Use of Equations of State and Coarse Grained Simulations to Complement Experiments: Describing the Interfacial Properties of Carbon Dioxide + Decane and Carbon Dioxide + Eicosane Mixtures

Abstract

We report surface tension measurements, coexisting densities, concentration profiles along the interfacial region, surface activities, and relative Gibbs adsorption isotherms for binary mixtures of carbon dioxide (CO 2 ) + n-decane (n-C 10 H 22 ) at 344.15 K and carbon dioxide (CO 2 ) + n-eicosane (n-C 20 H 42 ) at 323.15 K over a pressure range from 0.1 MPa to 10.35 MPa. The results are obtained by employing a broad approach that integrates experiments with both theory and molecular simulations to gain an enhanced multiscale description of the interfacial region. Measurements are based on the use of a high-pressure pendant drop tensiometer coupled to a high-pressure densimeter. Theoretical modeling is carried out using the Square Gradient Theory based on a version of the Statistical Associated Fluid Theory (SAFT-VR Mie) equation of state. At the molecular level, Molecular Dynamics is employed and molecules are represented by the SAFTγ coarse-grained force field. The novelty here is that both the theory and the simulations uniquely share the same underlying intermolecular potentials, hence the experimental data are employed to verify and inform in the same way both the theory and simulations. Reassuringly, theory, experiments, and molecular simulations agree with each other in the description of the bulk phase equilibria and interfacial tension. It is observed that for both mixtures, the interfacial tension decreases as the pressure (or the liquid mole fraction of CO 2 ) increases. Furthermore, there is quantitative agreement between the theoretical predictions and the results obtained from the molecular simulations of surface activities, concentration profiles along the interfacial region, and relative Gibbs adsorption isotherms at the interfaces. A remarkable high excess adsorption of CO 2 , larger in eicosane than in decane, is detected along the interface.

Interfacial tensions of industrial fluids from a molecular‐based square gradient theory

“…However, possibly, the most interesting feature of these equations is the direct and quantitative link to the underlying potential, such that information gathered experiments can be incorporated into intermolecular potentials of interest here, is to garner experience from the molecular simulation of vapor-liquid interfaces to directly feed into this framework, in order to build a robust and transferable model capable of predicting the properties of an interfacial system from a minimal amount of commonly available experimental information, such as critical constants (see Refs. [65][66][67][81][82][83][84][85][86][87] for a complete discussion).…”

On interfacial properties of tetrahydrofuran: Atomistic and coarse-grained models from molecular dynamics simulation

“…45,46 In this work we modeled THF as a single-and double-segment pearl-necklace model, without any additional electrostatic interactions, estimated from the corresponding states principle (or critical data) proposed by Mejía et al 41 This methodology has shown great flexibility to characterize vapor-liquid interfacial properties of pure fluids 47 and complex mixtures of dilute surfactant solutions 48 and natural gases and condensates. 47,[49][50][51] Table I summarizes the SAFT parameters for THF as used in molecular simulations in this work. Nevertheless, the methodology proposed by Mejía et al 41 cannot be used directly in a rigid configuration, because energy contribution in Eq.…”

High-pressure densities and interfacial tensions of binary systems containing carbon dioxide+n-alkanes: (n-Dodecane, n-tridecane, n-tetradecane)

“…Invoking the SGT, the interfacial tension of a binary mixture, γ, is given by the following integral expression: [23][24][25][26][27][28][29][30][31][32][33][34][35]66,67]…”

“…On the other hand, theoretical descriptions of these mixtures have been made by employing Density Functional Theory (DFT) [13,14,22], Density Gradient Theory (DGT) or Square Gradient Theory (SGT) [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38]. Furthermore, molecular simulations based either on Molecular Dynamics or Monte Carlo schemes have also been employed [19,30,31,39,40,41] to garner information on the interfacial properties of these systems. An analysis of the above mentioned references reveals that there are key points that must be taken into account: First, an unequivocal full description of interfacial properties requires -at least-two independent approaches, as some previous works have demonstrated (see for instance and references therein).…”

“…As part of our ongoing research work, which is devoted to the description of interfacial properties for CO 2 + n-alkanes mixtures [28][29][30][31], this work is focused on the experimental determination and theoretical modeling of bulk phase equilibrium densities and interfacial tensions of the CO 2 + ndodecane (n-C 12 H 26 ), CO 2 + n-tridecane (n-C 13 H 28 ), and CO 2 + n-tetradecane (n-C 14 H 30 ) binary mixtures at 344.15 K and over the pressure range 0.1 to 12, 13, and 14 MPa, respectively. CO 2 + n-alkane mixtures exhibit interesting and complex bulk phase and interfacial behavior and some results are available for the above-mentioned mixtures.…”