Na₂CO₃ nucleation behavior in sodium salt-water ternary system during hydrogen production process by supercritical water gasification: Coupling influence of pressure and inorganic salt concentration

During supercritical water gasification (SCWG) process for hydrogen production, inorganic sodium salts rapidly precipitate and deposit on the surface of reactors or heat exchange equipment due to the sudden change in solubility, causing safety issues like over-temperature and corrosion. This work investigated the evolution of nucleation characteristics of Na₂CO₃ in Na₂CO₃/Na₂SO₄-supercritical water (SCW) ternary system. The binding behavior of cations and anions over pressure and Na₂CO₃-to-Na₂SO₄ ratio was stressfully analyzed. The correlation between cluster growth and pressure along with Na₂CO₃-to-Na₂SO₄ ratio was furthermore clarified. It was found that pressure and Na₂CO₃-to-Na₂SO₄ ratio mutually regulated Na₂CO₃ nucleation rate. With changes in pressure, the nucleation rate under different Na₂CO₃-to-Na₂SO₄ ratios displayed two tendencies. One was steadily rising decreasing, while the other was first declining and then rising. The former's critical Na₂CO₃-to-Na₂SO₄ ratio point shifted with pressure fluctuations. In mixed solutions, Na₂CO₃ mostly contributed to final cluster size, whereas Na₂SO₄ accelerated particle nucleation.