High-temperature hydrolysis of sodium chloride

Abstract

The hydrolysis of sodium chloride according to the reaction NaCl(s,l)+H₂O(g)= NaOH(s,l)+HCl(g) has been investigated over the temperature range 600–950°C using a dynamic method. A mathematical model describing the hydrolysis reaction is derived which is in good agreement with the experimental data. Because of the solid-solid and liquid-liquid solubility of sodium hydroxide in sodium chloride, the activity of the sodium hydroxide is much less than unity and consequently the equilibrium partial pressures of hydrogen chloride generated are much greater than otherwise expected. The activity coefficient of sodium hydroxide in sodium chloride is evaluated and shown to be temperature-dependent, with a sharp discontinuity at the melting point of sodium chloride. It is further demonstrated that equilibrium is established very rapidly, even at temperatures where the sodium chloride is in the solid phase.