Molecular Simulation Of Properties For Ionic Liquids And Its Mixtures

Absorption heat pump, which can take advantage of a variety of low-grade heat to make higher quality heat, is important energy-saving equipment for utilizing low temperature waste-heat. It is not only energy-efficient and environmental-friendly but also creates huge social and economic benefits. In recent years, the development of the absorption heat pump is very rapid. Physical and chemical properties of the working pair have a great impact on performance of absorption heat pump. Because of its unique properties, i.e., thermal stability, very low vapor pressure and small corrosion, ionic liquid is possible to be exploited as a new type of working fluid for absorption heat pump by many scholars. A great number of ionic liquids can be obtained through different combinations of cations and anions. In addition, the physical and chemical data of ionic liquids are also quite deficient.With the rapid development of computer technology, simulation has become an important tool for the modern research. Quantum chemistry simulation can be used to study theoretically the structure, properties and atomic charge of materials at the molecular and electronic level; Molecular dynamics simulation can study effectively the microstructure, thermodynamic and transport properties of materials from the molecule interaction. VLE properties of the system can be achieved by using the Gibbs ensemble Monte Carlo simulation (GEMC) of computer simulation.The stable geometries, vibration frequency calculation, orbital interaction analysis and natural population analysis of the ionic liquid1-ethyl-3-methylimidazolium dimethyl phosphate ([EMIM][DMP]) have been investigated by performing density functional theory calculations at the B3LYP/6-311++G(d,p) level. The structural parameters of ions bond lengths, bond angles, dihedral, etc., and atomic charge distribution of cation and anion were obtained; Multiple hydrogen bonds between the cation and anion were occurred with charge transfer phenomena; Orbit interaction analysis showed the main source of the stabilization energy; The good agreement between the experimental IR spectra and the calculated vibrations indicates that the structures of the larger ion clusters provide a reasonable depiction for bulk ILs and the calculation method is reliable.Molecular dynamics simulations of [EMIM][DMP] and its mixtures were performed to study the macroscopic properties, such as thermodynamic properties (density and heat of mixing), transport properties (diffusion coefficient and viscosity) and microscopic structure (radial distribution function). The simulated mixing enthalpy of ionic liquid [EMIM][DMP] and its mixtures with different ILs concentration was obtained and compared with the experimental data. The results have shown that simulated and experimental values are in good agreement and that the heat released when water mixed with ionic liquid is more significantly greater compared with the mixing heat of [EMIM][DMP]+methanol. In addition, the diffusion coefficient and viscosity of ILs were also calculated and the simulations results have demonstrated that diffusion coefficient of cation is greater than anion’s.Vapor liquid equilibrium properties of the system of [EMIM][DMP]+H20were calculated at different pressure and temperature using NPT-Gibbs Ensemble Monte Carlo (GEMC) method by Towhee7.0.2packages. The simulation results are in accord with experimental data, which demonstrate the reliability of the calculation method and force field models.