Search

• An increase in the proportion "-NH-" functional groups causes lower ΔH abs. • Secondary amino functional groups appear to stimulate the growth of Δα CO2. • 2MPZR has a 10.7% lower ΔH abs than MEA. • The effective phase change solvent, 2MPRZ/TGBE/H 2 O, was proposed in this work. • The sensible heat of 2MPRZ/TGBE/H 2 O is 56 % lower than that of 5 M MEA. Energy consumption is one of the crucial factors in determining the suitability of the chemical absorbents for capturing carbon dioxide (CO 2). Polyamines have attracted increasing attention in recent years because of the existence of several amino functional groups that could effectively capture CO 2 in their molecules. In this work, the structures of seven polyamines with excellent CO 2 capture performance were investigated in relation to reaction rate and the CO 2 absorption heat. A high-precision microcalorimeter was applied to analyze the absorption heat of CO 2 directly, and a parameter defined as the CO 2 quasi-cycle capacity was employed to assess the cyclic capture capacity of CO 2 , absorption rate, and desorption rate. Experimental results revealed that for the selected polyamines, the increase in the ratio of the secondary amino functional group to the primary-one in the molecule leads to a decrease in the CO 2 absorption heat and an increase in the CO 2 cyclic capacity.The ΔH abs of the eight amines give out the order of HMDA (92.22 kJ/mol) > MAPA(90.91 kJ/mol) > AEEA (87.62 kJ/mol) > MEA (86.36 kJ/mol) > TEPA (82.95 k/mol) > AEP (82.36 kJ/mol) > 2MPRZ (77.08 kJ/mol) > PZ (74.41 kJ/mol). The CO 2 quasi-cycle capacity of 2MPZR is about twice that of the MEA. In addition, 2MPRZ was found to be an absorbent with phase change potential. The effective phase change solvent system, 2MPRZ + Triethylene glycol monobutyl ether (TGBE) + H 2 O, was developed in this work. Compared to the 5 M MEA aqueous solution, its sensible heat was reduced by 56.3 %, indicating that 2MPRZ is a promising absorbent. [ABSTRACT FROM AUTHOR]

• An improved quasi-cycle capacity screening method was proposed in this work. • Guidelines about the effective screening of solvents based on two parameters. • The CO 2 quasi-cyclic capacity was used to evaluate the reaction rate. • The CO 2 absorption heat of six amino acid salts was first accurately measured. • The sensible heat of different absorbent solutions was directly measured. Reaction rate and energy consumption are important factors that determine whether the chemical absorbent is suitable for capturing carbon dioxide (CO 2). In this work, a high-precision microcalorimetry instead of the traditional estimation method based on the Gibbs-Helmholtz equation was used to directly measure the CO 2 absorption heat of six amino acid salt absorbents (potassium taurinate (PT), potassium sarcosinate (PS), potassium L-Prolinate (PL-P), potassium β-Alaninate (Pβ-A), potassium L-Threonine (PL-T), and potassium glycinate (PG)) and the sensible heat of their solutions. In addition, the absorption rate, desorption rate, absorption time, desorption time, and CO 2 loading of the absorbents were studied and were integrated into a parameter called the CO 2 quasi-cycle capacity to evaluate the reaction rate. Based on thermodynamic data and CO 2 quasi-cycle capacity, the absorbent screening method was improved in this work, and PS was identified as a promising absorbent by this method. The CO 2 quasi-cycle capacity of the PS solution was similar to that of MEA. In addition, PS solution has the lowest CO 2 absorption heat (-75.79 kJ/mol CO 2) and the lowest sensible heat which were 14.1% and 23.2% lower than those of MEA solution. [ABSTRACT FROM AUTHOR]

• Novel biphasic solvent based on polyamine was developed for CO 2 capture. • Microcalorimetry strategy was used to directly measure the CO 2 absorption heat. • The energy consumption of this absorbent was 32.6 % lower than that of 5 M MEA. • This biphasic solvent has superior phase-splitting behavior. • The salting-out effect was the main reason for the phase-splitting behavior. The CO 2 phase change absorbents(CPCAs) formed by introducing phase-splitting agents have attracted increasing attention because of their great energy-saving potential. However, the volatilization problem of the phase-splitting agents and the high viscosity of the solution affect the application of CPCAs. In this work, a novel CPCAs based on 2-Methylpiperazine (2MPRZ)/H 2 O was established by introducing triethylene glycol monobutyl ether (TGBE) with a high boiling point as a phase-splitting agent, and the 2MPRZ/H 2 O/TGBE system exhibited low volatility and low viscosity. The CO 2 capture performance of the novel CPCAs with different ratios was investigated in this work. The best CO 2 absorption rate was achieved by 2.5 M 2MPRZ/H 2 O/TGBE. The viscosity of this system before and after the CO 2 absorption process was merely 7.68 mPa·s and 11.64 mPa·s, respectively, and no volatilization of the phase-splitting agent was observed simultaneously. A convenient and rapid titration method was employed to determine the distribution of the 2MPRZ products in the two phases, which showed that 98 % of the 2MPRZ products were located in the CO 2 -rich phase. In addition, the CO 2 -rich phase captured 99 % of the total CO 2 , indicating that this system has superior phase-splitting behaviors. The regeneration energy consumption of this biphasic absorbent was 2.59 GJ/t CO 2 , which was 32.6 % lower than that of traditional MEA. Furthermore, the salting-out effect was proved to be the cause of the phase-splitting behavior by 13C NMR analysis. [ABSTRACT FROM AUTHOR]

• Microcalorimetry strategy was used to directly measure the CO 2 absorption heat. • The structure–activity relationship for CO 2 capture by tertiary amines was studied. • Dual Descriptor was used to analyze the steric hindrance effects. • IRI was employed to visually evaluate the impact of intramolecular hydrogen bonds. • Electron density of N atom was investigated by employing natural population analysis. In comparison with primary and secondary amines, tertiary amines exhibit higher CO 2 equilibrium and lower CO 2 absorption heat, making them attractive for CO 2 capture applications. However, the relationship between the structure of tertiary amines and their CO 2 capture capacity needs to be further studied. This study aimed to investigate the structure–activity relationship between the molecular configuration of representative tertiary amines, and their CO 2 equilibrium solubility, as well as CO 2 absorption heat. The CO 2 absorption heat of nine tertiary amines with distinct structures was measured using a high-precision microcalorimeter, while quantum chemical calculations were employed to explore this relationship. The reactivity of tertiary amines was assessed by visualizing the effects of electron density and steric hindrance by using natural population analysis and dual descriptor analysis, respectively. The findings revealed that the stronger electron-donating effect of ethyl groups than the methyl groups enhanced the reactivity of tertiary amines. Additionally, the presence of methyl groups on the side chain of tertiary amines promoted the reactivity. By contrast, the presence of too many hydroxyl groups resulted in steric hindrance thus reducing the reactivity of tertiary amines. Furthermore, interaction region indicators were employed to visually evaluate the influence of intramolecular hydrogen bonds on the reactivity of tertiary amines. The results show that the presence of intramolecular hydrogen bonds enhanced the equilibrium solubility of CO 2 while facilitating the reduction of the CO 2 absorption heat. The results obtained from this study are important for the selection and development of efficient tertiary amines that are suitable for industrial applications in CO 2 capture. [ABSTRACT FROM AUTHOR]