Ion Association in Hydrothermal Sodium Sulfate Solutions Studied by Modulated FT-IR-Raman Spectroscopy and Molecular Dynamics

Saline aqueous solutions at elevated pressures and temperatures play an important role in processes such as supercritical water oxidation (SCWO) and supercritical water gasification (SCWG), as well as in natural geochemical processes in Earth and planetary interiors. Some solutions exhibit a negativ...

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Bibliographic Details
Published in:The journal of physical chemistry. B 2015-07, Vol.119 (30), p.9847-9857
Main Authors: Reimer, Joachim, Steele-MacInnis, Matthew, Wambach, Jörg M, Vogel, Frédéric
Format: Article
Language:English
Subjects:
Clusters
Gasification
Infrared spectroscopy
Molecular Conformation
Molecular dynamics
Molecular Dynamics Simulation
Phase boundaries
Precipitation
Saturation
Sodium Chloride - chemistry
Sodium sulfates
Solutions
Spectroscopy, Fourier Transform Infrared
Spectrum Analysis, Raman
Sulfates
Sulfates - chemistry
Temperature
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Summary:Saline aqueous solutions at elevated pressures and temperatures play an important role in processes such as supercritical water oxidation (SCWO) and supercritical water gasification (SCWG), as well as in natural geochemical processes in Earth and planetary interiors. Some solutions exhibit a negative temperature coefficient of solubility at high temperatures, thereby leading to salt precipitation with increasing temperature. Using modulated FT-IR Raman spectroscopy and classical molecular dynamics simulations (MD), we studied the solute speciation in solutions of 10 wt % Na2SO4, at conditions close to the saturation limit. Our experiments reveal that ion pairing and cluster formation are favored as solid saturation is approached, and ionic clusters form prior to the precipitation of solid sulfate. The proportion of such clusters increases as the phase boundary is approached either by decreasing pressure or by increasing temperature in the vicinity of the three-phase (vapor–liquid–solid) curve.
ISSN:1520-6106
1520-5207
DOI:10.1021/acs.jpcb.5b03192