Metal Organic Frameworks (MOFs) For Removal Of Sulfur Compounds

It is necessary to remove sulfur compounds from natural gas, coal gas and coke-oven gas. The sulfur compounds can damage catalyst in fuel cell, cause corrosion and decrease quality of the products. Industrial waste gas and fuel products directly discharged into the atmosphere can cause serious damage to human body health and pollute the environment. As environmental regulations increasingly strict, the depth removal of sulfur compounds from industrial gas source become a research hotspot. Commonly use the hydrogen desulfurization technology to remove sulfur ether, mercaptan and thiophene, which is difficult to get rid of. However, hydrodesulfurization needs high temperature and high pressure meanwhile it will consume large amounts of hydrogen. Removal sulfur compounds at room temperature is target our efforts.Sulfur compounds present in gases are commonly removed by gas-solid absorption technology with activated carbon and molecular sieve at ambient temperature. MOFs are new porous materials with large surface areas and porosity. These properties endow MOFs materials with great potential in gas adsorption, catalysis and photochemistry application. Recent research efforts have considered the application of MOFs materials to methane storage and sulfur removal.Metal-organic frameworks (MOFs) is composed of metal-oxide units joined by organic linkers through strong covalent bonds and is formed in a way of self-assembly with a porous structure framework polymeric organic compound. MOFs are well-known for their large surface area and porosity, controllable pore structure and versatile chemical composition. Which remarkable is metal-center and organic-ligand could provide active sites.IRMOF-3 and IRMOF-8 are porous crystalline materials which based on zinc metal active center and have large specific surface area. It is worth mentioning that there is a free amino group in IRMOF-3. In this thesis mainly discusses desulfurization performance and mechanism of IRMOF-3 and IRMOF-8 adsorbed dimethyl sulfide, ethyl mercaptan and hydrogen sulfide at ambient temperature in fixed bed reactor. IRMOF-3 and IRMOF-8 before and after exposure to sulfur compounds were characterized by means of Fourier infrared (FT-IR), X-ray diffraction (XRD), thermal gravimetric (TG) and X-ray photoelectron spectroscopy (XPS). The results show that IRMOF-3 exhibit the best performance for hydrogen sulfide removal with the highest breakthrough sulfur capacity, followed by ethyl mercaptan and dimethyl sulfide. This is in consistent with the interaction strength between IRMOF-3 and sulfur compounds. In case of dimethyl sulfide and ethyl mercaptan, the interaction comes from the weak interaction between the amino group in the MOFs and the sulfur atom of the adsorbate. This can also be considered as a hydrogen bond complex in which the amino group in the MOFs and the S atom of the sulfur compounds play the role of H-donor and H-acceptor, respectively. In the case of hydrogen sulfide, the interaction with sulfur atom originates from the amino group and zinc site in the MOFs. The former is more like an acid-base interaction, whereas the latter results in new products of ZnS and H2O and serious destruction of the MOFs.IRMOF-8 adsorbing more dimethyl sulfide at lower temperature. However, IRMOF-8 preferred to hydrogen sulfide at 60℃. Physical adsorption plays a dominant role in process of adsorbing organic sulfur compounds (dimethyl sulfide and ethyl mercaptan). Physical adsorption is responsible for the sulfur removal, in case of hydrogen sulfide, chemical adsorption is exist. Hydrogen sulfide interaction with zinc in IRMOF-8 generated ZnS.The specific surface area of IRMOF-8 is smaller than IRMOF-3 and there is not amino in IRMOF-8. The later is the main reason of the lower adsorption capacity of IRMOF-8.