Thermally Activated Nitrogen/Heat Generating Reaction: A Kinetic Study

Sodium nitrite and ammonium chloride are the most widely used thermochemicals in the oil and gas industry. The kinetics of this reaction when activated with acids or acid precursors were the subject of extensive research by several researchers. The activation of such a highly spontaneous/vigorous reaction by heat is considered a promising reaction control. In this work, a kinetic study was carried out for the reaction of sodium nitrite and ammonium chloride salt activated by heat at 1-5 M and temperatures of 50-90 °C. The study was carried out in both closed and open systems, with the monitoring of gas evolution and generated pressure. The study showed a relatively higher order for ammonium chloride than sodium nitrite. The excess amount of ammonium chloride, a weak acid, enhanced the reaction as it could be catalyzed by both heat and acid. The obtained kinetics of the nitrogen generating reaction is given as dc/dt = −7.66 × 10¹¹ C_o^2.45 e^{(−91.44 kJ/mol)/RT}. The reaction kinetics in this study differs from what is reported in the literature regarding the order of NH₄Cl, which was reported to be higher than that of NaNO₂ under examined conditions. This study has practical significance for controlling the reactivity of the NH₄Cl/NaNO₂ nitrogen/heat generating system and calculating/optimizing nitrogen generation for a specific field application.