Over the past decade, amine-loaded solid adsorbents for capturing CO2 from power plants have been widely studied. Various nitrogen (N) sources have been used for this purpose, and the current range of adsorbents, referred to here as N-functionalized solid adsorbent (NFSAs), are the subject of this review. The main synthesis methods of NFSAs are described and recent progress in the field discussed. Criteria for improving NFSA performance are highlighted with reference to a variety of solid supports, providing guidance on the selection of highly efficient, inexpensive adsorbents. A thorough assessment of adsorption mechanisms and factors influencing the adsorption process is given. The review concludes by exploring future research and development opportunities, as well as pathways for commercializing NFSAs.
The formation of bicarbonate ions in an amine solution during CO 2 absorption results in lowering the heat duty for amine solvent regeneration in the CO 2 capture process because bicarbonate breakdown needs the lowest energy input to release CO 2 . In this study, bicarbonate formation was conducted for two mixed solvents consisting of tertiary amines (1DMA2P (1 M) or MDEA (1 M)) blended with MEA in order to determine both formation rate and capacity of bicarbonate ions as compared to MEA alone. The amines and concentrations used in the study were MEA (5 M), MEA−MDEA (5:1 molar ratio, 6 M total), and MEA−1DMA2P (5:1 molar ratio, 6 M total) at various CO 2 loadings. The formation of bicarbonate ions was evaluated using 13 C NMR technique at 293.15 K. The results show that for the single tertiary amine system higher concentrations of bicarbonate ions were formed for MDEA than for 1DMA2P for the same CO 2 loading. The results for the blended amine systems showed that bicarbonate ions were generated at CO 2 loadings lower with MEA alone than with MEA−1DMA2P generating bicarbonate ions at a CO 2 loading (0.34 mol CO 2 /mol amine) lower than that with MEA−MDEA (0.38 mol CO 2 /mol amine). Thus, as an additive in MEA, 1DMA2P has a better potential than does MDEA to generate bicarbonate ions at a leaner CO 2 loading with the attendant lowering of the regeneration energy.
Chemical absorption
using aqueous amine-based solutions is the
leading method for large-scale CO2 capture in industrial
plants. This technology, however, still faces many challenges, in
particular the high-energy requirements for solvent regeneration,
which limit the economic viability of the technology. To guide the
development of more energy-efficient amine solvents, this work studied
the effect of molecular characteristics of diamines, including carbon
chain length and type of amino functional group, on CO2 absorption and desorption performances. Six linear terminal diamines
[NH2CH2CH2–R, where R = NH2, NHCH3, N(CH3)2, CH2NH2, CH2NHCH3, and CH2N(NH3)2] were investigated, and two
monoamines, monoethanolamine (NH2CH2CH2OH, MEA) and 3-aminopropanol (NH2CH2CH2CH2OH, 3AP), were also tested as benchmarks. The
CO2 absorption capacity in each amine was measured at 40
°C under atmospheric pressure using different CO2 gas
partial pressures. 13C and 1H nuclear magnetic
resonance spectroscopies were used to identify and quantify species
present in the CO2–amine–H2O system.
Computational modeling was also carried out using Gaussian software
to explain the effect of the chain length change on the stability
of monocarbamate. The experimental results showed that the chain length
extension from C2 to C3 led to a higher CO2 absorption capacity and more bicarbonate formation during
the CO2 absorption process, and the computational study
results supported this conclusion. In addition, the experimental results
also demonstrated that increasing the substitution on one N atom in
the tested diamines is favorable for a higher CO2 absorption
capacity and more bicarbonate formation under a CO2 partial
pressure of 101 kPa. Both chain length extension from C2 to C3 and an increase in the number of substituents on
one N atom yield better performance in the CO2 desorption
with regard to the CO2 higher cyclic capacity and faster
initial CO2 release rate for the tested amines.
Developing ideal amine solvents with a high CO 2 absorption capacity and a fast absorption rate is an attractive avenue to advance the amine scrubbing technology. In this regard, diamines bearing one primary and one tertiary amino group (1°/3°diamines) are proposed to be promising solvents for CO 2 absorption, which can exhibit the fast CO 2 absorption rate of primary amines while maintaining the diamines' intrinsic high absorption capacity. Here, we present a detailed kinetic study of four 1°/3°diamines for CO 2 absorption and investigate the relationship between the structure of various 1°/3°diamines and their CO 2 absorption rate. Results showed that increasing alkyl spacer between two amino groups within 1°/3°diamines promoted the CO 2 absorption rate, while a large decrease in their reactivity with CO 2 was observed when the tertiary amino group existed in the cyclic structure. Among these studied 1°/3°diamines, 3-(dimethylamino)-1-propylamine (DMAPA) displayed the highest absorption rate under relevant conditions and also exhibited higher overall mass transfer coefficients than those of monoethanolamine over the entire range of CO 2 loadings, and the main reaction routes for CO 2 absorption into DMAPA solution via formation of the protonated DMAPA-carbamate were proposed.
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