Preferential SO_x Adsorption in Mg-MOF-74 from a Humid Acid Gas Stream

Abstract

The preferential adsorption of SO x versus water in Mg-MOF-74 from a humid SO x gas stream has been investigated via materials studies and nuclear magnetic resonance (NMR). Mg-MOF-74 has been synthesized and subsequently loaded simultaneously with water vapor and SO x (62–96 ppm) in an adsorption chamber at room temperature over a time period of 4 days with a sample taken every 24 h. Each sample was analyzed by powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy, thermogravimetric analysis (TGA)–mass spectrometry, and scanning electron microscopy–energy-dispersive spectroscopy. The metal–organic framework (MOF) showed retained crystallinity and peak intensity in PXRD, and after 2 days, it showed no obvious degradation to the structure. Use of multiple techniques, including TGA, identified 10% by weight of SO x species, specifically H2S and SO2, within the MOF. 1H solid-state NMR shows a substantial reduction of H2O when SO x is present, which is consistent with SO x preferentially binding to the oxophilic metal site of the framework. After 14 weeks aging, the sulfur remains present in the three-dimensional MOF, with only half being desorbed after 23 weeks in air.

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“…Preferential binding, however, is the selective binding of one target gas from a mixture through judicious selection of metal centers and/or linkers. For example, the selective adsorption of SO x from a complex humid SO x stream using Mg-MOF-74 via binding to the Mg cation …”