Equilíbrio de fases e comportamento volumétrico de sistemas aquosos contendo CO2, monoetileno glicol e NaCl nas condições de explotação de gás natural

Abstract

Gas explotation in deep water in Brazil brings challenges due to high pressures, low temperatures, high content of CO2 and NaCl carried to the production fluids. The regeneration process of ethylene glycol (MEG) at low pressures, used as a hydrate inhibitor, also presents a field of study regarding the solubility and precipitation of NaCl salt. In this context, this work included the assembly of an experimental apparatus for the evaluation of volumetric behavior and phase equilibrium in mixtures, under conditions of temperature and pressure, close to those of gas exploration in deep waters, evaluating parameters such as density and solubility, at pressures from 4,0 to 31.0 MPa and temperatures of 293.15 and 323.15 K. The experimental apparatus was assembled through the interconnections between an Anton Paar 4200M densimeter, a syringe pump and thermostatic baths with two types of pressure vessels: the Parr reactor 4561 and a variable volume equilibrium cell. The density points obtained with the experimental apparatus were validated with data and models from the literature. For this purpose, simple systems such as the pure CO2 and water were used (mean deviations of 0.11%, ±0.00095 g/cm³, for CO2 and 0.15%, ±0.00015 g/cm³, for water when compared to specific equations for these components), and the CO2 + water (mean deviations below 0.07%, ±0.0007 g/cm³, when compared with models obtained from literature data). The calibration of the densimeter was carried out with tetrachloromethane and ethanol, to allow using at temperatures between 293.15 and 329.85 K, and pressures between 1.0 and 31.0 MPa, resulting in an uncertainty of 0.09% (±0.0014 g/cm³). In addition to the experimental data obtained from the previously mentioned pure components and the CO2 + water binary system, data were also obtained for the water + NaCl binary system, for the CO2 + water + NaCl ternary system (1 molal and 4 molal saline solutions) and the CO2 + water + MEG (30%, 50% and 80% m/m MEG aqueous solutions concentrations). The software Specs v5.63 and a code made in MATLAB were used to verify which equation of state (Soave-Redlich-Kwong or PengRobinson cubic equations, or Cubic Plus Association equation) was more adequate to predict the aqueous phase density of the binary and ternary systems in the absence of electrolytes under experimental conditions; it being concluded that the use of Cubic Plus Association equation (CPA) resulted in more coherent values for the density of the aqueous phase. In addition to the measured experimental densities, the CO2 solubilities in the aqueous phase of the systems were also obtained by modeling with the CPA equation, resulting in values close to those in the literature. In the case of systems containing electrolytes, literature data were primarily used for comparison with the experimental data of this work.