Thermodynamic data for CO2 absorption in aqueous 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ) solutions: CO2 solubility, N2O solubility, heat of absorption of CO2, pH and liquid speciation

Abstract

New thermodynamic data for CO₂ absorption in aqueous blends of 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ) are measured in this work. The CO₂ solubility in aqueous AMP/PZ solutions, including the CESAR1 blend, was measured at temperatures from 40 to 150 °C, extending the range of CO₂ loading and temperature previously investigated.

The heat of absorption of CO₂ of aqueous AMP and AMP/PZ solutions was measured from 40 to 80 °C. The results indicate that the heat of absorption is constant with the temperature but it is affected by the AMP/PZ concentration ratio.

The N₂O solubility in the CESAR1 solvent was measured from 25 to 80 °C and up to CO₂ loading of 0.52 $\text{mo}{l}_{C{O}_2}$/$\text{mo}{l}_{\text{amine}}$. The N₂O solubility decreases as a function of temperature and CO₂ loading as a result of the salting-out effect.

The effect of CO₂, AMP and PZ concentration on the pH was experimentally determined. Liquid speciation for the CESAR1 blend and an aqueous solution of 1.5 M AMP + 0.75 M PZ was measured at CO₂ loading from 0 to 0.80 $\text{mo}{l}_{C{O}_2}$/$\text{mo}{l}_{\text{amine}}.$ The results indicate that the CO₂ dissolved exists mainly as PZ-carbamate at relatively low CO₂ loading up to 0.40 $\text{mo}{l}_{C{O}_2}$/$\text{mo}{l}_{\text{amine}}$, while at higher CO₂ loading, the bicarbonate/carbonate and PZ-dicarbamate are the major products. The AMP carbamate is not a major product across the whole range of CO₂ concentration investigated.

The experimental data broaden the existing dataset and can support the development of rigorous thermodynamic models essential for evaluating energy requirements and environmental impacts of CO₂ capture using CESAR1 technology.