Regulated Threshold Pressure of Reversibly Sigmoidal NH₃ Absorption Isotherm with Ionic Liquids

Abstract

In this work, flexible hydrogen-bonded frameworks composed of amino pyridinium-based protic ionic liquids (ILs) marked as [X-PyH]­[Tf2N] were designed as NH3 absorption agents. Interestingly, NH3 absorption isotherm of these ILs present sigmoidal absorption isotherm (S mode), and the threshold pressure (TP) decreases from 75 to 6 mbar with the tunable of hydrogen bonded frameworks by varying the substituted group X. Combined with XRD characterizations, Fourier transform infrared and 1H NMR spectroscopies, thermometric analyses, and theory calculations, it indicates NH3 fixed by these ILs via acid–base interaction as well as hydrogen bonding based on the activation of sites through the fracture of the hydrogen-bonded frameworks, which would reform along with heat release when NH3 desorption. Therefore, S mode NH3 absorption with [3NH2-PyH]­[Tf2N] presents low TP of 6 mbar (6000 ppm) at 30 °C, and its NH3 capacity increases sharply and followed by a continuous increase to 3.85 mol/mol IL (175 mg/g IL) at 1.0 bar, which is higher than that of the reported ILs. The fixed NH3 could be desorbed completely in vacuum at 80 °C and 1 mbar. [3NH2-PyH]­[Tf2N] maintained its high capacity within 20 time recycles. The sigmoidal NH3 absorption would be considered as one of the potential approaches for its simultaneous efficient absorption and energy-saving separation at low concentrations.

A Mini-Review on NH3 Separation Technologies: Recent Advances and Future Directions

“…Qiu et al further demonstrated that the threshold pressure of sigmoidal NH 3 absorption can be much reduced through tuning the chemical structures of protonated ILs, which is very useful for the absorption of NH 3 at low pressure. 34 Hydroxyl groups were previously introduced into the chemical structures of ILs to improve the physical absorption of NH 3 , because they enable a hydrogen-bond interaction with NH 3 . Cai et al designed a series of Li-triethylene glycol (TEG) chelated ILs with a crown-ether-like cation and different anions for NH 3 absorption.…”

“…Thus, the capacities of NH 3 absorption were improved, and meanwhile the energy consumption of NH 3 desorption was decreased. Qiu et al further demonstrated that the threshold pressure of sigmoidal NH 3 absorption can be much reduced through tuning the chemical structures of protonated ILs, which is very useful for the absorption of NH 3 at low pressure …”

Role of Structure in the Ammonia Uptake of Porous Polyionic Liquids

“…In the past two decades, protic ionic liquids (ILs), − ILs substituted with the hydrogen donor, , and ILs with the metallic anion were developed for efficient and reversible absorption of NH 3 . Deep eutectic solvents mixed with hydrogen-bond acceptors and various hydrogen-bond donors − have been proposed as very promising NH 3 absorbents through Lewis acid–base interaction and hydrogen-bonding interaction by taking advantage of the essence of ammonia as a Lewis base and a hydrogen acceptor .…”

Room-temperature conversion of CO2 into quinazoline-2,4(1H,3H)-dione using deep eutectic solvents at atmospheric pressure with high efficiency

“…18 Liu et al found that protic ILs could serve as efficient catalysts for the synthesis of quinazoline-2,4(1 H ,3 H )-dione with 97% yield at room temperature and atmospheric pressure. 15 Beside CO 2 capture and conversion, ILs could also be favourable media for biomass utilization, 26 SO 2 uptake, 27 NO x absorption, 28 NH 3 separation 8,29–31 and lithium-ion batteries recovery. 32…”