Diffusion of Water in Liquid and Supercritical Carbon Dioxide:  An NMR Study

Abstract

Tracer diffusion coefficients have been measured for water in liquid and supercritical carbon dioxide (CO 2 ) from 10 to 35 °C in the pressure range from 130 to 300 bar. The measurements were performed by means of pulsed field gradient NMR (PFG-NMR) methods incorporating compensation for electrical eddy currents and mass convection. In the NMR active volume, the sample was contained in a 1.4 mm i.d. PEEK tube with provisions for recirculation and external sample loading. The diffusion coefficients are consistent with the Stokes-Einstein equation with "slip" boundary conditions and a hydrodynamic radius of 1.7 Å for water in the high temperature and low density region. In the low temperature and high density region, the diffusion coefficients indicate either a trend toward "stick" boundary conditions or the dynamic clustering of water molecules.

Atomistic molecular dynamics simulations of H2O diffusivity in liquid and supercritical CO2

“…In particular, such data were reported by Xu et al [17] at three different temperatures (i.e., 283, 298, and 308 K) and pressures in the range 130-300 bar, and Espinoza and Santamarina [18] [27] re-optimised the cross interaction parameters between CO 2 and H 2 O molecules using fixed-point-charges force-fields, based on the LennardJones and the Exponential-6 (Exp-6) functional forms, in order to improve the description of the mutual solubilities of the mixture. Specifically, the SPC/E-TraPPE (TraPPE, transferable potentials for phase equilibria) [28,29] combination was studied for the Lennard-Jones case, while for the Exp-6 case the H 2 O and CO 2 models proposed by Errington and Panagiotopoulos [30] and Potoff et al [31] were used, respectively.…”

“…In the Supplemental Information section, we provide MD simulation results for the self-diffusion coefficients of CO 2 over a broad range of conditions, including temperatures and pressures not measured experimentally. In Figure 3, the MD simulation results are presented and compared to experimental data by Xu et al [17] All force-field combinations follow the trend of the experimental data and show a decrease in diffusivity with the increase of pressure, but with variable accuracy. Specifically, at 283.15 K (Figure 3 top), the Exp-6 models and the TIP4P/2005-TraPPE combination follow the experiments very accurately.…”

Soret Effect Study on High-Pressure CO2-Water Solutions Using UV-Raman Spectroscopy and a Concentric-Tube Optical Cell

“…In particular, even though variations in composition (CO 2 in H 2 O) were measured between the two temperatures across the cell, the magnitude of the variations was very small. Soret coefficients calculated from this data were on the order of 10 -3 , several orders of magnitude less than expected from published values of the ordinary and thermal diffusion coefficients of the components (Xu 2003;Amirkhanov 1987;Swinney 1968). …”

“…The primary objective of the Fundamental Studies Task of Zero Emissions Research and Technology (ZERT) was to use laser Raman spectroscopy to study the Soret effect in CO 2 -water mixtures across a temperature gradient near the critical point of CO 2 . The proposed approach is based on other optical studies of the phenomenon (Xu 2003;Duhr 2006;Ning 2006;Koniger 2010 ) and the recognition that Raman spectroscopy is very sensitive to both H 2 O and CO 2 under both subcritical and supercritical conditions (Cabaco 2007(Cabaco , 2010a(Cabaco , 2010b. Two specific goals of the Task were (1) to determine whether the technique can be used to substantiate thermal diffusion in CO 2 -water mixtures and, if so, (2) to quantify the Soret effect as a function of conditions.…”

Brucite [Mg(OH2)] carbonation in wet supercritical CO2: An in situ high pressure X-ray diffraction study

“…This scCO 2 bubble is expected to remain intact for hundreds or thousands of years depending on reservoir rock chemistry, with only a small amount being dissolved into formation waters each year. Under moderate temperatures (35-122°C) and pressures (63-1620 bar), diffusion of H 2 O into scCO 2 occurs on the order of 10 À4 cm 2 s À1 (Xu et al, 2003;Danten et al, 2005). Hence, depending on plume thickness and ground water movement, a post-injected scCO 2 bubble would become water-saturated relatively quickly.…”