Predicting Speciation of Ammonia, Monoethanolamine, and Diethanolamine Using Only Ionic Radius and Ionic Charge

Abstract

This study investigates the speciation of CO2 involving the most common solvents used to capture carbon from the flue gas, i.e. ammonia, MEA and DEA. This requires the knowledge of both the activity coefficients of the species involved and the equilibrium constants of the relevant reactions. In contrast to the equilibrium constants, which can be obtained from the literature, the activity coefficients of the aqueous species are required to be estimated. Normally, semi-empirical models are used to estimate these activity coefficients, i.e. equations that contain unknown parameters that are obtained through regression against experimental data. In contrast, in this study the activity coefficients are predicted using equations that require only the knowledge of the ionic radii and charges of the species involved in the equilibrium. As a conclusion, the model developed shows a very good agreement with the experimental data obtained, either from spectroscopy or from Vapor Liquid Equilibrium (VLE), up to a solvent mass fraction of 20%.

Energy comparison of sequential and integrated CO2 capture and electrochemical conversion

“…It has been reported recently that the catalysts for gas-fed CO 2 electroreduction are selective to reduce CO 2 captured by amine-based capture media (RNH 2 ) 22 , 43 , 44 , 58 . In the CO 2 -rich amines, the zwitterions ions including RNHCO 2 - and RNH 3 + are the major CO 2 species in the case of 30 wt% monoethanolamine aqueous solution when the CO 2 loading is below 0.4–0.6 mol CO 2 per mol amine 32 , 33 . Further increase of CO 2 loadings could promote carbamate hydrolysis to produce (bi)carbonates.…”

“…In the amine-scrubbing cases, such a displacement could save 88–203 kJ mol CO2 −1 from amine regeneration 24 – 29 and 14–19 kJ mol CO2 −1 for compression 25 , 30 , which accounts for up to 90% of the total energy consumption of the capture process 31 . In the integrated route, the CO 2 -rich amines, containing substantially less free CO 2 (i.e., both CO 2 (g) and CO 2 (aq)) 32 , 33 , are directly fed into the integrated electrolysers. Although hydroxide ions are still produced from the electroreduction reactions, they will not form (bi)carbonate in the integrated electrolysis, because the majority of the captured CO 2 molecules are in the form of carbamate and bicarbonate.…”

Advancing integrated CO2 electrochemical conversion with amine-based CO2 capture: a review

“…The product concentrations in CO 2 -rich primary amines vary significantly with CO 2 loading. Aqueous MEA capture medium is a typical example 46 , as shown in Fig. 2.…”

“…Such speciation transformation with CO 2 loading usually takes place for primary ( e.g. , MEA) and secondary amines such as diethanolamine (DEA), 46 as shown in Fig. 2b.…”

“…At this stage, bicarbonate and freely dissolved CO 2 become the primary CO 2 species in the capture medium. Such speciation transformation with CO 2 loading usually takes place for primary (e.g., MEA) and secondary amines such as diethanolamine (DEA), 46 as shown in Fig. 2b.…”