(389a) Modeling Diffusion Coefficients of Carbon Dioxide in Water for Carbon Sequestration

Abstract

The
increase in atmospheric concentrations of carbon dioxide (CO₂) is
believed to be a key player in global warming, necessitating identification of
viable technological options for its capture and storage. Perhaps, the most
promising of these options is injection into saline aquifers whose merits
include large sink capacities, and enhanced storage integrity upon CO₂
dissolution. This growing interest in CO₂ injection calls for a
better understanding of CO₂ diffusion ? quantified by infinite dilution
(denoted as D^∞)
and Fickian (denoted as D) diffusion coefficients ? into water and brine.
However, there is neither sufficient experimental data for D^∞andD, nor unified models for accurate predictions. We propose a new
model for calculating D^∞for
CO₂-water mixtures. The model takes into account the temperature
dependence of the dipole moment of water and the polarizability of CO₂,and fits experimental CO₂-water data at low and high
pressures with an accuracy of 4.9%. Remarkably, the proposed model also
accurately predicts D^∞for
binary mixtures of methane (CH₄) and hydrogen sulfide (H₂S)
in water where solute polarizability is comparable in magnitude to that of CO₂.
Both CH₄ and H₂S are often present as impurities in CO₂-injection
streams. Moreover, we present ? to the best of our knowledge ? the first
predictions of composition-based D for CO₂-water over the
temperature range 298.15-413.15 K, and pressures up to 50 MPa.