Aqueous mixtures of AMP, HMDA-N,N′-dimethyl and TEG for CO₂ separation: a study on equilibrium and reaction kinetics

Abstract

The hindered amine 2-amino-2-methyl-1-propanol (AMP) is a capable CO₂ separation solvent. HMDA-N,N′-Dimethyl (or HMDA-N,N′), which is the dimethyl derivative of 1,6-hexamethyl diamine, is a prospective activator of the absorption rate in AMP/H₂O mixtures. If a less volatile co-solvent such as triethylene glycol (TEG) is used in AMP-based solutions, the regeneration energy constraint will be lowered. In this work, a formulated blend of AMP (2-3 M), HMDA-N,N′ (0.1–0.5 M), TEG (0.7–2 M) and water was suggested for improved CO₂ capture from flue gas in thermal power stations. Kinetics of the CO₂ reaction with the suggested blend was studied in a stirred cell at 35, 40, and 45 °C. The pathway was elucidated using the renowned zwitterion mechanism. Overall, it was envisaged that both AMP and HMDA-N,N′ react with CO₂ in parallel. The values of the pseudo-first order rate constant were determined. It was found that HMDA-N,N′ reacts with CO₂ according to a second-order reaction (rate constant k_2,HMDA-N,N^′ = 79,525 M⁻¹ s⁻¹ at 35 °C), whose energy of activation is 38 kJ mol⁻¹. Lastly, the loading capacity of the suggested blend was measured in an ambient-pressure equilibrium setup. Its highest value was 1.4 mol CO₂/mol amine, when equilibrium CO₂ pressure was 4 kPa.

Keywords:

• Absorption
• Alkanolamine
• Carbon dioxide
• Kinetics

Additional information

Funding

Mayurkumar P. Patil thanks the Department of Science and Technology (DST), New Delhi, for providing financial support (DST/IS-STAC/CO₂-SR-170/13(G)).