Polythermal investigation of carbohalogenation process of molten KBr-LiBr (0.4:0.6) eutectic

Abstract

The running of carbohalogenation process (the purification from oxide ion traces) in molten KBr-LiBr eutectic was performed in 943-1023 K temperature range. The treatment of the melt was performed by passing bromine vapour through the melt containing suspension of graphite. The rate of the carbohalogenation process was estimated on the basis of changing oxide ion concentration which was detected by a potentiometric methods with the use of an oxygen electrode Pt(O₂)ZrO₂(Y₂O₃). This reaction is characterized by 2^nd kinetic order with respect to oxide ions. The corresponding rate constants (kg∙mol^-1∙min^-1) are equal to: 2379±150 at 943 K, 2619±150 at 973 K, 2934±160 at 1000 K and 3314±250 at 1023 K. The purification limit of the studied melt is practically independent of temperature and is varied in (1.4¸1.8)∙10^-5 mol∙kg^-1 range with respect to O²⁻. The dependence of the rate constant against the temperature is described by the following equation: ln k=12.02(±1)-4011(±900)∙T^-1 that allows one to estimate the activation energy as 33.3±7.5 kJ∙mol^{-1. A considerable decrease of the activation energy comparing with the corresponding values for the carbohalogenation of chloride melts (}~170 kJ∙mol^-1) can be explained by lower strength of Br−Br bond in bromine Br₂ in comparison with C−Cl bond in CCl₄.