Thermodynamic modeling of CO2 solubility into an aqueous solution of N-methyldiethanolamine using EoS/GE approach and different Alpha-functions

Abstract

Carbon dioxide is among the most crucial impurity in natural gas and must be removed from the gas before any use to avoid environmental damage and problem. The CO2 absorption with the alkanolamine process is widely used for this purpose. This study has been dedicated to modeling the aqueous CO2+ N-methyldiethanolamine (MDEA) system's vapor-liquid equilibrium within the temperature range 297.7-413.15 K and gas loading in the range of 0.000249-1.507 CO2 mole/MDEA mole. In combination with the Wong-Sandler mixing rule and the NRTL activity coefficient model, the Peng-Robinson equation of state has been applied as an EOS/GE approach for modeling of vapor-liquid equilibrium of the CO2-MDEA-H2O system. For improving the performance of the model, five alpha,α, functions have been considered for the Peng-Robinson equation of state.Moreover, ions in the aqueous phase have been accounted for by contributions of the short-range, long-range interactions and the Born term in the Wong-Sandler mixing rule through the Peng-Robinson equation of state. Initially, the binary interactions of the CO2+H2O and MDEA+H2O systems are optimized. Using 283 experimental data of carbon dioxide solubility in the MDEA solution, one can calculate the other binary, and energy interaction parameters by applying simultaneous chemical and phase equilibrium computations. Consequently, to achieve the present modeling's predictability, the obtained parameters were used to predict the other 313 point data's phase equilibrium. The present model results showed that a good agreement is obtained between the calculated and experimental data. The Coquelet and Chapoy (C&C) and Twu alpha, α, functions present more accurate results than the others.