Ultraviolet (UV) Raman Spectroscopy Study of the Soret Effect in High-Pressure CO2–Water Solutions

Spatially resolved deep-ultraviolet (UV) Raman spectroscopy was applied to solutions of CO(2) and H(2)O or D(2)O subject to a temperature gradient in a thermally regulated high-pressure concentric-tube Raman cell in an attempt to measure a Soret effect in the vicinity of the critical point of CO(2). Although Raman spectra of solutions of CO(2) dissolved in D(2)O, at 10 MPa and temperatures near the critical point of CO(2), had adequate signal-to-noise and spatial resolution to observe a Soret effect with a Soret coefficient with magnitude |S(T)| > 0.03, no evidence for an effect of this size was obtained for applied temperature gradients up to 19 °C. In contrast, the concentration of CO(2) dissolved in H(2)O was shown to vary significantly across the temperature gradient when excess CO(2) was present, but the results could be explained simply by the variation in CO(2) solubility over the temperature range and not by kinetic factors. For mixtures of D(2)O dissolved in scCO(2) at 10 MPa and temperatures close to the critical point of CO(2), the Raman peaks for D(2)O were too weak to measure with confidence even at the limit of D(2)O solubility.