Prediction Of Thermodynamic Properties Of Complex Systems Based On COSMO-SAC Model And Molecular Simulation

The predictions of thermodynamic and kinetic properties of complex systems including polymer solutions, ionic liquid systems, the system of methanol and glycerol in limited space, and PCB systems were discussed based on COSMO-SAC model and molecular simulation in this thesis.The vapor liquid equilibriua of polymer solutions are important information of thermodynamics, which always has a lot of difficulties for measuring the accurate experimental data. In this thesis, the reasonable calculation method was proposed to compute the sigma profile, cavity volume and cavity surface area according to the structural feature of polymer. The assumption is that every polymer is constructed by the repeat units with same number, and the COSMO data of polymer chain is the linear summation of repeat unit information. Thus, the detailed algorithm was proposed by us for the generation of the structures of repeat unit and calculation of the COSMO data of repeat unit. The estimated effects of phase equilibrium behavior of several typical polymer solutions were presented. The examples showed that the quantum information of polymer chain was easily obtained when the special structure of repeat unit was built, and then the results of vapor-liquid equilibria of polymer solutions can be predicted without experimental data. The comparison between the calculations and experiments proves that this method is fairly reasonable.Ionic liquids as functional solvents have become popular research interest in green chemistry and their thermodynamics properties are key information. Three models were proposed to predict properties of ionic liquids based on COSMO-SAC (2007) denoted as COSMO-SAC (molecule), COSMO-SAC (ions) and COSMO-SAC (CA) in this thesis, respectively, which were extended to the prediction of vapor-liquid equilibria, liquid-liquid equilibria and infinite dilution activity coefficients of ionic liquids. These models were established according on the probable states of ionic liquids in solution, such as ionic liquids treated as whole molecules in COSMO-SAC (molecule), as free ions in COSMO-SAC (ions) or as the pairs of ions in COSMO-SAC (CA). Two global parameters were optimized in this thesis. Some real cases were calculated to check these models, and then the results of COSMO-SAC(CA) are better than COSMO-SAC(ions), but the worst results were obtained from COSMO-SAC (molecule). The conclusion is that the macroscopic nature of ionic liquids could not be described by the state of whole molecules, and then the scientific methods were supported for predicting the phase behavior of ionic liquids without experimental data.Glycerol, as a byproduct of biodiesel production, needs further investigation in different fields. In this thesis, the adsorption and diffusion of glycerol, methanol, and their mixtures in IRMOF-1 were investigated by molecular simulations. When the methanol molecules were added into the material, the adsorption capacity of glycerol is improved below the saturated adsorption of glycerol, and the adsorption of glycerol increases with the increasing numbers of methanol. The relationship between the diffusivities of glycerol and temperatures is accurately fitted by using Arrhenius equation at infinite dilution situation, and the activation energy and prefactor of glycerol in IRMOF-1 were obtained. There are different influences of methanol on glycerol diffusion at different temperatures. The high concentration of methanol increases the molecular diffusivities of glycerol and methanol at 300 K. However, at same situation the molecular diffusion of glycerol and methanol decreased at 600 K. As a result, the capacity of adsorption and diffusion of glycerol in MOF materials can be controlled by adding methanol molecules.Due to the toxicity and persistent organic pollution, PCBs would destroy the environment when it is long standing. Their physical chemistry properties are key information for an environmental scientist to make the plan of environment governance. In this thesis, the solvation free energies and partition coefficients of 36 PCBs compounds in water/1-octanol system were calculated by molecular dynamic simulation. The free energy can be accurately calculated by trapezoidal integration method and fitting equation integration method. The comparison between two methods showed that the fitting equation integration method can lead to more accurate results for the reason that it is continuous integration method even if the computational process is of complexity. The obtained partition coefficients are higher than experimental data when the atomic charges of hydrogen and chlorine atoms of PCBs were described through the atomic charges of chlorobenzene. Therefore, the charges of OPLS force fields did not reflect the real states of PCBs in water/1-octanol system. Meanwhile, the accurate values of partition coefficients were obtained by means of reasonable optimization of atomic charges, which of hydrogen and chlorine atoms are 0.16 and -0.27, respectively. From our researches the new charges can reflect the real states of PCBs in water/1-octanol system, and then there is another choice to estimate their physicochemical properties for environment governance.