Understanding the potential benefits of blended ternary amine systems for CO2 capture processes through 13C NMR speciation study and energy cost analysis

Enhancing CO2 capture of an aminoethylethanolamine-based non-aqueous absorbent by using tertiary amine as a proton-transfer mediator: From performance to mechanism

Non-aqueous absorbents (NAAs) have attracted increasing attention for CO2 capture because of their great energy-saving potential. Primary diamines which can provide high CO2 absorption loading are promising candidates for formulating NAAs but suffer disadvantages in regenerability. In this study, a promising strategy that using tertiary amines (TAs) as proton-transfer mediators was proposed to enhance the regenerability of an aminoethylethanolamine (AEEA, diamine)/dimethyl sulfoxide (DMSO) (A/D) NAA. Surprisingly, some employed TAs such as N,N-diethylaminoethanol (DEEA), N,N,N',N'',N''-pentamethyldiethylenetriamine (PMDETA), 3-dimethylamino-1-propanol (3DMA1P), and N,N-dimethylethanolamine (DMEA) enhanced not only the regenerability of the A/D NAA but also the CO2 absorption performance. Specifically, the CO2 absorption loading and cyclic loading were increased by about 12.7% and 15.5%-22.7%, respectively. The TA-enhanced CO2 capture mechanism was comprehensively explored via nuclear magnetic resonance technique and quantum chemical calculations. During CO2 absorption, the TA acted as an ultimate proton acceptor for AEEA-zwitterion and enabled more AEEA to form carbamate species (AEEACOO-) to store CO2, thus enhancing CO2 absorption. For CO2 desorption, the TA first provided protons directly to AEEACOO- as a proton donor; moreover, it functioned as a proton carrier and facilitated the low-energy step-wise proton transfer from protonated AEEA to AEEACOO-. Consequently, the presence of TA made it easier for AEEACOO- to obtain protons to decompose, resulting in enhanced CO2 desorption. In a word, introducing the TA as a proton-transfer mediator into the A/D NAA enhanced both the CO2 absorption performance and the regenerability, which was an efficient way to "kill two birds with one stone".

Comprehensive mass transfer analysis of CO2 absorption in high potential ternary AMP-PZ-MEA solvent using three-level factorial design

Mass transfer of CO₂ absorption in 2-amino-2-methyl-1-propanol (AMP) - piperazine (PZ) - monoethanolamine (MEA) was statistically investigated in terms of overall mass transfer coefficient ([Formula: see text]) and CO₂ removal percentage. The parameters of interest were lean solvent flux (A), rich gas flux (B), CO₂ loading in the lean solvent (C), and ratio of the sampling height to the total column height [Formula: see text] (D). From ANOVA, A was the most impactable parameter on both responses with three-quarters of the overall contribution. Regarding the three-level factorial design, a second-order polynomial increasing trend of [Formula: see text] was observed as C and/or D increased. Additionally, [Formula: see text] linearly increased as A increased but was not affected by B. On the other hand, the CO₂ removal percentage linearly increased as A and/or D increased but linearly decreased as B and/or C increased. Surface analysis suggested the optimum condition for both responses at a high level of A, low level of B, low level of C, and middle level of D. In this work, D was statistically investigated and included in the predictive correlation for [Formula: see text] for the first time. The main advantage of the proposed correlation over the recently reported correlations was that it did not require a measurement of CO₂ partial pressure along the column height. For each amine component in the blend, (i) AMP played a positive key role in cyclic capacity and solvent regeneration duty, (ii) PZ enhanced transfer rate, and (iii) MEA elevated total amine concentration. As a result, 1.5:1.5:3 was recommended due to (i) elevations of 68.2% [Formula: see text], 14% CO₂ removal percentage, 15.1% absorption capacity, and 66.7% cyclic capacity and (ii) reduction of 50% regeneration duty compared with 5 M MEA. With respect to the other literature-reported solvents, AMP-PZ-MEA is very competitive in terms of transfer coefficient, cyclic capacity, and solvent regeneration heat duty.