8 research outputs found
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Volumetric Properties and Phase Relations of Binary H{sub 2}O-CO{sub 2}-CH{sub 4}-N{sub 2} Mixtures at 300 C and Pressures to 1000 Bars
The volumetric properties and phase relations of binary mixtures of H{sub 2}0, CO{sub 2}, CH{sub 4} and N{sub 2} were determined experimentally at 3OO C, 74.4--999.3 bars, using a custom-built vibrating-tube densimeter. Densities of all single-phase fluids increase steadily with increasing pressure. At a given pressure, CO{sub 2}-rich H{sub 2}O-CO{sub 2} mixtures show a pronounced nonlinear decrease in density with increasing mole fraction CO, in marked contrast to the densities of N{sub 2}-rich H{sub 2}O-N{sub 2} mixtures which are nearly independent of composition. At pressure up to 500 bars, non-aqueous mixtures have much smaller excess molar volumes than gas-rich aqueous mixtures. H{sub 2}O-rich mixtures at pressures ca.86 bars, and CO{sub 2}-poor non-aqueous mixtures at 99.4 bars, exhibit negative excess molar volumes. Excess molar volumes for aqueous mixtures peak at 86 bars, then decrease monotonically with increasing pressure above 86 bars. The H{sub 2}O-CO{sub 2} liquid-vapor field widens continuously from 86 to ca.400 bars, then narrows with increasing pressure, closing at ca.565 bars, in sharp contrast to the H{sub 2}O-N{sub 2} liquid-vapor field, which widens continuously with increasing pressure to at least 1000 bars
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Excess Free Energies and Activity-Composition Relations for H{sub 2}O-CO{sub 2} Fluids at 400{degree}C and 1-4000 Bars
Experimentally determined excess molar volumes (V{sup ex}) for H{sub 2}O--CO{sub 2} fluids at 400{degree}C and 100-4000 bars have been used to calculate excess free energies (G{sup ex}) and activity-composition (a-X) relations for these mixtures. Excess free energies are continuously positive and asymmetric toward H{sub 2}O at all pressures up to 4000 bars, rising to peak values of approximately 1300, 1800, 2000 and 2100 J/mol at 500, 1000, 2000 and 4000 bars, respectively. Calculated activities for H{sub 2}O and CO{sub 2} vary correspondingly, increasing: substantially from 0 to 1000 bars, moderately from 1000 to 2000 bars, and slightly from 2000 to 4000 bars. In addition, because G{sup ex} is asymmetric toward H{sub 2}O at 400{degree}C and pressures up to at least 4000 bars, a-X relations for H{sub 2}O are distinctly different from a-X relations for CO{sub 2}. These results imply that H{sub 2}O--CO{sub 2} fluids are strongly nonideal at 400{degree}C and all pressures above approx. 300 bars, despite the fact that peak values for V{sup ex} decrease from approx. 50 cm{sup 3}/mol at 300 bars to approx. 1 cm{sup 3}/mol at 2000 bars, and remain small to pressures as high as 5000 bars. Excess free energies and a-X relations for H{sub 2}O--CO{sub 2} fluids at 400{degree}C and pressures up to 4000 bars calculated from semi-empirical equations of state generally suggest significantly smaller positive deviations from ideality
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Overview of fundamental geochemistry basic research at the Oak Ridge National Laboratory
Researchers in ORNL`s Geochemistry and High Temperature Aqueous Chemistry groups are conducting detailed experimental studies of physicochemical properties of the granite-melt-brine system; sorption of water on rocks from steam-dominated reservoirs; partitioning of salts and acid volatiles between brines and steam; effects of salinity on H and O isotope partitioning between brines, minerals, and steam; and aqueous geochemistry of Al. These studies contribute in many ways to cost reductions and improved efficiency in the discovery, characterization, and production of energy from geothermal resources
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Volumetric properties of CO{sub 2}-CH{sub 4}-N{sub 2} fluids at 200{degree}C and 1000 bars: A comparison of equations of state and experimental data. Chapter 4
Predictions of molar volume, excess molar volume, and isochoric P-T trajectories from 13 published equations of state are compared with one another and with preliminary volumetric data for CO{sub 2}-CH{sub 4}-N{sub 2} fluids at 200{degrees}C and 1000 bars. The equations of state investigated represent a wide variety of empirical and semi-empirical approaches to the modeling of fluids. The experimental data indicate that excess volumes of CO{sub 2}-CH{sub 4}-N{sub 2} mixtures are small (<3% of the total volume of the mixture, except near the critical point of CO{sub 2}). The NIST software package DDMIX yields volumetric properties that are most consistent with our experimental results. Differences in the calculated volumetric properties of mixtures from the different equations of state are significant For example, estimates of the equilibrium trapping temperature of a fluid inclusion (2000 bars, 60% CO{sub 2}-20% CH{sub 4}20% N{sub 2}mixture, V=59.10 cm{sup 3}/mole) calculated from various equations of state range from 462-570{degrees}C. The major source of error in calculated volumetric properties of fluid mixtures is the inability of equations of state to accurately predict the volumetric properties of the pure components
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Experimental Determinations of the Activity-Composition Relations and Phase Equilibria of H{sub 2}O-CO{sub 2}-NaCl Fluids
An understanding of activity-composition (a/X) relations and phase equilibria for halite-bearing, mixed-species supercritical fluids is critically important in many geological and industrial applications. The authors have performed experiments on the a/X relations and phase equilibria of H{sub 2}O-CO{sub 2}-NaCl fluids at 5OO C, 500 bars, to obtain highly accurate and precise data for this ternary system. H{sub 2}O-CO{sub 2}-NaCl samples were reacted at a (H{sub 2}O) = 0.350, 0.425, 0.437, 0.448, 0.560, 0.606, 0.678, 0.798, and 0.841. Results indicate that fluids with these activities lie in the vapor-NaCl two-phase region, and that a fluid with the last value has a composition close to the three-phase (vapor + brine + halite) field. Data from these experiments and NaCl solubility runs also suggest that the vapor comer of the three-phase field lies near X(H{sub 2}O) = 0.760, X(NaCl) = 0.065, which is a significantly more water-rich composition than suggested by the model of [1]
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Fundamental chemistry and thermodynamics of hydrothermal oxidation processes. 1998 annual progress report
'The objective of this research program is to provide fundamental scientific information on the physical and chemical properties of solutes in aqueous solutions at high temperatures needed to assess and enhance the applicability of hydrothermal oxidation (HTO) to the remediation of DOE hazardous and mixed wastes. Potential limitations to the use of HTO technology include formation of deposits (scale) from precipitation of inorganic solutes in the waste, corrosion arising from formation of strong acids on oxidation of some organic compounds (e.g., chlorinated hydrocarbons), and unknown effects of fluid density and phase behavior at high temperatures. Focus areas for this project include measurements of the solubility and speciation of actinides and surrogates in model HTO process streams at high temperatures, and the experimental and theoretical development of equations of state for aqueous mixtures under HTO process conditions ranging above the critical temperature of water. A predictive level of understanding of the chemical and physical properties of HTO process streams is being developed through molecular-level simulations of aqueous solutions at high temperatures. Advances in fundamental understanding of phase behavior, density, and solute speciation at high temperatures and pressures contribute directly to the ultimate applicability of this process for the treatment of DOE hazardous and mixed wastes. Research in this project has been divided into individual tasks, with each contributing to a unified understanding of HTO processing problems related to the treatment of DOE wastes. This report summarizes progress attained after slightly less than two years of this three-year project.