Molecular Simulation Of Properties For1-butyl-3-methylimidazolium Bromide Aqueous Solutions

In chemical engineering field, absorption heat pump (AHP) is an important industrial device for energy recovery. The properties of AHP working pair are vitally important to its effects. In recent years, many studies have shown that it is possible to exploit ionic liquid as a new type of absorbent in absorption heat pump working pairs, which has the characteristics of high efficiency and environmental protection. Ionic liquids (ILs), composed of cations and anions, are a class of organic salts which remain in liquid at room temperature or near room temperature. Because of its non-volatility, thermal stability and recycling, ILs are regarded as environmentally benign solvents. Furthermore, a great deal of target-aimed ILs can be designed through different combinations of cations and anions.Molecular simulation is one of the most promising approaches to investigate structural and dynamic properties of molecules and materials. In this paper, quantum chemical methods, Monte Carlo (MC) and molecular dynamics simulations (MD) method are used to obtain the microcosmic structure, thermodynamic and transport properties of the [BMIM]Br aqueous solutions.Firstly, this paper conducted calculations on the microcosmic properties of ionic liquid of [BMIM]Br on the basis of molecular orbit theory and valence bond theory. The optimization molecular structure of [BMIM]+ion, which consists of bonds, angles and dihedrals, was obtained by the ab initio method. Besides, Partial atomic charges, molecular orbit analysis and Cartesian coordinates were also derived from this geometry optimization method with Gaussian03for further research.Secondly, vapor liquid equilibrium properties of [BMIMjBr aqueous solutions at different temperature and pressure were simulated by NPT-Gibbs Ensemble Monte Carlo (GEMC) method with Towhee packages basing on Linux system. A modifying dielectric constant method was proposed to calculate the long-range force. The results of modifying dielectric constant method, polarizable and nonpolarizable models were compared with experimental results. The results show that compared to the polarizable and nonpolarizable models, the modifying dielectric constant method has better accuracy.Finally, molecular dynamics simulation of [BMIM]Br aqueous solutions was carried out with DL_POLY packages on the basis of Linux system. Thermodynamic, microcosmic structure and transport properties were calculated with the same forcefield in MC. The simulated enthalpy of mixing (△Hmix) with different IL concentration was obtained and compared with the experimental data. The simulated results demonstrate that the results of polarizable model and modifying dielectric constant method have a quite good correspondence with experimental data. In addition, the diffusion coefficients of [BMIM]Br in neat [BMIM]Br and [BMIM]Br aqueous solutions were also calculated, the viscosities for neat IL with different temperature were obtained from correlating with Stokes-Einstein equations. The simulation results are slightly lower than experimental data.