Predicting the thermodynamic properties and dielectric behavior of electrolyte solutions using the SAFT‐VR+DE equation of state

We extend the SAFT‐VR+DE equation of state to describe 19 aqueous electrolyte solutions with both a fully dissociated and a partially dissociated model. The approach is found to predict thermodynamic properties such as the osmotic coefficient, water activity coefficient, and solution density, across different salt concentrations at room temperature and pressure in good agreement with experiment using only one or two fitted parameters. At higher temperatures and pressures, without any additional fitting, the theory is found to be in qualitative agreement with experimental mean ionic activities and osmotic coefficients. The behavior of the dielectric constant as a function of salt concentration is also reported for the first time using a statistical associating fluid theory (SAFT)‐based equation of state. At high salt concentrations, the stronger electrostatic interactions between the ionic species due to the dielectric decrement, is captured through the inclusion of ion association. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3053–3072, 2015     

Interfacial tensions of industrial fluids from a molecular‐based square gradient theory

This work reports a procedure for predicting the interfacial tension (IFT) of pure fluids. It is based on scaling arguments applied to the influence parameter of the van der Waals theory of inhomogeneous fluids. The molecular model stems from the application of the square gradient theory to the SAFT‐VR Mie equation of state. The theory is validated against computer simulation results for homonuclear pearl‐necklace linear chains made up to six Mie (λ ? 6) beads with repulsive exponents spanning from λ = 8 to 44 by combining the theory with a corresponding states correlation to determine the intermolecular potential parameters. We provide a predictive tool to determine IFTs for a wide range of molecules including hydrocarbons, fluorocarbons, polar molecules, among others. The proposed methodology is tested against comparable existing correlations in the literature, proving to be vastly superior, exhibiting an average absolute deviation of 2.2%. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1781–1794, 2016     

On the simultaneous description of h‐bonding and dipolar interactions with point charges in force field models

H‐bonding and polar interactions occur together in real fluids, but are of different nature and have different effects on macroscopic properties. Nevertheless, both are usually described by point charges in force field models. Despite this, the two effects can be separated. A simple model fluid is studied: a single Lennard‐Jones (LJ) site with two opposing point charges q placed in the center of the LJ site and at a distance d. By suitably varying both d and q, the dipole moment μ is kept constant. Both μ and d are systematically varied to study the properties of the resulting models, including H‐bonding, which is determined using a geometric criterion from literature. d can be used for tuning the H‐bonding strength and, thus, polarity and H‐bonding can be adjusted individually. The study of a second related model with symmetrically positioned point charges does not reveal this separation. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2926–2932, 2015     

Phase‐dependent binary interaction parameters in industrial low‐density polyethylene separators

In the production process of low‐density polyethylene (LDPE), an important step is the flash separation of monomers and other small molecules from the polymer produced. The process is carried out adiabatically in two stages. To improve the performance of thermodynamic models, it is very important to analyze the use of model binary interaction parameters (BIP) dependent on the phase characteristics for each phase (phase‐dependent BIP). In this work the PC‐SAFT (perturbed‐chain statistical associating fluid theory) equation of state (EOS) is applied to the flash simulation of LDPE industrial separators using eight different resins. The main numerical aspects are examined with emphasis on the optimization strategy for the EOS BIP that explicitly characterizes each phase involved separately. The results demonstrate good predictive behavior. As a result of improved and more consistent modeling, a new strategy for optimized operation can be envisaged for the sequence of separators. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2106–2117, 2013     

A hierarchical method to integrated solvent and process design of physical CO2 absorption using the SAFT‐γ Mie approach

Molecular‐level decisions are increasingly recognized as an integral part of process design. Finding the optimal process performance requires the integrated optimization of process and solvent chemical structure, leading to a challenging mixed‐integer nonlinear programming (MINLP) problem. The formulation of such problems when using a group contribution version of the statistical associating fluid theory, SAFT‐γ Mie, to predict the physical properties of the relevant mixtures reliably over process conditions is presented. To solve the challenging MINLP, a novel hierarchical methodology for integrated process and solvent design (hierarchical optimization) is presented. Reduced models of the process units are developed and used to generate a set of initial guesses for the MINLP solution. The methodology is applied to the design of a physical absorption process to separate carbon dioxide from methane, using a broad selection of ethers as the molecular design space. The solvents with best process performance are found to be poly(oxymethylene)dimethylethers. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3249–3269, 2015     

Predicting phase behavior in aqueous systems without fitting binary parameters II: Gases and non‐aromatic hydrocarbons

This investigation continues a series of studies evaluating the capability of the recently proposed CP‐PC‐SAFT and sPC‐SAFT of Liang et al. to estimate the thermodynamic properties of aqueous systems in the entirely predictive manner. Similarly to the previously considered systems, CP‐PC‐SAFT remains a realistic estimator of the available data on critical loci, high pressure‐high temperature phase equilibria and volumetric properties also in the cases of non‐polar gases and non‐aromatic hydrocarbons from argon and nitrogen till n‐eicosane and squalene while keeping zero values of binary parameters. Nevertheless, such application of the model poses certain unavoidable compromises on its accuracy. Inter alia, CP‐PC‐SAFT is a particularly inaccurate estimator of the water‐rich liquid phases away from the critical points. sPC‐SAFT predicts these data in a more reliable manner. Moreover, its predictive capability goes beyond the liquid phases and it exhibits a remarkable accuracy in forecasting various phase equilibria below the critical point of water. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Solvent effects on esterification equilibria

Solvents are known to have strong impacts on the yields of equilibrium reactions. This work focuses on the thermodynamic investigation of these solvent effects on esterification reactions of acetic acid and propionic acid with ethanol. Esterification of acetic acid was performed in the solvents acetone, acetonitrile (ACN), dimethylformamide (DMF), and tetrahydrofurane as well as in mixtures thereof. ACN promotes the esterification of acetic acid, whereas it is strongly suppressed by DMF. The esterification of propionic acid was investigated with various reactant concentrations in acetone. The experimental equilibrium data in pure solvents and solvent mixtures were modeled using the thermodynamic equilibrium constant K_a and the reactant/product activity coefficients predicted by the perturbed chain‐statistical associating fluid theory (PC‐SAFT). For a given K_a, PC‐SAFT is able to predict the influence of the solvent and even solvent mixtures on the equilibrium concentrations of esterification in almost quantitative agreement with the experimental data. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3000–3011, 2015     

Outer approximation algorithm with physical domain reduction for computer‐aided molecular and separation process design

Integrated approaches to the design of separation systems based on computer‐aided molecular and process design (CAMPD) can yield an optimal solvent structure and process conditions. The underlying design problem, however, is a challenging mixed integer nonlinear problem, prone to convergence failure as a result of the strong and nonlinear interactions between solvent and process. To facilitate the solution of this problem, a modified outer‐approximation (OA) algorithm is proposed. Tests that remove infeasible regions from both the process and molecular domains are embedded within the OA framework. Four tests are developed to remove subdomains where constraints on phase behavior that are implicit in process models or explicit process (design) constraints are violated. The algorithm is applied to three case studies relating to the separation of methane and carbon dioxide at high pressure. The process model is highly nonlinear, and includes mass and energy balances as well as phase equilibrium relations and physical property models based on a group‐contribution version of the statistical associating fluid theory (SAFT‐γ Mie) and on the GC⁺ group contribution method for some pure component properties. A fully automated implementation of the proposed approach is found to converge successfully to a local solution in 30 problem instances. The results highlight the extent to which optimal solvent and process conditions are interrelated and dependent on process specifications and constraints. The robustness of the CAMPD algorithm makes it possible to adopt higher‐fidelity nonlinear models in molecular and process design. © 2016 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 62: 3484–3504, 2016     

Three‐dimensional numerical simulation of coalescence and interactions of multiple horizontal bubbles rising in shear‐thinning fluids

The dynamics of multiple horizontal bubbles rising from different orifice arrangements in shear‐thinning fluids was simulated numerically by three‐dimensional Volume of Fluid method. The effects of bubble size, rheological properties of shear‐thinning fluids, and orifice structure arrangements on multiple bubbles interaction and coalescence were analyzed, and the mechanisms of bubble coalescence and breakup were fully discussed and elucidated. The variation of bubble rising velocity during coalescence process and freely rising processes for different orifice arrangements was also deeply investigated. The critical initial horizontal intervals for coalescence of multiple horizontal bubbles with various orifice arrangements were attained by simulation, which could serve as the critical criterion of bubble coalescence or noncoalescence. Furthermore, the critical bubble interval was predicted based on the film drainage model, the prediction accords well with the simulation result and is quite conducive for the design and optimization of perforated gas–liquid contact equipment. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3528–3546, 2015     

Predicting phase behavior in aqueous systems without fitting binary parameters I: CP‐PC‐SAFT EOS,aromatic compounds

This study examines an accuracy of CP‐PC‐SAFT attached by the 4C cross‐association scheme and zero values of binary parameters in predicting the high temperature‐high pressure phase behavior in aqueous systems of aromatic compounds containing one and two benzoic rings, CO₂ and cis‐decalin. In spite of the noteworthy complexity of these systems and the entirely predictive nature of the current approach, it correctly predicts the topology of phase behavior and typically yields the quantitatively accurate estimations of critical loci and the hydrocarbon–rich liquid phases in wide range of conditions. The available single phase volumetric data are also predicted accurately. Unfortunately, it is not a case of the water–rich phases exhibiting very small hydrocarbon concentrations. Nevertheless, the model is still capable of capturing the solubility minima characteristic for these phases around the room temperature. Predictions of the recent version of Simplified PC‐SAFT proposed by Liang et al. (2014) are also discussed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4124–4135, 2017     

Solubility Calculation of Oil‐Conta‐minated Drill Cuttings in Supercritical Carbon Dioxide Using Statistical Associating Fluid Theory (PC‐SAFT)

Supercritical fluid extraction is a new technology that could be effectively used to treat oil‐contaminated drill cuttings generated during drilling for oil and gas. In this work, the solubility of oil‐contaminated drill cuttings in supercritical carbon dioxide is obtained by an experimental flow type apparatus. The solubility was measured at 200 bar pressure, over a temperature range of 55–79.5 °C. The measured solubility and experimental data for oil in drill cuttings were correlated using the PC‐SAFT, PR and SRK EOS models, without any adjustable parameters. Average absolute derivations of less than 15.1 %, 98.7 %, and 99.3 % are achieved between predicted and experimental values for the PC‐SAFT, PR and SRK EOS models, respectively, over a wide range of temperatures.     

Application of the functional renormalization group method to classical free energy models

A simple functional renormalization group method is presented to correct the behavior of classical free energy models near the critical point. This approach is applied to the Soave–Redlich–Kwong equation of state to illustrate its ability to better reproduce the phase behavior of simple fluids and to understand the influence of its parameters on the shape of the vapor‐liquid phase diagram. The method is then extended to account for the correlations induced by intramolecular bonds. It is then applied to a first‐order thermodynamic perturbation theory for chain fluids to examine fluids composed of linearly bonded Lennard‐Jones atoms. Unlike previous approaches for applying renormalization group corrections to chain fluids, this is able to accurately reproduce the critical point without predicting an overly flat liquid‐vapor coexistence region. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2985–2992, 2015     

Modeling of solid–liquid equilibria for polyethylene and polypropylene solutions with equations of state

We modeled solid–liquid equilibria (SLEs) in polyethylene and polypropylene solutions with a Soave–Redlich–Kwong (SRK) cubic equation of state (EOS) and a perturbed‐chain statistical associating fluid theory (PC‐SAFT) EOS. Two types of mixing rules were used with SRK EOS: The Wong–Sandler mixing rule and the linear combination of the Vidal and Michelsen mixing rules (LCVM), both of which incorporated the Bogdanic and Vidal activity coefficient model. The performance of these models was evaluated with atmospheric‐pressure and high‐pressure experimental SLE data obtained from literature. The basic SLE equation was solved for the equilibrium melting temperature instead of for the composition. The binary interaction parameters of SRK and PC‐SAFT EOS were estimated to best describe the experimental equilibrium behavior of 20 different polymer–solvent systems at atmospheric pressure and 31 other polymer–solvent systems at high pressure. A comparison with experimental data showed that SRK–LCVM agreed very well with the atmospheric SLE data and that PC‐SAFT EOS was more efficient in high‐pressure conditions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

On the construction of binary mixture p‐x and T‐x diagrams from isochoric thermodynamics

In this work, we describe how to efficiently and reliably calculate p‐x and T‐x diagrams for binary mixtures of fluids. The method is based on the use of the Helmholtz energy density as the fundamental thermodynamic potential. Through the use of temperature and molar concentrations of the components as the independent variables, differential relationships can be constructed along the phase envelope surface, and this system of differential equations is then integrated to construct isotherms and isobars cutting through the phase envelope. The use of the Helmholtz energy density as the fundamental potential allows several models to be considered in this formalism, including cubic equations of state (Peng‐Robinson, GC‐VTPR, etc.) as well as high‐accuracy multifluid equations of state (the so‐called GERG mixture model). Examples of each class are presented, demonstrating the flexibility of this method. Source code, examples, and comprehensive analytic derivatives are provided in the Supporting Information. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2745–2757, 2018     

Molecular dynamic simulation and equation of state of Lennard-Jones chain fluids

In order to study the thermodynamic properties of chain and polymeric fluids at the molecular level, we perform constant temperature molecular dynamics simulations of ‘repulsive’ and ‘full’ Lennard-Jones (LJ) chain fluids of lengths up to 16. In the simulation, the RATTLE algorithm to determine constraint forces and the Nose-Hoover thermostat to sample the canonical ensemble are used. For repulsive LJ chains, the compressibility factor of the chain fluids is predicted from first-order thermodynamic perturbation theory combined with the Week-Chandler-Andersen (TPT1-WCA) perturbation theory, and is compared to the simulation results. A good agreement between the theory and the simulation results is found particularly at liquid-like densities. For full LJ chains, two different versions of TPT1 are used to calculate the compressibility factor: one is TPT1-WCA, and the other is TPT1 with the Percus-Yevick approximation for the radial distribution function of the LJ spheres (TPT1-PY). At low and intermediate densities, TPT1-PY gives better predictions for the compressibility of the LJ chain fluids, whereas at high densities TPT1-WCA is more reliable.     

Shear creep resistance of styrene–isoprene–styrene (SIS)‐based hot‐melt pressure‐sensitive adhesives

The effects of the properties of substrates and tackifier on the shear creep of SIS‐based HMPSAs were investigated. The holding power (t_b) and shear adhesion failure temperature (SAFT) were measured. The relationship between the complex viscosity and the holding power was examined. The holding power and SAFT values of the triblock SIS blends were higher than those of the diblock‐containing SIS blends, perhaps because blends using triblock SIS have higher crossover temperature and complex viscosity than those using diblock‐containing SIS. Higher levels of aromatic resin‐modified aliphatic tackifier and rosin ester were found to decrease the holding power of the HMPSAs. This maybe due to the fact that rosin ester and aromatic‐modified aliphatic resin are compatible with both the ends and midblocks of SIS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 825–831, 2006     

Complexation chemistry in liquid–liquid extraction of rhenium

This review addresses the dearth of knowledge about the interaction of rhenium species with organic solvents during the liquid–liquid extraction of rhenium. To describe such interactions, the aqueous chemistry of rhenium in unlike media, the extraction mechanism and the salient role of thermodynamic properties are also discussed. Formation of a rhenium‐complexed species inorganic phase and competition between the extracted species during extraction is described by inner and outer sphere coordination. Emergence of a stabilized complex in a hydrophobic environment is greatly affected by the interaction of electrostatic and/or H‐bonding. The chemistry of liquid–liquid extraction of rhenium that can further assist future studies in this area is also relevant to other metal ion systems. © 2015 Society of Chemical Industry