Kyoo Y. Song

Water Content of CO2 in Equilibrium With Liquid Water and/or Hydrates

Experimentally measured water content in CO/sub 2/-rich fluid in the gaseous or liquid state in equilibrium with liquid water or hydrate is presented for pressures ranging from 100 to 2,000 psia (0.69 to 13.79 MPa) and temperatures from -19 to 77/sup 0/F (-28.33 to 25.0/sup 0/C). The water content of the CO/sub 2/-rich phase along the three-phase equilibria, i.e., liquid water/liquid CO/sub 2//gas to the three-phase critical endpoint, is also reported. The experimental results from this study on the water content in the CO/sub 2/-rich phases have been combined with earlier research results of the CO/sub 2//water binary system in the hydrate-free region from 77 to 200/sup 0/F (25.0 to 93.33/sup 0/C) and pressures to 3,000 psia (20.69 MPa) to produce a comprehensive plot. The high degree of complexity in the phase behavior of a CO/sub 2//water binary system, which exhibits several pairs of equilibrium phases for the conditions, is shown. To make the data more intelligible than they are in their raw form, the data are presented in terms of the pressure enhancement of the water content along isotherms. Finally, the activity coefficients of water in the CO/sub 2/-rich phases are summarized.

Solubility measurements of methane and ethane in water at and near hydrate conditions

The isobaric solubility of pure methane and ethane gases in liquid water was measured under different conditions, including hydrate formation points, using a ramping method in which measurements are made through the entire and continuous hydrate formation/decomposition cycle. The work was conducted for methane at 3.45 MPa (500 psia) and temperatures ranging from 17.0 to 0.0°C (290.2 to 273.2 K), and for ethane at 0.66 MPa (95 psia) and a temperature range of 17.0 to 0.0°C (290.2 to 273.2 K). The isobaric solubilities obtained show a significant divergence from (normal) Henrys law solubility as the temperature is lowered. The increase in the solubility is presumably the result of the onset of a sorption process that traps the gas molecules in the water structure. Several sub-processes were observed as the hydrate formation was taking place: (1) the dissolution of the gas in the liquid water, or interstitial solubility, (2) the onset of the sorption sub-process and build-up of the hydrate precursors, (3) the catastrophic formation and the existence of the solid phase with its slushy characteristics, and (4) the solidification of the hydrates, therefore causing the total plugging of the experimental cell.

Final hydrate stability conditions of a methane and propane mixture in the presence of pure water and aqueous solutions of methanol and ethylene glycol

Abstract Final hydrate stability conditions have been measured for an 88-13 mol.% methane, balance propane mixture. The aqueous phase ranged for pure water, used as the reference solution, to 1.5, 8.82, 16.20 and 22.47 mol.% ethylene glycol (corresponding to 5.00, 25.00, 40.00 and 50.00 wt.% ethylene glycol respectively) and 4.06, 9.02, and 23.22 mol.% methanol (corresponding to 7.00, 15.00, and 35.00 wt.% methanol respectively). The gas-aqueous glycol studies were conducted from 0.69 MPa (100 psia) to 17.24 MPa (2500 psia) and the aqueous methanol-gas studies ranged from 0.83 MPa (120 psia) to 17.93 MPa (2600 psia). Both solutions exhibited minima in the hydrate depression curves at high inhibitor concentrations, but not at low inhibitor concentrations. The latter behavior at low inhibitor concentrations differs both qualitatively and quantitatively from the figures of Makogon and coworkers. Since the empirical Hammerschmidt equation for the prediction of hydrate inhibition shows no pressure dependence, it was found to be inapplicable at high inhibitor concentration and high pressures. The serious discrepancies point to the need for the development of an activity-coefficient model for the prediction of hydrate inhibition. Hydrate stability conditions of a similar mixture which have been reported by Deaton and Frost show serious discrepancies at low pressure, but agree well at moderate and higher pressures.

The water content of ethane, propane and their mixtures in equilibrium with liquid water or hydrates

Abstract Song, K.Y. and Kobayashi, R., 1994. The water content of ethane, propane and their mixtures in equilibrium with liquid water or hydrates. Fluid Phase Equilibria, 95: 281-298. Experimental results for the water content are reported for the ethane-rich phase in the liquid and gaseous states in equilibrium with hydrates for pressures of 360 psia (2.483 MPa) and 500 psia (3.448 MPa), and at temperatures from −27.5°F (−33.1°C) to 50.9°F (10.5°C), as well as in the three-phase coexistence non-hydrate conditions at pressures ranging from 500 psia (3.448 MPa) to 700 psia (4.828 MPa) and temperature from 60°F (15.6°C) to 89°F (31.7°C), respectively. Also included are the water content measurements of the propane-rich phase in equilibrium with hydrates covering temperatures from −35.5°F (−37.5°C) to 37.4°F (3.0°C) at a constant pressure of 159 psia (1.097 MPa). Above the hydrate region the experimental conditions range from 48°F (8.9°C) to 80°F (26.7°C) and pressures of 90 psia (0.621 MPa) to 130 psia (0.897 MPa). Isobaric water content data at 600 psia (4.138 MPa) for the liquid hydrocarbon-rich phase are reported for four ethane-propane mixtures containing 30.5, 50.0, 75.0 and 89.5 mol% ethane with the remainder propane, in equilibrium with liquid water or hydrate at temperatures ranging from −0.4°F (−18°C) to 77°F (25°C). The water content data for two binary systems, ethane-water and propane-water, and four ternary systems, ethane-propane-water mixtures, have been used to estimate the equilibrium conditions for three-phase coexistence: (liquid water-liquid hydrocarbon-hydrate I or II, liquid hydrocarbon-hydrate I-hydrate II), and for a quadruple point (liquid water-liquid hydrocarbon-hydrate I-hydrate II). Equilibrium constants for water in the hydrocarbon-rich phases, i.e. the ratio of mole fraction of water in the gaseous hydrocarbon-rich phase to that of water in the liquid hydrocarbon-rich phase, are graphically presented along the three-phase coexistence locus, and along the non-hydrate conditions for the ethane-water and the propane-water systems.

Solubility Measurements for CO2 and Methane Mixture in Water and Aqueous Electrolyte Solutions near Hydrate Conditions

The gas solubility of the CH 4 + CO 2 mixture in pure water, and electrolyte solutions containing NaCl and Na 2 SO 4 was measured in the temperature range of 280–292 K. Within the experimental accuracy, the experimentally measured gas solubility obeys the Henry’s law in the form of the Krichevsky-Kasarnovsky equation near (but above) hydrate formation temperature. The ternary solubility data can be predicted by the binary ones. It was found that the CO 2 solubility in the aqueous phase decreases in the presence of the electrolytes. Very accurate methane solubility data in the ternary system are required to identify the effects of electrolytes on solubility and selectivity.