چكيده به لاتين
The use of nanoparticles is a new method used to accelerate the process of hydrate formation and increase gas storage in hydrate crystals. Hydrate crystals are formed at high pressures and low temperatures. Lack of knowledge about the thermodynamic conditions of hydrate formation leads to a sharp increase in production costs. Therefore, it has been important for researchers to predict the conditions under which hydrates are formed in the presence of nanoparticles in recent years. Due to the strong hydrogen bonding between water molecules, the importance of using the proper equation of state in Van der Waals-Platteeaw computational method is more recognized. One approach to model these mixtures with associating components is to append a cubic EOS, with an additional term that accounts for the association. Lee and Firoozabadi's CPA which uses the Peng and Robinson(EOS) in the physical interaction contribution and uses thermodynamic perturbation theory with the new hypotheses in the association contribution, is the equation of state obtained in this work. Nanoparticles affect the thermodynamics of hydrate formation for various reasons, such as porous structure, the interaction between water molecules and nanoparticles, increasing system entropy and so on. Depending on the type of nanoparticle, these effects can improve the thermodynamic conditions of hydrate formation or make the conditions of hydrate formation more difficult. Water activity, Langmuir constant and the fugacity of gas components are the main factors in thermodynamic modeling of hydrate formation in the presence of nanoparticles. Applying changes and modifications to these factors in this dissertation is the basis of the three types of modeling provided for the two carbon-dioxide and methane gases in the presence of three types of nanoparticles. Knowing the amount of gas dissolving in nanofluid that affects water activity helps us in modeling. To model the dissolution of hydrate gases in nanofluid, the nanofluid is considered as a pseudo-pure solvent which its chemical properties are similar to water, however, its ability to enhance the absorption of CO2 is different from water, which leads to a different binary interaction coefficients for water-based nanofluid in CPA equation of state. The results show that the average absolut deviation of CO2 hydrate formation pressure predicted by models for ZnO nanofluid and graphite nanofluid are 1.15% and 2.02%, respectively. Also abtained 1.34% average absolut deviation for CH4 hydrate formation pressure in MWCT nanofluid. The experiments of CO2 solubility in graphite nanofluid, which was performed to thermodynamic model the formation of CO2 hydrate in the presence of graphite nanoparticles, shows a 6.5% increase in CO2 dissolution in the graphite nanofluid relative to pure water.
