(462h) Efficient and Reversible Separation of Ammonia with Ionic Liquid-Based Materials

Shaojuan Zeng ^a, Dawei Shang ^a, Haifeng Dong ^a,Xiangping Zhang ^a,*, Suojiang Zhang ^a,*

^a Institute of Process Engineering, Chinese Academy of Sciences, 100190, Beijing, China

*Corresponding author: xpzhang@ipe.ac.cn; sjzhang@ipe.ac.cn

As one typical alkaline and poisonous gas, NH₃ emission inevitably causes serious air pollution problems, such as fog and haze, which has raised extensive attentions worldwide. The commercial methods, like water scrubbing and acid scrubbing, can purify the NH₃-containing gas mixtures, but they substantially transfer the NH₃ pollute from gas phase to liquid or solid phase, which doesnot mean total elimination¹. Therefore, how to efficiently separate NH₃ and simultaneously recover high purity of NH₃ easily is the most fundamental way but also a great challenge. The emerging of Ionic liquids (ILs) provides a promising way to efficient separation of NH₃ owing to their peculiar properties, like nonvolatility, designability and high stability².

In this work, the interaction between NH₃ and ILs and the structure-property relationship was firstly revealed by combining simulation calculations and experimental characterizations. The results indicated that the H-bond and cations play an important role in NH₃ absorption, and the stronger H-bond means higher NH₃ capacity. Meanwhile, the introduction of the metal center into ILs greatly improves NH₃ absorption through chemical complexion. Based on these results, a series of functionalized Lewis-acid ILs with the metal center on anions and Brønsted-acid ILs with the acidic H groups on cations were designed for efficient and reversible absorption of NH₃, respectively. For example, the Brønsted-acid IL [Bim][Tf₂N] can absorb 2.69 molNH₃·molIL^-1 at 40℃ and 0.10 MPa through the strong hydrogen bonding between NH₃ and cations³. The cobalt ILs [C_nmim]₂[Co(NCS)₄] not only have exceptional NH₃ capacity and high NH₃/CO₂ selectivity, but also excellent recyclability. The maximal NH₃ capacity is up to 6.09 molNH₃·molIL^-1 at 30℃ and 0.10 MPa, which is over 30 times higher than the conventional ILs⁴. On the other hand, considering the higher viscosity of these ILs, the ILs and porous materials were combined to form new adsorbents for NH₃ separation. Compared with pure silica gel, NH₃ adsorption capacity of IL-based materials increases by 70-100%, and the adsorption and desorption process is also very fast. These findings will provide significant theoretical basis to develop efficient and reversible IL-based technologies for NH₃separation.

1. J. W. Erisman, A. Bleeker, J. Galloway and M. S. Sutton, Environ Pollut, 2007, 150, 140-149.
2. S. J. Zeng, X. P. Zhang, L. Bai, X. C. Zhang, H. Wang, J. J. Wang, D. Bao, M. D. Li, X. Y. Liu and S. J. Zhang, Chem Rev, 2017, 117, 9625-9673.
3. D. W. Shang, X. P. Zhang, S. J. Zeng, K. Jiang, H. S. Gao, H. F. Dong, Q. Y. Yang and S. J. Zhang, Green Chem, 2017, 19, 937-945.
4. S. J. Zeng, L. Liu, D. W. Shang, J. P. Feng, H. F. Dong, Q. X. Xu, X. P. Zhang and S. J. Zhang, Green Chem, 2018, DOI: 10.1039/c8gc00215k.