CO₂ absorption into primary and secondary amine aqueous solutions with and without copper ions in a bubble column

Chemical absorption of CO₂ into aqueous amine solutions using a nonstirred bubble column was experimentally investigated. The performance of CO₂ absorption of four different primary and secondary amines including monoethanolamine (MEA), piperazine (PZ), 2-piperidineethanol (2PE), and homopiperazine (HPZ) were compared. The effects of initial concentration of amine, the inlet mole fraction of CO₂, and solution temperature on the rate of CO₂ absorption and CO₂ loading (mol CO₂/mol amine) were studied in the range of 0.02-1 M, 0.10-0.15, and 25-40 °C, respectively. The effect of the presence of copper ions in the amine solution on CO₂ loading was also studied. By comparison of the breakthrough curves of the amines at different operational conditions, it was revealed that the shortest and longest time for the appearance of the breakthrough point was observed for MEA and HPZ solutions, respectively. CO₂ loading of MEA, 2PE, PZ, and HPZ aqueous solutions at 25 °C, 0.2 M of initial concentration of amine, and 0.15 of inlet mole fraction of CO₂ were 1.06, 1.14, 1.13, and 1.18 mol CO₂/mol amine, respectively. By decreasing the inlet mole fraction of CO₂ from 0.15 to 0.10, CO₂ loading slightly decreased. As the initial concentration of amine and temperature decreased, CO₂ loading increased. Also, the presence of copper ions in the absorbent solution resulted in a decrease in the CO₂ loading of MEA and HPZ aqueous solutions. In case of PZ and 2PE amines, adding copper ions led to precipitation even at low copper ion concentrations.