Removal Of Sulfur Compounds By Metal Organic Frameworks (MOFs) At Ambient Temperature

Sulfur-containing compounds such as hydrogen sulfide, mercaptans,thioether, and others widely exist in nature gas and coal gas, and they are thechief culprit in pollution of environment, corrosion of equipment and pipelines,and catalyst deactivation. As environmental regulations increasingly strict, theremoval of sulfur compounds from industrial gas source has become an filedbeing intensely researched. Commercial hydrogen sulfide removing techniquescannot reach the requirements due to the low sulfur capacity and precision, aswell as the low utilization. To remove the organic sulfur compounds(mercaptan, thioether, thiophene), hydrodesulfurization is widely used. However,it needs high temperature and high pressure, and it will consume large amountsof hydrogen. Therefore, removal sulfur compounds at ambient conditions istarget our efforts. Adsorption desulfurization is an effective way for finedesulfurization and deep desulfurization. The most applied porous materials areactivated carbon and zeolite.MOFs, is a new kind of crystalline porous material which connect the metaloxide and organic linkers by covalent bonds. MOFs has high surface area andlarge porosity. The properties of unique pores and structural diversity make themeasy to be assembled and designed. What’s more, because of the characters of large specific surface area, porosity and the controllable pores for MetalOrganic Frameworks(MOFs), this material has widely researched for gs storageand purification. As for desulfurization, in recent years, it has been considered asone of the most promising adsorbent.In this paper, MOF-199and MOF-74which own the unsaturatedcoordinatively metal sites has been studied, and they were used for the removalof dimethyl sulfide, ethyl mercaptan, and hydrogen sulfide at ambient conditionsin fixed bed. MOF-199and MOF-74were synthesized by hydrothermal method,and characterization of the samples before and after desulfurization were carriedout by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR),and X-ray photoelectron spectroscopy (XPS). The results show that MOF-199can remove sulfides effectively and the open metal site played an important role.MOF-199was strongly interacted with hydrogen sulfide and ethyl mercaptan,and caused the formation of CuS, release of carboxyl and serious damage of thestructure. The sulfur capacity for dimethyl sulfide removal is the highest8.48%(8.48g sulfur per100g MOF-199). This kind of interaction relativelyweak and can be attributed to the weak coordination effect and electrostaticforce which led to easy recovery of MOF-199by thermal regeneration. As forMOF-74, the structure was damaged after desulfurization, and it result in theformation of ZnS releasing of hydroxyl. The force of the interaction betweenMOF-74and the organic sulfur compounds originate from coordination effectwith different strength. The adsorbed sample for dimethyl sulfide can easily be recovered by thermal regeneration. Whereas, the sample for ethyl mercaptanremoval can’t be regenerated. Based on the studies, it was believed that thedifferent desulfurization behaviors for the three sulfur compounds were resultedfrom the steric effect. The open metal sites in these two MOFs are the mostsignificant factor for sulfur removal. The difference of breakthough sulfurcapacity for MOF-199and MOF-74may be caused by the kind of metal sitesand pore structures.