The capacity of NH3 in PIL [Bim][NTf2] was up to 2.69 mol NH3 per mol IL under ambient conditions.

Cobalt ionic liquids with highly efficient and reversible absorption of NH3 through Lewis acid–base and hydrogen bond interactions were designed.

In this work, three kinds of ether-functionalized pyridinium-based ILs [E n Py]­[NTf2] with low viscosity were designed and synthesized and used for highly selective separation of CO2 from CH4. It was found that the ether groups play an important role on physicochemical properties and CO2/CH4 selectivity in these three ILs. Compared with the nonfunctionalized analogues [C m Py]­[NTf2], the viscosities of [E n Py]­[NTf2] are lower and obviously decrease with the increasing number of ether oxygen atoms. The presence of ether groups on the cation has weak impacts on CO2 solubility of the ILs, but it contributes to a much lower CH4 solubility, which leads to the great increase of CO2/CH4 selectivity using [E n Py]­[NTf2]. Moreover, CO2/CH4 selectivity in all investigated ILs greatly decreases with the increasing temperature due to the weaker temperature dependence of CH4 solubility. In addition, the thermodynamic properties including the Gibbs free energy, enthalpy, and entropy of CO2 and CH4 in these ILs were also obtained, and the CO2 and CH4 dissolution mechanisms were further analyzed. The results demonstrated that the gas–IL interaction plays a dominate role in CH4 solubility in the investigated ILs, but CO2 dissolution in ILs is determined by both the IL–gas interaction and free volume of ILs. This work will offer new insights into designing more competitive ILs for selective separation of CO2 from CH4.

BACKGROUND Ionic liquids have become potential absorbents to treat exhausted gases containing NH3, which threatens the living environment of human beings. RESULTS In this study, 10 kinds of protic and conventional ILs were synthesized and characterized and their densities, viscosities and thermal decomposition temperatures measured. The NH3 solubility in ILs from the vapor liquid equilibrium (VLE) experiments revealed that the chain length of cations had little influence on the NH3 solubility of the protic ILs because of the high NH3 capacities in protic ILs resulting from protic hydrogen atom compared with conventional ILs. The 2‐H atom on the cation influenced the NH3 solubility in both protic and conventional ILs with different trends as the pressure was increased. Considering the effect of anions with the same cation [Bim]+, the order of NH3 solubility in protic ILs was [Bim][NTf2] > [Bim][SCN] > [Bim][NO3]. Dynamic absorption of NH3 in [Eim][NTf2] preliminarily revealed that the absorption was fast under ambient pressure and through 5 cycles of absorption and desorption, the NH3 absorption ability remained stable. CONCLUSIONS The relationship between the NH3 solubility and the structures of both protic and conventional ILs was revealed, indicating the protic ILs as an alternative material for the treatment of NH3‐containing exhaust gases. © 2017 Society of Chemical Industry

No abstract