Adsorption of hydrogen sulfide by MOFs loaded with polyethyleneimine (PEI)

The development of coal resources is currently focused on the clean and efficient use of coal. Coal processing and use generates sulfides, primarily hydrogen sulfide (H₂S), which has a severe impact on production and environment. Adsorption desulfurization has become a popular desulfurization process in recent years because of its high desulfurization effectiveness, high precision, and ease of operation. With their large specific surface area and porosity, ease of modification and functionalization, the metal-organic frameworks(MOFs) have great potential in the field of gas adsorption. The introduction of polyethyleneimine (PEI), a polymer containing both primary, secondary and tertiary amines, has a strong affinity for H₂S and undergoes reversible chemical reactions, and the introduction of PEI into MOFs is expected to further enhance the H₂S adsorption performance. To this end, the PEI-loaded MIL-101(Cr), UiO-66, MOF-801, and ZIF-8 adsorbents were prepared by the impregnation method. The effect of carrier type and PEI loading on the H₂S adsorption performance was investigated, and the recyclability of the adsorbents was examined. The results showed that the adsorption capacity of all carriers increased after PEI loading, with ZIF-8 increasing the most, which was attributed to the large specific surface area and pore volume of the ZIF-8 carrier itself, the maintenance of the crystal structure after loading, and the interaction between PEI and ZIF-8. The rest of the MOFs showed an unsatisfactory adsorption capacity after PEI loading due to their small specific surface area and pore volume or structural damage after PEI loading. The loading of PEI affected the pore structure and skeleton stability of ZIF-8. The highest ZIF-8 breakthrough capacity after 50% PEI loading was 56.3 mg/g, which is 55 times higher than the carrier itself. Regeneration cycling experiments showed that ZIF-8 loaded with PEI could only partially regenerate, that the adsorbent with low loadings had a better adsorption cycling performance than those with high loadings, and that the introduction of PEI made ZIF-8 more susceptible to the attack of H₂S to form ZnS.