Group Contribution Equation Of State Research Articles

Thermodynamic modelling of systems involved in natural gas dehydration with triethylene glycol using a group contribution association model

Natural gas (NG) dehydration through absorption into Triethylene Glycol (TEG) is one of the most important applications in the NG industry. The optimal design of the TEG dehydration process requires a deep understanding of the thermodynamic behavior of mixtures containing TEG, water, hydrocarbons, and other compounds present in natural gas. In this work, the recently developed Universal Mixing Rule – Cubic Plus Association (UMR-CPA) group contribution equation of state (EoS) is extended to these systems. UMR-CPA combines the PR-CPA EoS with the UNIFAC group contribution activity coefficient model through the Universal Mixing Rules. Parameters for pure water, TEG and NG components were determined by accurately fitting vapor pressure, density and heat capacity data. For non-associating compounds, the model leads to overall deviations of 1.2 % in vapor pressures and 6.1 % in isobaric heat capacities. Water properties are also quite accurately described, with overall deviations of approximately 0.4 %, 1.2 % and 5.7 % in vapor pressures, liquid densities and isobaric heat capacities, respectively. The model was then applied to mixtures of water and TEG with gases and hydrocarbons by correlating the proper group interaction parameters. Very satisfactory results were obtained for both vapor-liquid and liquid-liquid phase equilibria in these systems, where also an adequate reproduction of the minimum of hydrocarbon solubility in water was noted. Finally, the UMR-CPA EoS was further validated through the prediction of the phase behavior of ternary systems including TEG and/or water and NG compounds. Very good predictions were achieved for the low TEG and water content in the vapor phase of the TEG-H2O-CH4 ternary system, with absolute deviations of around 0.05 and 23.26 ppm, respectively. Overall, the model yields accurate predictions, suggesting its suitability for designing the TEG dehydration process.

Development of a New Group Contribution Equation of State for associating compounds

Development of a New Group Contribution Equation of State for associating compounds

Vapor-liquid equilibrium of acid gases with imidazolium-based ionic liquids using the UMR-PRU model

The UMR-PRU group contribution equation of state (EoS), which couples the Peng-Robinson EoS with UNIFAC via the Universal Mixing Rules, is extended to pure imidazolium-based ionic liquids (ILs), as well as to their mixtures with CO2 and H2S. The studied ILs consist of alkyl-methylimidazolium cations and tetrafluoroborate, hexafluorophosphate and bis(trifluoromethylsulfonyl)imide anions. The EoS parameters of pure ionic liquids, are determined by fitting experimental vapor pressure and liquid density data. For the extension of UMR-PRU to binary CO2/IL and H2S/IL mixtures, the model parameters are determined by fitting experimental binary vapor-liquid equilibrium data of acid gases with ionic liquids. For comparison, the Peng-Robinson coupled with the conventional van der Waals one-fluid mixing rules (vdW1f) is also applied to the same systems, using adjustable attractive and co-volume cross interaction parameter. It is shown that Peng-Robinson accurately describes pure ionic liquid vapor pressures and liquid densities, while UMR-PRU yields very satisfactory vapor-liquid equilibrium results for binary and ternary mixtures containing ILs and acid gases. Overall, UMR-PRU yields much better results than Peng-Robinson coupled with the vdW1f mixing rules, which indicates the superiority of the UMR mixing rules over the vdW1f ones.

Thermodynamic modelling of industrially important associating mixtures with a group-contribution equation of state

The accurate prediction of phase equilibria of mixtures containing hydrocarbons and associating components such as water, alcohols and glycols is very important from an industrial perspective, since it ensures product quality and process safety, leading to a more effective design. To this purpose, a new model, that combines the Peng-Robinson equation of state coupled with the Universal Mixing Rules (UMR) with the association term based on Wertheim's perturbation theory is developed. The new model, referred as UMR-CPAPRU, is a predictive group contribution equation of state since it utilizes the UNIFAC activity coefficient model. UMR-CPAPRU leads to improved results in binary mixtures with a 5.4% average absolute relative deviation in bubble point pressure as compared to the 8.8% obtained by UMR-PRU, while it yields improved predictions over UMR-PRU for liquid-liquid equilibrium in alkane/water/methanol mixtures and dew points of wet natural gasses.

SAFT-γ-Mie Cross-Interaction Parameters from Density Functional Theory-Predicted Multipoles of Molecular Fragments for Carbon Dioxide, Benzene, Alkanes, and Water.

Determining unlike-pair interaction parameters, whether for group contribution equation of state or molecular simulations, is a challenge for the prediction of thermodynamic properties. As the number of components and their respective complexity increase, it becomes impractical to fit all the unlike interactions. Lorentz-Berthelot combining rules work well for systems, where the main interactions are dispersion forces, but they do not account for electrostatics. In this work, we derive predictive combining rules within the SAFT-γ-Mie framework. In the resulting model, the unlike-pair interactions account for the effect of ionization energies, partial charges, dipole moments, and quadrupole moments. We then estimate these properties for molecular fragments using density functional theory calculations and demonstrate their use to obtain realistic cross-interaction energies without the need for experimental data. An open-source python package, Multipole Approach to Predictively Scale Cross-Interactions, is included to facilitate use of the methods presented in this work. A good qualitative agreement was obtained for all phase equilibria calculations of binary mixtures containing carbon dioxide with propane, hexane, benzene, and water, as well as mixtures of hexane and benzene. Finally, we discuss future improvements to our methodology, including the use of physical insights when fitting self-interaction parameters.

Prediction of Excess Enthalpy Using Volume-Translated Peng–Robinson Equation of State

In this work volume-translated Peng–Robinson group contribution equation of state was used to calculate excess enthalpies. Four model systems were selected with the purpose to compare experimental and predicted enthalpy values at different temperatures. After the calculations were performed in Matlab software, results were verified with free software tool of Dortmunder Datenbank (DDB). In a next step, the mixing process and interaction forces were described on the basis of the sign and course of enthalpy values. The endothermic behavior of three systems could be well predicted, while for the most polar system, predictions were less precise. Furthermore, the discrepancy between experimental data from the literature and predicted values was discussed to evaluate the accuracy of the selected model. Lowest mean deviations (<75 J/mol and <15% at all temperatures) could be stated for alkane/benzene mixtures, while highest deviations could be again observed for the most polar mixture. Although the magnitude of deviations was in agreement with the literature, it could be shown that the selected temperature is of major importance for the quality of predictions. Furthermore, a review of different literature values for the n-hexane/benzene system could reveal that the reliability of experimental data has to be carefully checked.

Solubility of CO2 in three cellulose‐dissolving ionic liquids

AbstractThe solubility of CO2 in three cellulose‐dissolving ionic liquids (1‐ethyl‐3‐methylimidazolium diethylphosphate, [Emim][DEP], 1‐allyl‐3‐methylimidazolium chloride, [Amim][Cl], and 1‐butyl‐3‐methylimidazolium chloride, [Bmim][Cl]) at temperatures within 298 and 356 K and pressures up to 6.5 MPa was determined using a Van Ness‐type apparatus (static isochoric). It was demonstrated that this device can work in isothermal and isoplethal modes, being the latter faster and more precise. Moreover, it was possible to determine CO2 solubilities in metastable liquid [Bmim][Cl]. Experimental data were modeled using the Extended Henry's law correlation and the group contribution equation of state. New parameters for the binary interaction of CO2 with ionic liquid groups were calculated.

Modelling the thermodynamic properties and fluid-phase equilibria of n-perfluoroalkanes and their binary mixtures with the SAFT-γ Mie group contribution equation of state

The SAFT-γ Mie group-contribution approach is extended to describe the thermodynamic properties and fluid-phase behaviour of n-perfluoroalkanes and their binary mixtures. New molecular interaction parameters characterising the functional chemical groups forming these molecules (CF4, CF3 and CF2) are estimated from experimental vapour pressure and saturated-density data of the pure compounds. The vapour–liquid equilibria of four mixtures are then described predictively and compared to recent experimental data from the literature. Additionally, new experimental data for the excess volume of the (n-C6F14 + n-C8F18) mixture is measured over the whole range of compositions, between 278.15 and 318.15 K. The mixture presents small negative excess volumes, which increase in absolute value with increasing temperature. The results are compared with the excess volume for the corresponding mixture of n-alkanes of the same chain length, and with the SAFT-γ Mie predictions. The theory provides a very good description of the properties of both the pure compounds and their binary mixtures.

Solubility of three natural compounds with insecticidal activity in supercritical carbon dioxide: Experimental measurements and predictive modeling with the GC-EoS

In this work, the solubility of thymoquinone, R-(+)-pulegone and 1-octen-3-ol in supercritical CO2 is determined in a range of conditions typical of supercritical fluid processes such as extraction, fractionation and impregnation. These compounds were selected based in their insecticidal activity which may enable to apply them as biopesticides. Solubility was measured using a semicontinuos method in the temperature range of 45–65 °C and pressure of 8–12 MPa, at a CO2 flowrate of 0.05–0.10 g/min, which was verified to be low enough to ensure saturation. Solubilities were predicted using the Group Contribution Equation of State (GC-EoS) and compared to the experimental results, with a good agreement. Consistency of the data was tested using the density-based Chrastil equation.

A Group Contribution Equation of State for Biorefineries. GCA-EOS Extension to Bioether Fuels and Their Mixtures with n-Alkanes

Fil: Gonzalez Prieto, Mariana. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Bahia Blanca. Planta Piloto de Ingenieria Quimica. Universidad Nacional del Sur. Planta Piloto de Ingenieria Quimica; Argentina. Universidad Nacional del Sur. Departamento de Ingenieria Quimica; Argentina

Molecular design of solvents for CO2 capture using a group contribution EOS

After a brief revision of the literature, this work develops a computer-aided molecular design procedure (GCMOLD), based on the Group Contribution Equation of State, GC-EOS. The selection of solvents, for CO2 capture in pre-combustion processes by GCMOLD, allows a systematic study of the effect of molecular functionality on solvent properties. For this problem, after the selection of a number of paraffinic and CO2-phylic groups for the synthesis of molecular structures, the GCMOLD program generates a list of solvents ranked by their solvent power. On this basis, the effect of paraffinic and polar structures on solvent power and solvent loss gives a rationale for optimum solvent selection. Finally, an innovative scheme of an absorption cycle with low energy consumption is proposed.

GC-EoS extension to alkylphosphate imidazolium ionic liquids

In this work, the Group Contribution Equation of State (GC-EoS) is extended to model two new ionic liquid families, namely, 1-alkyl-3-methylimidazolium dimethylphosphate ([-MeIm]+[Me2PO4]-) and 1-alkyl-3-methylimidazolium diethylphosphate ([-MeIm]+[Et2PO4]-). Pure group parameters for the functional groups [-MeIm]+[Me2PO4]- and [-MeIm]+[Et2PO4]- and interaction parameters between these groups and the main paraffinic and aromatic subgroups (CH3, CH2, ACH, AC, ACCH3, CH2=CH) were estimated using infinite dilution activity coefficients from literature. In order to evaluate the performance of the new parameters, the model was compared with experimental data on the phase behavior of binary mixtures, showing an average relative deviation of 4.5%.

Predicting $$\hbox {CO}_{2}$$ CO 2 Solubility in Imidazole Ionic Liquids for Use in Absorption Refrigeration Systems by Using the Group Contribution Equation of State Method

Traditional absorption refrigeration such as \(\hbox {H}_{2}\hbox {O}\)–LiBr- and \(\hbox {NH}_{3}\)–\(\hbox {H}_{2}\hbox {O}\)-based refrigeration has limited applications because of several issues, including crystallization, corrosion, and large volume. \(\hbox {CO}_{2}\)–ionic liquids (ILs) as new absorption working pairs were investigated in this study. The objective was to use the group contribution equation of state (GC-EOS) method to predict the solubilities of binary systems containing high-pressure \(\hbox {CO}_{2}\)–imidazole bis(trifluoromethanesulfonimide) ILs and to investigate the applicability and accuracy of the GC-EOS model. The results showed that at pressures up to 11.0 MPa and temperatures of 273 K to 400 K, the \(\hbox {CO}_{2}\) solubility in the ILs increased with increasing system pressure but decreased with increasing temperature, and its variation rate was lower at higher pressures or temperatures. Also, \(\hbox {CO}_{2}\) solubility increased in the order of [emim][\(\hbox {Tf}_{2}\hbox {N}\)] < [bmim][\(\hbox {Tf}_{2}\hbox {N}\)] < [hmim][\(\hbox {Tf}_{2}\hbox {N}\)] < [omim][\(\hbox {Tf}_{2}\hbox {N}\)], indicating that longer alkyl chains of identical IL families resulted in higher \(\hbox {CO}_{2 }\) solubility. The model prediction of \(\hbox {CO}_{2}\) solubility in the four different ILs showed reasonable consistency with the corresponding experimental results from the literature; the largest deviation was 5.7 % for \(\hbox {CO}_{2}\)-[emim][\(\hbox {Tf}_{2}\hbox {N}\)]. Therefore, it can be concluded that the GC-EOS model is a promising theoretical solution that can be used to search for suitable \(\hbox {CO}_{2}\)–IL working pairs for absorption refrigeration systems.

Industrial waste-heat recovery through integrated computer-aided working-fluid and ORC system optimisation using SAFT-[formula omitted] Mie

A mixed-integer non-linear programming optimisation framework is formulated and developed that combines a molecular-based, group-contribution equation of state, SAFT-γ Mie, with a thermodynamic description of an organic Rankine cycle (ORC) power system. In this framework, a set of working fluids is described by its constituent functional groups (e.g., since we are focussing here on hydrocarbons: CH3, CH2, etc.), and integer optimisation variables are introduced in the description the working-fluid structure. Molecular feasibility constraints are then defined to ensure all feasible working-fluid candidates can be found. This optimisation framework facilitates combining the computer-aided molecular design of the working fluid with the power-system optimisation into a single framework, thus removing subjective and pre-emptive screening criteria, and simultaneously moving towards the next generation of tailored working fluids and optimised systems for waste-heat recovery applications. SAFT-γ Mie has not been previously employed in such a framework. The optimisation framework, which is based here on hydrocarbon functional groups, is first validated against an alternative formulation that uses (pseudo-experimental) thermodynamic property predictions from REFPROP, and against an optimisation study taken from the literature. The framework is then applied to three industrial waste-heat recovery applications. It is found that simple molecules, such as propane and propene, are the optimal ORC working fluids for a low-grade (150°C) heat source, whilst molecules with increasing molecular complexity are favoured at higher temperatures. Specifically, 2-alkenes emerge as the optimal working fluids for medium- and higher-grade heat-sources in the 250–350°C temperature range. Ultimately, the results demonstrate the potential of this framework to drive the search for the next generation of ORC systems, and to provide meaningful insights into identifying the working fluids that represent the optimal choices for targeted applications. Finally, the effects of the working-fluid structure on the expander and pump are investigated, and the suitability of group-contribution methods for evaluating the transport properties of hydrocarbon working-fluids are considered, in the context of performing complete thermoeconomic evaluations of these systems.

Density prediction of pyridinium, imidazolium, pyrrolidinium, ammonium, and phosphonium-based ionic liquids using an equation of state

A group contribution equation of state (EOS) has already been developed to calculate the density of imidazolium-based ionic liquids (ILs) with good accuracy. IL was divided into several groups, i.e. cation head, anion, and alkyls. In order to further prove the widely applicability of the model and the group segmentation method for IL, the densities of 1-alkyl-3-methylimidazolium salts containing metal of group III and a large number of pyridinium, pyrrolidinium, ammonium, and phosphonium-based pure ILs were correlated/predicted in this work. First, a total of 222 data points of density for 27 pure ILs, were regressed to obtain the new soft-core diameter and dispersive energy parameters. Then, 908 density data points of 42 pure ILs from 278.15 to 393.15 K and up to 65.01 MPa were predicted on the basis of the obtained parameters. The results indicated that the EOS could well capture the effects of temperature, pressure and alkyl types on density. Finally, the EOS was further evaluated to predict the density data for binary IL mixtures without introducing any new parameters, and testified the extensive applicability of the EOS with average relative deviation of 0.70%.

Present status of the group contribution equation of state VTPR and typical applications for process development

For the development and design of industrial processes the reliable knowledge of thermophysical properties, in particular phase equilibria is most important. Assuming that 1000 components are of technical interest, vapor-liquid equilibrium data for approximately 500,000 binary systems are needed to fit all required binary interaction parameters. Due to the fact that the measurement of all needed properties is nearly impossible, the process engineer depends on factual data banks.Besides the different phase equilibria, the Dortmund Data Bank as worldwide largest factual data bank for thermophysical properties contains nearly all worldwide available pure component, excess and transport properties. Although more than 66,300 binary VLE data sets for non-electrolyte systems are currently stored in the DDB, in total up to now VLE data for only 13,540 different binary systems are available. The reason is that some systems are very popular and were measured very often, e.g. ammonia – water, ethanol-water and so on. When the 1000 most important components are considered, VLE data for only 8635 binary systems are available. This means for only 1.73% of the systems the required binary interaction parameters can be fitted. Since the assumption of ideal behavior for the missing binary systems can be very erroneous and measurements are very time consuming, predictive group contribution models can be successfully applied to estimate the missing thermophysical properties.To cover sub- and supercritical conditions, group contribution equations of state have to be applied. They automatically take into account both phases and can be used up to high pressures and supercritical conditions. This allows for example the calculation of phase envelopes. Furthermore, the introduction of Henry coefficients for gaseous compounds is not required. At the same time, enthalpies, heat capacities, densities and so on can be predicted. Today the most sophisticated group contribution equation of state is the volume translated Peng-Robinson group contribution equation of state VTPR. In this paper, typical applications of VTPR for process development are shown and new parameters for 24 additional group combinations are given.

P–T–x Measurements for 1,1,1,2-Tetrafluoroethane (R134a) + N,N-Dimethylacetamide (DMA) and N-Methyl-2-pyrrolidone (NMP)

The present study concerns p–T–x phase equilibria measurements involving two working fluid pairs (refrigerant + organic solvent), namely, 1,1,1,2-tetrafluoroethane (R134a) + N,N-dimethylacetamide (DMA) and, 1,1,1,2-tetrafluoroethane + N-methyl-2-pyrrolidone (NMP), using the static–analytic method at temperatures varying between 303 and 353 K. The experimentally measured data were successfully correlated using the Peng–Robinson equation of state (PR-EoS) in combination with Huron–Vidal mixing rule, and the nonrandom two-liquid activity coefficient model (NRTL), contrarily to the predictive Soave–Redlich–Kwong (PSRK) group contribution equation of state which failed to reproduce accurately enough such data.

Application of the SAFT-γ Mie group contribution equation of state to fluids of relevance to the oil and gas industry

The application of the SAFT-γ Mie group contribution approach [Papaioannou et al., J. Chem. Phys., 140 (2014) 054107] to the study of a range of systems of relevance to the oil and gas industry is presented. In particular we consider carbon dioxide, water, methanol, aromatics, alkanes, and their mixtures. Following a brief overview of the SAFT-γ Mie equation of state, a systematic methodology for the development of like and unlike group parameters relevant to the systems of interest is presented. The determination of group–group interactions entails a sequence of steps including: the selection of representative components and mixtures (in this instance carbon dioxide, water, methanol, aromatics, and alkanes); the definition of an appropriate set of groups to describe them; the collection of target experimental data used to estimate the group–group interactions; the determination of the group–group interaction parameters; and the assessment of the adequacy of the parameters and theoretical approach. The predictive capability of the SAFT-γ Mie group contribution approach is illustrated for a selection of mixtures, including representative examples of the simultaneous description of vapour–liquid and liquid–liquid equilibria, the densities of the coexisting phases, second derivative thermodynamic properties, and excess properties of mixing. Good quantitative agreement between the predictions and experimental data is achieved, even in the case of challenging mixtures comprising carbon dioxide and water, n-alkanes and water, and methanol and methane.

Experimental Density of Ionic Liquids and Thermodynamic Modeling with Group Contribution Equation of State Based on the Lattice Fluid Theory

In this work are reported densities of protic and aprotic ionic liquids in a wide temperature range, at ambient pressure, and a thermodynamic modeling is performed through Mattedi–Tavares–Castier, the EOS is based on lattice gas theory. The results are quite satisfactory with deviations smaller than 0.05%. The densities of aprotic ionic liquids are presented with greater magnitudes compared to protic ILs, revealing significant differences between levels of cohesion and electrostatic contributions among the protic and aprotic ionic liquids.

Modeling gas solubilities in imidazolium based ionic liquids with the [Tf2N] anion using the GC-EoS

The group contribution equation of state (GC-EoS) is extended to model gas solubilities in the homologous 1-alkyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl) imide family. The gases considered in this work are CO2, CO, H2, CH4, and C2H6. The model parameters were estimated on the basis of 1400 experimental data points in the temperature range of 278–460 K and pressures up to 160 bars. A correlation is also presented to calculate the critical diameter, a characteristic parameter of the GC-EoS repulsive term, as a function of the ionic liquid molar volume. Density data is most often available for ionic liquids; hence, the correlation provides a predictive method for ionic liquids not included in the parameterization process. The new parameters were then used to predict the phase behavior of binary mixtures containing different solutes (including C3H8, C4H10, and C6H14) and ionic liquids with different chain lengths than those used in the parameterization process.