Effect of Salinity on CO₂ Thermodiffusion in Aqueous Mixtures by Molecular Dynamics Simulations

FM Coelho and LFM Franco and A Firoozabadi, ACS SUSTAINABLE CHEMISTRY & ENGINEERING, 11, 17086-17097 (2023).

DOI: 10.1021/acssuschemeng.3c05269

Some geothermal formations may contain a large concentration of CO2 and a very high vertical temperature gradient. It is likely that there may be significant variation in the CO2 concentration in these formations due to the Soret effect. In our work, we evaluate, for the first time, the CO2 thermodiffusion in brine mixtures via molecular dynamics simulations. In the past, cross-diffusion effects on thermodiffusion have been neglected in the evaluation of thermal diffusion in three or more species despite their significance. In this work, we present a methodology to compute the thermal diffusion factor in multicomponent mixtures by combining equilibrium and nonequilibrium molecular dynamics simulations. As in binary CO2-H2O, the CO2-brine Soret effect may have a pronounced dependency on temperature; by increasing temperature, CO2 migrates from thermophobic to thermophilic conditions. Water structure may have a dominant effect on CO2 thermal diffusion. The more organized the hydrogen bond network, the more thermophobic the CO2; an increase in temperature or salinity may make CO2 more thermophilic. Our results and formulations advance the knowledge of CO2 distribution in subsurface formations and set the stage for accurate modeling of formations aimed at carbon sequestration and heat extraction.

Return to Publications page