Mass transfer and kinetic measurement and modeling for CO2 absorption into aqueous EAE and water-lean EAE/NMP solvents

Abstract

Chemical absorption using amine solvent is currently available technology for CO2 capture from post-combustion flue gas. It is hindered by high operating cost and high capital cost due to high regeneration energy and slow CO2 absorption rate of amine solvent. Water-lean solvent of 2-(ethylamino) ethanol (EAE)/1-methyl-2-pyrrolidinone (NMP)/water could be a potential solution as it achieved significantly low regeneration energy of 2.3 GJ/tCO2 tested in a pilot plant. However, kinetics of CO2 reaction with EAE and mass transfer rate of CO2 absorption into EAE/NMP solvent are not fully understood. In this work, kinetics of CO2 absorption into unloaded aqueous EAE in 1–5 mol/L at 300–313 K and mass transfer of CO2 absorption into CO2-loaded EAE/NMP water-lean solvent in 5 mol/L with equilibrium CO2 partial pressure (PCO2*) range of 0.3–7 kPa at 312 K were studied in a wetted wall column. Kinetic data of aqueous EAE is interpreted by zwitterion mechanism, and the reaction is of first order with respect to EAE concentration in 1–5 mol/L at 300–313 K. CO2 absorption rate (kg’) of EAE/NMP water-lean solvent is 1.3–2.1 times greater than aqueous EAE due to the greater CO2 physical solubility. At lean and rich loading conditions, 5 M EAE in 3NMP/1water and 9NMP/1water show 2–7 times faster kg’ than 30 % MEA, and 1.4–2.5 times faster kg’ than 30 % PZ. It is found that EAE activity coefficient may increase in the presence of NMP in the solvent, and the estimated EAE activity coefficient in 1NMP/1water, 3NMP/1water, and 9NMP/1water are 2.13, 3.50, and 4.72, respectively. CO2 capacity of EAE/NMP solvent is 2–3.7 times greater than 30 % MEA and 1.2–2 times greater than 30 % PZ.