Aliphatic amine decorating metal–organic framework for durable SO2 capture from flue gas

Abstract

The efficient capture of SO2 using porous adsorbents is of great significance in flue gas desulfurization (FGD) process as the reversible physical adsorption can avoid solvents/water consumption and minimize waste generation. Metal organic frameworks (MOFs) are interesting and promising candidates to sequestrate SO2 in flue gas as their high porosities, regular pore sizes and easy functionalization. However, the coordination bond nature of MOFs makes stably and persistently capture acidic SO2 gas remains a challenge in MOF. Herein, an aliphatic amine decorating strategy was introduced in a MOF (MIL-101(Cr)) with open metal sites for reversible and durable SO2 capture. The successful synthesis of N,N'-dimethylethylenediamine (mmen) decorated MIL-101(Cr) named mmen-MIL-101(Cr), was confirmed by powder X-ray diffraction (PXRD), Fourier transform-infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive spectra (EDS) and nitrogen adsorption–desorption isotherm. Compared with chemisorption of SO2 on open Cr sites in MIL-101(Cr), the SO2 adsorption sites are transferred from Cr to N atom in mmen-MIL-101(Cr), leading to reversible SO2 adsorption and desorption. The dipole–dipole interaction between N atom and S(SO2) atom, combining with hydrogen bonding interaction between O(SO2) and H in mmen can increase the SO2 absorption capacity of mmen-MIL-101(Cr) under low SO2 partial pressure. The SO2 adsorption capacity and cycle stability properties were studied in detail by adsorption isotherm and dynamic breakthrough measurement. An unprecedented high SO2 adsorb capacity (upto 4.27 mmol·g−1) at SO2 partial pressure (0.5 mbar) is achieved in mmen-MIL-101(Cr), which is a great improvement compared to 2.92 mmol·g−1 SO2 adsorption capacity for primordial MIL-101(Cr) under the same condition. Moreover, mmen-MIL-101(Cr) manifests reversible SO2 adsorption–desorption performance while MIL-101(Cr) gradually loses its adsorption capacity during dynamic breakthrough cycles. The high SO2 sorption capacity in low partial pressure and impressive cycle stability of mmen-MIL-101(Cr) demonstrate aliphatic amine decorating strategy is an efficient way to improve MOF’s SO2 capture capability, which also can extend to other porous adsorbents for low concentration FGD process.