Equilíbrio de fases experimental de hidratos de dióxido de carbono e metano na presença de isopropanol e cloreto de sódio

Abstract

Under certain thermodynamic conditions, water molecules can combine with low molecular weight molecules to form crystalline structures known as hydrates. Blocking pipes due to the formation of hydrates is a major concern in ensuring flow, which can cause damage and prevent normal operation in the oil and gas industries. Thermodynamic inhibitors (such as MEG, NaCl and isopropanol) act by altering water activity, modifying the phase balance in order to achieve a safe operating condition. In oil exploration and production, isopropanol is a by-product often used during stimulation and to improve workover operating conditions. In the open literature isopropanol is said to be a thermodynamic inhibitor for some hydrated systems, however some reports point it as a hydrate promoter when it is on systems where a help gas such as methane or propane exist. The water from production lines is naturally inhibited by the presence of salts, such as NaCl. The accuracy of prediction software products and models (such as MultiflashTM, PVTSimTM and CSMGemTM) rely on experimental data for parameter optimization. In the present work, new experimental data for the equilibrium phase of inhibited carbon dioxide and methane hydrates were obtained for pressures between 20 and 260 bar, under concentrations ranging from 1 to 25%, in mass, of isopropanol and concentrations of 5 and 10%, in mass, of NaCl, in a high-pressure cell, using the isochoric method of experimental characterization. Systems with pure water and aqueous isopropanol and NaCl solutions also were evaluated experimentally. A thermodynamic model, previously developed, was applied and validated with the hydrate equilibrium conditions. This model uses the Cubic Plus Assosiation (CPA) equation of state for the fluid phases and a statistical approach, based on the van der WaalsPlatteeuw Theory, for the hydrated phase. The experimental data were obtained to optimize parameters of binary interactions, as well as kihara parameters, given the scarcity of data in the literature. Isopropanol was characterized as an inhibitor of CO2 hydrates and a promoter of CH4 hydrates, collaborating in the structural transition from the sI type to the sII type.