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We describe a method for extending radial distribution functions obtained from molecular simulations of pure and mixed molecular fluids to arbitrary distances. The method allows total correlation function integrals to be reliably calculated from simulations of relatively small systems. The long-distance behavior of radial distribution functions is determined by requiring that the corresponding direct correlation functions follow certain approximations at long distances. We have briefly described the method and tested its performance in previous communications [R. Wedberg, J. P. O'Connell, G. H. Peters, and J. Abildskov, Mol. Simul. 36, 1243 (2010); Fluid Phase Equilib. 302, 32 (2011)], but describe here its theoretical basis more thoroughly and derive long-distance approximations for the direct correlation functions. We describe the numerical implementation of the method in detail, and report numerical tests complementing previous results. Pure molecular fluids are here studied in the isothermal-isobaric ensemble with isothermal compressibilities evaluated from the total correlation function integrals and compared with values derived from volume fluctuations. For systems where the radial distribution function has structure beyond the sampling limit imposed by the system size, the integration is more reliable, and usually more accurate, than simple integral truncation. [ABSTRACT FROM AUTHOR]

Modeling inconsistencies exhibited in previous work (O'Connell, 2017) associated with post-combustion methanolamine (MEA) and ammonia (NH 3 ) absorption processes have been revealed. The origin of the problem was that entropies for ionic reactions were not evaluated from input model equilibrium constants regressed from data. Revised calculations have been made using only properties of formation. Positive and consistent entropy generation rates ( S ˙ g e n ) are now found for all units and sections, and process convergence was achieved for multiple sections rather than for only single sections as before. Only minor changes in material, energy and overall S ˙ g e n appeared in the new simulations. Results for S ˙ g e n values show that the greatest irreversibilities for the MEA process are in the stripping section, though significant effects appear in the chiller, heat exchanger, and stripper flash. For the NH 3 process, roughly equal and large contributions to S ˙ g e n are in the absorption, heat exchange, and stripping sections. Process improvements should focus on these sections. Applying the methodology to proposed changes would quantitatively reveal the amounts of increased efficiency. [ABSTRACT FROM AUTHOR]

Systematic analyses of chemical process systems with steady-state balance equations for Material, Energy and Entropy can yield insights about energy efficiency and property model consistency, with entropy generation being the indicator quantity. Calculations of different sets of independent overall and subsection variables can reveal inefficient locations as well as the impacts of changes in process configuration and conditions. Demonstration is also made of how the analysis tests properties models because values of entropy generation must be positive, and the sum of heat rejections and entropy generations from sections must equal those from an overall analysis. Examples focus on chemical processes with internal circulation of complex mixtures, including thermochemical decomposition of water, and three different carbon-capture processes having essentially the same flue gas feed and gaseous products. Ranking of the CO 2 capture processes is made, while negative entropy generation is encountered with some property models. [ABSTRACT FROM AUTHOR]

Mixtures with azeotropes cannot be separated by simple distillation since the vapor and liquid compositions are the same. One option to overcome this limitation is to vary the applied pressure to shift the azeotropic composition out of the range of a single column or use pressure-swing operation of two columns. Because operating costs are highly sensitive to the pressure dependence of azeotropic compositions, reliable and accurate phase equilibrium thermodynamic property information is needed to computationally explore pressure variation for such processes. An analysis of property modeling has been done for the pressure sensitivity of azeotropic composition, and examples are given of modeling strategies for binary and ternary mixtures. A quantitative criterion for the need to consider nonideality effects in both modeling and parameter regression has been established, based on similarity of mixture excess enthalpies and pure component enthalpies of vaporization. [ABSTRACT FROM AUTHOR]

Abstract: Process simulations of HI decomposition via reactive distillation in the Sulfur–Iodine (S–I) cycle have been performed using heat pumps for energy recovery and a recently developed thermodynamic properties model. Several differences from previous flow sheets have been found through manual optimization of reflux ratio, number of stripping and rectifying stages, and pressure of the distillation column for typical inlet conditions to the HIx Section III. In particular, the RD column should have a minimal stripping section, can have as few as 10 total stages, an operating pressure of 12 bar, and a reflux ratio of 0.75, while achieving the production requirements. Though this design has limited improvement in energy requirements because the General Atomics energy recovery system is extremely effective, these results mean there should be a significant reduction in capital costs from prior estimates. In addition, as the inlet flow rate is increased, the input energy requirements decrease because of an increased ratio of H2O to I2 in the reboiler, lowering its temperature, and reducing the temperature differences for heat pump operations. The optimal inlet flow is between 126 and 140 mol/mol H2, with a Section energy requirement of 367 kJ/mol H2, and an overall process thermal efficiency estimated to be 41.5% relative to the higher heating value of hydrogen. These findings suggest there may be greater flexibility in conditions for the Bunsen reaction section as well as other possibilities for further energy efficiency improvement. [Copyright &y& Elsevier]

Abstract: The possibility for obtaining derivative properties for mixtures from integrals of spatial total and direct correlation functions obtained from molecular dynamics simulations is explored. Theoretically well-supported methods are examined to extend simulation radial distribution functions to long range so the integrals can converge. A previously published method developed for pure atomic fluids is here extended to handle simulations of molecular mixtures using all-atom force fields. We first test the method on simulations of Lennard-Jones/Stockmayer mixtures and show that that the results are consistent with an excess Helmholtz energy model fitted to available simulations. In addition, simulations of water/methanol and water/t-butanol mixtures have been carried out. The method yields results for partial molar volumes, activity coefficient derivatives, and individual correlation function integrals in reasonable agreement with smoothed experimental data. The proposed method for obtaining correlation function integrals is shown to perform at least as well as or better than two previously published approaches. [Copyright &y& Elsevier]

A method is proposed for obtaining thermodynamic properties via Kirkwood-Buff (KB) integrals from molecular simulations. In order to ensure that the KB integration converges, the pair distribution function is extrapolated to large distances using the extension method of Verlet, which enforces a theoretical limiting behaviour on the corresponding direct correlation function. The method is evaluated for the pure Lennard-Jones and Stockmayer fluids. The results are verified by comparing pure fluid isothermal compressibilities obtained from the KB integrals with values from derivatives of equations of state fitted to simulation results. Good agreement is achieved for both fluids at densities larger than 1.5 times the critical density. [ABSTRACT FROM AUTHOR]

Abstract: A model for the phase equilibria and energetics of the HI–I2–H2O–H2 system has been developed for use in process simulations of reactive distillation to form H2 from HI in the Sulfur–Iodine cycle for thermochemical decomposition of water. Comparisons with data and other models demonstrate that this approach is uniquely successful in describing the phase equilibria and properties of this complex system. In particular, it is able to follow the pressure minimum of the HI–H2O binary and HI–I2–H2O ternary when x HI ≈0.15; the dramatic increase of pressure and HI vapor composition, as well as formation of two liquid phases with greater amounts of HI; and the emergence of a single liquid phase in the ternary, even though binaries of HI and of I2 with H2O are only partially miscible. The model incorporates two novel speciation reactions and the Electrolyte-NRTL excess Gibbs energy model with parameters that cover wide ranges of temperature, pressure and composition. The model is formulated so that process simulation, design and optimization may be done reliably to explore feasibility and innovations of the S–I process. [Copyright &y& Elsevier]

Thermodynamic properties have always played essential roles in the engineering of chemical products and in the processes that manufacture them. Further, contemporary and future chemical technologies depend more than ever on property model formulation and application. This work explores how properties are utilized in process and product engineering, including opportunities and constraints of current property models, the current status of data availability and needs, and the interplay of data and models. Several case studies are given to illustrate underlying concepts, strategies for development, and methods of application to some industrial systems. [ABSTRACT FROM AUTHOR]

Abstract: Material, energy, and entropy balances, which depend only on stream conditions and flows entering and leaving a system, have been used to evaluate different scenarios for thermochemical decomposition of water to manufacture hydrogen using the Sulfur–Iodine cycle. Energy efficiencies have been found for idealized systems with variable stream amounts, as well as for a common flowsheet, to locate the greatest effects on energy requirements and inefficiencies. Aspen Plus®, OLI Engine, and ProSimPlus property models have been used on the sections of a General Atomics process to reveal the effects of differences in computed energies and entropy generation. While the calculated efficiencies are generally consistent with those of the literature, differences in stream properties and phase behaviors suggest that optimal process configurations from simulations may have significant uncertainties. [Copyright &y& Elsevier]

Abstract: Amide hydrogen-deuterium exchange labeling has been used to study the effects of salt and protein loading on α-lactalbumin (BLA) stability during hydrophobic interaction chromatography (HIC). Stability in the adsorbed phase increased dramatically with increasing loading, and unfolding was nearly undetectable close to the resin saturation capacity. We also found that a butyl surface destabilized BLA more than a phenyl surface, despite the fact that BLA was bound more strongly on the phenyl surface. These observations have important implications for HIC process design and indicate that in some cases column capacity does not have to be sacrificed to preserve protein stability. [Copyright &y& Elsevier]

A thermodynamic analysis is presented to correlate and predict reaction equilibrium properties for enzyme-catalyzed synthesis of valuable chemical compounds, such as small-molecule pharmaceuticals. Utilization of group-contribution methods is shown for obtaining reference-state ideal gas and standard-state solution Gibbs energies of formation of reactants and products, as well as for estimating solution nonidealities. Several transaminase reactions have been treated. These cases were previously shown not to be accurately predicted by estimates of Gibbs energies of formation from group contributions. This work achieves accurate descriptions of the data by regressing some unknown component values with a method that accounts for uncertainties in property and data uncertainties. The results and methodology can be applied to many biosystems, but having some reaction equilibrium measurements with uncertainties that involve the species of interest are essential for reliable results. [ABSTRACT FROM AUTHOR]

Fugacity coefficients of dilute aqueous solutions of six noble gases and five simple fluids have been correlated from ambient conditions (298 K, 0.1 MPa) to high temperatures (up to 2000 K) and water densities as high as 1500 kg m−3. A correlation is developed for the function, A 12 ∞ = V 2 ∞ / κ T R T , that includes known constraints: second virial coefficients at low-water densities, rigid-body behavior at high-water densities, near-critical principles, and corresponding-states relations. Reasonable agreement with an extensive, evaluated database of volumetric and solubility measurements has been achieved over the entire range of conditions, though comparisons of calculated with recommended Henry's constants suggest reconsiderations of recommendations for He and CO at temperatures above 550 K. Image 1 [ABSTRACT FROM AUTHOR]

A simple model for binary liquid-liquid equilibrium data correlation is explored. The model describes liquid-liquid equilibrium in terms of Henry's law and unsymmetrically normalized activity coefficients in each phase. A procedure for parameter estimation including an approach to initial guesses, uncertainty analysis of regression results, obtained parameters, and predicted mole fractions has been formulated. The procedure is applied to three cases: hydrocarbons + water, ionic liquids + water, and nitroethane + hydrocarbons. The model has four parameters in the most basic formulation. Depending upon the available data, this number can be extended in a systematic fashion. We compare results of correlation to results obtained with a four-parameter nonrandom two-liquid (NRTL) equation and COSMO-SAC. In general, the new model does nearly as well as NRTL. Advantages of the presented model are a simple form and a parameter set that can be extended in a systematic fashion with an interpretation in terms of thermodynamic properties. The model may be developed further for validation of experimental data. [ABSTRACT FROM AUTHOR]

Evaluations of equations of state (EoS) should include uncertainty. This study presents a generic method to analyse EoS from a detailed uncertainty analysis of the mathematical form and the data used to obtain EoS parameter values. The method is illustrated by comparison of Soave–Redlich–Kwong (SRK) cubic EoS with perturbed-chain statistical associating fluid theory (PC-SAFT) EoS for an organic Rankine cycle (ORC) for heat recovery to power from the exhaust gas of a marine diesel engine using cyclopentane as working fluid. Uncertainties of the EoS input parameters including their corresponding correlation structure, are quantified from experimental measurements using a bootstrap method. Variance-based sensitivity analysis is used to compare the uncertainties from the departure function and the ideal-gas contribution. A Monte Carlo procedure propagates fluid parameter input uncertainty onto the model outputs. Uncertainties in the departure function (SRK or PC-SAFT EoS) dominate the total uncertainties of the ORC model output. For this application and working fluid, SRK EoS has less predictive uncertainty in the process model output than does PC-SAFT EoS, though it cannot be determined if this is due to differences in the data for parameter estimation or in the mathematical form of the EoS or both. [ABSTRACT FROM PUBLISHER]

This article is the second of three projected IUPAC Technical Reports on reference materials for phase equilibrium studies. The goal of this project was to select reference systems with critically evaluated property values for the verification of instruments and techniques used in phase equilibrium studies of mixtures. This report proposes seven systems for solid–liquid equilibrium studies, covering the four most common categories of binary mixtures: aqueous systems with organic solutes, aqueous systems with inorganic solutes, non-aqueous systems, and systems with low solubility. For each system, the available literature sources, accepted data, smoothing equations, and estimated uncertainties are given. [ABSTRACT FROM AUTHOR]

In hydrophobic interaction chromatography (HIC), interactions between buried hydrophobic residues and HIC surfaces can cause conformational changes that interfere with separations and cause yield losses. This paper extends our previous investigations of protein unfolding in HIC chromatography by identifying protein structures on HIC surfaces under denaturing conditions and relating them to solution behavior. The thermal unfolding of three model multidomain proteins on three HIC surfaces of differing hydrophobicities was investigated with hydrogen exchange mass spectrometry (HXMS). The data were analyzed to obtain unfolding rates and Gibbs free energies for unfolding of adsorbed proteins. The melting temperatures of the proteins were lowered, but by different amounts, on the different surfaces. In addition, the structures of the proteins on the chromatographic surfaces were similar to the partially unfolded structures produced in the absence of a surface by temperature as well as by chemical denaturants. Finally, it was found that patterns of residue exposure to solvent on different surfaces at different temperatures can be largely superimposed. These findings suggest that protein unfolding on various HIC surfaces might be quantitatively related to protein unfolding in solution and that details of surface unfolding behavior might be generalized. [ABSTRACT FROM AUTHOR]

Recent studies with proteins indicate that conformational changes and aggregation can occur during ion exchange chromatography (IEC). Such behavior is not usually expected, but could lead to decreased yield and product degradation from both IEC and multi mode chromatography (MMC) that has ligands of both hydrophobic and charged functionalities. In this study, we used hydrogen exchange mass spectrometry to investigate unfolding of the model protein BSA on IEC and MMC surfaces under different solution conditions at 25°C. Increased solvent exposure, indicating greater unfolding relative to that in solution, was found for protein adsorbed on cationic IEC and MMC surfaces in the pH range of 3.0 to 4.5, where BSA has decreased stability in solution. There was no effect of anionic surfaces at pH values in the range from 6.0 to 9.0. Differences of solvent exposure of whole molecules when adsorbed and in solution suggest that adsorbed BSA unfolds at lower pH values and may show aggregation, depending upon pH and the surface type. Measurements on digested peptides showed that classifications of stability can be made for various regions; these are generally retained as pH is changed. When salt was added to MMC systems, where electrostatic interactions would be minimized, less solvent exposure was seen, implying that it is the cationic moieties, rather than the hydrophobic ligands, which cause greater surface unfolding at low salt concentrations. These results suggest that proteins of lower stability may exhibit unfolding and aggregation during IEC and MMC separations, as they can with hydrophobic interaction chromatography. [ABSTRACT FROM AUTHOR]

Abstract: The solubilities of gases in ionic liquids and compressed liquid densities have been successfully described over a wide range of conditions using a reformulated corresponding-states formulation for direct correlation function integrals. In addition, comparisons with experimental data show reliable prediction of ionic liquid characteristic properties from simple rules. [Copyright &y& Elsevier]

Abstract: A corresponding-states form of the generalized van der Waals equation, previously developed for mixtures of an ionic liquid and a supercritical solute, is here extended to mixtures including an ionic liquid and a solvent (water or organic). Group contributions to characteristic parameters are implemented, leading to an entirely predictive method for densities of mixed compressed ionic liquids. Quantitative agreement with experimental data is obtained over wide ranges of conditions. Previously, the method has been applied to solubilities of sparingly soluble gases in ionic liquids and in organic solvents. Here we show results for heavier and more-than-sparingly solutes such as carbon dioxide and propane in ionic liquids. [ABSTRACT FROM AUTHOR]

Abstract: Two corresponding-states forms have been developed for direct correlation function integrals in liquids to represent pressure effects on the volume of ionic liquids over wide ranges of temperature and pressure. The correlations can be analytically integrated from a chosen reference density to provide a full equation of state for ionic liquids over reduced densities from 1.5 to more than 3.6. One approach is empirical with 3 parameters, the other is a 2-parameter theoretical form which is directly connected to a method for predicting gas solubilities in ionic liquids. Parameters for both methods have been obtained for 28 different ionic liquid systems by reduction of carefully validated PρT data. The results show excellent agreement with the experimental data for nearly all substances over all ranges of conditions. Group contributions to parameters are also explored, leading to an entirely predictive method for ambient pressure densities and densities of compressed ionic liquids. Extensive comparisons are made with other techniques. [Copyright &y& Elsevier]

Abstract: We describe a method for correlating and estimating gas solubilities and liquid densities of ionic liquids based on a corresponding-states form for direct correlation function integrals (DCFIs) from fluctuation solution theory, as previously applied to nonionic systems. A quantitative description is obtained for the volumetric behavior of pure liquids at elevated pressures. Solubilities and partial molar volumes are given over wide ranges of conditions using only pure component information and a binary parameter for hydrogen, carbon monoxide, oxygen and methane in the ionic liquids 1-butyl-3-methyl-imidazolium hexafluorophosphate, [bmim][PF6], and 1-hexyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide, [hmim][Tf2N]. Comparisons are made with other literature treatments and a predictive approach is described. [Copyright &y& Elsevier]

Abstract: A two-conformation adsorption model that includes the effects of salt concentration and temperature on both stability and adsorption has been developed to describe the effects of secondary protein unfolding on hydrophobic interaction chromatography (HIC). The model has been applied to a biotech protein and to β-lactoglobulin on Phenyl Sepharose 6FF low sub HIC media. Thermodynamic property models for adsorption and protein stability with parameters obtained from experimental chromatographic data successfully describe observed chromatographic behavior over ranges of temperature and salt concentration, provide predictions of distribution among different conformers, and give a basis for calculating trends in retention strength and stability with changing conditions, that might prove useful in HIC process development. [Copyright &y& Elsevier]

Hydrogen-exchange mass spectrometry analysis of the stable protein aprotinin during reversed-phase liquid chromatography shows both native and unfolded protein. The behavior is consistent with only two conformational states, a near-native state and a fully solvent-accessible state, with reversible interchange of species within and between the mobile and stationary phases. The amount of unfolded form is greater on C18 relative to C4 alkyl modified silica surfaces. The addition of (NH4)2SO4, Na2SO4, NaCl, or NaSCN to the mobile phase stabilized native conformation on the chromatographic surface, especially on the C4 media. Finally, the retention and the proportion of denatured form increases with added salts in an order consistent with the lyotropic series, but reversed from that observed for small molecules. [Copyright &y& Elsevier]

This article is the first of three projected IUPAC Technical Reports resulting from IUPAC Project 2011-037-2-100 (Reference Materials for Phase Equilibrium Studies). The goal of this project is to select reference systems with critically evaluated property values for the validation of instruments and techniques used in phase equilibrium studies of mixtures. This report proposes seven systems for liquid–liquid equilibrium studies, covering the four most common categories of binary mixtures: aqueous systems of moderate solubility, non-aqueous systems, systems with low solubility, and systems with ionic liquids. For each system, the available literature sources, accepted data, smoothing equations, and estimated uncertainties are given. [ABSTRACT FROM AUTHOR]

Scientific projects frequently involve measurements of thermophysical, thermochemical, and other related properties of chemical compounds and materials. These measured property data have significant potential value for the scientific community, but incomplete and inaccurate reporting often hampers their utilization. The present IUPAC Technical Report summarizes the needs of chemical engineers and researchers as consumers of these data and shows how publishing practices can improve information transfer. In the Report, general principles of Good Reporting Practice are developed together with examples illustrating typical cases of reporting issues. Adoption of these principles will improve the quality, reproducibility, and usefulness of experimental data, bring a better level of consistency to results, and increase the efficiency and impact of research. Closely related to Good Reporting Practice, basic elements of Good Research Practice are also introduced with a goal to reduce the number of ambiguities and unresolved problems within the thermophysical property data domain. [ABSTRACT FROM AUTHOR]

We comment on work by Ruszczyński et al., who extended the regression method of Cunico et al. (Fluid Phase Equilibria, 2014) and proposed certain Gibbs free energy models for binary liquid-liquid equilibria. We find that their regression method considers only necessary criteria for stability, and we derive constraints to be imposed on the thermodynamic parameters during regression such that the criteria become sufficient and the models thus become numerically easy to use. We respond to the comments by Glass and Mitsos regarding our approach to validation of binary liquid-liquid equilibrium data. [ABSTRACT FROM AUTHOR]

Biphasic reacting systems contain effectively immiscible aqueous and organic liquid phases in which reactants, products, and catalysts can partition. These conditions allow novel synthesis paths, higher yields, and faster reactions, as well as facilitate product(s) separation. A systematic modeling framework of three modules has been developed to describe phase equilibria, reactions, mass transfer, and material balances of such processes. The recently developed group-contribution electrolyte model, e-KT-UNIFAC, is used to predict the partitioning and equilibria of electrolyte and nonelectrolyte species for a wide variety of reacting substances. Reaction kinetics and mass transfer are described by nonelementary reaction rate laws. Extents of reaction are used to calculate the species material balances. The resulting mathematical model contains only a few rate parameters to be regressed to a minimum of time-dependent data. In addition to describing the behavior of such systems, predictions can be made of the effectiveness in rates and ultimate amounts of product formation using different organic solvents. The present paper briefly describes the framework and applies it to the cases of epoxidation of palm oil and production of furan derivatives. [ABSTRACT FROM AUTHOR]

Phase-transfer catalyst systems contain two liquid phases, with a catalyst (PTC) that transfers between the phases, driving product formation in one phase and being regenerated in the other phase. Typically the reaction involves neutral species in an organic phase and regeneration involves ions in an aqueous phase. These reacting systems are receiving increased attention as novel organic synthesis options due to their flexible operation, higher product yields, and ability to avoid hazardous or expensive solvents. Major considerations in the design and analysis of PTC systems are physical and chemical equilibria, as well as kinetic mechanisms and rates. This paper presents a modelling framework for design and analysis of PTC systems that requires a minimum amount of experimental data to develop and employ the necessary thermodynamic and reaction models and embeds them into a reactor model for simulation. The application of the framework is made to two cases in order to highlight the performance and issues of activity coefficient models for predicting design and operation and the effects when different organic solvents are employed. [ABSTRACT FROM AUTHOR]

Inthis study, the behavior of derivative properties estimatedby equations of state, including isochoric heat capacity, isobaricheat capacity, speed of sound, and the Joule–Thomson coefficientfor pure compounds and a mixture, has been investigated. The Schmidt–Wagnerand Jacobsen–Stewart equations of state were used for predictionsof derivative properties of 10 different pure compounds from variousnonpolar hydrocarbons, nonpolar cyclic hydrocarbons, polar compounds,and refrigerants. The estimations were compared to experimental data.To evaluate the behavior of mixtures, the extended corresponding statesprinciple (ECS) was studied. Analytical relationships were derivedfor isochoric heat capacity, isobaric heat capacity, the Joule–Thomsoncoefficient, and the speed of sound. The ECS calculations were comparedto the reference surface data of methane + ethane. The ECS principlewas found to generate data of high quality. [ABSTRACT FROM AUTHOR]

Highlights: [•] Consistency of measured phase equilibrium data of lipids is considered before regression of model parameters. [•] A new thermodynamic consistency test for solid–liquid equilibrium (SLE) data is proposed. [•] An activity coefficient model for testing of SLE data is created. [•] Regressed model parameters for NRTL, UNIQUAC and UNIFAC models valid for lipids are given. [ABSTRACT FROM AUTHOR]

Abstract: The ‘State Conditions Transferability’ category of IFPSC 2006 tests prediction of binary vapor–liquid isotherms for mixtures of ethanol and the refrigerant HFF-227ea (1,1,1,2,3,3,3-heptafluoropropane). We predict these isotherms using fluctuation solution theory (FST). The method is based on isobaric–isothermal molecular dynamics (NPT-MD) simulations, using force field parameters published in the literature and fitted CHARMM force field parameters. Systems studied previously [S. Christensen, G.H. Peters, F.Y. Hansen, J.P. O’Connell, J. Abildskov, Molecular Simulation 33 (2007) 449–457] comprise the nearly ideal benzene/methyl acetate system, and the less ideal benzene/ethanol system at ambient temperatures. Both are at low pressures and remote from the pure component critical points. For the IFPSC system, we have used the same method even though predictions are for conditions remote from those of the provided data, the pressures are elevated, and the temperatures are near the critical temperature of one of the components. We first describe the computational method and thermodynamic modeling for the entry submitted, which assumed the vapor was an ideal gas and no Poynting correction was included. Then we discuss the effects of using common modeling methods to estimate the effects of elevated pressures. [Copyright &y& Elsevier]

Abstract: A general analysis is presented to focus on the mathematical and numerical elements of property models for stand-alone results as well as within other calculations. This includes listing all of the equations that constitute a property model and articulating the sets of known and unknown variables for given problems. Ordering of equations is done to determine if a direct solution is feasible where the incidence matrix of unknown variables and equations can be written in tridiagonal form or if simultaneous or iterative solution of multiple equations is required. Example pure compound and mixture property models are: cubic equations of state; more advanced non-cubic equations of state; activity coefficient models; and models for polymer and electrolyte systems. Uses of this analysis are discussed for property calculations as a part of other calculations, such as for process models and parameter regression. [Copyright &y& Elsevier]

The ALLD simulation software implements a mesoscopic lattice method to model hydrophobic chromatographic systems and biomembranes. The basis and some initial results of these applications emphasizing reversed phase chromatography of peptides are reviewed. The program structure and coding are described along with concepts for parallelization to simulate massive systems and large biomolecules. Extensions of the method for simulations with variable temperature, solute and solvent polarization, effects of ionized solutes and added salts and heterogeneous media are presented. [ABSTRACT FROM AUTHOR]

Mesoscopic simulations using Langevin dipoles on a lattice for the solvent and calculated partial charges for the solute have been used to estimate free energies of adsorption from data on reversed-phase chromatography on nine protected peptides covering a wide range of structures. There is a single parameter, the effective solvent dipole moment, that is fit to data for one peptide and used to predict properties of the other eight peptides. Good agreement of adsorption chemical potentials, including order of chromatographic retention times, is found for calculations that are Boltzmann-averaged over a set of orientations. In addition, the results suggest that there are preferential orientations for each peptide at the model hydrophobic chromatographic surface. Estimation methods for adsorption based on molecular descriptors and hydrophobicity scales are shown to be unreliable for these systems. With refinements and extensions, this simulation method should be applicable to solvents containing salt, such as in hydrophobic interaction chromatography, and to larger solutes including proteins. [ABSTRACT FROM AUTHOR]