Experimental method and mathematical method for VLE plots in 3DMA1P-CO₂-H₂O system

The concentration profiles of all chemicals obtained in the Amine-CO₂-H₂O system based on the Vapor-liquid equilibrium (VLE) plots are essential for the analysis and understanding of the kinetics. This work aims at obtaining accurate and reliable VLE plots of 3DMA1P via both experimental and mathematical methods. VLE plots are essential for understanding the reaction process and mechanism of carbon dioxide absorption into amine solutions. The experiments were conducted over a concentration range of 1 ∼ 2 mol/L, temperature of 298 K, and CO₂ partial pressure of 15 kPa. Regarding the experimental method, ¹³C NMR detection was performed to generate concentrations of Amine and AmineH⁺ based on the protonation calibration equation. The results showed that the ¹³C NMR method had little difference between the results of mass conservation calculation and charge conservation calculation under different CO₂ loading. Among the mathematical methods, the results obtained by the pH method involving charge conservation were quite different from those calculated by mass conservation, while the D-M model method strictly following the theoretical system satisfied both the mass and charge conservation. The distribution curves of the concentration of each species obtained by the three methods were compared. It was found that ¹³C NMR and D-M model method could secure closer and more accurate results than the pH method. In conclusion, both the ¹³C NMR method and the D-M model method plots are useful for obtaining accurate and reliable VLE plots for the 3DMA1P-CO₂-H₂O system, as well as for other monoamine and mixed amine systems.