Metal Organic Frameworks(MOFs)/Carbon Materials Compounds For Sulfur Removal At Ambient Temperature

Natural gas contains a certain amount of sulfide,not only poisoning catalyst used in the technology,once burned,they exhaust the atmosphere,but also causing serious pollution to the environment.Therefore,it must be removed.One of the most competitive ways for desulfurization has been mainly addressed via adsorption due to its simple operation,high desulfurization precision and mild experimental conditions.Metal organic frameworks(MOFs)are stereo crystalline structure formed by self-assembly of organic ligands and transition metal ions through Coordination bonds.Compared with the traditional porous materials,MOFs has the characteristics of large specific surface area,porosity,structural diversity and adjustable pore size,which has been used in gas storage,separation and catalysis.Nevertheless,there are some weak points that greatly hinder the full potential of MOFs.The low density of atoms and fully open pore space in MOFs result in weak dispersive reactions that may decrease the retention forces for small adsorbate molecules.In order to circumvent the above-mentioned challenges,MOFs should be modified to improve its physical and chemical properties.In this paper,MOF-199 was modified by incorporating activated carbon(AC)or graphite oxide(GO)during its synthesis under hydrothermal conditions to improve its performance in the removal of hydrogen sulfide(H2S),dimethyl sulfide(CH3SCH3)and ethyl mercaptan(C2H5SH).The dynamic adsorption properties of the composites MAC and MGO for hydrogen sulfide,methyl sulfide and ethyl mercaptan were evaluated on a fixed bed.A variety of different characterization techniques including X-ray diffraction(XRD),Fourier transform infrared(FT-IR)spectroscopy,nitrogen adsorption/desorption isotherms,scanning electron microscopy(SEM),pyridine adsorption infrared spectroscopy(Py-IR),thermogravimetric-mass spectroscopy(TG-MS)and X-ray photoelectron spectroscopy(XPS)were used to analyze the fresh and exhausted composites.The morphology of the composite MAC is similar to that of the MOF-199,but exhibits a more ordered crystal structure,a higher specific surface area and a smaller pore size.Py-IR characterization results indicate an increase in the unsaturated metal sites of the MAC.Compared with MOF-199,the morphology of the composite MGO changed,the crystal structure was more ordered and the specific surface area increased.The performance of MAC and MGO composites were evaluated at ambient temperature in a fixed bed.The results showed that the adsorption of three kinds of sulfides was higher than that of MOF-199,which was related to the improvement of the specific surface area and porosity of the MAC.It is helpful to improve the physical adsorption properties of the composites.In addition,the increase of unsaturated metal centers in MAC also contributes to the adsorption of sulfides.It was found that the adsorption temperature would affect the adsorption behavior.The adsorption performance of composite MAC is better than that of MGO,because the former has higher specific surface area and pore volume than that of the latter.The decrease of the pore size and the increase of the unsaturated metal sites in MAC are also beneficial to the improvement of desulfurization performance.Interactions between the unsaturated copper sites in MOFs and the sulfur compounds differed because of the steric effect which was caused by the different properties of the sulfides.Dimethyl sulfide molecules with methyl groups on both ends have the largest diameter,which generated the steric hindrance on the MOFs.It can not be combined with MOFs metal center,leading to a weak coordination effect.A strong interaction was apparent during adsorption of ethyl mercaptan and hydrogen sulfide,which resulted in the formation of CuS.The relatively weak interaction with dimethyl sulfide originated from a weak coordination effect,which lead to easy recycling and recovery of MOF-199.