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• Water markedly affected phase change behaviors of anhydrous biphasic absorbents. • The presence of water was negative for CO 2 absorption but beneficial to desorption. • The main CO 2 -product was HCO 3 - in the presence of water rather than carbamate. • Effect of water on CO 2 absorption mechanism of [N 1111 ][Gly]/ethanol was clarified. The ionic liquids (ILs)-based biphasic absorbents are viewed as promising substitutes for CO 2 capture due to their remarkable CO 2 absorption performance, excellent stability and low energy requirement for regeneration. Further decreasing the regeneration heat requirement can be achieved by utilizing ILs-based anhydrous biphasic absorbents, whose solid CO 2 -rich phase contained small volume and low specific heat capacity. Given the high hygroscopicity of ILs and the water present in the flue gas, comprehending the effect of water is crucial for post-combustion carbon capture using ILs-based anhydrous biphasic absorbents. In this work, the effect of water on CO 2 absorption by an anhydrous biphasic absorbent, tetramethylammonium glycinate ([N 1111 ][Gly])/ethanol, was studied. The experimental results demonstrated that the CO 2 loading and absorption rate were decreased in the presence of water, but the CO 2 desorption efficiency was enhanced. Besides, the presence of water slightly reduced the reaction heat of CO 2 absorption by [N 1111 ][Gly]/ethanol to 69.48 kJ/mol CO 2 , which was 20% lower than that of monoethanolamine (MEA) absorbent. Furthermore, the 13C NMR results indicated that the primary CO 2 -product was bicarbonate in the presence of water rather than carbamate. There were three possible pathways for bicarbonate generation: zwitterion hydrolysis, carbamate hydrolysis, and base-catalyzed CO 2 hydration. Water and ethanol competed to react with carbamate. When a large amount of water was present (≥70 wt%), the reaction of ethanol with the carbamate hardly occurred. [ABSTRACT FROM AUTHOR]

• 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]

• Amino acid salt was firstly introduced into EMAR process for carbon capture. • UV–Visible spectroscopy was used to analyze copper complex change during absorption. • Electrochemical behaviors and performance were discussed by comparing with MEA. • A one-step oxidation reaction was beneficial to reduce the energy consumption. • Homogeneity of electrode surface was observed in our proposed system. Electrochemically mediated amine regeneration (EMAR) for CO 2 capture is a promising substitute for traditional organic amine–based CO 2 capture by replacing the thermal process with electricity. To avoid problems such as oxidative degradation, toxicity, volatilization, and precipitation of organic amine absorbent, potassium β–alanine was suggested as an absorbent using EMAR process for the first time in this study. The CO 2 absorption performance under different copper loading and chemical reactions were studied, and cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry and the Taffel extrapolation method were used to study the electrochemical characterization. Compared to the benchmark monoethanolamine (MEA) system, a smaller potential difference between oxidation and reduction peak was acquired in the potassium β–alanine system, of which the energy consumption was only 44.1% of the MEA system at the current of 100 A/m2. The cathode Faraday efficiency in the potassium β–alanine system was 101.9% higher than that in the MEA system at the current density of 25 A/m2. Furthermore, the result of scanning electron microscope of the electrode surface after desorption showed that potassium β–alanine absorbent improved the inhomogeneity of the electrode surface and was in favor of uniform current distribution. Overall, potassium β–alanine can be used as a more environmentally friendly absorbent in the EMAR system and has great potential to further reduce the actual energy consumption and improve the Faraday efficiency and cycling performance. [ABSTRACT FROM AUTHOR]

• Screening and evaluation of amine/alcohol/H 2 O absorbents were conducted. • The difference of ΔGsol in alcohol and in water confirms phase change behavior. • Alcohol could not only trigger phase change but also facilitate CO 2 absorption. Phase change absorbents have recently drawn increasing attention due to the potential of for low energy-consuming CO 2 capture. When forming two phases after CO 2 absorption, only the CO 2 -rich phase is heated in the desorption process thus reducing the sensible heat. In this work, five amine and three alcohol blends were used to investigate their phase change behavior after reacting with CO 2. Phase separation could easily occur for DETA/alcohol/water combinations after CO 2 absorption, which was confirmed by the large difference of the solvation free energy in alcohol and in water (i.e. DETA-CO 2 has 12.5 kcal/mol ΔGsol in 1-propanol less than that in water). The optimization of the DETA/1-propanol/H 2 O solution was confirmed to be 30% DETA + 30% 1-propanol + 40% H 2 O (D30P30H40). It was found that above 90% of CO 2 loading was enriched in lower phase. 13C NMR spectrum indicated that carbamate and bicarbonate was formed in lower phase and 1-propanol acted as a good physical solvent to trigger phase separation and facilitate the reaction between amine and CO 2. [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]

[Display omitted] • Nanostructured metal oxyhydroxide AlOOH was synthesized for catalytic CO 2 capture for the first time. • A simple but precise heat transfer model was created for heat duty assessment. • The use of AlOOH exhibited the best catalytic performance in increasing the CO 2 desorption rate and decreasing the energy consumption in comparison with other catalysts reported. • A thorough catalytic mechanism was proposed and preliminarily validated. In order to alleviate the intensive energy demand of amine-based post-combustion carbon capture technology, metal oxyhydroxide AlOOH of nanoscale was synthesized through the hydrothermal method and applied to accelerate the CO 2 desorption rate and reduce the regeneration heat duty of aqueous monoethanolamine (MEA) solution for the first time. Results showed that the use of AlOOH could accelerate the desorption rate by up to 560% and increase the desorption amount by 251%. By comparing the performance between AlOOH and Al 2 O 3 , it can be found that the presence of extra hydroxyl groups is 20.6% more efficient in catalyzing CO 2 desorption. According to a simplified heat transfer model created in this work, AlOOH could reduce the heat duty by 17% with only 0.1 wt% loading, which exhibited the highest performance cost ratio among related literature. In addition, the cyclic stability of AlOOH was confirmed through various characterization methods, including XRD, FT-IR, SEM, and N 2 adsorption–desorption. More importantly, a possible catalytic mechanism of AlOOH was discussed and proved where it could change reaction pathways in different CO 2 loading regions. This work reveals a promising research direction towards cost-efficient and high-performance metal oxyhydroxide catalysts in the catalytic amine regeneration field to approach the net-zero carbon emission goal. [ABSTRACT FROM AUTHOR]