Hydrate dissociation conditions for gas mixtures containing carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons using SAFT (original) (raw)
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EPJ Web of Conferences, 2012
are non-stoichiometric crystallized solutions of gas molecules in the metastable water lattice. Two or more components are associated without ordinary chemical union but through complete enclosure of gas molecules in a framework of water molecules linked together by hydrogen bonds. The clathrates are important in the following applications: the pipeline blockage in natural gas industry, potential energy source in the form of natural hydrates present in ocean bottom, and the CO 2 separation and storage. In this study, we have modified an analytical solid-liquid-vapor equation of state (EoS) [A. Yokozeki, Fluid Phase Equil. 222-223 (2004)] to improve its ability for modeling the phase equilibria of clathrates. The EoS can predict the formation conditions for CO 2 -and CH 4 -hydrates. It will be used as an initial estimate for a more complicated hydrate model based on the fundamental EoSs for fluid phases. Republic
The Journal of Chemical Thermodynamics, 2018
Statistical Thermodynamics was used to derive an expression for hydrate enthalpy of dissociation. From this expression, a parameter regression methodology was proposed in which calorimetric experiments were included along with cage occupancies, guest mole fraction and equilibrium condition experiments. Since not all the experiments depend on the whole set of hydrate parameters, we developed a stepwise methodology that reduces hydrate estimation problem to three simple sub problems, being two of them analytically solvable. The solution of the stepwise methodology is then the initial guess of the hydrate global parameter estimation that can be solved using a deterministic algorithm. From the parameter estimation, we observed that the hard-core sphere parameter of the Kihara potential was not statistically significant in the case studied here. It was rejected with a significance degree of 5%, which lead to the use of the Lennard-Jones potential. After estimating hydrate parameters for carbon dioxide and methane sI hydrates, we could relate hydrate enthalpy of dissociation to equilibrium conditions for this binary mixture. We found that the empirical law that states that enthalpy of dissociation of mixed hydrates increases with the increase of occupancy of the largest guest in the large cavity was verified only when the waterpoor fluid phase is a vapor. This means that fluid phases also have an important role in hydrate enthalpy of dissociation. Highlights 1-Expression for hydrate enthalpy of dissociation from Statistical Thermodynamics. 2-Parameter estimation using calorimetric experimental data for hydrate formation. 3-A new stepwise and non-exhaustive parameter estimation methodology. 4-Enthalpy of dissociation and its relations to hydrate properties.
International journal of molecular sciences, 2016
Monte Carlo and molecular dynamics simulations were done with three recent water models TIP4P/2005 (Transferable Intermolecular Potential with 4 Points/2005), TIP4P/Ice (Transferable Intermolecular Potential with 4 Points/ Ice) and TIP4Q (Transferable Intermolecular Potential with 4 charges) combined with two models for methane: an all-atom one OPLS-AA (Optimal Parametrization for the Liquid State) and a united-atom one (UA); a correction for the C-O interaction was applied to the latter and used in a third set of simulations. The models were validated by comparison to experimental values of the free energy of hydration at 280, 300, 330 and 370 K, all under a pressure of 1 bar, and to the experimental radial distribution functions at 277, 283 and 291 K, under a pressure of 145 bar. Regardless of the combination rules used for σC,O, good agreement was found, except when the correction to the UA model was applied. Thus, further simulations of the sI hydrate were performed with the uni...