High pressure differential scanning calorimetry of the hydrothermal salt solutions K2SO4–Na2SO4–H2O and K2HPO4–H2O

Abstract

Aqueous salt solutions under hydrothermal conditions play an important role in geochemistry as well as in processes using hot compressed water as the process medium such as supercritical water oxidation (SCWO) and supercritical water gasification (SCWG). Isochoric high pressure differential scanning calorimetry (HP-DSC) was used as an accurate technique to investigate the phase behavior of such solutions under hydrothermal conditions. New data in the low concentration range (0.14-15.0 mass%) has been collected for the binary systems K 2 SO 4 -H 2 O, Na 2 SO 4 -H 2 O and K 2 HPO 4 -H 2 O. Furthermore we have discovered a liquid-liquid immiscibility in the ternary system K 2 SO 4 -Na 2 SO 4 -H 2 O, which has not been reported before.

Speciation and Structural Properties of Hydrothermal Solutions of Sodium and Potassium Sulfate Studied by Molecular Dynamics Simulations

“…The onset of salt precipitation occurs in the solution of Na 2 SO 4 at about 280 °C (Figure ), which is about 40 °C below the experimental value, as reported previously . The pure solution of K 2 SO 4 shows the onset of precipitation at around 360 °C (Figure ), which is close to the experimental value (355 °C) . The underestimated precipitation temperature for the solution of Na 2 SO 4 and the unexpectedly gradual decrease in solubility with temperature for solutions of K 2 SO 4 (e.g.…”

“…[7,40,41] Moreover,t his metastable phenomenoni ss tabilized in ternary mixtures of H 2 O-Na x K 2Àx SO 4 . [38,42] The same effect is also known in the H 2 O-Li x K 2Àx SO 4 system. [43][44][45] In light of this observation, the present resultsm ight be considered to indicateacorrelation between the abundance of mediumsized clusters and the stabilization of liquid immiscibility.F or example, this result may suggest that liquid immiscibilityi sf avored by the increased presence of medium-sized clusters.…”

“…[11] The pure solution of K 2 SO 4 showst he onset of precipitation at around 360 8C ( Figure 2), which is close to the experimental value (355 8C). [38] The underestimated precipitation temperature for the solution of Na 2 SO 4 and the unexpectedly gradual decrease in solubility with temperature for solutionso fK 2 SO 4 (e.g. the solubility of K 2 SO 4 should decrease dramatically towards the H 2 Oc ritical point at % 374 8C) highlight some drawbacks of classical MD simulations.…”

Hydrothermal Production of SNG From Wet Biomass

“…Such a mixture can be continuously withdrawn from a separator device, as opposed to the "sticky" solid deposits formed by Type 2 salts (cf. The formation of two immiscible liquid phases of the system na 2 SO 4 -K 2 SO 4 -H 2 O was confirmed by HP-dSC [42]. The formation of two immiscible liquid phases of the system na 2 SO 4 -K 2 SO 4 -H 2 O was confirmed by HP-dSC [42].…”

“…Figure 10.6 shows the three-phase equilibrium line (G-L1-L2) for an average fluid density of 300 kg/m 3 [42]. upon further lowering the fluid density a salt-rich phase will precipitate from the supercritical fluid.…”