A modified SAFT equation of state is developed by applying the perturbation theory of Barker and Henderson to a hard-chain reference fluid. With conventional one-fluid mixing rules, the equation of state is applicable to mixtures of small spherical molecules such as gases, nonspherical solvents, and chainlike polymers. The three pure-component parameters required for nonassociating molecules were identified for 78 substances by correlating vapor pressures and liquid volumes. The equation of state gives good fits to these properties and agrees well with caloric properties. When applied to vapor-liquid equilibria of mixtures, the equation of state shows substantial predictive capabilities and good precision for correlating mixtures. Comparisons to the SAFT version of Huang and Radosz reveal a clear improvement of the proposed model. A brief comparison with the Peng-Robinson model is also given for vapor-liquid equilibria of binary systems, confirming the good performance of the suggested equation of state. The applicability of the proposed model to polymer systems was demonstrated for high-pressure liquid-liquid equilibria of a polyethylene mixture. The pure-component parameters of polyethylene were obtained by extrapolating pure-component parameters of the n-alkane series to high molecular weights.

The perturbed-chain SAFT (PC-SAFT) equation of state is applied to pure associating components as well as to vapor-liquid and liquid-liquid equilibria of binary mixtures of associating substances. For these substances, the PC-SAFT equation of state requires five purecomponent parameters, two of which characterize the association. The pure-component parameters were identified for 18 associating substances by correlating vapor pressure and liquid density data. A comparison to an earlier version of SAFT confirms the good results for pure substances. When only one associating compound is present in a mixture, the PC-SAFT equation of state does not require mixing rules for the association term. Using one binary interaction parameter k ij for the dispersion term only, the model was applied to azeotropic and nonazeotropic vapor-liquid equilibria at low and at high pressures, as well as to liquid-liquid equilibria. Simple mixing and combining rules were adopted for mixtures with more than one associating compound, introducing no additional binary interaction parameter. The simultaneous description of liquidliquid and vapor-liquid equilibrium was also possible with a single k ij parameter.

The perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state is applied to binary and ternary mixtures of polymers, solvents, and gases. The three pure-component parameters required for nonassociating molecules were identified for six polymer compounds. The phase equilibrium of polymer systems, which often involves high-pressure liquid-liquid mixtures as well as vapor-liquid mixtures at lower pressures, was investigated. Using a constant binary interaction parameter (k ij ), the PC-SAFT equation of state gives good correlations of the appropriate phase behavior over wide ranges of conditions. Comparisons to an earlier version of SAFT reveal an improvement of the proposed model.

No abstract

The vapor pressures and liquid densities of single-salt electrolyte solutions containing NaCl, LiCl, KCl, NaBr, LiBr, KBr, NaI, LiI, KI, Li 2 SO 4 , Na 2 SO 4 , and K 2 SO 4 were modeled with an equation of state based on perturbed-chain statistical associated fluid theory (PC-SAFT). The PC-SAFT model was extended to charged compounds using a Debye-Hu ¨ckel term for the electrostatic interactions. Two model parameters for each ion were fitted to experimental pVT and vapor-pressure data. The model is able to excellently reproduce the experimental data up to high salt molalities and even to predict vapor pressures in mixed-salt solutions.

The perturbed-chain SAFT equation of state is extended to heterosegmented molecules and is applied to copolymers with a well-defined (alternating) repeat-unit sequence as well as to systems with a statistical sequence of the monomers in the backbone. Copolymers with a statistical sequence of the constituting repeat units usually require an assumption on the sequence of neighboring repeat units within the chain. A simple approach for defining such repeat-unit arrangements is proposed. Systems containing polyolefine copolymers (poly(ethylene-co-propylene) and poly(ethylene-co-1-butene)) covering the complete range of copolymer composition (including both of the appropriate homopolymers) were modeled in a mixture with solvents. Good results were found for mixtures of copolymer/solvent systems using constant interaction parameters. Copolymers comprising both nonpolar and polar repeat units, for example, poly-(ethylene-co-vinyl acetate) and poly(ethylene-co-methyl acrylate), require an interaction parameter correcting the interactions between repeat units of different types, which depends on the repeat-unit composition.

No abstract

The perturbed-chain polar statistical associating fluid theory (PCP-SAFT) equation of state is applied to mixtures containing polar as well as associating components where cross association may occur. In this work, we focus on mixtures in which at least one of the components does not self-associate but is able to form hydrogen bonds with other compounds, for example, water and alcohols. On the basis of the mixing rules from Wolbach and Sandler 1 for associating components, we propose a simple approach to account for this type of cross association (referred to as induced association) only from the knowledge of pure-component parameters. The application to vapor−liquid and liquid−liquid equilibria of numerous binary and ternary mixtures of polar components with alcohols and/or water revealed the strength of the proposed approach. It is confirmed that accounting for induced-association interactions improves the predictive capability as well as the ability of the model to correlate mixture phase equilibria quantitatively. It is worth mentioning that only temperature-independent parameters are used for all calculations, and no additional adjustable parameters are introduced.