(398k) Experimental Determination and Modeling of Hydrate Phase Equilibrium for Systems Containing Hexane, Decane, Tetradecane and Hexadecane in the Presence of Tbab or Ethanol

Gas hydrates are crystalline water molecules that surround a specific gas under certain pressure and temperature conditions. In the last decade, this innovative technique has gained significant importance, and its applications have been increasing including gas storage (CO₂, CO), cryogenic processes, seawater desalination, separation of water from contaminated effluents, and others. Regarding this last application, particularly water contaminated with liquid hydrocarbons, and with the aim of proposing and/or developing new processes, phase equilibrium data on gas hydrates containing liquid alkanes are necessary. For this reason, this work aims to develop a thermodynamic model capable of representing gas hydrate dissociation points in mixtures containing linear alkanes and/or thermodynamic promoters and inhibitors, based on experimental data and other models already published in international literature. For this reason, this work reports hydrate phase equilibrium data for CO₂ + H₂O + C₆H₁₄ + C₁₀H₂₂ + C₁₄H₃₀ + TBAB (w_i=0.1, 0.2 and 0.3) and CO₂ + H₂O + C₁₆H₃₄ + ethanol (w_i= 0.05, 0.1 and 0.15) systems. The reported data were determined by isochoric pressure-search technique using a high-pressure equilibrium blind cell.

Prior to measurements, pressure and temperature indicators were calibrated using primary and secondary standards, respectively. The method used was validated by experimentally determining the phase equilibrium of hydrates from known systems and comparing it with data published in international literature. For all measurements reported in this work, the experimental uncertainty was estimated to be 0.012 MPa and 0.15 K for pressure and temperature, respectively.

However, the measurements performed are finite and specific, which limits the amount of data available in international literature for application purposes. Therefore, in this work, a thermodynamic model was formulated based on the original Chen-Guo model (1998) and implementing a modification to the Helmholtz molar free energy term using a polynomial equation based on the temperature and/or solubility of the compounds involved.

At the end of this work, new experimental data and a thermodynamic model capable of representing the hydrate phase equilibria were obtained.