CO2 absorption into N-methyldiethanolamine aqueous-organic solvents

Abstract

The present work studied the CO2 absorption into N-methyldiethanolamine hybrid (chemical and physical) solutions, using pure water, pure methanol and water+methanol mixtures as solvents. The variables considered were amine concentration (0%, 5%, 15% and 30% in mass), methanol ratio in the solvent according to molar fractions (0, 0.4, 0.7 and 1) and temperature (283.15, 293.15, 303.15 and 313.15K). Experiments were carried out at atmospheric pressure in a batch-operated stirred reactor, and the direct measurement of the CO2 absorbed was performed in a calibrated bubble meter.The absorbed CO2 per unit area, Q (kmolm−2), and CO2 flow density, NA (kmolm−2s−1), were determined for each experimental series. The ratio between the CO2 flow density in MDEA aqueous solutions, Nw, and the value in aqueous organic solutions, Nw+m, was also analyzed. Individual mass transfer coefficients in the liquid phase, kL (ms−1), were determined from physical absorption experiments, as well as data on the CO2 solubility. Both CO2 diffusivity, DCO2 (m2s−1), and N-methyldiethanolamine, D0MDEA (m2s−1), diffusivity values in the liquid phase were also provided.The CO2 absorption experiments were significantly influenced by the effect of temperature, amine concentration and water/methanol ratio. The performance of CO2 absorption into aqueous MDEA solutions was compared to that into hybrid MDEA solutions. It was concluded that MDEA aqueous solutions demonstrated lower performance than amine solutions using pure methanol or water–methanol mixtures as solvents, even at high temperatures and amine concentrations. Results showed that at high temperatures, amine concentration and chemical absorption had no relevant influence on the process. The methanol effect was noticed to improve the diffusivity and solubility in the process, by means of physical absorption.