Two-liquid-phase boundaries and critical phenomena at 275-400.degree.C; for high-temperature aqueous potassium phosphate and sodium phosphate solutions. Potential applications for steam generators

Abstract

Two-llquld-phase boundaries at temperatures between 275 and 400 °C were determined for potassium phosphate and sodium phosphate aqueous solutions for compositions from 0 to 60 wt % dissolved salt. The stoichiometric mole ratios, K/P04 or Na/P04, were varied from 1.00 to 2.12 and from 1.00 to 2.16 for the potassium and sodium systems, respectively. Liquid-vapor critical temperatures were also determined for most of the dilute liquid phases that formed. The minimum temperatures (below which a single solution existed) of two-llquld-phase formation were 360 °C for the potassium system and 279 °C for the sodium system at mole ratios of 2.00 and 2.16, respectively. For the sodium system at mole ratios greater than 2.16, solids crystallized at lower temperatures as expected from earlier studies. In contrast, potassium solutions that were explored at mole ratios from 2.12 to 3.16 and at temperatures below 360 °C did not produce solid phases or liquid-liquid Immlsclbllltles. Aside from the generally unusual observations of two immiscible liquids In an aqueous Inorganic salt system, the results could possibly be applied to the use of phosphate additives In steam power generators.

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

“…No phase density data is available in the literature for this system and therefore the correction for the liquid phase concentration could not be applied. Comparing our measurements to those of Marshall et al, 40,41 which were also taken at isochoric conditions, but probably at higher densities, we see a consistent trend of the data points (Fig. 5).…”

On Coulombic and Solvophobic Liquid‐Liquid Phase‐Separation in Electrolyte Solutions

“…This is in agreement with experimental observations for UOzS04-H20 at 559 K [6], and with evidence for similar immiscibilities of other 2: 2-electrolytes, suppressed by crystallization [ 11. Liquid-liquid immiscibilities in aqueous solutions of unsymmetrical electrolytes like Na3P04 [7], BaC12 [8] or Na2W04 [9] at high temperatures may also fall into this category. Also in line with the theoretical predictions are immiscibilities of 1 : 1-electrolytes in solvents of low dielectric constant near room temperature, typically with E I 5.…”

Aqueous solutions of the mono- and di-hydrogenphosphate salts of sodium and potassium at elevated temperatures. Isopiestic results

“…Indeed, aqueous solutions of the alkali metal phosphates do phase separate into light and dense liquids as observed by Marshall et al (33) and Marshall. (34) Two-liquid-phase formation in K 2 HPO 4 (aq) was observed to have a 1-1 critical temperature of about 633 K with the phase separation occurring over the range of mass fraction w between 0.01 and 0.6 at the higher temperatures. For KH 2 PO 4 (aq), the 1-1 critical temperature was reported by Marshall (33) to be 660 K with phase separation over the concentration range of w = 0.02 to w = 0.33 at higher temperatures.…”