Capturing CO 2 from flue gas streams under near ambient conditionse.g. coal-fired power plantshas traditionally involved the use of aqueous alkanol amine solutions. Aqueous solvent-based processes are energy intensive, as solvent regeneration can be costly. With growing concern over climate change, alternative CO 2 capture technologies that are energy and cost efficient are required. We have established that nonaqueous silylamines can be used to efficiently and reversibly capture and release CO 2 via the formation of reversible ionic liquids. We now report their unique, enhanced CO 2 uptake at room temperature under 1 atm of CO 2 , as silylamines exhibit CO 2 capture capacities greater than that expected from the conventional stoichiometry of a 2:1 amine to CO 2 mole ratio. Experimental evidence is presented supporting the formation of a carbamic acid species in equilibrium with an ionic liquid network of ammonium−carbamate ion pairs to give a 3:2 amine to CO 2 mole ratio. This is the f irst report of the stabilization of carbamic acid by reversible ionic liquids. Stabilization of carbamic acid leads to a significant increase in CO 2 capacity (30% on average) over conventional amine solutions for CO 2 capture.

The quantum-chemical approach COSMO-RS was used to develop structure−property relationships of reversible ionic-liquid (RevIL) solvents for CO 2 capture. Trends predicted for the thermodynamic properties of the RevILs using COSMO-RS, such as CO 2 solubility, solvent regeneration enthalpy, and solvent reversal temperature, were verified by experimental data. This method was applied to a range of structures, including silylamines with varying alkyl chain lengths attached to the silicon and amine functionality, silylamines with fluorinated alkyl chains, sterically hindered silylamines and carbon-based analogues. The energetics of CO 2 capture and release and the CO 2 capture capacities are compared to those of the conventional capture solvent monoethanolamine. The results of this study suggest that the simple COSMO-RS computational approaches reported herein can act as a guide for designing new RevILs. COSMO-RS allows for the determination of the relative thermodynamic properties of CO 2 in these and related systems.

A series of silylated amines have been synthesized for use as reversible ionic liquids in the application of post‐combustion carbon capture. We describe a molecular design process aimed at influencing industrially relevant carbon capture properties, such as viscosity, temperature of reversal, and enthalpy of regeneration, while maximizing the overall CO2‐capture capacity. A strong structure–property relationship among the silylamines is demonstrated in which minor structural modifications lead to significant changes in the bulk properties of the reversible ionic liquid formed from reaction with CO2.

Abstract:The introduction and removal of protecting groups is ubiquitous in multi-step synthetic schemes. From a green chemistry standpoint, however, alternative strategies that employ in situ and reversible protection and deprotection sequences would be attractive. The reversible reactions of CO2 with amines could provide a possible vehicle for realizing this strategy. Herein, we present (1) the products of reaction of benzylamines with CO2 in a variety of solvents with and without the presence of basic additives; (2) 498(4-aminomethyl)phenyl) methanol with isopropenyl acetate in acetonitrile containing DBU in the absence and presence of CO2.

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Reversible systems such as silylamines are neutral amines that can react reversibly with CO2 to form the corresponding ammonium carbamate ionic pair. The ionic-to-neutral ‘switch’ capability provides an advantageous means for efficient synthesis and facile deposition of nanoparticles onto a solid support. Herein, we first illustrate the surface active/non-surface active duality of the silylamine systems with the reversible solubilization-precipitation of methyl orange from a hexane solution of the 3-(aminopropyl)tripropylsilane (TPSA) system (0·275 M). The authors then demonstrate the application of this system to the controlled reduction of an ionic gold salt to yield gold nanoparticles using two reversible silylamine systems: TPSA and 3-(aminopropyl)trihexylsilane (THSA). The post-synthesis deposition of the THSA-stabilized gold nanoparticles from solution onto a support using the surface active/non-surface active duality of these systems was also demonstrated.

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