Fernando García-Sánchez

An equation-of-state-based viscosity model for non-ideal liquid mixtures

Abstract A viscosity model based on the Eyring’s theory and a cubic equation of state (Peng–Robinson–Stryjek–Vera) has been applied to the correlation and prediction of experimental liquid viscosities of binary mixtures containing polar fluids within a wide range of temperature, pressure and composition (encompassing low-pressure and compressed liquid conditions). Highly non-idealities of the binary mixtures considered in this study were conveniently handled via the application of the Wong–Sandler approach for the mixing rules used in the cubic equation of state. The results obtained were highly satisfactory for various non-ideal binary mixtures over the whole composition range at a low pressure. The predictive capabilities of the present approach were also verified in the representation of liquid viscosities at elevated pressures preserving the same model parameters previously obtained at low pressure.

Modeling of microemulsion phase diagrams from excess Gibbs energy models

Abstract Projects on tertiary oil recovery by means of microemulsions have been mainly concerned with, first, the ability of a microemulsion to dissolve oil and water simultaneously and, second, the attainment of very low interfacial tensions. Therefore, the design and analysis of chemical flooding processes for enhanced oil recovery must be based on calculations of phase equilibria for these systems, which are composed of water (brine), oil, surfactant and co-surfactant (usually an alcohol). Consequently, the understanding of phase behavior of these systems is of fundamental importance to the development of any surfactant-based chemical flooding process. The purpose of this work was to give a thermodynamic analytical representation of the phase diagram of microemulsion systems similar to those used in enhanced oil recovery. The algorithms presented for the calculation of multiphase liquid equilibria and the methods for the estimation of the excess Gibbs energy model interaction parameters were successfully tested for the representation of experimental multiphase liquid equilibrium data of an oil−brine−surfactant−alcohol model system. In addition, to represent effectively the phase diagram of this system, an empirical expression was introduced into the selected excess Gibbs energy model to account for the specific role of the surfactant in these complex systems.

Vapor pressures of pure compounds using the Peng-Robinson equation of state with three different attractive terms

Abstract Accurate representation of pure compounds vapor pressures is required to increase the robustness of equations of state when predicting phase equilibria for mixtures. Using cubic equations of state, this representation largely depends on improving the temperature-dependent attractive term of the equation of state (EOS) to cover data from the triple to critical points. With this purpose, the Peng–Robinson equation of state is applied with three different attractive terms: Mathias, Mathias–Copeman, and Carrier–Rogalski–Peneloux. Experimental vapor pressures for 311 pure compounds (9000 experimental values) have been fitted. The studied compounds include nitrogen compounds, oxides, sulfides, chlorides, oxyhalides, inorganic compounds, alkanes, cycloalkanes, alkenes, alkadienes, alkynes, aromatic hydrocarbons, halogenated alkanes, halogenated cycloalkanes, halogenated alkenes, halogenated aromatic hydrocarbons, alcohols, ethers, aldehydes, ketones, alkanoic acids, esters, phenols, heterocyclic oxygen compounds, heterocyclic nitrogen compounds, hydrocarbon nitrogen compounds, and sulfur compounds. Overall average absolute deviations of 0.416, 0.214 and 0.276% have been found for the resulting Peng–Robinson–Mathias (PRM), Peng–Robinson–Mathias–Copeman (PRMC), and Peng–Robinson–Carrier–Rogalski–Peneloux (PRCRP) equations of state, respectively.

Critical point calculations for oil reservoir fluid systems using the SPHCT equation of state

Abstract Garcia-Sanchez, F., Ruiz-Cortina, J.L., Lira-Galeana, C. and Ponce-Ramirez, L., 1992. Critical point calculations for oil reservoir fluid systems using the SPHCT equation of state. Fluid Phase Equilibria , 81: 39-84. The ability for predicting the critical points of reservoir fluids using the Simplified Perturbed Hard-Chain Theory (SPHCT) equation of state proposed by Kim et al. is analyzed. The computational procedure developed by Heidemann and Khalil was used for locating the critical points in any multicomponent mixture described by this equation of state. Experimental binary vapor-liquid equilibrium data of interest in the petroleum industry have been used to evaluate the interaction coefficients in this equation for 164 binary mixtures. The performance of the SPHCT EOS to predict critical points is demonstrated on four oil reservoir fluid systems containing up to forty-eight components. Convergence to all the critical points existing in these large systems was obtained in a few iterations without any difficulty.

Vapour pressure and critical constants of 1,2-dichloroethane

Abstract Experimental vapour pressures are reported for 1,2-dichloroethane. The measured values have been fitted by the Cragoe equation. The critical temperature was determined by direct observation of the disappearance of the gas-liquid meniscus whereas the critical pressure was derived from the Cragoe equation.

Vapour pressure, critical temperature, and critical pressure of dichloromethane

Abstract Experimental vapour pressures of dichloromethane are reported. The critical temperature and critical pressure were determined by direct observation of the disappearance of the gas-to-liquid meniscus. Coefficients are given of Cragoe and of Wagner equations which fit the complete set of measured vapour pressures up to the critical point.

Equation of state associated with activity coefficient models to predict low and high pressure vapor–liquid equilibria

Abstract A simple and thermodynamically consistent method is presented to establish an equation of state for mixtures by using activity coefficient model parameters. All current solution models such as NRTL, van Laar, UNIFAC, or any other thermodynamic model can be used. The main feature of the method presented is that only a single scaling factor value determined at a given reference temperature is required to predict the vapor–liquid equilibria in a wide range of temperature and pressure. The performance of the method is tested on the prediction of the vapor–liquid equilibria at low, moderate, and high pressures for six binary systems (methanol−benzene, acetone−water, methanol−acetone, methanol−water, ethanol−water, and 2-propanol−water) and a ternary system (acetone−water−methanol). For comparison, vapor–liquid equilibrium calculations were carried out with the Wong and Sandler method by using the PRSV equation of state associated with the van Laar and scaling factors. On the whole, it is found that at high pressures both methods give similar predictions but at low pressures the proposed method gives sometimes better results than that of Wong and Sandler method.

Bubble streams in Titan’s seas as a product of liquid N 2 + CH 4 + C 2 H 6 cryogenic mixture

Liquid methane lakes dot Titan’s polar regions. Numerical models reveal that the creation of buoyant bubbles through nitrogen exsolution near the bed of the Ligeia Mare lake can explain transient brightenings observed by Cassini on the lake’s surface.

Generalization of composition-dependent mixing rules for multicomponent systems: prediction of vapor–liquid and liquid–liquid equilibria

Abstract A consistent generalization to mixing rules depending on the composition proposed by Adachi and Sugie, Panagiotopoulos and Reid, and Stryjek and Vera for the two-parameter mixing rule and by Schwartzentruber and Renon for the three-parameter mixing rule is presented. The invariance problem and dilution effect shortcomings pointed out by Michelsen and Kistenmacher when the original mixing rules are applied to multicomponent mixtures, are avoided by the generalized mixing rules. The proposed mixing rules involving their respective excess function models associated with a cubic equation of state (PRSV or PRCRP), were used on the representation of binary vapor–liquid (hydrocarbon–hydrocarbon, acetone–alcohol, acetone–water, alcohol–water, and alcohol–hydrocarbon) and liquid–liquid (hydrocarbon–water) equilibrium data. The binary interaction parameters of the model were used to test the performance of the generalization on the prediction of ternary vapor–liquid (acetone–methanol–water, acetone–ethanol–water and hexane–ethanol–benzene) and liquid–liquid (water–methanol–benzene, water–ethanol–hexane and water–1-propanol–benzene) equilibria. In addition, it is shown that a more satisfactory prediction of the ternary vapor–liquid and liquid–liquid equilibria can be obtained by using a limit form of the generalized three-parameter excess function model.

Isothermal Multiphase Flash Calculations with the PC-SAFT Equation of State

A computational approach for isothermal multiphase flash calculations with the PC‐SAFT (Perturbed‐Chain Statistical Associating Fluid Theory) equation of state is presented. In the framework of the study of fluid phase equilibria of multicomponent systems, the general multiphase problem is the single most important calculation which consists of finding the correct number and types of phases and their corresponding equilibrium compositions such that the Gibbs energy of the system is a minimum. For solving this problem, the system Gibbs energy was minimized using a rigorous method for thermodynamic stability analysis to find the most stable state of the system. The efficiency and reliability of the approach to predict and calculate complex phase equilibria are illustrated by solving three typical problems encountered in the petroleum industry.