Mesoporous Multiproton Ionic Liquid Hybrid Adsorbents for Facilitating NH3 Separation

Abstract

Ionic liquids (ILs), as promising candidates for ammonia (NH3) separation and recovery, have attracted extensive attention due to their extremely low pressures, high gas affinity, and adjustable structures. However, the development of new absorbents or adsorbents for highly efficient, fast, and reversible separation is still a great challenge. In this work, multiproton ILs (MPILs) by simultaneously introducing two or more −H, −OH, or −SO3H sites into the cations were designed to enhance NH3 uptake, and the MPIL N,N,N′,N′-tetrakis (2-hydroxyethyl)ethylenediamine trifluoromethane sulfonate ([EdteH6][TfO]2) with four −OH and two −H sites exhibited a superhigh capacity of 5.08 mol NH3·(mol IL)−1 at 40 °C and 1 bar. To solve the slow gas–liquid mass transfer due to the high viscosity of MPILs, the designed MPILs were highly dispersed onto the molecular sieve HZSM-5 with abundant pore structures to prepare a series of porous MPIL-based hybrid adsorbents for NH3 adsorption. The highest capacity of 140.42 mg NH3·(g adsorbent)−1 at 30 °C and 1 bar was achieved by 60 wt % [EdteH6][TfO]2@HZSM-5-60 (HZ60) due to multiple hydrogen bonding and mesopore effects, which is superior to all of the nonmetal IL-based adsorbents reported to date. Meanwhile, the 60 wt % [EdteH6][TfO]2@HZ60 also exhibited high NH3/CO2 and NH3/N2 selectivities, which are almost 16 and 14 times greater than that of pure HZ60, respectively, along with excellent reversibility. This work provides a feasible way to design novel porous IL-based adsorbents for gas separation and recovery.