, density and composition were estimated to be not greater than ±15 mK, ±20 kPa, ±0.2%, and between −0.17 and +0.01 wt.% HCFC-22 (between −0.12 and +0.06 wt.% HFC-152a and between −0.01 and +0.11 wt.% HCFC-142b) respectively. The purity of the samples was 99.97 wt.% for HCFC-22, 99.9 wt.% for HFC-152a and 99.8 wt.% for HCFC-142b. The bubble point pressures were reproduced satisfactorily well by the Peng-Robinson equation of state with the optimum binary interaction parameters, i.e. temperature-dependent k 13 and k 23, and temperature-independent k 12. The saturated liquid densities were reproduced reasonably well by the Hankinson-Brobst-Thomson equation with the optimum temperature-independent binary interaction parameters, k 12 , k 13 , k 23, l 12, l 13 and l 23.

Correlation of solubilities of gases and hydrocarbons in water

The density dependent local composition (DDLC) model for the Heimholtz energy of a fluid mixture is shown to correlate accurately the solubility of inert and acidic gases and of hydrocarbons from C 1 to C 6 in water at pressures to 300 bar. Further, the local composition model correctly reproduces the experimentally observed maximum in the Henry's law constant curve for gas solubilities in water. The quadratic mixing rules on the other hand, predict no maxima. The new model has been applied to flash problems related to wet sour gas mixtures where the model reproduces the experimental data. The model contains up to three temperature independent binary interaction parameters. When the interaction parameter in the DDLC term is zero, this correction vanishes and the model reduces to one with the conventional classical quadratic mixing rules usually applied to hydrocarbon - hydrocarbon mixtures. The DDLC mixing rule can be applied to any equation of state, which can be divided into a repulsive and an attractive contribution. In this work, we have applied it in conjunction with the Redlich-Kwong equation of state with a temperature dependent a-parameter.