PρT Data Research Articles

Solubility study of carbon dioxide in pentaerythritol esters: Based on SAFT-VR-Mie equation of state

Lubricants are almost necessary for carbon dioxide systems in the energy, chemical, and refrigeration industries. The study of the solubility behavior of lubricants with working fluids requires a proper equation of state as necessary tools. The solubility of CO2 in synthetic precursors for polyol esters lubricants has been investigated by SAFT-VR-Mie EoS with variable fluid potential, including pure component pentaerythritol esters (PEC) molecules and CO2-PECs mixed system. The correlations between the molecular parameters in SAFT-VR-Mie EoS and mass of PECs with different branched lengths are given under the constraints of experimental PρT data. According to the parameterized molecular model, the prediction of the critical point and the constant-pressure specific heat of the PECs is introduced in this work. The dissolution balance model of CO2 in PECs was developed by the quantitative model of temperature and molecular mass dependent molecular interaction factor kij. The explanation for the variation of the interaction factors is given by the analysis of the intermolecular volume differences effect, and the extension of this model to commercial lubricants still proves to be valid and accurate.

Insights into molecular interactions gleaned from a lattice-based Helmholtz equation of state

A bulk phase thermodynamic potential is used to account for molecular interaction energy. It is derived from the partition function and is equal to the internal energy minus the product of temperature multiplied by thermal entropy. Bulk interaction energy is a function of volume, temperature, and quantity. Thermal entropy is the negative derivative of bulk interaction energy with respect to temperature at constant volume. A Helmholtz equation of state for pure fluids, with models of bulk interaction energy and configurational entropy, is proposed and used to correlate PρT data generated by REFPROP equations for hydrogen, parahydrogen, deuterium, helium, neon, argon, krypton, xenon, and nitrogen. The difference between the proposed equation of state and REFPROP density values are on average within the reported uncertainty in REFPROP over the REFPROP range of applicability. The equation of state satisfies the ideal curves assessment indicating reasonable extrapolation behavior beyond the range of applicability. Plots of implied interaction energy isotherms versus molecular separation distance (cube root of molar volume divided by Avogadro's number) all have the same characteristic features. The strongest attraction between molecules occurs at the triple point temperature for a liquid with a density approximately 5% larger than the triple point liquid density. The separation distance at the minimum potential energy is on average within 0.1 Ả of the average value derived from empirical Lennard-Jones potential. At separations closer than this attraction drop off sharply changing rapidly to repulsion. At a given separation along the coexistence line attraction is stronger than at any other temperature with the same separation. Interactions become strictly repulsive beyond some temperature in the critical region.

PρT and liquid-gas phase transition properties ([formula omitted]) of binary n-hexane + methyl octanoate mixture near the critical point of pure n-hexane

PρT and phase transition properties (PS,ρS,TS) of the dilute binary mixture of n-hexane + methyl octanoate have been studied near the critical point of pure n-hexane (solvent). The measurements were performed along 11 liquid, vapor and near-critical isochores between (39.3 and 621.1) kg·m-3 over a temperature range from (293 to 622) K at pressures up to 17.7 MPa for the fixed concentration of x = 0.088 mole fraction (or 0.05 mass fraction) of methyl octanoate. The measurements were made using a constant-volume piezometer technique. The study was concentrated in the single - and two- phase regions near the critical point of pure n-hexane to precisely determine the phase boundary properties (PS,ρS,TS) and the critical property (PC,ρC,TC) data of the mixture. The measured critical property data for the mixture were used to study of the isomorphic critical behavior of strongly singular properties such as isothermal compressibility KTX and isobaric heat capacity CPX along the critical isochore and the critical isotherm, i.e., Fisher renormalization (mixture-like behavior) of the critical exponent, -γ⇒γ/(1−α), for strongly singular properties of mixture under study. The measured PρT data were also used to estimate the values of physical meaningful (theoretically important) parameters such as characteristic reduced temperature τ1and density differencesΔρ1 of the mixture. We found that KTX and CPX of the studied mixture exhibit pure-like behavior along the critical isochore at temperature above 508.52 K (slightly above the critical temperature of pure n-hexane, 507.44 K) and along the critical isotherm at densities above 279.82 kg⋅m-3 (above the critical density of pure n-hexane, 232.8 kg⋅m-3). The measured data were used to estimate the Krichevskii parameter Kkr,structural (Nexc)and volumetric (V¯2∞) properties of the dilute mixture near the critical point of pure solvent (n-hexane).

Simulations of internal energy and pρT properties of monatomic fluids from accurate ab initio potentials and their uncertainty analysis

Ab initio potentials available in the literature are used to investigate the internal energy and pρT properties of helium, neon, argon, krypton, and xenon by molecular dynamics simulations. The total uncertainty of the simulation data is evaluated by reasonably quantifying the contributions from both the simulation method and the potential models. The theoretical predictions of this work are compared with recent experimental pρT data as well as the NIST data for the gas and supercritical phases to check the quality of this work. In most cases, agreement is found between the internal energy and pρT property values of this work and the literature data and the differences are smaller than the corresponding simulation uncertainty. It is concluded that the simulation data of this work are accurate enough to be used with confidence in different technical and practical applications over a wide temperature and density range.

Development of a robust soft-SAFT model for protic ionic liquids using new high-pressure density data

New experimental density data in a wide range of temperatures (283–363) K and pressures (0.1–95) MPa is here reported for five protic ILs based on the N,N-diethylethanolammonium ([DEEA]) cation, combined with the following anions: acetate ([Ace]), propanoate ([Prop]), butanoate ([But]), pentanoate ([Pent]) and hexanoate ([Hex]) in a 1:1 acid:base proportion. The molar volumes of the different ILs and derivative properties such as the isothermal compressibility and isobaric thermal expansivity were determined from the experimental density data. Moreover, considering the importance of having a robust and transferable thermodynamic model of these ILs that can be used in further studies including CO2 capture, the new experimental data was used to develop a coarse-grain molecular model of the studied ILs, in the framework of the soft-SAFT EoS, employing a 2/2 association scheme to account for the hydrogen bonding character of the ILs. The proposed model was found to provide an excellent description of the experimental pρT data with average relative deviations lower than 0.11% for all the ILs, while still providing reasonable predictions of the second-order derivative properties. Furthermore, the optimized molecular parameters were found to be correlated with the ILs molecular weight, highlighting the physical meaning and consistency of the parameters obtained.

High-temperature and high-pressure density and liquid–vapor phase transition properties of methyl octanoate as main biofuel component

Thermodynamic properties of compressed fuels as density at liquids phase (PρT data) and two liquids-gas phases as saturated pressure, density, and temperature (PS,ρS,TS) are extremely important for engine performance as well as the transportation and storage of fuels. In this work single – and two–phase PρT data and liquid + gas phase equilibrium properties (PS,TS,ρS) of methyl octanoate (caprylate) as one of the key components of biofuels have been studied. The measurements were performed along 15 liquid and vapor isochores between (44.7 and 832.0) kg·m−3 over a temperature range from (298 to 438) K at pressures up to 17.33 MPa using a constant-volume piezometer technique. The study was concentrated in the two-phase region to accurately determine vapor-pressures and in the immediate vicinity of the phase-transition temperatures to precisely determine the phase boundary properties (PS,ρS,TS) on the liquid + gas equilibrium curve. In the low temperature range (far from the critical point) where the values of vapor-pressure are negligible small (<1 kPa, approximately at temperatures below 350 K), the saturated vapor phase of methyl octanoate was considered as ideal gas with volume of VG=RT/PS and ΔVLG≈VG=RT/PS, where the saturated liquid volume can be neglected, VG>>VL. This approach was used to simplify the calculation of the thermodynamic properties of methyl octanoate at saturation.

Experimental study of PVT and phase-transition properties of binary water+n-hexane mixture near the upper critical endpoint

The PρT and phase transition (LLV and LV) properties (PS,TS,ρS) of binary water+n-hexane mixture with fixed concentration of 0.5 mol fraction of n-hexane (equimolar mixture) were measured. Measurements were focused in the immediate vicinity of the upper critical endpoint (UCEP) and supercritical regions in order to closely study the features of the mixture critical behavior near the UCEP. Measurements were made along 15 liquid and vapor isochores between (63.16 and 554.41) kg·m−3 and over a temperature range from (373.15 to 673.15) K at pressures up to 53.3 MPa. Phase transition phenomena on isochoric heating of the binary mixture was detailed study. For each isochore most measurements were made in the immediate vicinity of the LLV and LV phase transition temperatures (in the single-, two-, and three-phase regions) where the break of the P-T isochore's slopes are observing. Temperatures and pressures (PS,TS) at the LLV and LV phase transition points for each fixed density (isochore, ρ) were measured using the isochoric P-T break-point technique in the immediate vicinity of the UCEP of the mixture. The UCEP property data TUCEP = 469.15 K, PUCEP = 5.229 MPa, and ρUCEP = 263.95 kg·m−3 for the binary H2O + n-hexane mixture (x = 0.5 mol fraction of n-hexane) were extracted from the detailed PρT and three-phase equilibrium data (PLLV, TLLV, ρLLV) measurements near the UCEP. The combined expanded uncertainty of the density, ρ, pressure, P, temperature, T, and concentration, x, measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.2% (density in the liquid phase), 0.3% (density in the gas phase), 0.5% (density in the critical and supercritical regions); 0.05% (pressure); 15 mK (temperature); and 0.01 mol% (concentration). The excess molar volumes (VmE) of the binary mixture were calculated using the measured molar volumes Vm of the mixture and the reference molar volumes of the pure components (water and n-hexane) for various experimental temperatures and pressures in the supercritical region. Also, the measured PρT data at low densities (vapor phase) and high temperatures were used to calculated the second, third, and cross-term virial coefficients of the mixture.

Experimental study of the critical and supercritical phenomena in ternary mixture of water + 1-propanol + n-hexane

The liquid-gas phase transition (PS, TS, ρS) and PρT properties of the ternary water + 1-propanol + n-hexane mixture with fixed concentration of 0.3333 mole fraction of each component (equimolar mixture) were measured. Measurements were focused in the immediate vicinity of the critical and supercritical regions in order to closely observe the features of the mixture critical behavior. Measurements were made along 29 liquid and vapor isochores between (25.03 and 646.59) kg·m−3 and over the temperature range from (373.15 to 673.15) K at pressures up to 60 MPa. For each isochore most measurements were made in the immediate vicinity of the liquid-gas phase transition temperature (in the single- and two-phase regions) where the break of the P-T isochore's slopes is observing. Temperatures and pressures (TS, PS) at the liquid-gas phase transition point for each fixed density (isochore, ρ) were measured using the isochoric P–T break point technique in the immediate vicinity of the critical point of the mixture. The critical property data TC = 510.85 K, PC = 6.09 MPa, and ρC = 255.22 kg·m−3 for the ternary mixture were extracted from the detailed PρT and (PS, TS, ρS) measurements near the critical point. The combined expanded uncertainty of the density, ρ, pressure, P, temperature, T, and concentration, x, measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.2% (density in the liquid phase), 0.3% (density in the gas phase); 0.5% (density in the critical and supercritical regions); 0.05% (pressure), 15 mK (temperature), and 0.01 mol% (concentration). The excess molar volumes (VmE) of the ternary mixture were calculated using the measured molar volumes Vm of the mixture and the reference molar volumes of the pure components for various experimental temperatures and pressures in the supercritical region. Also, the measured PρT data at low densities (vapor phase) were used to calculated the second and third virial coefficients of the mixture at high temperatures.

Thermodynamic properties and sPC-SAFT modeling of 2-ethoxyethanol, 2-propoxyethanol and 2-butoxyethanol from T = (293.15–413.15) K and pressure up to 30 MPa

New experimental PρT data of three glycols ethers, namely, 2-ethoxyethanol, 2-propoxyethanol and 2-butoxyethanol were measured in a wide range of temperatures (293.15–413.15) K and pressures (0.1–30) MPa with a vibrating-tube densimeter. The experimental PρT data were correlated with the modified Tait equation. The study is completed with modeling in terms of the simplified perturbed-chain statistical associating fluid theory (sPC-SAFT) equation of state. The pure compound parameters of the sPC-SAFT equation are generally determined by fitting the equation to experimental saturated vapor pressure and liquid density data. In this work, by simultaneously minimizing the total objective function of temperature, pressure and density new correlation were developed to estimate the sPC-SAFT equation parameters with two association scheme for three glycols ethers including, 2-ethoxyethanol, 2-propoxyethanol and 2-butoxyethanol by using PρT data and with a fitting AAD% of 0.17 on average. The validity of the parameters and the employed association scheme were tested by the evaluation of densities and derivative properties such as isobaric thermal expansion coefficients, αP, isothermal compressibility, κΤ, isobaric heat capacities, CP, and speed of sound, u. All correlated/predicted results were compared with the modified Tait equation and experimental literature data. The obtained results showed that the sPC-SAFT equation of state, along with the proposed correlations, presents good results for modeling these glycols ethers.

Measurement of pρT Properties of 1,1,1,2,2,4,5,5,5-Nonafluoro-4-(trifluoromethyl)-3-pentanone in the Near-Critical and Supercritical Regions

In this work, measurements of pρT (pressure–density–temperature) properties of 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone in the near-critical and supercritical regions were carried out. This novel fluid has potential for use in next generation organic Rankine cycle systems because its GWP (global warming potential) is 1. However, there is insufficient data available especially near the critical point. In this work, 155 pρT data points of 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone along 21 isochores were obtained for densities between 107 and 1526 kg·m–3, for temperatures ranging from 333.5 to 523.5 K, and at pressures up to 10 MPa. The experimental uncertainties in the measurements of temperatures, pressures, and densities were estimated to be 0.028 K, 4 kPa, and 0.5%, respectively. For densities above 200 kg·m–3, the uncertainty is 0.4%.

PρT Property of trans-1-Chloro-3,3,3-trifluoropropene (R 1233zd(E)) near Critical Density

In this work, measurements of pρT (pressure–density–temperature) properties of trans-1-chloro-3,3,3-trifluoropropene (R 1233zd(E)) near the critical density were performed. This novel fluid has been proposed for organic Rankine cycle systems. However, there is no data near the critical density. In this work, 97 pρT data points of R 1233zd(E) along 21 isochores for densities between 161 kg·m–3 and 1202 kg·m–3 were obtained in the temperature range from 328 to 443 K and at pressures up to 10 MPa. Almost all of the data were obtained near the critical density. The experimental uncertainties in the measurements of temperatures, pressures, densities below 200 kg·m–3, and higher densities were estimated to be 0.028 K, 4 kPa, 0.5%, and 0.4%, respectively.

PρT measurement and PC-SAFT modeling of N,N-dimethyl formamide, N -methyl formamide, N,N-dimethyl acetamide, and ethylenediamine from T = (293.15–423.15) K and pressures up to 35 MPa

The PρT data of N,N -dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) were measured at temperature range of (293.15–413.15) K and pressures up to 30 MPa. The same properties also were measured for N-methylformamide (NMF) and ethylenediamine (EDA) over the temperature range within (293.15 to 423.15) K and (293.15–383.15) K and at pressures up to 35 MPa and 30 MPa, respectively. The measurements at 10 K intervals and along eight isobars were done. The experimental density values were correlated with the Tait equation. Based on the obtained result, other thermodynamic properties, such as, isothermal compressibility, κT, thermal expansion coefficient, αP, and thermal pressure coefficient, γV, were calculated. Also, the PC-SAFT model was used to correlate the densities of the pure solvents at the above-mentioned temperature and pressure range. In general, both models yield comparable and satisfactorily good correlation of the high pressure and temperature density.

Thermodynamic Properties of cis-1,1,1,4,4,4-Hexafluoro-2-butene (HFO-1336mzz(Z)): Measurements of the pρT Property and Determinations of Vapor Pressures, Saturated Liquid and Vapor Densities, and Critical Parameters

In this work, comprehensive measurements of pρT (pressure–density–temperature) properties of cis-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(Z)) were performed. Although this novel fluid has been proposed for various applications, including its use as a possible working fluid for organic Rankine cycle systems, reliable experimental data on its thermodynamic properties are scarcely available. In this work, the isochoric method was employed to obtain the properties of this fluid along 26 isochores for densities between 88 and 1295 kg·m–3, and 344 pρT data points were obtained in the temperature range from 323 K (49.85 °C) to 503 K (229.85 °C) and at pressures up to 10 MPa. The data covered single-phase liquid and vapor regions, two-phase region, and supercritical region. The data in the critical region were correlated with a simple polynomial expression, which was used to determine the critical parameters analytically. The vapor pressures and the densities of the saturated liquid and vapor were obtained fr...

Helmholtz energy and extended corresponding states model for the prediction of thermodynamic properties of mixtures of refrigerants

This work was concerned with developing an accurate model for the prediction of thermodynamic properties of mixtures of refrigerants. That model was the extension to mixtures of a recent work by the author about a Helmholtz and extended corresponding states model for refrigerants.In the proposed model the residual Helmholtz energy of the mixture was expressed as the contribution of three terms: one from an extended corresponding states model and the other two were corrections in terms of one-fluid mixing rules of functions of reduced temperature and density. The extended corresponding states model was based on the temperature- and density-dependent shape factors that the author has presented previously in the literature and the reference fluid was R-32 with properties calculated with the Tillner-Roth and Yokozeki reference equation of state.The fluids of interest were six binary systems and two ternary systems: (R-32+R-125), (R-32+R-134a), (R-125+R-134a), (R-125+R-143a), (R-134a+R-143a), (R-134a+R-152a), (R-32+R-125+R-134a) and (R-125+R-134a+R-143a). The following were the obtained percentage overall average absolute deviations: 0.347 in pρT data, 1.836 in isochoric heat capacities, 1.108 in isobaric heat capacities, 0.073 in speeds of sound, 0.467 in bubble-point saturation pressures and an overall average absolute difference of 3.367cm3mol−1 was obtained in second virial coefficients. These results compared satisfactorily with those from other models for mixtures of refrigerants.

Helmholtz energy and extended corresponding states model for the prediction of thermodynamic properties of refrigerants

This work was concerned with developing an accurate model for the prediction of thermodynamic properties of refrigerants. The work capitalised on previous works by the author about the development of accurate Helmholtz energy models for non-polar fluids, mixtures of those fluids and natural gas systems.The proposed model was formulated in terms of the residual Helmholtz energy, which was expressed as the contribution of two terms: one from an extended corresponding states model and the other was a correction term. The extended corresponding states model was based on the temperature- and density-dependent correlations for shape factors that the author has presented previously in the literature, and the R-32 was chosen as the reference fluid. The correction term was a weighted term from the reference equation of state.The fluids of interest were 19 refrigerants: R-11, R-12, R-22, R-41, R-113, R-116, R-123, R-124, R-125, R-134a, R-141b, R-142b, R-143a, R-152a, R-218, R-227ea, R-236ea, R-236fa and R-245fa. The following percentage overall absolute average deviations were obtained: 0.187 for pρT data, 0.229 for saturation pressures, 0.206 for saturated-liquid densities, 1.053 for saturated-vapour densities, 1.734 for isochoric heat capacities, 1.238 for isobaric heat capacities and 0.662 for speeds of sound. These results showed an overall good agreement with the accuracy demanded of the equations for technical applications of refrigerants.

An improved Helmholtz energy model for non-polar fluids and their mixtures. Part 3: Application to natural gases and related systems

In this work a Helmholtz energy mixture model that had been previously published by the author was applied to natural gases and the related multicomponent systems. The Helmholtz energy of the mixture is the sum of two terms: one is an extended corresponding states model and the other is a correction term that is mixing rule, in terms of local compositions, of a temperature- and density-dependent function. Local compositions are calculated with a coordination number model for square-well fluids.The systems of interest were ternary, quaternary, multicomponent systems and natural gases. Deviations were calculated for pρT data, speeds of sound, isobaric heat capacities, isobaric and isenthalpic enthalpy differences, saturated-liquid densities of liquefied natural gases and vapour pressures of ternary systems. Representative percentage average absolute deviations were: 0.060 in pρT data of pipeline-quality natural gases; 0.099 in pρT data of unusual-composition natural gases; 0.249 in pρT data of rich natural gases; 0.220 in speeds of sound; 1.150 in isobaric heat capacities; 0.146 in saturated-liquid densities of liquefied natural gases and 1.267 in vapour pressures of ternary systems. Those results met the international standards of accuracy in the prediction of natural gas thermodynamic properties and were also comparable with those obtained with the GERG-2004 equation of state.

An improved Helmholtz energy model for non-polar fluids and their mixtures. Part 2: Application to mixtures of non-polar fluids

This is the second part of a series of two communications in which a Helmholtz energy model is developed and applied to the prediction of thermodynamic properties of non-polar fluids and their mixtures. In this second part, the application is concerned only with mixtures of non-polar fluids.The Helmholtz energy model is based on previous work by the author and colleagues in which the Helmholtz energy of the fluid is represented as a contribution of two terms: one is an extended corresponding states model and the other is correction term. In the case of mixtures, this correcting term is mixing rule, in terms of local compositions, of a temperature- and density-dependent function. Local compositions are calculated with a coordination number model for square-well fluids.The mixtures that were considered were eight “primary” systems and 29 “secondary” systems of methane, ethane, propane, isobutane, n-butane, nitrogen, carbon dioxide, carbon monoxide, hydrogen and argon and a few ternary and quaternary systems. Percentage absolute average deviations (AADs) were calculated with the following results: 0.114 and 0.255 for pρT data of primary and secondary mixtures, respectively; 0.094 and 0.052 for pρT data of ternary and quaternary systems, respectively; 1.153 and 0.108 for isobaric heat capacities and speeds of sound of primary mixtures, respectively; 1.210 and 1.280 for bubble-point vapour pressures of primary and secondary mixtures, respectively; and absolute average deviations of 0.744cm3/mol and 288cm6/mol2 for second and third virial coefficients, respectively. This performance was found to be very satisfactory when compared with the expected accuracy of mixture Helmholtz energy models, i.e. that by Lemmon and Jacobsen, which is cited further ahead.

An improved Helmholtz energy model for non-polar fluids and their mixtures. Part 1: Application to non-polar pure fluids

This is the first part of a series of two communications in which a Helmholtz energy model is developed and applied to the prediction of thermodynamic properties of non-polar fluids and their mixtures. In this first part, the application is concerned only with pure non-polar fluids.The Helmholtz energy model is based on previous work by the author and co-workers in which the Helmholtz energy of the fluid is represented as a contribution of two terms: one is an extended corresponding states model and the other is a correction term. In the case of single components, this correcting term is a function of temperature and density.In this study 18 fluids were considered, namely: the normal alkanes from ethane to octane, isobutane, ethylene, cyclohexane, benzene, toluene, nitrogen, carbon dioxide, carbon monoxide, oxygen and argon. Percentage absolute average deviations (AADs) were calculated with the following results: 0.175 for pρT data; 0.279 for saturation pressures; 0.168 and 0.324 for saturated-liquid and saturated-vapour densities, respectively; 1.364 and 1.563 for isochoric and isobaric heat capacities, respectively, and 0.638 for speeds of sound. This performance is, by and large, quite comparable with the demanded accuracy of modern technical Helmholtz energy models for fluids of industrial interest and practical applications in process design and simulation.

Prediction of fluid density at extreme conditions using the perturbed-chain SAFT equation correlated to high temperature, high pressure density data

At pressures below ∼55MPa, the perturbed chain – statistically associated fluid theory (PC-SAFT) gives reliable density predictions within ±2% for n-alkanes and other hydrocarbons. However, PC-SAFT tends to over-predict density values by as much as 5% at higher pressures, particularly for normal and branched alkanes. For many compounds, literature values for the three pure-component PC-SAFT parameters m, σ, and ɛ/kB are typically obtained by fitting the equation to sub-critical PρT data or occasionally both sub-critical and supercritical density data. A new set of pure-component PC-SAFT parameters for density prediction at extreme conditions is reported here by fitting the PC-SAFT equation to single-component density data collected at temperatures from ambient to 533K and pressures from ∼6.9 to 276MPa, rather than sub-critical density data since these high temperature, high pressure (HTHP) conditions are similar to conditions typically associated with petroleum recovery from ultra-deep formations. Density predictions made using the new, HTHP PC-SAFT pure-component parameters at HTHP conditions are clearly superior to those obtained using the original PC-SAFT parameters. Although a correction term can be applied to the ɛ/kB parameter to make HTHP PC-SAFT pure-component density predictions at pressures below 6.9MPa only slightly inferior to predictions with the original PC-SAFT parameters, vapor–liquid equilibrium predictions with the original PC-SAFT parameters are clearly superior to predictions made with the HTHP parameters. Correlations are developed to accurately predict the HTHP PC-SAFT parameters for normal and branched alkanes for which there are either incomplete or nonexistent experimental density data sets.

Application to mixtures of non-polar fluids of a three-parameter three-fluid corresponding states model based on reference equations of state

In this work a three-parameter three-fluid corresponding states model is applied to the prediction of thermodynamic properties of mixtures of non-polar fluids. Residual thermodynamic properties were calculated by quadratic interpolation between those of three reference fluids, i.e. methane, ethane and carbon dioxide. The properties of these three fluids were obtained from the corresponding multiparameter reference equations of state: the Setzmann and Wagner equation for methane, the Bücker and Wagner equation for ethane and the Span and Wagner equation for carbon dioxide. By this device, the accuracy of the model was quite satisfactory as is demonstrated in this work by comparison with a recent generalised corresponding states model by Sun & Ely. Also, the proposed model showed to be more accurate than the Peng−Ronbison equation of state with volume translation. The percentage average absolute deviations for binary systems were: 0.194 in pρT data, 1.696 in isobaric heat capacities, 0.174 in speeds of sound and 1.322 in bubble-point vapour pressures. Percentage average absolute deviations in pρT data of ternary systems were 0.134 and 0.094 for quaternary systems.