Determination Of Phase Coexistence Properties Of Binary System: Nitrogen-Water And Oxygen-Water By The Gibbs Ensemble Monte Carlo Simulation

Monte Carlo simulation technique is a modern method in chemicalthermodynamics. Recently, with the increase of the cost of experiments, more andmore researchers focus their interests on the technology of computer simulation. Onthe brief review of the origin, principle and development of Monte Carlo techniques,we discussed the advantages and disadvantages, scopes of application of different MCmethods for determination of phase equilibrium and the involved ensemble. Gibbsensemble Monte Carlo method based on simultaneous calculations in two regionsrepresenting equilibrium phases is now commonly used for obtaining phaseequilibrium of fluids because of its simplicity and speed. The vapor-liquid equilibriumof Lennard-Jones model fluid, real gas represented by simple LJ model such asoxygen and nitrogen and water were investigated by NVT-GEMC; while coexistenceproperties of highly non-ideal hydrogen bonding mixtures: nitrogen-water andoxygen-water were calculated by NPT-GEMC. The main contents of this dissertationare as follow:Vapor-liquid phase equilibrium of the Lennard-Jones model fluid was simulatedby NVT-GEMC. Meantime, we discussed the effect of the initial conditions on thecoexistence property. The results showed that the coexistence property itself was notinfluenced by these initial conditions. However, in view of the computational time,less number of molecules but should be enough to represent each phase were muchbetter.The method was also applied to the calculation of the coexistence envelope fornon-polar nitrogen and oxygen from the vicinity of the triple point to close to thecritical point. Good overall agreement with experimental data and previouslyavailable literature results was obtained.From the research for MSPC/E water, the deviation between simulated resultsand experimental data increased obviously when temperature was higher than 550K.NPT-GEMC simulations were used to calculate gas-liquid equilibrium of highlynon-ideal hydrogen bonding mixtures: nitrogen-water and oxygen-water.Nitrogen-water simulations were performed from 323K to 503K at a fixed pressure;oxygen-water simulations were performed from 105bar to 173bar at a fixedtemperature. The effective intermolecular potential models that describe accurately iABSTRACTthe pure component (for water: MSPC/E; for nitrogen and oxygen; LJ) phaseequilibrium were applied. The interactions between gas and water were estimatedwith the standard Lorentz-Berthelot combining rules without any adjustable binaryparameter. Simulated results were compared to experimental data. Predictedproperties in gas phase of nitrogen-water agreed well with experimental data.Simulated liquid composition of coexisting phases showed the same trend as theexperimental data. For water content in gas phase for oxygen-water, the simulatedresults were larger than the calculated value from a semi-empirical method because thesimulation was done at 560.93K which was in the vicinity of MSPC/E water critical point602K. It showed that only the vapor-liquid equilibrium of pure components at the sametemperature and pressure was predicted accurately, good results could be got in the simulationfor mixture. Meanwhile, from the radial distribution functions of mixtures, the effect oftemperature on the structure of liquids was obvious while the effect of pressure couldbe negligible in the investigated range of state.GEMC method was a good tool to predict the phase behaviour of fluid and their mixturesnot only in quality but also in quantity.