Direct CO₂ Capture from Air via Crystallization with a Trichelating Iminoguanidine Ligand

Abstract

Effectively reducing the concentration of CO 2 in ambient air is essential to mitigate global warming. Existing carbon capture and storage technology can only slow down the carbon emissions of large point sources but cannot treat the already accumulated CO 2 in the environment. Herein, we demonstrated a simple direct CO 2 capture method from air via reactive crystallization with a new trichelating iminoguanidine ligand (BTIG). It could strongly bind CO 2 to form insoluble carbonate crystals that could be easily isolated. In the crystal, CO 2 was transformed to CO 3 2– and trapped in a dense hydrogen bonding network in terms of carbonate–water clusters. This capture process was reversible, and the BTIG ligand could be regenerated by heating the BTIG–CO 2 crystal at a mild temperature, which was much lower than the decomposition temperature of CaCO 3 (∼900 °C). Thermodynamic and kinetics analyses indicate that the crystallization process was exothermic with an enthalpy of −292 kJ/mol, and the decomposition energy consumption was 169 kJ per mol CO 2 . In addition, BTIG could also be employed for CO 2 capture from flue gas with a capacity of 1.46 mol/mol, which was superior to that of most of the reported sorbents.

Liquid amine–solid carbamic acid phase-separation system for direct capture of CO2 from air

“…29 The intramolecular arrangement of the amino groups of IPDA should result in efficiency in both the formation of the solid precipitate and the reverse reaction. Compared with the reported liquid-solid pair of insoluble carbonate crystals, 25 the high solubility of IPDA in DMSO leads a higher density of captured CO2 than that of chelate-ligating iminoguanidine, which has a low solubility. Moreover, the strong hydrogen-bonding network between the iminoguanidinium cation and the bicarbonate anion required a desorption energy of 81 kJ molCO2 −1 and heating to >393 K. 25 The Gibbs free energy for the carbamation reaction has been reported to be >40 kJ molCO2 −1 for a series of primary and secondary amines, [34][35][36] which is close to that of the present system.…”

“…1A-c). 25 Although CO2 desorption from the CO2-incorporated crystal 5 began at 333 K, complete CO2 release required high temperatures above 393 K. In addition, this system requires a large amount of solvent because of low solubility of the sorbent. Custelcean et al recently developed DAC system using amino acid potassium solution followed by the reaction with guanidine compound resulting in crystallization of insoluble carbonate salt.…”

“…To satisfy these demands, a number of solid amine-based sorbents [13][14][15][16][17][18][19] and CO2absorption systems that utilize phase separation [20][21][22][23][24][25][26][27] have been developed. The ability of homogeneous liquid-phase systems to absorb CO2 has been improved by modifying the structures of the amine sorbents.…”

Direct air capture: process technology, techno-economic and socio-political challenges

“…214,215 To overcome some of the issues above, aqueous amino acids have been investigated for DAC, as they are non-volatile and environmentally friendly. [217][218][219][220][221] The approach generally relies on the crystallisation of a guanidinium carbonate salt of low aqueous solubility, which upon heating regenerates the amino acid sorbent (guanidine) and releases CO 2 . As this stage is endothermic, concentrated solar power has been used as an energy input, to try to improve the sustainability of the Energy & Environmental Science Review process.…”

Research progress in metal–organic frameworks (MOFs) in CO2capture from post-combustion coal-fired flue gas: characteristics, preparation, modification and applications

“…Since 2015, the CO 2 concentration in the atmosphere has risen from 280 ppm in pre-industrial times to 410 ppm. 3 Fig. 1 shows the cumulative CO 2 emissions around the world from 1751 to 2019, which indicates that the United States, Russia, and China are the main contributors.…”