Fluid Phase Equilibria最新文献

Accurate ${\mathrm{CO}}_2$ properties are crucial for the development of carbon capture, utilization, and storage (CCUS) technologies. This work assesses the performance of two volume translation models for ${\mathrm{CO}}_2$, integrated into the I-PC-SAFT equation of state (EoS) to refine the original volume translation constant ($c$). The models introduce a temperature-dependent volume translation function and a distance function-based volume translation function, with the latter explored in two forms: ${\left(\frac{\partial P}{\partial V}\right)}_T$ and ${\left(\frac{\partial T}{\partial V}\right)}_P$. The outcomes reveal that the I-PC-SAFT models, incorporating either the temperature-dependent function or the distance functions ${\left(\frac{\partial P}{\partial V}\right)}_T$ and ${\left(\frac{\partial T}{\partial V}\right)}_P$, enhance the prediction accuracy of ${\mathrm{CO}}_2$ saturated densities over the baseline I-PC-SAFT and PC-SAFT models. Specifically, when estimating liquid ${\mathrm{CO}}_2$ densities at fixed pressures ranging from 0.5$P_c$ to 10.0$P_c$, the I-PC-SAFT model with the temperature-dependent volume translation function exhibits reduced predictive deviation at lower pressures. At elevated pressures, however, the deviation is more pronounced. In contrast, the I-PC-SAFT model utilizing the distance function based on ${\left(\frac{\partial T}{\partial V}\right)}_P$ achieves the lowest percentage average deviation ($\text{\%}AAD$) of 0.63%.

Homologous series (or compound series with repeated incremental structural changes) are frequently used for analysis and prediction of properties of chemical substances. They are usually constructed by adding CH₂ or other functional groups to the parent molecule and form one-dimensional spaces where the molecule or substance properties are a function of one variable, the number of added groups. Analysis of the property changes in such a series can help to identify anomalies. Interpolation and limited extrapolation can also be used for property prediction. A simple method is proposed for an automated generation of such series. It shows all possible changes in molecular structure leading to the construction of series within a given collection of compounds, including non-intuitive combinations of changes. The series constructed using this algorithm may include sets of isomers, the properties of which are expected to be similar, thus increasing the coverage in sparsely populated collections of chemical compounds.

We show that the class of combinatorial entropy models, such as the Guggenheim–Staverman model, in which the many conformations of a molecule are taken into account, does not fulfill the Gibbs probability normalization condition. The root cause for this deviation lies in the definition of the pure and mixture state. In the athermal limit, mandatory to define the combinatorial entropy, the number of molecules in a particular conformation does not change upon mixing. Therefore each set of molecules with a particular conformation in the pure state can be regarded as a distinguishable subclass of rigid molecules. When this subdivision is applied to the ‘shape’ models, they fulfill the Gibbs probability normalization condition. The resulting equations simplify to the Flory–Huggins entropy model. Implications of this finding to the existing activity coefficient models are discussed.

The current work reports densities and sound speeds, and related thermodynamic excess properties, namely excess molar volumes and excess isentropic compressibilities, measured at temperatures from (293.15 to 323.15) K and under atmospheric pressure conditions for binary mixtures of n-hexane with benzene, toluene, ethylbenzene, o-xylene, m-xylene, and p-xylene. Redlich-Kister polynomial correlated the thermodynamic excess properties to test the quality of experimental data. Excess properties contributed to understanding molecular interactions between involved molecules and the peculiarities of their packing in the mixture. The Jouyban-Acree model was used to correlate the mixtures' experimental densities, sound speeds, and their related derived properties, namely isobaric thermal expansivities and isentropic compressibilities. The average absolute percentage deviation of the correlated values from the experimental ones was better than 0.036 %, 0.058 %, 0.040 %, and 0.146 % for density, sound speed, isobaric thermal expansivity, and isentropic compressibility, respectively, attesting to the robustness of the Jouyban-Acree correlations. Additionally, the Perturbed Chain Statistical Associating Fluid Theory Equation of State modeled the densities of the current mixtures. Schaaff's Collision Factor Theory and Nomoto's relation were compared for their ability to model the sound speeds of the mixtures. The efficacy of these models was tested by computing the average absolute percentage deviations between experimental and computed values. The modeled densities are reasonably concordant with experimental data, with an overall deviation of 0.02 %. Notably, Nomoto's relation exhibited superior performance over Schaaff's theory in modeling sound speeds of current mixtures, with an overall deviation of 0.33 %. The current findings underline the efficacy and versatility of the used models for thermodynamic modeling in systems of varying complexity.

New density data has been reported for 3-aminopropan-1-ol (AP) and N-(2-hydroxyethyl)morpholine (NHEM) at temperatures ranging from (293.15–473.15) K at 19 pressures ranging from (0.1–40) MPa. The experimental measurements were carried out using an Anton Paar high-pressure vibrating tube densimeter with a combined expanded uncertainty of 1 kg m⁻³ at a 95 % confidence level. Contributions considered in the uncertainty analysis included the impurities in the materials used and apparatus specification. In addition, the density and speed of sound at ambient pressure (81.5 kPa) and temperatures (293.15–343.15) K were measured. The experimental density data were correlated with the modified Tait equation. Values of thermal expansion coefficient (${\alpha }_P$ ) and isothermal compressibility (${\kappa }_T$) were calculated. The work is completed with the modeling of the experimental data using the perturbed-chain statistical associating fluid theory equation of state (PC-SAFT EOS). The parameters of the PC-SAFT equation of state, for the pure compounds, were determined by fitting the equation to the liquid PρT experimental data. Thermodynamic properties such as thermal expansion coefficient (${\alpha }_P$), isothermal compressibility (${\kappa }_T$), isobaric heat capacity ($C_P$), and speed of sound ($u$) were calculated with the obtain parameters. Good agreement between experimental data and derived properties represented the modeling accuracy with the obtained parameters.

The calculation of three-phase equilibrium in CO₂-hydrocarbon-water mixtures holds significant importance within numerical simulations, particularly in applications such as CO₂-enhanced oil recovery and carbon dioxide sequestration. However, due to the non-ideality of CO₂ and the polarity of water, three-phase equilibrium calculations often encounter convergence challenges. The augmented free-water flash algorithm [6], specifically focusing on CO₂ dissolution in the aqueous phase, addresses the convergence challenges encountered by traditional three-phase flash algorithms. Despite its accuracy diminishes under conditions of high pressure and high CO₂ concentrations, limiting its capability to accurately describe CO₂ dissolution in oil-gas-water multiphase systems. The G^E (excess Gibbs free energy) type mixing rule can be effectively integrated with equations of state, including PR and SRK, by utilizing activity models like NRTL and UNIFAC, which can be applied to the calculation of thermodynamic parameters for both nonpolar and polar systems and high-pressure complex systems. In this study, based on the augmented free-water assumption, we have developed a new augmented free-water three-phase flash algorithm for CO₂/hydrocarbon/water mixtures. This algorithm integrates the PR equation of state with the NRTL activity model, employing the HV mixing rule for CO₂-water interactions and the Van der Waals rule for other non-polar components. Furthermore, to enhance computational efficiency, the algorithm incorporates the simulated annealing global optimization algorithm, replacing Newton iteration to more effectively identify the global minima of the complex objective function. The example calculations show that the improved augmented free-water flash algorithm has higher accuracy and efficiency than the traditional augmented free-water flash algorithm. The augmented free-water three-phase flash algorithm proposed in this paper offers a precise model for phase equilibrium calculations essential for numerical simulations in CO₂-enhanced oil recovery and carbon dioxide sequestration.

Ammonia is a promising energy carrier for the green transition, but its hygroscopicity and toxicity necessitate in-depth understanding of its interaction with water. This work examines the bulk and interfacial thermodynamics of the ammonia–water system. Parameters for three equations of state are fitted to experimental data and compared to parameters from literature: PC-SAFT, Cubic Plus Association and Peng–Robinson. Peng–Robinson stands out as most accurate for bulk thermodynamics. Introducing a temperature-dependent volume shift for water with Peng–Robinson yields a highly accurate model without introducing problematic inconsistencies, with errors of 0.05% for saturation pressures, and 0.5% for liquid densities. For the mixture, Peng–Robinson with a two-parameter Huron–Vidal mixing rule reproduces measurements mostly within their uncertainties, whereas the standard mixing rules for PC-SAFT and CPA are less accurate. A literature review of surface tension measurements of ammonia–water mixtures reveals that accurate measurements exist only at ambient temperature. We apply density gradient theory and density functional theory based on PC-SAFT, finding that both models fail at reproducing qualitative features of the surface tensions and adsorptions of dilute solutions of aqueous ammonia. Whereas bulk properties are well characterized, understanding and describing the interfacial thermodynamics of the ammonia–water system demands more work both on the experimental and modeling side.

Equations of state (EoS) are powerful tools for estimating a wide variety of physical properties. However, the applicability of parameter sets derived from specific physical properties for the correlation and estimation of various other physical properties has received limited attention. Additionally, the estimation of physical properties using EoS is anticipated to be affected by the association of molecules. The densities of homogeneous phase fluid mixtures comprising carbon dioxide (CO₂)/methanol (MeOH) and CO₂/ethanol (EtOH) binary systems were measured in the current study using a high-pressure vibration-type density meter equipped with a circulation pump and a variable-volume viewing cell. Homogeneity was ensured by observing the fluid through the viewing window of the variable volume cell. The measurements were carried out at a temperature range of 313–353 K, the CO₂ mole-fraction range of 0–80 mol%, and at pressures up to 20 MPa. Subsequently, the as-obtained experimental data were correlated with two EoSs, viz. Sanchez-Lacombe (SL) EoS and Perturbed Chain statistical associating fluid theory (PC-SAFT) EoS. The density correlations between SL and PC-SAFT EoS were almost identical in accuracy. Additionally, the association between CO₂ and alcohols in PC-SAFT EoS had no discernible effect on the reliability of the density correlations. The vapor liquid equilibria (VLE) of the CO₂/MeOH and CO₂/EtOH mixtures were further estimated using parameter sets determined from the density measurements. Both the EoSs demonstrated comparable estimation accuracy; however, the pressure was estimated primarily near the critical region of the mixture, which yielded a lower estimation accuracy. Additionally, the densities of the binary systems were determined using characteristic parameters derived from the VLE correlations. Of the EoSs, the PC-SAFT EoS yielded a good correlation of the VLE, including the region near the mixture's critical region, while taking the association between CO₂ and alcohols into consideration. Although few of the correlations were observed to be inferior, the density of the homogeneous fluid mixture was accurately estimated using the two EoSs, with the parameters obtained from the VLE correlations. The findings of the study thus suggest that in order to estimate the density and VLE using EoS-shared parameters, the parameter sets must first be determined using a VLE that exhibits a wide range of conditions affected by the system's associations.

The cubic-two-state (CTS) equation of state (EoS) was employed for modeling the liquid-liquid and vapor-liquid equilibria of nitriles + hydrocarbons (alkanes and aromatics) or water mixtures. For nitriles, the five pure compound parameters were determined by fitting the model simultaneously to experimental saturation pressure, density of saturated liquid, enthalpy of vaporization and liquid-liquid equilibrium data when mixed with n-dodecane. For alkanes, the pure parameters were those determined from conventional corresponding states correlations for Soave-Redlich-Kwong EoS. The van der Waals mixing and combining rules were applied for dispersive parameter and covolume, with a temperature-dependent binary parameter. In the case of nitrile mixtures with aromatics and water, cross-association were considered with the previously published CTS combining rules, and no association binary parameters were required. The correlations were very good in all cases. The model was also able to predict selective extraction of sulfur compounds (benzothyophene and benzothyophene 1,1-oxide) from alkanes. Because of its simplicity, therefore, the CTS EoS is a very attractive option for process simulation involving this class of mixtures.