Solubility isotope effects in aqueous solutions of methane

Abstract

The isotope effect on the Henry's law coefficients of methane in aqueous solution ͑H/D and 12 C/ 13 C substitution͒ are interpreted using the statistical mechanical theory of condensed phase isotope effects. The missing spectroscopic data needed for the implementation of the theory were obtained either experimentally ͑infrared measurements͒, by computer simulation ͑molecular dynamics technique͒, or estimated using the Wilson's GF matrix method. The order of magnitude and sign of both solute isotope effects can be predicted by the theory. Even a crude estimation based on data from previous vapor pressure isotope effect studies of pure methane at low temperature can explain the inverse effect found for the solubility of deuterated methane in water.

Automated, in situ measurements of dissolved CO2, CH4, and δ13C values using cavity enhanced laser absorption spectrometry: Comparing response times of air‐water equilibrators

“…For each equilibrator, the 12 C and 13 C time constants were practically identical, except for < 1 s difference between 12 CO 2 and 13 CO 2 (discussed below). This finding is expected due to the very small difference in solubility between 12 CO 2 and 13 CO 2 (∼0.1%, Vogel et al ) and between 12 CH 4 and 13 CH 4 (∼0.05%, Bacsik et al ), as well as the negligible kinetic fractionation factors which under experimental diffusive conditions is between ∼0.9‰ and 1.3‰ for CO 2 (Inoue and Sugimura ; Wanninkhof ) and ∼0.8‰ for CH 4 (Knox et al ). The kinetic fractionation is likely to be much less in the equilibrators tested due to the higher turbulence within the equilibrators compared with the diffusive experiments used to determine kinetic fractionation associated with gas exchange.…”

“…). The same was not observed for CH 4 isotopologues, likely due to the smaller differences in solubility between 12 CH 4 and 13 CH 4 (∼0.05%,) than 12 CO 2 and 13 CO 2 (∼0.1%) (Vogel et al ; Bacsik et al ). Figure illustrates this kinetic fractionation when looking at the response in δ 13 C‐CO 2 values during initial low‐high and high‐low switch.…”

Isotope fractionation of methane during natural gas flow with coupled diffusion and adsorption/desorption

“…(15) describes the carbon isotope fractionation of methane between gas phase and adsorbate phase at various temperature points. In a similar way, the fractionation due to methane dissolution in water is obtained calculated from experiments (Bacsik et al, 2002). The relations at 0-200°C are shown in Fig.…”

“…Isotope fractionation factor of methane ( 12 CH 4 and 13 CH 4 ) between condensed phase and gas phase. Experimental data of fractionation between dissolved gas and free gas is from Bacsik et al (2002).…”

D/H fractionation in the H2–H2O system at supercritical water conditions: Compositional and hydrogen bonding effects

“…Indeed, previous studies report isotope effects induced by differences in the solubility of H-D isotopologues of H 2 (and CH 4 ) in aqueous solutions associated with differences in zero-point energies between the H-D species. (Muccitelli and Wen, 1978;Calado et al, 1989;Gomes and Grolier, 2001;Bacsik et al, 2002;Jancso, 2002). These changes in zero-point energies are introduced because of hindrance of the translational/rotational vibrations with species being dissolved in the solvent's cages.…”