Theoretical study on thermal stability of molten salt for solar thermal power

Molten salt (HTS) composed of 53% KNO3, 40% NaNO2 and 7 wt.% NaNO3 has been used as heat transfer media and thermal storage fluid in the solar thermal power, but thermal decomposition will occur at higher temperature because of the oxidation of nitrite to nitrate in the air. In this paper, the reaction mechanism of NO2− oxidation is researched by quantum mechanical method. The results show that two components of the transition state (O2NO2−) and intermediate ([NO4−]) are found in the reaction. This reaction is an exothermic reaction and the activation barrier is 94.0 kJ mol−1. The energy difference of this reaction is very large, so the reaction rate is very slow.

► The mechanism of the oxidation of nitrite salt in HTS is explained.
► Two components of the transition state (O2NO2−) and intermediate ([NO4−]) are found.
► The activation barrier of the nitrite oxidation is determined.