Bulk and interfacial properties of decane in the presence of carbon dioxide, methane, and their mixture

Interfacial tension and adsorption in the binary system ethanol and carbon dioxide: Experiments, molecular simulation and density gradient theory

The perturbed-chain statistical associating fluid theory (PC-SAFT) and density-gradient theory (DGT) are used to construct an equation of state (EOS) applicable for the phase behaviors of supercritical carbon dioxide (CO2) and hydrocarbon binary mixtures. In the bulk phases, the nonuniform EOS reduces to PC-SAFT, which is able to accurately describe the vapor−liquid equilibria (VLE) below the critical region. In the vapor−liquid surface, this EOS is able to predict the surface tensions for binary mixtures with the bulk properties and the influence parameters of pure components as input. The surface tensions of CO2−butane, CO2−decane, CO2−benzene, CO2−cyclohexane, and CO2−tetradecane binary mixtures are predicted, and the results are satisfactory compared with the experimental data.

Interfacial properties of the alkane+water system in the presence of carbon dioxide and hydrophobic silica

Molecular dynamics simulations and theoretical analysis were carried out to study the bulk and interfacial properties of carbon dioxide-methane-water and carbon dioxide-methane-brine systems under geological conditions. The density gradient theory with the bulk phase properties estimated using the cubic-plus-association (CPA) equation of state (EoS) can well describe the increase in the interfacial tension (IFT) of the CO2-water system in the presence of methane. The theoretical estimates of species mole fractions in the carbon dioxide-methane-water system are in good quantitative agreement with the experimental results. Furthermore, simulations of carbon dioxide-methane-brine system show that the IFT of the CaCl2 case is generally higher than that of the NaCl case. This is probably due to the stronger hydration of Ca2+ ions and their stronger repulsion from the interface compared to Na+. While the overall shape of the ionic profiles is not much affected by the ion type, the water profiles show a local enrichment at the interface in the system with CaCl2. In contrast to the case of NaCl, the slopes of the plots of IFT vs CaCl2 concentration are dependent on temperature. Species mole fractions in the carbon dioxide-methane-brine system predicted by combining the CPA EoS with the Debye-Hückel electrostatic term are in good agreement with simulation results.

New experimental measurements (at 10 MPa and 323.15 K) and molecular dynamics (MD) simulations (at 10 MPa and 323.15 K, 50 MPa and 344.25 K, and 50 MPa and 375.5 K) are reported in order to measure/predict the aqueous solubilities of the ternary methane–carbon dioxide–water system under two-phase (vapor–liquid) equilibrium conditions. The TIP4P/ice, TraPPE-UA, and OPLS-UA force fields for water, carbon dioxide, and methane, respectively, are used, according to the modifications introduced in the recent study by Michalis et al. (Phys. Chem. Chem. Phys., 2016, 18, 23538–23548) for the binary methane–carbon dioxide hydrate. The MD calculated values for the solubility are in good agreement with the newly available experimental measurements. The molecular dynamics simulations clearly indicate that the solubility of each gas decreases by the addition of the other gas. The particular conclusion is in excellent agreement with the conclusion obtained from the new experimental measurements reported in the current s...

Interfacial and bulk properties of vapor-liquid equilibria in the system toluene + hydrogen chloride + carbon dioxide by molecular simulation and density gradient theory + PC-SAFT

Measurement and modelling of interfacial tension in methane/water and methane/brine systems at reservoir conditions

A new method for predicting homogeneous bubble nucleation rates of pure compounds from vapor-liquid equilibrium (VLE) data is presented. It combines molecular dynamics simulation on the one side with density gradient theory using an equation of state (EOS) on the other. The new method is applied here to predict bubble nucleation rates in metastable liquid carbon dioxide (CO2). The molecular model of CO2 is taken from previous work of our group. PC-SAFT is used as an EOS. The consistency between the molecular model and the EOS is achieved by adjusting the PC-SAFT parameters to VLE data obtained from the molecular model. The influence parameter of density gradient theory is fitted to the surface tension of the molecular model. Massively parallel molecular dynamics simulations are performed close to the spinodal to compute bubble nucleation rates. From these simulations, the kinetic prefactor of the hybrid nucleation theory is estimated, whereas the nucleation barrier is calculated from density gradient theory. This enables the extrapolation of molecular simulation data to the whole metastable range including technically relevant densities. The results are tested against available experimental data and found to be in good agreement. The new method does not suffer from typical deficiencies of classical nucleation theory concerning the thermodynamic barrier at the spinodal and the bubble size dependence of surface tension, which is typically neglected in classical nucleation theory. In addition, the density in the center of critical bubbles and their surface tension is determined as a function of their radius. The usual linear Tolman correction to the capillarity approximation is found to be invalid.

Properties of the vapor‐liquid interface of 16 binary mixtures were studied using molecular dynamics simulations and density gradient theory in combination with the PCP‐SAFT equation of state. All binary combinations of the heavy‐boiling components (cyclohexane, toluene, acetone, and carbon tetrachloride) with the light‐boiling components (methane, carbon dioxide, hydrogen chloride, and nitrogen) were investigated at 0.7 times the critical temperature of the heavy‐boiling component in the whole composition range. Data on the surface tension, the enrichment, the relative adsorption, and the interfacial thickness, as well as for the vapor‐liquid equilibrium and Henry's law constant are reported. The binary interaction parameters were fitted to experimental data in a consistent way for all systems and both methods. Overall, the results from both methods agree well for all investigated properties. The interfacial properties of the different studied systems differ strongly. We show that these differences are directly related to the underlying phase equilibrium behavior.

An overview of the molecular simulation studies of the oil+brine two-phase system in the presence of CO2, CH4, and their mixture at geological conditions is presented. The simulation results agreed well with the experimental results and the density gradient theory predictions on the basis of the cubic–plus–association equation of state (CPA EoS) (withDebye–Hückel electrostatic term) and the perturbed chain statistical associating fluid theory (PC-SAFT) EoS. The interfacial tension (IFT) of the alkane+H2O system showed almost a linear increase with an increasing number of carbon atoms in the alkane molecule. These IFTs are approximately equal for linear, branched, and cyclic alkanes. Here, the negative surface excess of the alkanes might explain the increase in the IFTs with an increase in the pressure. The surface excesses of the alkanes increased with decreasing temperature. This may explain the decrease of the slopes in the IFT versus pressure plot with a decrease in the temperature. The IFT behavior of the alkane+water+CH4/CO2 system was found to be similar to that observed for the alkane+water system. The addition of CO2 had a more significant influence on the IFT than the addition of CH4. Here, CH4 and CO2 exhibited a positive surface excess. The negative surface excess of the salt ions probably explains the increase in the IFTs of the alkane+brine system with increasing salt content. The solubilities of CH4 and/or CO2 in the H2O-rich phase of the alkane+brine+CH4/CO2 system increased with decreasing salt content (salting-out effect). The IFT of the aromatic hydrocarbon+H2O system is much lower than that of the alkane+H2O system. The surface excess followed the order o-xylene > ethylbenzene > toluene > benzene for the aromatic hydrocarbon+H2O system. This trend has a direct correlation with the aromatic–aromatic interaction.

A combined density gradient theory with equation of state model for the study of surface tension of refrigerant fluids

Measurement and modelling of high pressure density and interfacial tension of (gas + n-alkane) binary mixtures

Vapor-liquid interfacial properties of the system cyclohexane + CO2: Experiments, molecular simulation and density gradient theory

Interfacial behaviors of the H2O+CO2+CH4+C10H22 system in three phase equilibrium: A combined molecular dynamics simulation and density gradient theory investigation

PHOTOSYNTHESIS, PHOTOREDUCTION AND DARK REDUCTION OF CARBON DIOXIDE IN CERTAIN ALGAE