A cubic equation of state model for phase equilibrium calculation of alkane + carbon dioxide + water using a group contribution kij

Thermodynamic modelling of aqueous CH 4-bearing fluid inclusions trapped in hydrocarbon-rich environments

Parameter estimation for cubic equations of state models subject to sufficient criteria for thermodynamic stability

Modeling of enhanced / improved oil recovery processes that takes into account mass transfer between phases depends on the correct prediction of thermodynamic properties and composition of phases in equilibrium. In a steam flood process, the mutual water / hydrocarbons solubility is a function of the temperature, pressure and fluid composition of the system and may not be negligible at flooding conditions. The most used equations of state (EoS) in the petroleum industry fail to accurately correlate saturation properties of polar substances that self-associate through hydrogen bonding and as a consequence, do not calculate the distribution of the components among equilibrium phases precisely. In this paper, we present the development of the Association Peng-Robinson and Association Soave-Redlich-Kwong equations of state. The proposed equations of state are composed of two parts, one physical (the original cubic equation of state model) and one chemical (an empirical chemical reaction term which accounts for the self-association of a component) and can be used to model systems in equilibrium that contain one associating component such as water or alcohol. In the extended equations of state which includes the self-association chemical reaction, the degree of the molar volume polynomial is increased from its normal value of three to six but, in general, there are only three positive roots. The chemical part of the extended EoS includes three parameters that can be adjusted to match data, the entropy and enthalpy of the association chemical reaction and one free parameter. The fugacity calculations for the extended EoS can be split into physical and chemical parts, where the physical part has exactly the same form as the original equation of state fugacities. In order to estimate the new parameters of the proposed equations of state, the differences between the experimental and calculated saturation pressure and saturated liquid molar volume of pure water are minimized using a Particle Swarm Optimization (PSO) algorithm. The equations of state presented here enhance the original ones through the addition of a chemical part to deal with self-associating polar components. The average relative deviation between the experimental and calculated saturated data using the association forms of the Peng-Robinson and Soave-Redlich-Kwong equations of state are smaller than those obtained from the original models. The chemical reaction approach is robust and improves the prediction of thermodynamic equilibrium properties of self-associating pure components by adding only three adjustable parameters, where two of them have a clear physical meaning (self-associating reaction enthalpy and entropy).

Correlation and prediction of ionic liquid viscosity using Valderrama-Patel-Teja cubic equation of state and the geometric similitude concept. Part I: Pure ionic liquids

The development of the Peng - Robinson equation and its application to phase equilibrium in a system containing methanol

Thermodynamic and thermo physical properties of refrigerants are essential for the equipment designs used in refrigeration and air-conditioning systems. For accurate and fast representation of thermodynamic and thermo physical properties of refrigerants equation of state (EOS) is required. Because these properties are essential for the equipment designs. This work represents the cubical equation of state (EOS) model for HC-290. A promising refrigerant with zero ozone depletion potential and very low global warming potential conduct to be potential green refrigerant for the replacement of R-22. Vapour specific volume property is calculated in this work. Several two and three parameter based equation of states root mean square deviation has been presented. Berthelot, Harmens-Knapp, Redlich-Kwong and Schmidt-Wenzel state promising results for HC-290.

A comparison of the performances of two different approaches of cubic equations of state models, based on a classical van der Waals and mixing rules incorporating theG E equation, was carried out for correlation of Vapor-Liquid Equilibria (VLE), HE and C P E data alone, and simultaneous correlation of VLE+HE, VLE+C P E , HE +C P E and VLE+HE +C P E data for the diethers (1,4-dioxane or 1,3-dioxolane) with n-alkane systems. For all calculations the Peng-Robinson-Stryjek-Vera cubic equation of state (PRSV CEOS) was used. A family of mixing rules for the PRSV CEOS based on the Modified van der Waals one-fluid mixing rule (MvdW1) and two well-known CEOS/GE mixing rules (MHV1 and MHV2), was considered. The NRTL equation, as the GE model with linear or reciprocal temperature dependent parameters, was incorporated in the CEOS/GE models. The results obtained by the CEOS/GE models exhibit significant improvement in comparison to the MvdW1 models.

Two- and three-phase equilibria in systems containing benzene derivatives, carbon dioxide, and water at 373.15 K and 10–30 MPa

Fluid phase equilibria in water: natural gas component mixtures and their description by the hole group-contribution equation of state

Application of the hole quasi-chemical group contribution equation of state for phase equilibrium calculation in systems with association

ABSTRACTThe cubic equation of state (CEoS) is a powerful method for calculation of (vapor + liquid) equilibrium (VLE) in polymer solutions. Using CEoS for both the vapor and liquid phases allows one to calculate the non‐ideality of polymer solutions based on a single EoS approach. In this research, vapor–liquid equilibria calculations of polyvinyl acetate (PVAc)/solvent solutions were performed. In this approach, eight models containing PRSV and SRK CEoS separately combined with four mixing rules namely vdW1, vdW2, Wong–Sandler (WS), and Zhong–Masuoka (ZM) were applied to calculations of bubble point pressure. For the better prediction, the adjustable binary interaction parameters existing in any mixing rule were optimized. The results were very acceptable and satisfactory. Absolute average deviations (%AAD) between predicted results and experimental bubble point pressure data were calculated and presented. The capability of two cubic equations of state had a good agreement with experimental data and predict the correct type of phase behavior in all cases, but the performance of the PRSV + vdW2 was more reliable than the other models with 2.65% in AAD for total of solution systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40651.

Reliable computation of phase stability using interval analysis: Cubic equation of state models

The reliable prediction of phase stability is a challenging computational problem in chemical process simulation, optimization, and design. The phase stability problem can be formulated either as a minimization problem or as an equivalent nonlinear equation-solving problem. Conventional solution methods are initialization dependent and may fail by converging to trivial or nonphysical solutions or to a point that is a local but not a global minimum. Thus, there has been considerable recent interest in developing more reliable techniques for stability analysis. Recently, the authors have demonstrated, using cubic equation of state models, a technique that can solve the phase stability problem with complete reliability. The technique, which is based on interval analysis, is initialization independent and, if properly implemented, provides a mathematical guarantee that the correct solution to the phase stability problem has been found. However, there is much room for improvement in the computational efficiency of the technique. In this paper, the authors consider two means of enhancing the efficiency of the method, both based on sharpening the range of interval function evaluations. Results indicate that, by using the enhanced method, computation times can be reduced by nearly an order of magnitude in some cases.

Reliable phase stability analysis for cubic equation of state models

Geologic formations with abnormally high pressure and temperature are capable of storing huge amounts of methane, the production of methane while storing CO2 in aquifer could help offset the cost of CO2 capture and sequestration. The effect of dissolved CO2 in the water-rich phase on the total methane recovery from a CH4-saturated aquifer is still not clear, due to the lack of reliable equation of state to model water-containing reservoir gas systems. Modeling vapor-liquid phase equilibria of water-containing reservoir gas systems is previously considered a challenge for the cubic equation of state models. A concise and reliable phase behavior model for compositional reservoir simulation is presented that uses a modified Wong-Sandler mixing rule with Non-Random-Two-Liquid (NRTL) model to perform flash calculation and stability analysis for gas-water systems (CH4-H2O, CO2-H2O, CO2-CH4-H2O, etc) at reservoir temperatures and pressures. The proposed model is able to handle both strongly polar fluid system and hydrocarbon fluid system under the same thermodynamic framework. The model performance for the CH4-H2O and CO2-CH4-H2O systems was validated by a large amount of experimental data. As for the CH4-H2O system, the average absolute deviation of model calculated phase composition from the experimental data is around 5% for the gas phase and 7% for the aqueous phase. The model was used to simulate the two processes of CH4 recovery by CO2 injection: 1) the forward multiple-contact process; and 2) the backward multiple-contact process. The results showed that the forward multiple-contact process dominates CH4 recovery by CO2 injection. The maximum CH4 recovery factor (MRF) from CH4-saturated water by CO2 injection is approximately 50% to 70% and it is achieved only within a narrow temperature range (350 to 370K), regardless of pressure. The multiple-contact phase behavior simulation showed that, in typically reservoir pressures and temperatures (20 to 160 MPa, and 300 to 470K), 5 to 12 mole CO2 may be needed to recovery 1 mole of CH4 from CH4-saturated water.