Probing Metal-Organic Framework Design for Adsorptive Natural Gas Purification.

Parent and amine-functionalized analogues of metal-organic frameworks (MOFs), UiO-66(Zr), MIL-125(Ti), and MIL-101(Cr), were evaluated for their hydrogen sulfide (HS) adsorption efficacy and post-exposure acid gas stability. Adsorption experiments were conducted through fixed-bed breakthrough studies utilizing multicomponent 1% HS/99% CH and 1% HS/10% CO/89% CH natural gas simulant mixtures. Instability of MIL-101(Cr) materials after HS exposure was discovered through powder X-ray diffraction and porosity measurements following adsorbent pelletization, whereas other materials retained their characteristic properties. Linker-based amine functionalities increased HS breakthrough times and saturation capacities from their parent MOF analogues. Competitive CO adsorption effects were mitigated in mesoporous MIL-101(Cr) and MIL-101-NH(Cr), in comparison to microporous UiO-66(Zr) and MIL-125(Ti) frameworks. This result suggests that the installation of HS binding sites in large-pore MOFs could potentially enhance HS selectivity. In situ Fourier transform infrared measurements in 10% CO and 5000 ppm HS environments suggest that framework hydroxyl and amine moieties serve as HS physisorption sites. Results from this study elucidate design strategies and stability considerations for engineering MOFs in sour gas purification applications.