Ammonium salts formation in impure CO2 transport streams

• Thermodynamics and kinetics of ammonium salt formation in impure CO2. • CO2 and NH3 react rapidly to form ammonium carbamate under CCS transport conditions. • In the presence of water vapor, bicarbonate may be more stable than carbamate salt. • Thermodynamic model predicts salt formation conditions. • Greater potential for salt formation in gas phase transport than in dense phase. An experimental and modelling study is presented concerning the thermodynamics and kinetics of ammonium salts formation in an impure carbon dioxide stream. Thermodynamic modelling is used to determine the conditions at which ammonium carbamate and ammonium bicarbonate are stable in terms of temperature, pressure and the mole fractions of both ammonia and water in the CO 2 stream. The conditions investigated are gas, liquid and supercritical states at temperatures between (273 and 313) K with pressures up to 10 MPa. The calculations show that ammonium carbamate may form in dry gaseous CO 2 when the ammonia mole fraction exceeds 10 ppm. If water is also present at 50 ppm, then ammonium bicarbonate is more stable in a wide range of conditions and may form at the lowest temperature even with 1 ppm of ammonia present. These salts ate predicted to exhibit even greater stability in cryogenic liquid CO 2 . Batch reactor experiments show that ammonium carbamate forms very rapidly and, in our study, both ex situ FTIR and in situ Raman spectroscopy were used to identify the salts formed. In the presence of water impurity, ammonium bicarbonate was found to form either directly from the gas phase or via hydrolysis of ammonium carbamate.