The pH of CO<inf>2</inf>-saturated aqueous NaCl and NaHCO<inf>3</inf>solutions at temperatures between 308 K and 373 K at pressures up to 15 MPa
File(s)
Accepted version
Author(s)
Li, X
Peng, C
Crawshaw, JP
Maitland, GC
Trusler, JPM
Type
Journal Article
Abstract
The pH is a critical variable for carbon storage in saline aquifers because it affects the reaction rate and equilibrium state of the reservoir rocks, thus influencing the rates of mineral dissolution or precipitation and the integrity of caprocks. In this work, high-pressure pH and Ag/AgCl-reference electrodes were used to measure the pH of CO 2 -saturated aqueous solutions of NaCl and NaHCO 3 . The expanded uncertainty of the pH measurements is 0.20 at 95% probability. For CO 2 -saturated NaCl(aq), measurements were carried out at total pressures from (0.37 to 15.3) MPa and temperatures from (308 to 373) K with NaCl molalities of (1, 3 and 5) mol·kg −1 . For CO 2 -saturated NaHCO 3 (aq), the pH was measured at total pressures from (0.2 to 15.3) MPa and temperatures from (308 to 353) K with NaHCO 3 molalities of (0.01, 0.1 and 1) mol·kg −1 . The pH was found to decrease with increase in pressure and with decrease in temperature for both CO 2 -saturated NaCl and NaHCO 3 solutions. For CO 2 -saturated NaCl(aq), the pH was observed to decrease with increase of salt molality, while for CO 2 -saturated NaHCO 3 , the opposite behaviour was observed. The results have been compared with predictions obtained from the PHREEQC geochemical simulator (version 3.3.9) incorporating the Pitzer activity-coefficient model with parameters taken from the literature. For CO 2 -saturated NaCl(aq), agreement to within ±0.2 pH units was observed in most cases, although deviations of up to 0.3 were found at the highest molality. In the case of CO 2 -saturated NaHCO 3 (aq), the experimental data were found to deviate increasingly from the model with increasing salt molality and, at 1 mol·kg −1 , the model underestimated the pH by between 0.3 and 0.7 units.
Date Issued
2017-11-22
Date Acceptance
2017-11-14
Citation
Fluid Phase Equilibria, 2017, 458, pp.253-263
ISSN
0378-3812
Publisher
Elsevier
Start Page
253
End Page
263
Journal / Book Title
Fluid Phase Equilibria
Volume
458
Copyright Statement
© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0/
Sponsor
Qatar Shell Research and Technology Center QSTP LLC
Grant Number
490000724
Subjects
0203 Classical Physics
0904 Chemical Engineering
Chemical Engineering
Publication Status
Published