Microscopic Structure and Interaction Analysis for Supercritical Carbon Dioxide−Ethanol Mixtures: A Monte Carlo Simulation Study

Abstract

Configurational-bias Monte Carlo simulations in the isobaric-isothermal ensemble using the TraPPE-UA force field were performed to study the microscopic structures and molecular interactions of mixtures containing supercritical carbon dioxide (scCO(2)) and ethanol (EtOH). The binary vapor-liquid coexisting curves were calculated at 298.17, 333.2, and 353.2 K and are in excellent agreement with experimental results. For the first time, three important interactions, i.e., EtOH-EtOH hydrogen bonding, EtOH-CO(2) hydrogen bonding, and EtOH-CO(2) electron donor-acceptor (EDA) bonding, in the mixtures were fully analyzed and compared. The EtOH mole fraction, temperature, and pressure effect on the three interactions was investigated and then explained by the competition of interactions between EtOH and CO(2) molecules. Analysis of the microscopic structures indicates a strong preference for the formation of EtOH-CO(2) hydrogen-bonded tetramers and pentamers at higher EtOH compositions. The distribution of aggregation sizes and types shows that a very large EtOH-EtOH hydrogen-bonded network exists in the mixtures, while only linear EtOH-CO(2) hydrogen-bonded and EDA-bonded dimers and trimers are present. Further analysis shows that EtOH-CO(2) EDA complex is more stable than the hydrogen-bonded one.

Hydrogen bond, electron donor-acceptor dimer, and residence dynamics in supercritical CO2-ethanol mixtures and the effect of hydrogen bonding on single reorientational and translational dynamics: A molecular dynamics simulation study

“…18 Furthermore, the local environment redistribution dynamics revealed that the time dependent redistribution of the first solvation shell of ethanol is much slower in comparison with the first shell of CO 2 and this observation has been interpreted in terms of the existence of weaker interactions between the CO 2 -CO 2 and EtOH-CO 2 molecules in comparison with the EtOH-EtOH ones, which could be a result of stronger hydrogen bonding ͑HB͒ interactions. Moreover, another recent Monte Carlo simulation study 37 has revealed that the EtOH-EtOH HB network is the most im-portant in these mixtures, having as a result the appearance of aggregates between the EtOH molecules in the fluid.…”

“…Although a small number of experimental and theoretical studies devoted to the properties of sc CO 2 -methanol mixed solvents ͑with X methanol ϳ 0.01-0.11͒ have been reported up to now, [18][19][20][21][22][23][24][25][26][27][28][29] studies on the properties of scCO 2 -ethanol ͑EtOH͒ systems are quite rare and most of them correspond mainly to dilute mixtures. 24,[30][31][32][33][34][35][36][37] In a quite recent study, two of the authors presented a molecular dynamics ͑MD͒ simulation study on the local intermolecular structure and related dynamics for the sc CO 2 -EtOH binary mixture at a mole fraction X ethanol ϳ 0.1. 36 The results obtained in that study have revealed a nonideal mixing behavior of the mixture and the existence of a somewhat restricted aggregation between the ethanol molecules.…”

“…At this point we have to mention that previously reported experimental and theoretical studies have revealed that the addition of alcohols, which act as Lewis bases, in CO 2 ͑which exhibits an acid behavior through the carbon atom͒ leads to the observation of a Lewis acid-base-type interaction and to the formation of an electron donor-acceptor ͑EDA͒ dimer. 30,35,37,38 In a previous Monte Carlo simulation study Xu et al 37 proposed a geometric criterion and performed a static analysis of EDA dimers in EtOH-CO 2 mixtures. According to the results obtained in that study, the EDA EtOH-CO 2 dimer is more stable than the hydrogen bonded one.…”

Molecular dynamics simulation of diffusion coefficients and structural properties of ketones in supercritical CO2 at infinite dilution

“…With respect to computer simulations, they are very useful for investigating dynamic, structural and thermodynamic properties, allowing researchers to complement other existing studies and get valuable information not directly obtained by experiment [21,[27][28][29] as, for instance, radial distribution functions, coordination numbers, and energetic data.…”

Monte Carlo simulations of phase behavior and microscopic structure for supercritical CO2 and thiophene mixtures

“…Molecular simulation has previously been applied successfully to determine solubility of naphthalene, benzoic acid, hydroxybenzoic acid, etc. in ScCO 2 [22][23][24][25]. Here, we attempt to study the thermodynamic properties in solution mixtures of thiophene and ScCO 2 and provide molecular level insights on the interactions between the thiophene and CO 2 in supercritical phase.…”