Solvent selection is an important element to enable low energy requirement in post combustion CO2 capture process by means of chemical absorption. In this paper, we investigated the CO2 capture performance of 132 different aqueous amine solvents available in the literature. The properties studied were absorption capacity, cyclic capacity and the pKa -absorption capacity relationship. In addition, fast solvent screening was critically evaluated.Based on published data, no single amine showed superior performance in terms of absorption capacity and cyclic capacity. However, most of the studied amine solvents showed a better performance than MEA. In some cases, amines studied using the different screening techniques showed results which contradicted with the equilibrium value; the screening work seemed to lead to results where the equilibrium value was exceeded. Further, it was indicated that a solvent with promising cyclic capacity with desorption at 70 °C or 80 °C, not necessarily show the same potential with desorption at 120 °C.Thus, the value of the screening experiments can be questioned. At last, it was found a linear relationship between the pKa value of an amine solvents and its absorption capacity.

The diamine 3-(Methylamino)propylamine (MAPA) and eight tertiary amines were studied as single and blended aqueous CO2 absorbents at different concentrations and ratios to investigate the reaction mechanisms. After absorption (40 °C) and desorption (80 °C) experiments, quantitative 13 C NMR experiments were performed on each liquid sample.After absorption, the following CO2-derived species were identified and quantified:(bi)carbonate in each amine system; primary and secondary MAPA carbamate, and MAPA dicarbamate in MAPA-systems; tertiary amine carbonate in tertiary amine-systems.Concerning desorption, the main CO2-species removed was (bi)carbonate, followed in the blends by MAPA dicarbamate.Since, after CO2 absorption, the concentration of MAPA dicarbamate was negligible in single MAPA and, in the blends, mainly increased at increasing pKa of the tertiary amines, it is concluded that the tertiary amines increase the availability of MAPA species to react further with CO2. MAPA and tertiary amines appear to influence each other also for the CO2 release.

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This work studies the potential of using the tertiary amines 3-dimethylamino-1-propanol (3DMA1P), 3-diethylamino-1-propanol (3DEA1P) and 1-(2hydroxyethyl)pyrrolidine (1-(2HE)PRLD) as an alternative to 2-(diethylamino)ethanol (DEEA) in the blend with 3-(methylamino)propylamine (MAPA). Vapour pressure of the three tertiary amines and vapour-liquid equilibrium (VLE) of the binary mixtures 3DMA1P/H2O, 3DEA1P/H2O and 1-(2HE)PRLD/H2O at T = (353, 363 and 373) K were measured in a modified Swietoslawski ebulliometer. The vapour pressure of the pure amines was fitted to the Antoine equation , and the P-T-x-y data were fitted to NRTL equations. VLE of the CO2 loaded blended amines were measured in the temperature range of T = 313 to 393 K, and speciation data of equilibrated samples at different CO2 loadings were obtained by NMR spectroscopy. The study showed that the tertiary amines 3DMA1P, 3DEA1P and 1-(2HE)PRLD in the binary amine/ H2O system were less volatile than DEEA in aqueous solution. The CO2 loaded blended amines showed comparable VLE behaviour, as well as speciation, and obtained a cyclic capacity higher than that of 30 wt% MEA but similar to most of the blended amines studied in the literature. The overall results indicated that the tertiary amines studied in this work can be used as an alternative to DEEA.

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Based on NMR speciation, heat of absorption and pH data, the reactions occurring in aqueous MAPA (3-(Methylamino)propylamine), DEEA (2-(Diethylamino)ethanol) and their blend at various carbon dioxide (CO2) loadings were identified and discussed. At increasing CO2 loading, the basicity of the solutions decreased. In the MAPA solvent, this led to the hydrolysis of the carbamate species, which corresponded to a drop in the heat of absorption. In the blend, due to the activity of DEEA, such a drop in both pH and heat of absorption was not noticeable. In the presence of MAPA, in the early loadings DEEA had not

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