Solvent Effect on Decomposition Kinetics of Ammonium Carbamate for a Chemical Heat Pump

Low-grade heat can be efficiently managed and utilized with a chemical heat pump based on ammonium carbamate (AC). However, the limited knowledge of AC’s reaction properties restricts its further development. AC is often dissolved in a solvent to enhance the circulation. Therefore, the effects of dissolution in solvents on the decomposition kinetics of AC were investigated. Ethylene glycol (EG) was selected as the solvent. It is found that the decomposition of AC-EG solutions can be considered as a coupling of dissolved AC decomposition and EG evaporation. By decoupling these two processes, the respective kinetic parameters can be computed by using thermal analysis methods. The dissolution of AC in EG results in a decrease in both activation energy and pre-exponential factors, which ultimately leads to a slight decrease in reaction rate. A coupled reaction rate model for the decomposition of AC-EG solutions was developed. Kinetic predictions for the AC-based endothermic reactor were conducted. It was demonstrated that AC has excellent instantaneous cooling capability thanks to its advantageous huge reaction heat, with heat absorption power reaching up to 2114.01 W·mol-1 AC at 85 °C for the solution with 15% AC concentration, indicating its potential for efficient low-grade heat absorption and management.