Part 2. Phase Equilibria of Liquid and Gaseous Mixtures at High Pressures

Summary Molecular simulation is a powerful technique for obtaining thermodynamic properties of a system of given composition at a specific temperature and pressure, and it enables us to visualize microscopic phenomena. In this work, we used simulations to study interfacial phenomena and phase equilibria, which are important to CO2-enhanced oil recovery (EOR). We conducted molecular dynamics (MD) simulation of an oil/water interface in the presence of CO2. It was found that CO2 was enriched at the interfacial region under all thermal conditions. Whereas the oil/water interfacial tension (IFT) increases with pressure, CO2 reduces the IFT by approximately one-third at low pressure and one-half at higher pressure. Further analysis on the basis of our MD trajectories shows that the O=C=O bonds to the water with a “T-shaped” structure, which provides the mechanism for CO2 enrichment at the oil/water interface. The residual nonnegligible IFT at high pressures implies that the connate or injected water in a reservoir strongly influences the transport of CO2/oil solutes in that reservoir. We used Gibbs ensemble Monte Carlo (GEMC) simulation to compute phase equilibria and obtain ternary phase diagrams of such systems as CO2/n-butane/N2 and CO2/n-butane/n-decane. Simulating hydrocarbon fluids with a mixture of CO2 and N2 enables us to evaluate the effects of N2 impurity on CO2-EOR. It also enables us to study the phase behavior, which is routinely used to evaluate the minimum miscibility pressure (MMP). We chose these two systems because experimental data are available for them. Our calculated phase equilibria are in fair agreement with experiments. We also discuss possible ways to improve the predictive capability for CO2/hydrocarbon systems. GEMC and MD simulations of systems with heavier hydrocarbons are straightforward and enable us to combine molecular-level thinking with process considerations in CO2-EOR.

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Phase Equilibria in Molecular Hydrogen-Helium Mixtures at High Pressures

The Astrophysical Journal ◽

10.1086/152575 ◽

1973 ◽

Vol 186 ◽

pp. 1107 ◽

Cited By ~ 59

Author(s):

W. B. Streett

Keyword(s):

Phase Equilibria ◽

Molecular Hydrogen ◽

High Pressures ◽

Helium Mixtures

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Investigation of droplet nucleation in CCS relevant systems – design and testing of the expansion chamber

EPJ Web of Conferences ◽

10.1051/epjconf/201818002015 ◽

2018 ◽

Vol 180 ◽

pp. 02015 ◽

Cited By ~ 1

Author(s):

Miroslav Čenský ◽

Jan Hrubý ◽

Václav Vinš ◽

Jiří Hykl ◽

Bohuslav Šmíd

Keyword(s):

Acoustic Waves ◽

High Pressures ◽

Systems Design ◽

Helmholtz Resonator ◽

Rapid Expansion ◽

Acoustic Oscillations ◽

Expansion Chamber ◽

Gaseous Mixtures ◽

Experimental Apparatus ◽

Design And Testing

A unique in-house designed experimental apparatus for investigation of nucleation of droplets in CCS relevant systems is being developed by the present team. The apparatus allows simulating various processes relevant to CCS technologies. Gaseous mixtures with CO2 are prepared in a Mixture Preparation Device (MPD) based on accurate adjustment of flow rates of individual components [EPJ Web of Conferences 143, 02140 (2017)]. The mixture then flows into an expansion chamber, where it undergoes a rapid adiabatic expansion. As a consequence of adiabatic cooling, the mixture becomes supersaturated and nucleation and simultaneous growth of droplets occurs. In this study, we describe the design and testing of the expansion part of the experimental setup. The rapid expansion was realized using two valve systems, one for low pressures (up to 0.7 MPa) and the other for high pressures (up to 10 MPa). A challenge for a proper design of the expansion system is avoiding acoustic oscillations. These can occur either in the mode of Helmholtz resonator, where the compressible gas in the chamber acts as a spring and the rapidly moving gas in the valve system as a mass, or in the “flute” mode, where acoustic waves are generated in a long outlet tubing.

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