Understanding the Phase Behavior of Tetrahydrofuran + Carbon Dioxide, + Methane, and + Water Binary Mixtures from the SAFT-VR Approach

The high-pressure phase diagrams of the tetrahydrofuran(1) + carbon dioxide(2), + methane(2), and + water(2) mixtures are examined using the SAFT-VR approach. Carbon dioxide molecule is modeled as two spherical segments tangentially bonded, water is modeled as a spherical segment with four associating sites to represent the hydrogen bonding, methane is represented as an isolated sphere, and tetrahydrofuran is represented as a chain of m tangentially bonded spherical segments. Dispersive interactions are modeled using the square-well intermolecular potential. In addition, two different molecular model mixtures are developed to take into account the subtle balance between water–tetrahydrofuran hydrogen-bonding interactions. The polar and quadrupolar interactions present in water, tetrahydrofuran, and carbon dioxide are treated in an effective way via square-well potentials of variable range. The optimized intermolecular parameters are taken from the works of Giner et al. (Fluid Phase Equil. 2007, 255, 200), Galindo and Blas (J. Phys. Chem. B 2002, 106, 4503), Patel et al. (Ind. Eng. Chem. Res. 2003, 42, 3809), and Clark et al. (Mol. Phys. 2006, 104, 3561) for tetrahydrofuran, carbon dioxide, methane, and water, respectively. The phase diagrams of the binary mixtures exhibit different types of phase behavior according to the classification of van Konynenburg and Scott, ranging from types I, III, and VI phase behavior for the tetrahydrofuran(1) + carbon dioxide(2), + methane(2), and + water(2) binary mixtures, respectively. This last type is characterized by the presence of a Bancroft point, positive azeotropy, and the so-called closed-loop curves that represent regions of liquid–liquid immiscibility in the phase diagram. The system exhibits lower critical solution temperatures (LCSTs), which denote the lower limit of immiscibility together with upper critical solution temperatures (UCSTs). This behavior is explained in terms of competition between the incompatibility with the alkyl parts of the tetrahydrofuran ring chain and the hydrogen bonding between water and the ether group. A minimum number of unlike interaction parameters are fitted to give the optimal representation of the most representative features of the binary phase diagrams. In the particular case of tetrahydrofuran(1) + water(2), two sets of intermolecular potential model parameters are proposed to describe accurately either the hypercritical point associated with the closed-loop liquid–liquid immiscibility region or the location of the mixture lower- and upper-critical end-points. The theory is not only able to predict the type of phase behavior of each mixture, but also provides a reasonably good description of the global phase behavior whenever experimental data are availabl

Molecular dynamics simulation of CO2 hydrates: Prediction of three phase coexistence line

The three phase equilibrium line (hydrate-liquid water-liquid carbon dioxide) has been estimated for the water + carbon dioxide binary mixture using molecular dynamics simulation and the direct coexistence technique. Both molecules have been represented using rigid nonpolarizable models. TIP4P/2005 and TIP4P/Ice were used for the case of water, while carbon dioxide was considered as a three center linear molecule with the parameterizations of MSM, EPM2, TraPPE, and ZD. The influence of the initial guest occupancy fraction on the hydrate stability has been analyzed first in order to determine the optimal starting configuration for the simulations, paying attention to the influence of the two different cells existing in the sI hydrate structure. The three phase coexistence temperature was then determined for a pressure range from 2 to 500 MPa. The qualitative shape of the equilibrium curve estimated is correct, including the high pressure temperature maximum that determines the hydrate re-entrant behaviour. However, in order to obtain quantitative agreement with experimental results, a positive deviation from the classical Lorentz-Berthelot combining rules must be considered

Simulacion molecular de hidratos de CO2

Simulation moléculaire d'hydrates de CO

Molecular Dynamics Simulations of the CO2-CH4 mixed hydrates

Gas hydrates are crystalline, nonstoichiometric inclusion compounds formed under high pressure and at moderately low temperatures. Their structure consists of a three dimensional framework of hydrogen-bonded water molecules which can incorporate a number of relatively small 'guest' molecules, such as CH4, CO2, H2S. The interest on CO2-CH4 mixed hydrates characterization has increased remarkably over the last few years due to the possibility of using them for waste CO2 recovery, capture and storage. Nevertheless, the modelling of CO2 and CH4 mixed hydrates has received less attention so far, and the theoretical estimation of their phase equilibria and thermophysical and transport properties still needs further contributions. In this case, rigid non polarizable molecular models have been used to describe H2O, CO2 and CH4, and the three phase CO2 Hydrate-Liquid H2O-Liquid CO2 equilibrium line has been determined using Molecular Dynamics by direct coexistence technique. Finally, CO2-CH4 separation was evaluated at different pressure and temperatures conditions and compared with experimental results

Determination of the Global Phase Behavior of THF + CH4, +CO2, and + H2O Binary Mixtures using the SAFT-VR Approach

Determination of the Global Phase Behavior of THF + CH4, +CO2, and + H2O Binary Mixtures using the SAFT-VR Approac

Determination of the global phase behaviour of binary mixtures: THF+CH4, THF+ CO2 and THF+ H2O using the SAFT-VR approach

Determination of the global phase behaviour of binary mixtures: THF+CH4, THF+ CO2 and THF+ H2O using the SAFT-VR approac

Prediccion de la linea de coexistencia trifasica en hidratos de CO2 mediante Dinamica Molecular

Prediction of the trifasic coexistence line dof CO2 hydrates by molecular dynamic

Estimation of the three phase coexisting line for carbon dioxide type I hydrates using molecular dynamics

Estimation of the three phase coexisting line for carbon dioxide type I hydrates using molecular dynamic

Simulación molecular de hydratos de CO2

La línea de equilibrio trifásico (hidrato-H2O líquida-CO2 líquido) que presenta el diagrama de fases de la mezcla binaria H2O+CO2 a bajas temperaturas y que delimita la zona de estabilidad de la fase hidrato ha sido estimada en este trabajo mediante el método de simulación molecular en combinación con la técnica de coexistencia directa. Ambas moléculas han sido representadas mediante modelos rígidos no polarizables. Para el caso del agua, ésta ha sido representada mediante los modelos TIP4P/2005 y TIP4P/Ice, mientras que el CO2 ha sido modelado mediante diferentes parametrizaciones de un mismo modelo lineal compuesto por tres sitios interaccionantes: MSM, TraPPE, EPM2 y ZD. La estabilidad del hidrato ha sido analizada variando su fracción de ocupación inicial con el objetivo de determinar la influencia que ejercen en ésta los dos tipos de cavidades diferentes que forman la estructura SI de hidratos de CO2. La temperatura de coexistencia de las tres fases ha sido determinada para un rango de presiones comprendido entre 2 y 500 MPa