Study on the thermal decomposition kinetics of ammonium carbamate for low-grade heat utilization

Abstract

The thermochemical reaction of ammonium carbamate (AC) holds significant potential for low-grade heat utilization. However, the insufficient understanding of reaction kinetics limits its further applications. Therefore, a detailed study on the kinetic mechanism of AC decomposition was conducted using both the model-free and model-fitting thermal analysis methods with kinetic data from multiple heating program experiments. The results obtained from various methods are consistent, supporting the concept that AC decomposition is a single-step controlled multi-step reaction. The activation energy E, preexponential factor A, and most probable reaction model were determined to be 56.38 kJ∙mol⁻¹, 2.75 × 10⁶ s⁻¹, f(α)=(1-α)^0.7811, respectively. The reaction mechanism can be hypothesized as involving the rapid generation of numerous nucleation sites on the surface of solid AC, where surface reactions occur, with the movement of reaction interface governing the reaction rate. Consequently, a kinetic equation accounting for the AC decomposition was developed and evaluated, and the heat absorption specific power under different temperature conditions was predicted.