Validation of the thermodynamic model in vapor phase

https://doi.org/10.1039/C9RA00164F

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Fig. 3 shows the predicted NH₃ and CO₂ partial pressure at T = 20 °C and different NH₃ molality. The model is in good agreement with the experimental data from different laboratories, which indicates the reliability of the model results.^31,57 There is no NH₃ equilibrium partial pressure reported in Jilvero’s article. Therefore, only the CO₂ equilibrium partial pressure is exhibited in Fig. 3(b). With increasing CO₂ molality, the equilibrium partial pressure of NH₃ decreases. Because free NH₃ in solution is consumed to form nitrogenous compounds at a higher CO₂ molality, it lowered the mass transfer driving force for ammonia escaping. Therefore, a high CO₂ molality is recommended in order to reduce, not only ammonia escape⁵⁸ but also the regeneration energy consumption.⁵⁹ It can be observed that at low NH₃ concentration (less than 1 mol NH₃/kg H₂O), both CO₂ and NH₃ partial pressures can match experimental data within about 15% error. However, the model underestimates slightly the NH₃ partial pressure and overestimated CO₂ partial pressure at higher NH₃ concentration and lower CO₂ molality, which may be caused by the volatility of NH₃. Nonetheless, under the conditions considered here, the largest difference between the calculation and experiments is about 12%.

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