Liquid Molar Volume Research Articles

Electrolyte CPA equation of state for very high temperature and pressure reservoir and basin applications

In this work, an electrolyte version of the Cubic Plus Association (eCPA) equation of state has been adapted to systems containing CH4, CO2, H2O and NaCl (up to 5molal) at pressures up to 200MPa and temperatures up to 773K for salt-free systems and 573K for salt-containing systems. Its purpose is to represent the phase behavior (including salting-out effect and critical point) and the phase densities in a range of temperature and pressure encountered in deep reservoirs and basins. The goal of the parameterization proposed is not to reach a very high accuracy for phase equilibrium and volumetric properties, but rather to develop a semi-predictive approach to model the phase and volumetric behavior of this system while allowing an easy extension to other compounds.Without salt, predictions for pure component vapor pressures and liquid molar volumes present an average absolute deviation (AAD) lower than 3% compared to experimental reference values. The pure component molar volumes out of saturation show an AAD lower than 4%. The highest deviations in densities are observed as expected in the vicinity of the critical coordinates of pure water and this effect increases when gases or salts are added to the system. For each binary system, CH4+CO2, CH4+H2O and CO2+H2O, binary interaction parameters have been fitted to correctly represent the shape of the fluid phase envelopes (including all critical points) in the entire temperature and pressure range considered (219K to 633K and up to 250MPa). The methane concentration in both phases of the CH4+CO2 binary system is represented with an AAD lower than 9%. The methane solubility in water is represented within 16% and 8% for the methane content of the vapor. The CO2 solubility in water is within 26%, while the CO2 in the vapor phase shows an average deviation of 12%. All molar volumes are represented with an AAD lower than 3%. The few VLE experimental data for the CH4+CO2+H2O ternary system are fairly well predicted with the model without extra parameter, which confirm the ability of the eCPA equation of state to be extended to multi-component systems. In the presence of salts, gas+ion binary interaction parameters have been fitted, and all phase equilibrium are qualitatively correctly described, and more specifically the salting out effect. The solubility of methane or CO2 in brines, up to 5molal, is represented with an AAD of 33% in a large temperature and pressure range (up to 673K and 150MPa). It should be noticed that for high temperatures, experimental data are relatively scarce and not always consistent. No data exist for water content of the vapor phase in these conditions.The new eCPA model can be easily extended to other components (including ions) to better represent real fluid behavior in very deep reservoir conditions.

Measurements and group contribution analysis of 0.1 MPa densities for still poorly studied ionic liquids with the [PF6] and [NTf2] anions

Experimental data over the temperature range from (262 to 365)K are presented on the 0.1MPa densities for seven imidazolium and pyridinium based ionic liquids with hexafluorophosphate and bis(trifluoromethylsulfonyl)imide anion. Four of them almost have not been studied in this respect yet. The reported density data were obtained using a single-sinker buoyancy method. The estimated expanded combined uncertainty at 0.95 confidence level ranges from 0.1kg·m−3 for [BMPy][PF6] to 1.0kg·m−3 for [EMIM][NTf2], that is, from (0.8·10-4 to 6.7·10-4)ϱ (T=298.15K). The Krűss K100MK2 tensiometer was used to determine the buoyancy forces. For the contribution to the ionic liquid molar volume at T=298.15K and 0.1MPa follows from the obtained density data for a CH3 group bound to a nitrogen atom in the imidazolium ring a value of (17.65±0.16)cm3·mol−1, for a CH3 group bound to a carbon atom in the imidazolium ring a value of (17.71±0.3)cm3·mol−1, and for an inner CH2 group in the alkyl side chain the value of (16.99±0.02)cm3·mol−1, where 0.95 confidence level uncertainties are given arising from the data scatter. Nonlinearity of the dependence of the alkyl side chain contribution to the molar volume on the number of its carbon atoms limits the accuracy attainable using the group contribution method to about 0.1cm3·mol−1, that is, 5·10-4ϱ. A model is proposed to generate recommended values of density at0.1MPa for 1-Cn-3-methylimidazolium bis(trifluoromethylsulfonyl)imides with n=2 to 14 at temperatures from (260 to 473)K.

Application of GC-PPC-SAFT EoS to ammonia and its mixtures

The GC-PPC-SAFT equation of state (EoS) is a combination of the PC-SAFT EoS proposed by Gross and Sadowski [J. Gross, G. Sadowski, Ind. Eng. Chem. Res. 40 (2001) 1244–1260] and a group contribution method proposed by Tamouza [S. Tamouza et al., Fluid Phase Equilib. 222–223 (2004) 67–76; S. Tamouza et al., Fluid Phase Equilib. 228–229 (2005) 409–419] which was extended to polar molecules by Nguyen-Huynh [D. Nguyen-Huynh et al., Fluid Phase Equilib. 264 (2008) 62–75]. It is here applied to ammonia for which parameters have been regressed on pure component data (vapour pressures and liquid molar volumes), and some mixture vapour–liquid equilibrium data. Ammonia is described with an association scheme containing four associating sites (one donor site on the nitrogen atom and an acceptor site on each hydrogen atom). It also contains a dipole moment. These resulting parameters have then been tested on vapour–liquid equilibrium (VLE) and liquid–liquid equilibrium (LLE) of mixtures with n-alkanes, cycloalkanes, aromatics and small molecules such as methane, hydrogen or nitrogen whose parameters were previously published. The vapour–liquid equilibrium and the mixing enthalpy have also been evaluated for the ammonia+water binary system. For these systems a binary interaction parameter kij and corrective parameters for the cross-association energy wαβ and volume uαβ have been used in some cases.The agreement with experimental data is encouraging as correlations and predictions are both qualitatively and quantitatively satisfactory. In terms of pure component properties, the mean absolute average deviation (AAD) for the vapour pressures is about 2.5% whereas it is about 2.7% for the saturated liquid volumes. Furthermore, predictions on mixtures with n-alkanes, cycloalkanes or aromatics show that LLE lines predicted by GC-PPC-SAFT are perfectly well-located. Finally, results for VLE with n-alkanes, aromatics, small molecules or water are as accurate as it was for previously investigated systems. These results also show that the model is able to correctly represent the sign and the order of magnitude of the mixing enthalpy for the ammonia+water system.For systems containing ammonia with alkylbenzenes, this study have highlighted that a re-adjustment of alkybenzenes groups parameters was necessary. This paper explains the fitting procedure used for the new alkylbenzenes groups parameters and show satisfactory results for VLE and LLE of systems containing ammonia and alkylbenzenes.

GC-PPC-SAFT Equation of State for VLE and LLE of Hydrocarbons and Oxygenated Compounds. Sensitivity Analysis

Group-contribution polar versions of SAFT equations of state are very useful for predictive calculations of mixtures containing diverse polar molecules. In this work, we have evaluated the predictive performance of one such model, the so-called polar perturbed-chain (PPC) SAFT model for phase-equilibrium properties of 290 hydrocarbons and monofunctional oxygenated compounds. Emphasis has been given on carrying out an extensive evaluation considering diverse types of phase behavior (vapor–liquid and liquid–liquid equilibria) and properties/conditions (Henry’s law constant for H2, N2, and CH4; infinite-dilution activity coefficient in water; solubility in water; infinite-dilution n-octanol/water partition coefficient). In general, considering the predictive nature of the calculations, encouraging results were obtained. For pure-component vapor pressures and liquid molar volumes, the deviations are very small, at 20% and 3%, respectively. The deviations in the prediction of the Henry’s law constants are within a factor of 2, with the best results found for the methane and nitrogen solubilities. For solubilities in water and, consequently, for infinite-dilution n-octanol/water partition coefficients, deviations are within a factor of 2 for hydrocarbons and within a factor of 4 for alcohols and aldehydes, but they are large for the other oxygenated families. To identify paths for improvement, a sensitivity analysis was performed, indicating that all of the parameters make large contributions to almost all properties. In addition, the sensitivity of the infinite-dilution activity coefficient in water to the molecular size parameters was extremely high. This suggests that a small change in these parameters might improve the results significantly.

CO2 separation applying ionic liquid mixtures: the effect of mixing different anions on gas permeation through supported ionic liquid membranes

In order to increase flexibility in tailoring the permeability and selectivity of supported ionic liquid membranes (SILMs) for flue gas separation and natural gas purification, this work explores the use of ionic liquid mixtures. For that purpose, gas permeation properties of CO2, CH4 and N2 in several binary ionic liquid mixtures based on a common cation ([C2mim]+) and different anions such as bis(trifluoromethylsulfonyl)imide ([NTf2]−), acetate ([Ac]−), lactate ([Lac]−), dicyanamide ([DCA]−) and thiocyanate ([SCN]−) were measured at 293 K using a time-lag apparatus. In addition to gas permeation results, the thermophysical properties of those mixtures, namely viscosity and density, were also determined so that trends between the two types of properties could be evaluated. The results show that mixing [Ac]− or [Lac]− with [NTf2]− promotes the decrease of gas permeability and diffusivity of the SILMs based on those binary mixtures, essentially due to their high viscosities. The pure ionic liquids containing anions with nitrile groups, [DCA]− or [SCN]−, and also their mixtures with [C2mim][NTf2] exhibit permselectivities ranging from 19.1 to 23.0 for CO2/CH4, and from 36.6 to 67.8 for CO2/N2, as a consequence of a reduction in the CH4 and N2 permeabilities, respectively. Furthermore, it is shown that mixing anions with different chemical features allows variations in ionic liquid viscosity and molar volume that impact the gas permeation properties of SILMs, offering a clear pathway for the optimization of their CO2 separation performances.

Studies about an Equation of State for Pure Associated Fluids: Temperature Dependent Co-Volume Accounting a Physically Consistent Repulsive Term

Studies related to the development of equations of state (EOS) to represent thermophysical properties of pure compounds are considered as important tools for engineers to design and optimize industrial equipment and processes. Furthermore, these tools also contribute to amplify the researchers’ knowledge related to molecular interaction types, in attempting to predict and correlate both energetic and volumetric effects existing in the compounds. From several equations of state existing, the cubic plus association (CPA) EOS are employed in the calculations of thermophysical properties of compounds, in which the molecular interactions occurring are the association type. In spite of good representation of these properties, it is possible to improve the predictive and correlative capability of the CPA EOS by substitution of terms whose physical meaning can be better. In this way, modifications of the cubic plus association equation of state are proposed: the original repulsive term is replaced by the Carnahan-Starling repulsion term; the attractive term is changed to an attraction term similar to the Peng-Robinson EOS. Furthermore, both attraction and repulsion terms are taken to be temperature dependent when alpha and beta functions are employed in calculations. All implementations make the equation of state non-cubic in relation to volume. Vapor pressure and liquid molar volumes of 1-alkanols (C1 to C10) and water were correlated to experimental data using this non-CPA–EOS format, and good agreement is observed.

Studies about an Equation of State for Pure Associated Fluids: Temperature Dependent Co-Volume Accounting a Physically Consistent Repulsive Term

Studies related to the development of equations of state (EOS) to represent thermophysical properties of pure compounds are considered as important tools for engineers to design and optimize industrial equipment and processes. Furthermore, these tools also contribute to amplify the researchers’ knowledge related to molecular interaction types, in attempting to predict and correlate both energetic and volumetric effects existing in the compounds. From several equations of state existing, the cubic plus association (CPA) EOS are employed in the calculations of thermophysical properties of compounds, in which the molecular interactions occurring are the association type. In spite of good representation of these properties, it is possible to improve the predictive and correlative capability of the CPA EOS by substitution of terms whose physical meaning can be better. In this way, modifications of the cubic plus association equation of state are proposed: the original repulsive term is replaced by the Carnahan-Starling repulsion term; the attractive term is changed to an attraction term similar to the Peng-Robinson EOS. Furthermore, both attraction and repulsion terms are taken to be temperature dependent when alpha and beta functions are employed in calculations. All implementations make the equation of state non-cubic in relation to volume. Vapor pressure and liquid molar volumes of 1-alkanols (C1 to C10) and water were correlated to experimental data using this non-CPA–EOS format, and good agreement is observed.

Simple yet accurate prediction of liquid molar volume via their molecular structure

Molecular structure based study of liquid molar volume can be helpful in better understanding of liquid behaviors among a wide variety of scientific phenomena. Here, the most responsible molecular parameters for the pure liquid molar volume of organic and simple inorganic chemicals were determined through a robust quantitative molecular structural analysis. Using rank based ant system (RBAS) which is an encouraging optimization program, 1741 pure liquid molecules comprising 76 diverse chemical classes along with more than 3200 calculated molecular parameters for each liquid molecule were terminated in a simple yet accurate theoretical model with high accuracy. The result of three-parametric RBAS-MLR model is able to reach a prediction performance far better than the existing ones with a squared correlation coefficient (R2) of 0.97 and root mean square error (RMSE) of 15.34cm3/gmol for the entire dataset. Based on chemical structural similarities, distribution of the average absolute relative errors were calculated and sorted.

An improved generalized three-parameter cubic equation of state for pure fluids

An improved simple generalized three-parameter cubic equation of state for pure fluids is proposed to estimate pure component fluid properties by incorporating substance dependent epsilon-function and almost substance independent sigma-function in the generic cubic equation of state, followed by temperature and acentric factor dependent attractive term. The proposed cubic equation of state is utilized to predict critical compressibility factor, liquid molar volume, vapor molar volume, and pure component vapor pressure for several simple hydrocarbons and fatty acid of methyl esters, and the predicted properties are compared with the actual values. In this study, most of the pure fluid properties are considered from literature; however experimentation is carried out for few fatty acid of methyl esters to determine pure fluid vapor pressure at elevated temperature and pressure. The proposed cubic equation of state is found to be accurate in predicting both literature reported and experimentally determined pure fluid properties. The overall performance of the proposed cubic equation of state is also compared with commonly used cubic equations of state and is found to be superior for predicting critical compressibility factors and other pure fluid properties.

Thermodynamic properties and vapor–liquid equilibria of associating fluids, Peng–Robinson equation of state coupled with shield-sticky model

Combining Peng–Robinson (PR) equation of state (EOS) with Liu et al.’s association contribution derived from shield-sticky model (SSM), a new cubic-plus-association (CPA) EOS is proposed to describe the thermodynamic properties of pure associating fluids and their mixtures. The CPA-SSM EOS contains five molecular parameters (a0, c1, b, ω and δɛ/k) for the pure associating fluids, while for non-associating fluids it reduces to PR EOS with three molecular parameters (a0, c1, b). The molecular parameters are obtained by fitting the saturated pressures and/or liquid molar volumes at wide temperature ranges. The overall average absolute deviations (AADs) of 58 pure associating fluids and 20 non-associating fluids are 0.74% and 0.54% for saturated vapor pressure, 2.00% and 1.85% for liquid molar volumes respectively. The enthalpies of vaporization for 13 pure associating fluids are well predicted by using these molecular parameters. The molecular parameter b for homologous substances shows a good linear relationship with respect to their corresponding molecular weights. Using one temperature-independent binary adjustable parameter kij, satisfactory results of vapor–liquid equilibria (VLE) for both self- and cross-associating systems are obtained. The overall AADs of the equilibrium temperatures, pressures and vapor phase mole fractions are 1.46K, 1.26kPa and 0.0197 respectively for 25 self-associating systems, and 0.75K, 0.50kPa and 0.0155 respectively for 29 cross-associating systems. Other caloric properties such as the excess molar enthalpies of mixing are also successfully computed. The CPA-SSM EOS proposed has been proved to have comparable accuracy as other models but with much simpler form.

Influence of the anion on the surface tension of 1-ethyl-3-methylimidazolium-based ionic liquids

The air–liquid interfacial tensions of eight ionic liquids, from (298 to 343)K, are presented in this work. The studied ionic liquids are formed by the fixed 1-ethyl-3-methylimidazolium cation combined with the anions acetate, dicyanamide, dimethylphosphate, methylphosphonate, methanesulfonate, thiocyanate, tosylate, and trifluoromethanesulfonate. The selected ionic liquids allowed a comprehensive study through the influence of the anion nature on the surface tension and on their surface ordering. A slight dependence of the surface tension with the ionic liquid molar volume was identified. The surface thermodynamic functions are mainly controlled by the anion which constitutes a given ionic liquid. The hypothetical critical temperatures of all ionic liquids were estimated by means of the Eötvos and Guggenheim correlations and are presented.

Group-contribution+ (GC+) based estimation of properties of pure components: Improved property estimation and uncertainty analysis

The aim of this work is to present revised and improved model parameters for group-contribution+ (GC+) models (combined group-contribution (GC) method and atom connectivity index (CI) method) employed for the estimation of pure component properties, together with covariance matrices to quantify uncertainties in the estimated property values. For this purpose, a systematic methodology for property modeling and uncertainty analysis of GC models and CI models using maximum-likelihood estimation theory is developed. For parameter estimation, large data-sets of experimentally measured property values of pure components of various classes (hydrocarbons, oxygenated components, nitrogenated components, poly-functional components, etc.) taken from the CAPEC database are used. In total 18 pure component properties are analyzed, namely normal boiling point, critical temperature, critical pressure, critical volume, normal melting point, standard Gibbs energy of formation, standard enthalpy of formation, normal enthalpy of fusion, enthalpy of vaporization at 298K, enthalpy of vaporization at the normal boiling point, entropy of vaporization at the normal boiling point, flash point, auto ignition temperature, Hansen solubility parameters, Hildebrand solubility parameter, octanol/water partition coefficient, acentric factor, and liquid molar volume at 298K. Important issues related to property modeling such as reliability and predictive capability of the property prediction models, and thermodynamic consistency of the predicted properties (such as, relation of normal boiling point versus critical temperature) are also analyzed and discussed. The developed methodology is simple, yet sound and effective and provides not only the estimated pure component property values but also the uncertainties (e.g. prediction errors in terms of 95% confidence intervals) in the estimated property values. This feature allows one to evaluate the effects of these uncertainties on product-process design, simulation and optimization calculations, contributing to better-informed and more reliable engineering solutions.

Prediction of the PC-SAFT Associating Parameters by Molecular Simulation

In this work, we propose a new methodology to determine association scheme and association parameters (energy and volume) of a SAFT-type EoS for hydrogen-bonding molecules. This paper focuses on 1-alkanol molecules, but the new methodology can also be applied for any other associating system. The idea is to use molecular simulation technique to determine independently monomer and free hydrogen fractions from which the association scheme can be deduced. The 3B scheme thus appeared to be the most appropriate for 1-alkanols. Once the association scheme is defined, the association strength can be back-calculated from molecular simulation results and used as an independent property for the equation of state parameters regression, in addition of the classical phase properties such as vapor pressure and liquid molar volume. A new set of parameters for 1-alkanol for the PPC-SAFT equation of state has been proposed following this methodology. Results are found in good agreement with experimental data for both phase properties and free hydrogen-bonding sites. Hence, this new methodology makes it possible to optimize parameters allowing an accurate reproduction of pure compounds data and yielding physically significant values for associating energy and associating volume.

Determination and Correlation of Solubility of Decahydropyrazino[2,3-b]pyrazine in Methanol, Ethanol, and 2-Propanol

The solubilities of decahydropyrazino[2,3-b]pyrazine (DHPP) in methanol, ethanol, and 2-propanol were measured at temperatures ranging from 274.95 to 354.75 K. The last crystal disappearance method was used to determine the solubility of DHPP. The experimental data were correlated by the van’t Hoff plot, λh (Buchowski) equation, modified Apelblat equation, and two local composition models (Wilson and NRTL). Moreover, the densities of (DHPP + water) solution were measured from 274.25 to 355.95 K, and the liquid molar volume of DHPP, Vm1(T), was obtained and used to calculate the parameters in the Wilson model. It was found that NRTL model gave the best correlation results. On the basis of the NRTL model and experimental data, the thermodynamic excess functions (ΔGE, ΔSE, and ΔHE) of DHPP + alcohols (methanol, ethanol, and 2-propanol) systems were determined. Furthermore, the infinite-dilution activity coefficient and the infinite-dilution reduced excess enthalpy (γ1∞ and ΔHE1∞) were derived.

Applications of the Soave-Redlich-Kwong Equations of State Using Matlab

In this paper, using Matlab to solve Soave-Redlich-Kwong (SRK) EOS, as well as the estimation of pure component properties, plotting of vapor-liquid equilibrium (VLE) diagram and calculation of chemical equilibrium, is presented. First the SRK EOS is used to predict several pure-component properties, such as liquid and gas molar volumes for isobutane. The vapor-liquid isobaric diagram is then plotted for a binary mixture composed of n-pentane and n-hexane under the pressures of 1.5*10^5 and 7*10^5 Pa respectively. Finally, the extent of ammonia synthesis reaction under high pressure is calculated.

Thermophysical properties of pure and water-saturated tetradecyltrihexylphosphonium-based ionic liquids

In this work, the solubility of water in several tetradecyltrihexylphosphonium-based ionic liquids at 298.15 K, and densities and viscosities of both pure and water-saturated ionic liquids in a broad temperature range were measured. The selected ionic liquids comprise the common tetradecyltrihexylphosphonium cation combined with the following anions: bromide, chloride, bis(trifluoromethylsulfonyl)imide, decanoate, methanesulfonate, dicyanamide and bis(2,4,4-trimethylpentyl)phosphinate. The isobaric thermal expansion coefficients for pure and water-saturated ionic liquids were determined based on the density dependence with temperature. Taking into account that the excess molar volumes of the current hydrophobic water-saturated ionic liquids are negligible, the solubility of water was additionally estimated from the gathered density data and compared with the experimental solubilities obtained. Moreover, the experimental densities were compared with those predicted by the Gardas and Coutinho model while viscosity data were correlated using the Vogel–Tammann–Fulcher method.

A critical assessment of capillary condensation and evaporation equations: A computer simulation study

Grand Canonical Monte Carlo simulation (GCMC) is used to study the capillary condensation and evaporation of argon adsorption in finite-length carbon cylindrical nanopores. From the simulation results of local density distributions in the radial and axial directions we obtain the contact angle and the core radii just before condensation and just after evaporation. These are then used in the Kelvin equation (evaporation) and Cohan equation (condensation) to obtain the product of surface tension and liquid molar volume. This product is found to be always greater than for the bulk liquid. We test this deviation with pores of different length and radius and find that both affect the derived product of surface tension and liquid molar volume. The implication of this finding is that if the values of surface tension and liquid molar volume of the bulk phase are used in the Kelvin equation the pore radius will be underestimated. For argon adsorption in cylindrical pores we propose that the Kelvin and Cohan equations should be modified to take account of the difference between the fluid in the adsorbed phase in the confined space and that in the bulk phase.

Application of GC-PPC-SAFT EoS to amine mixtures with a predictive approach

The GC-PPC-SAFT equation of state (EoS) is a combination of a group contribution method [S. Tamouza et al., Fluid Phase Equilib. 222–223 (2004) 67–76; S. Tamouza et al., Fluid Phase Equilib. 228–229 (2005) 409–419] and the PC-SAFT EoS [J. Gross, G. Sadowski, Ind. Eng. Chem. Res. 40 (2001) 1244–1260] which was adapted to the polar molecules [D. Nguyen-Huynh et al., Fluid Phase Equilib. 264 (2008) 62–75]. It is here applied to the vapour pressure and liquid molar volume of primary, secondary and tertiary amines and their mixtures with n-alkanes, primary and secondary alcohols, using previously published group parameters. The mixing enthalpy is also evaluated for the binary systems. Binary interaction parameters k ij are computed using a group-contribution pseudo-ionization energy, as proposed by Nguyen-Huynh [D. Nguyen-Huynh et al., Ind. Eng. Chem. Res. 47 (2008) 8847–8858]. A unique corrective parameter for the cross-association energy between amines and alcohols is used. The agreement with experimental data in correlation and prediction were found rather encouraging. The mean absolute average deviation (AAD) on bubble pressure is about 3.5% for pure amines. The mean AAD on the vapour–liquid equilibria (VLE) are respectively 2.2% and 5.5% for the amine mixtures with n-alkanes and alcohols. The AADs on saturated liquid volume are about 0.7% for the pure compounds and 0.9% for the mixtures. Prediction results are qualitatively and quantitatively accurate and they are comparable to those obtained with GC-PPC-SAFT on previously investigated systems.

Equation of state for square-well chain molecules with variable range, extension to associating fluids

The equation of state developed in our previous work for square-well chain molecules with variable range (SWCF-VR EOS) was further extended to associating fluids. The association contribution is directly calculated by Liu et al.’s association equation which was proposed based on the sticky-shield method. For the real pure associating fluids, the SWCF-VR EOS has six temperature-independent model parameters obtained by fitting the saturated pressures and/or liquid molar volumes. The results are satisfactory with the overall average absolute deviations (AADs) of 0.76% and 0.75% for saturated vapor pressures and liquid molar volumes of 78 pure fluids in wide temperature ranges. The heat of vaporization for 17 associating fluids were well predicted using these molecular parameters. The good relations between the molecular parameters and the molecular weights were observed. By using a simple mixing rule with only one adjustable binary interaction parameter k ij for the cross well depth ɛ ij , the SWCF-VR EOS can satisfactorily reproduce the vapor–liquid equilibria (VLE) of binary mixtures at reduced and elevated pressures containing self- and cross-associating interaction. Furthermore, the VLE for ternary mixtures can be successfully predicted by using the obtained binary interaction parameters.

A numerical scheme to calculate temperature and salinity dependent air-water transfer velocities for any gas

Abstract. The ocean-atmosphere flux of a gas can be calculated from its measured or estimated concentration gradient across the air-sea interface and the transfer velocity (a term representing the conductivity of the layers either side of the interface with respect to the gas of interest). Traditionally the transfer velocity has been estimated from empirical relationships with wind speed, and then scaled by the Schmidt number of the gas being transferred. Complex, physically based models of transfer velocity (based on more physical forcings than wind speed alone), such as the NOAA COARE algorithm, have more recently been applied to well-studied gases such as carbon dioxide and DMS (although many studies still use the simpler approach for these gases), but there is a lack of validation of such schemes for other, more poorly studied gases. The aim of this paper is to provide a flexible numerical scheme which will allow the estimation of transfer velocity for any gas as a function of wind speed, temperature and salinity, given data on the solubility and liquid molar volume of the particular gas. New and existing parameterizations (including a novel empirical parameterization of the salinity-dependence of Henry's law solubility) are brought together into a scheme implemented as a modular, extensible program in the R computing environment which is available in the supplementary online material accompanying this paper; along with input files containing solubility and structural data for ~90 gases of general interest, enabling the calculation of their total transfer velocities and component parameters. Comparison of the scheme presented here with alternative schemes and methods for calculating air-sea flux parameters shows good agreement in general. It is intended that the various components of this numerical scheme should be applied only in the absence of experimental data providing robust values for parameters for a particular gas of interest.