水热反应釜中高温高压离子水溶液热力学性质

对水热反应釜中高温高压NaOH和KOH水溶液的热力学性质进行了研究，采用Pitzer表观摩尔体积模型获得了容器中溶液填充度与压力的关系;在考虑溶液中离子缔合现象的基础上对Pitzer活度因子模型进行了改进，建立了能够描述溶液中真实离子组成的NaOH和KOH水溶液热力学模型，并给出了模型参数随温度和压力的变化关系式.计算结果表明，与纯水体系相比，相同反应温度、初始填充度下，NaOH和KOH 水溶液产生的压力显著降低，这意味着实际操作中可以进一步升高反应温度和增加填充度;100℃时，5 mol·kg^-1的NaOH溶液的缔合度就已达到30％，并随反应温度和溶液初始浓度的增加缔合度还将显著升高，表明实际水热反应的氢氧根自由离子浓度远远小于溶液的初始浓度，这为进一步深入研究水热反应机理奠定了理论基础.

Thermodynamics of alkali aqueous solution in hydrothermal reaction vessel

The thermodynamics of aqueous NaOH/KOH solution at high temperatures and pressures in a hydrothermal vessel was studied.The Pitzer model for apparent molar volume was used to investigate the relationship of filling degree and pressure.The Pitzer model for activity coefficient was modified by considering the ion association effect and the new model parameters were given.The results showed that the pressure of 10 mol·kg^-1 NaOH solution was 11.16 MPa while that of pure water was 136.7 MPa at 250℃ with the same filling degree of 90%, indicating that the pressures of alkali solutions were much lower than that of pure water under the same temperature and initial filling degree and a higher reaction temperature and a higher filling degree in the actual hydrothermal vessel was possible.In addition, the association degree of 5 mol·kg^-1 aqueous NaOH/KOH was over 30% at 100℃, and it increased remarkably with temperature and initial molality, indicating that the real concentration of OH- was much lower than the apparent molality.This work would facilitate the study of the reaction occurring in the hydrothermal vessel.