13C NMR investigation of solvent effect on the reversible reaction of ammonium carbamate for chemical heat pump

The reversible decomposition of ammonium carbamate (AC) shows significant potential for application in chemical heat pumps. While AC is typically dissolved in a solvent and used in solution form, the impact of dissolution on its reaction reversibility remains insufficiently understood. To address this, the effects of commonly used solvents, namely ethylene glycol (EG), propylene glycol (PG), and monoethanolamine (MEA), on the decomposition reaction of AC were investigated using 13C NMR spectroscopy. A quantitative method was developed to better interpret the spectra of AC solutions. The results reveal that AC reacts with the glycol solvents EG and PG during dissolution generating the corresponding alkyl carbonates. These latter species can decompose synchronously with the dissolved AC, indicating minimal impact on the reaction reversibility. In contrast, the generated MEA-carbamate requires temperature above 120°C for decomposition. Corrosivity experiments demonstrated that AC is non-corrosive towards stainless steel 316 and aluminum, but exhibits high corrosivity toward copper.