Group Contribution Lattice Fluid Research Articles

Predictive Thermodynamic Models for Ionic Liquid–SO2 Systems

Two types of predictive thermodynamic models, i.e., the UNIFAC model and GCLF EOS (group contribution lattice fluid equation of state), were applied to predict the solubility of SO2 in ionic liquids (ILs). The group interaction parameters were estimated by correlating the solubility data of SO2 in ILs exhaustively collected from the articles published until July 2015. It was verified that both the UNIFAC model and GCLF EOS could be used for predicting the solubility of SO2 in ILs, but the UNIFAC model gives results that are better than those of GCLF EOS. The UNIFAC model then was used to identify the structure–property relation for SO2 solubility and selectivity of CO2 to SO2, whereas GCLF EOS was used to investigate the volume expansivity of ILs upon the addition of SO2. The results showed that volume expansivity is independent of the different combinations of cations and anions and exhibits a linear relationship with SO2 solubility in ILs.

Trends in the Athermal Entropy of Mixing of Polymer Solutions

Polymeric mixtures of hydrocarbons and alcohols have been simulated with discontinuous potential models to characterize the Helmholtz energy of the repulsive reference fluids. This quantity is equivalent to the athermal mixture entropy. The reference compressibility factor and Helmholtz free energy have been correlated for various molecular structures from single to infinite chain lengths. The mixtures included small n-alkanes, branched alkanes, aromatics, and alcohols, with polymeric molecules of: n-alkanes, ethyl-styrenes, ethyl-propylenes, and isoprenes. We find that the athermal entropy of mixing at constant packing fraction deviates significantly from ideality as the volume ratio increases, but the nonideality is fairly insensitive to structural details like branching and rings. Volume ratio alone does not provide a complete characterization, however. For example, a mixture of C40 and C80 would yield a small deviation whereas a mixture of C2 and C4 would provide a relatively large deviation. This observation leads to the introduction of a characteristic parameter in terms of entropy density, designated as an entropic solubility parameter. In both ideal and nonideal solutions, the trends still follow van der Waals (vdW) mixing. This leads to an accurate characterization of the entropic contribution to the χ parameter (χS) of Flory–Huggins theory for mixtures of all sizes, shapes, and compositions of molecular structures. A general rule is developed for predicting the athermal entropy of mixing based on knowledge of the volume ratios and entropic solubility parameter of the constituent molecules. The simulations are compared to Flory–Huggins (FH), group contribution lattice fluid theory (GCLF), statistical associating fluid theory (SAFT), Sanchez–Lacombe (SL), and Guggenheim-Staverman (GS) theories of polymer chains.

Group contribution lattice fluid equation of state for CO2–ionic liquid systems: An experimental and modeling study

The group contribution lattice fluid equation of state (GCLF EOS) was first extended to predict the thermodynamic properties for carbon dioxide (CO2)–ionic liquid (IL) systems. The group interaction parameters of CO2 with IL groups were obtained by means of correlating the exhaustively collected experimental solubility data at high temperatures (above 278.15 K). New group parameters between CO2 and IL groups were added into the current parameter matrix. It was verified that GCLF EOS with two kinds of mixing rules could be used for predicting the CO2 solubility in ILs, and volume expansivity of ILs upon the addition of CO2, as well as identifying the new structure–property relation. Moreover, it is the first work on the measurement of the solubility of CO2 in ILs at low temperatures (below 278.15 K), manifesting the applicability of predictive GCLF EOS over a wider temperature range. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4399–4412, 2013

Group contribution lattice fluid equation of state (GCLF EOS) for ionic liquids

This work focuses on the extension of group parameters and application of the group-contribution lattice-fluid equation of state (GCLF EOS) for the systems with ionic liquids (ILs). The new group parameters ekk and Rkk for ILs in GCLF EOS were obtained by means of correlating the liquid density of pure ILs at different temperatures, while the group binary interaction parameters αmn were obtained by means of correlating the activity coefficients of solutes at infinite dilution in ILs at different temperatures, which were exhaustively collected from references. New IL groups were added into the current parameter matrix. It was verified that GCLF EOS for ILs can be used for predicting liquid densities of pure ILs or the mixture of IL and solute, vapor–liquid equilibria (VLE) and liquid–liquid equilibria (LLE) at finite concentration, as well as identifying the structure–property relation in separation science. This is the first work for us to extend the predictive GCLF EOS to the systems with ILs.

Solubility and diffusivity measurements in nitrogen–poly(vinyl acetate) and nitrogen–toluene–poly(vinyl acetate) systems with the differential pressure decay technique

AbstractIn creating thin films of polymers by solution processing, a common problem is the undesirable formation of bubbles during the drying process. Practical experience shows that bubbles can be created well below the boiling point of the solvent. Also, it has been observed that the degassing of the polymer solutions results in reduced bubble formation, and this indicates a relationship between the presence of air and bubble formation. This work is based on the hypothesis that if the solubility of air in the polymer solution increases with the solvent concentration, then the solution can become supersaturated with air as the concentration of the solvent is reduced during the drying process. To test this hypothesis, knowledge of the thermodynamics of the mixture is required. This study concentrated on the system of poly(vinyl acetate), toluene, and nitrogen. A thermodynamic model to predict phase behavior of this system was developed. The solubility of nitrogen in poly(vinyl acetate) and poly(vinyl acetate)–toluene as a function of the toluene composition over wide ranges of temperatures and pressures was measured with the pressure decay technique. The group‐contribution lattice–fluid equation of state was employed to correlate the thermodynamic behavior of the binary and ternary systems. In addition, experiments were conducted to measure the diffusion coefficients of the nitrogen in poly(vinyl acetate). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Solubility of mixed gases containing carbon dioxide in ionic liquids: Measurements and predictions

Solubilities of pure carbon dioxide and propane and those of the mixed gases carbon dioxide + nitrogen and carbon dioxide + propane in 1-hexyl-3-methylimidazolium tri(bisfluoromethylsulfonyl)imide were experimentally studied at 298.15 K and up to 1 MPa. A group-contribution lattice fluid equation of state was applied for the prediction of the solubility of pure and mixed gases with ionic liquids. Predicted results were found in reasonably good agreements with experimental data.

On the information and methods for calculation of Sanchez-Lacombe and group-contribution lattice-fluid equations of state

The algorithms for calculation of densities from Sanchez-Lacombe (S-L) and group-contribution latticefluid (GCLF) equations of state have been put forward, respectively. From the S-L equation of state the relationship between the equation characteristic parameters and critical properties was deduced, and the influence of molecular weight of the polymers on critical properties was investigated. However, for the GCLF equation of state, it was surprising to find that there as many as four roots were found at a saturation temperature and pressure for gases, while still two roots above the critical temperature. For polymers, only two roots could be found. So the formerly accepted consistency between the magnitude of the density and vapor or liquid phase is not applicable yet. A way about how to identify the root and corresponding phase was suggested.

Applications of the group-contribution, lattice-fluid equation of state

The group-contribution, lattice-fluid (GCLF) equation of state (EoS) is now more than 10 years old. The primary objective of our effort has been to develop a predictive model for the phase equilibria in polymer-solvent systems. The model has been developed by introducing group-contribution to the Panayiotou-Vera EoS. This paper reviews and updates the application of this approach along with its shortcomings. This EoS has been applied to prediction of the density of pure polymers, VLE of vapors, supercritical gas solubility, LLE, solubility parameters, and glass transition temperatures. Homopolymers and random copolymers can be successfully treated. The key features of this model are that it is purely predictive based only on the molecular structure of the molecules, and it is able to describe the pressure as well as temperature and composition effects because it is based on an EoS.

Predicting liquid–liquid transitions in polymer solutions using the GCLF equation of state

Group contribution lattice fluid equation of state (GCLF-EOS) have been extended and used to calculate phase equilibria in polymer solutions. Group parameters for three group contributions and nine new group contributions have been calculated. Saturation vapor pressure for pure solvent and weight fraction activity coefficients in polymer solutions have been calculated and the agreement obtained with experimental data indicated the accuracy of the parameters. A combining rule consisting a pair interaction parameter with temperature dependency was proposed. The area method was used with GCLF-EOS to obtain phase diagram for liquid equilibrium (LLE) of polymer solutions. The method was able to predict both lower critical solution temperature (LCST) and upper critical solution temperature (UCST).

Correlation and prediction of Henry constants for liquids and gases in five industrially important polymers using a CS-type correlation based on the van der Waals equation of state. Comparison with other predictive models

A simple two-parameter corresponding states-type method for the prediction of Henry constants of gases and liquid solvents in polymer solutions recently presented in the literature is thoroughly evaluated here and compared with the predictions of other models used for polymers. The corresponding states-type method is based on the van der Waals equation of state which has been recently extended to mixtures including polymers. Results are presented for systems containing five polymers in a variety of gases and nonpolar and polar liquid solutes. It is shown that agreement between experimental and calculated Henry constants is, in most cases, quite good and that the estimations with the new method compare favorably with the UNIFAC-FV and Entropic-FV activity coefficient models, the GC-Flory liquid-phase equation of state while they are somewhat better than the Group Contribution Lattice-Fluid (GCLF) equation of state. The proposed method is currently limited to five polymers but it is applicable to supercritical solvents, where the two activity coefficient models and the GC-Flory equation of state cannot be used.

Equations of state and activity coefficient models for vapor‐liquid equilibria of polymer solutions

AbstractFour noncubic equations of state, (EOS) and five activity coefficient models are applied to binary polymer and solvent solutions. Solvent activities at intermediate concentrations and equilibrium pressures are predicted with the perturbed‐soft‐chain theory (PSCT), group‐perturbed‐soft‐chain theory, (GPSCT), group‐contribution‐lattice fluid (GCLF) EOS, GC‐Flory EOS, UNIFAC‐FV, entropic‐FV and GK‐FV models, “new” UNIFAC, and modified Flory‐Huggins model. Free‐volume activity coefficient models (UNIFAC‐FV, entropic‐FV) are simpler and, when applied to polymer solutions, more accurate than the EOS. Activity coefficient models are restricted to low‐pressure calculations and require accurate values of pure‐component volumes. Mixture parameters for activity coefficient models and GC‐Flory EOS have been previously evaluated from experimental vapor‐liquid equilibrium data for mixtures with only low‐molecular‐weight compounds. The GC‐Flory EOS, though more complicated than activity coefficient models, provides equally good or in some cases better predictions. The application of GC‐Flory EOS developed as an activity coefficient model is restricted to low‐pressure calculations. On the other hand, PSCT and GCLF developed as “true” EOS provide reliable equilibrium predictions using mixture parameters evaluated solely from pure‐component properties together with standard mixing and combining rules. PSCT EOS performs generally better than GCLF EOS for polymer solutions considered in this study.

A group contribution equation of state for polymer solutions

A new group contribution lattice-fluid (GCLF) equation of state has been developed for polymers and polymer solutions. The lattice fluid theory of Panayiotou and Vera has been revised to include group contributions for solvent and polymer molecules. A lattice model containing holes is a convenient means of representing a polymer solution. The holes in the lattice serve as a means of varying the density of the fluid and are analogous to the free volume in generalized van der Waals models. An external degree of freedom parameter, the “C” parameter is not required. The GCLF equation of state reduces to forms similar to well established models for polymer solutions such as the Flory-Huggins equation. The group contributions for the model were calculated from the saturated liquid density and vapor pressures of small molecules. These group contributions are able to predict liquid densities, vapor pressures and VLE of small molecular systems with reasonable accuracy. The extension of the GCLF model to polymer solutions requires no pure component data and only one binary parameter.