CO₂ absorption characteristics of a piperazine derivative with primary, secondary, and tertiary amino groups

Thermodynamic and kinetic data are important for designing a CO₂ absorption process using aqueous amine solutions. A piperazine derivative, 1-(2-aminoethyl)piperazine (AEP), was blended with aqueous amine solutions due to its thermal degradation stability, high CO₂ loading (mole of CO₂-absorbed per mole of amine) and high solubility in water. In this study, the vapor liquid equilibrium (VLE), absorption rate, and species distribution of aqueous AEP solutions were studied to develop an optimum amine solution in a post-combustion capture process. The VLE and apparent absorption rate of the aqueous 30wt% AEP solution were measured using a batch-type reactor at 313.15, 333.15, and 353.15 K. The AEP exhibited approximately twice higher CO₂ loading compared with monoethanolamine (MEA) at all temperatures. The apparent AEP absorption rate (k_app=0.1 min⁻¹) was similar to that of diethanolamine (DEA) at 333.15 K. Speciation of the CO₂-absorbed AEP was analyzed using ¹³C NMR. Although AEP featured a primary amino group and secondary amino group, it did not form bicarbamate upon reaction with CO₂ based on analysis results. AEP-1-carbamate was primarily formed by reactions between AEP and CO₂ during the initial reaction. Bicarbonate species formed as the quantity of absorbed CO₂ increased.