Development of High‐Capacity and Water‐Lean CO₂ Absorbents by a Concise Molecular Design Strategy through Viscosity Control

Abstract

The exponentially increasing viscosity of water‐lean CO2 absorbents during carbon capture processes is a critical problem for practical application, owing to its strong correlation with systems’ mass transfer properties, as well as convenience of transportation. In this work, a concise strategy based on structure–viscosity relationships is proposed and applied to construct a series of functionalized ethylenediamines as single‐component absorbents for post‐combustion CO2 capture. These nonaqueous absorbents have outstanding viscosities (50–200 cP, 25 °C) at their maximal CO2 capacities (up to 22 wt % or 4.92 mol kg−1, 1 bar), and are readily regenerated at low temperatures (50–80 °C) under ambient pressure. Additional capture of CO2 through physisorption could also be achieved by operating at high pressures. The CO2 capture and release process is systematically investigated by means of 13C NMR spectroscopy, differential scanning calorimetry (DSC), in situ FTIR analysis, and density functional theory (DFT) calculations, which could provide sufficient spectroscopic details to reveal the ease of reversibility and enable rational interpretation of the absorption mechanism.

Molecular‐Level Overhaul of γ‐Aminopropyl Aminosilicone/Triethylene Glycol Post‐Combustion CO2‐Capture Solvents

“…We have previously reported that tuning the speciation and hydrogen‐bond orientation can be used as critical molecular descriptor to decrease the viscosity of water‐lean solvents . Other groups have also derived new less viscous formulations based on these principles, showing that the viscosity of single‐component water‐lean solvents can be kept low by simple chemical modifications . The GAP‐1/TEG system differs from single‐component formulations in that it uses a cosolvent, although we hypothesize that the principles that govern viscosity are the same.…”

“…[12] Other groups have also derived new less viscous formulations based on these principles, showing that the viscosity of single-component water-lean solvents can be kept low by simple chemical modifications. [13] The GAP-1/TEG system differs from single-component formulations in that it uses a co-solvent, though we hypothesized that the principles that govern viscosity are the same.…”

Diffusivity in Novel Diamine-Based Water-Lean Absorbent Systems for CO2 Capture Applications

“…30 A viscosity of 124.0 mPa•S −1 was obtained for an N,N′-dimethyl-N-(2methoxyethyl) ethylenediamine (MeO-DMEDA)-based nonaqueous absorbent at its maximum CO 2 loading (0.7 mole CO 2 •mole amine −1 ). 31 While it is still high compared to that of aqueous MEA 32 (2.7 mPa•S −1 with 0.5 mole CO 2 •mole amine −1 at 40.0 °C), this is a substantial improvement for these water-lean absorbents and positions them for further investigations.…”

“…It is found that the viscosity of 1-alkyl-3-methylimidazolium tricyanomethanide ionic liquids ([C n mim]­[TCM], n = 2, 4, 6, 7, and 8) surprisingly decreased upon absorption of CO 2 , leading to an enhanced diffusion coefficient, which shows significant promise for utilization of this phenomena in industrial applications . A viscosity of 124.0 mPa·S –1 was obtained for an N , N′ -dimethyl- N -(2-methoxyethyl) ethylenediamine (MeO-DMEDA)-based non-aqueous absorbent at its maximum CO 2 loading (0.7 mole CO 2 ·mole amine –1 ) . While it is still high compared to that of aqueous MEA (2.7 mPa·S –1 with 0.5 mole CO 2 ·mole amine –1 at 40.0 °C), this is a substantial improvement for these water-lean absorbents and positions them for further investigations.…”

Alkoxy-Functionalized Amines as Single-Component Water-Lean CO2 Absorbents with High Efficiency: The Benefit of Stabilized Carbamic Acid

“…In our continuous efforts to develop new concepts as well as efficient strategies for CO 2 capture and further transformation, − we envision that the viscosity of several traditional aliphatic amines at the CO 2 -saturated state could be significantly reduced though careful alkoxy functionalization. , The alkoxy arm embedded within the amine structure could create more free volume through its high conformational flexibility, thereby greatly enhance the flowability, and would ultimately intensify the interior mass transfer behavior to increase CO 2 capacity and thermoreversibility. , Ether-functionalized ionic liquids has also been separately studied for CO 2 /SO 2 capture through chemi- and/or physisorption. − Meanwhile, carbamic acid is considered to be a feasible form of sequestrated CO 2 in the amine scrubbing process due to the full utilization of the nitrogen moiety (1:1 stoichiometry between CO 2 and nitrogen) and its relatively easy reversal compared with that of ammonium carbamate. ,, Furthermore, intramolecular hydrogen bonding is preferable if carbamic acid as an uncharged species dominates within the chemisorption system after CO 2 uptake, thus leading to lower operating viscosity than in the intermolecular hydrogen bonding scenarios . Notably, the alkoxy chain has been proved by recent reports to be a viable hydrogen bond acceptor that could bind the acidic proton to form multiple complexation. , We then propose a simple structural modification method for aliphatic primary amines that involves fixation of an appropriate alkoxy substituent to such a cheap and versatile industrial commodity, aiming to acquire reduced operating viscosity that enables smooth processing at the water-lean status under industrially relevant conditions and, in the meantime, increase capture capacity via stabilization of the in situ formed carbamic acid through intramolecular hydrogen bonding.…”