Natural gas is a naturally occurring hydrocarbon gas mixture consisting primarily of methane, but commonly including varying amounts of other higher alkanes, and sometimes a small percentage of carbon dioxide, nitrogen, hydrogen sulfide, or helium. There are so many ways to efficency increase the production of LNG. but the process used to upgrade natural gas, biogas and refinery-off-gas directly influences the cost of producing the fuel and often requires complex separation strategies and operational systems to remove contaminants such as hydrogen sulfide (H2S) and carbon dioxide (CO2). Here we report a fluorinated metal–organic framework (MOF), AlFFIVE-1-Ni, that allows simultaneous and equally selective removal of CO2 and H2S from CH4-rich streams in a single adsorption step. The simultaneous removal is possible for a wide range of H2S and CO2 compositions and concentrations of the gas feed. Pure component and mixed gas adsorption, single-crystal X-ray diffraction and molecular simulation studies were carried out to elucidate the mechanism governing the simultaneous adsorption of H2S and CO2. The results suggest that concurrent removal of CO2 and H2S is achieved via the integrated favourable sites for H2S and CO2 adsorption in a confined pore system. This approach offers the prospect of simplifying the complex schemes for removal of acid gases.
DFT-geometry optimized pure and binary gas loaded structures a,b, Views of CO2-loaded AlFFIVE-1-Ni with optimized position of CO2 in the structure. Yellow polyhedra represent AlF5²⁻ pillars, whereas other atoms follow the CPK colouring scheme. c,d, Views of H2S-loaded AlFFIVE-1-Ni structure with optimized position of H2S. e,f, The co-adsorbed CO2-H2S-loaded AlFFIVE-1-Ni with their respective optimized positons.
MOF adsorbents with the ability to simultaneously remove H2S and CO2 from gas mixtures containing CO2, H2S and CH4 for a wide range of temperatures, concentrations and compositions. The ability to simul-taneously remove two acid gases with different physical properties (CO2 and H2S) is a distinctive property of AlFFIVE-1-Ni adsorbent. The MOFs presented in our study can provide a very simple alter-native solution to existing complex and costly technologies used for the cyclic removal of acid gases (H2S, CO2) at different com-positions. This study further highlights the uniqueness of MOF adsorbents, where their intrinsic properties and functionalities can be fine tuned to address a given application. Work is in progress to structure and shape these fluorinated MOFs, and then explore and test them for NG upgrading in miniaturized pressure swing adsorption (PSA) and pressure–temperature swing adsorption (PTSA) systems.
Source : Youssef Belmabkhout, Prashant M. Bhatt
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