Validation of the thermodynamic model in liquid phase

https://doi.org/10.1039/C9RA00164F

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Fig. 4 shows the calculated solution speciation and experimental results reported by Lichtfers and Rumpf.⁶⁰ The corresponding conditions are m(NH₃) = 4.44 mol kg⁻¹ H₂O and T = 60 °C. It concludes that the calculated results agree well with the experimental data within less than 6% error. The increase in carbamate molality is greater than for those of carbonate and bicarbonate in the presence of excess NH₃ at the initial stage of absorption. The carbamate concentration reaches its maximum value at about m(CO₂) = 2.2 mol CO₂/kg H₂O (CO₂ loading = 0.5 mol CO₂/mol NH₃). However, at high CO₂ molality (m(CO₂) greater than 2.5 mol CO₂/kg H₂O) the bicarbonate is the dominant species. Meanwhile, the concentration of carbamate decreases.⁶¹

The deviation for NH₄HCO₃(s) solubility in ammonia solution between calculated and different literature values^62,63 are shown in Fig. 5 at temperatures from 0 to 60 °C. The maximum and average deviations are 5% and 2%, respectively. The deviation of NH₄HCO₃(s) solubility between calculated and literature value at temperatures more than 40 °C is slightly higher than those at lower temperatures. However, considering the temperature ranges in the present study (from 2 to 40 °C), the relative deviation is less than 5% which confirms the accuracy of the thermodynamic model in this study.

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