Solvent Effect on the Chemical Equilibrium of Ammonium Carbamate for Chemical Heat Pump

Chemical heat pump based on ammonium carbamate (AC) is a promising low-grade heat utilization technology. It is essential to know the chemical equilibrium properties in the application of AC-based technologies. AC is usually mixed with solvents to realize circulation. However, the existing studies mainly focus on AC in the solid phase. Therefore, the influence of solvents on the chemical equilibrium of AC was experimentally investigated in this work. The results confirm the solvent effect on the equilibrium pressure of AC in the range of 10~90 °C. For solvents capable of dissolving AC, the equilibrium pressure increases with both AC concentration and temperature. The solvent effect is mainly due to the influence on both the reaction enthalpy and entropy change terms. An equilibrium pressure-temperature-concentration relationship of AC solution is established. These results provide essential parameters for the design and operation of low-grade heat management and utilization systems based on AC.