Modification Of Metal Organic Frameworks(MOF-199) For Sulfur Removal At Room Temperature

Sulfides produced during the use of fossil fuels can corrode pipeline equipment,poison downstream catalysts,pollute the environment and endanger human health.As the country pays more and more attention to environmental pollution problems,the search for more effective desulfurization methods has attracted people's attention.The periodic network Metal-organic frameworks?MOFs?made up of organic linkers bonded with metal ions,which have advantages of high specific surface area,diverse structure and easy functionalization,are a kind of desulfurization material warmly welcomed by scientists in recent years.However,MOFs have the disadvantage of low desulfurization capacity in the removal of small molecular sulfides such as hydrogen sulfide.And modification of MOFs to improve their desulfurization performance is the focus of current research.This paper mainly studies from the following aspects:1.Screening suitable MOF as the modified base material is studied.Firstly,UIO-66?Zr?and MIL-53?Al?are prepared by hydrothermal synthesis method,and their removal performances of H₂S are evaluated by fixed bed experiment.At the same time,the desulfurization mechanisms of two kinds of MOFs are analyzed combinding with DFT calculation method.The results show that UIO-66?Zr?and MIL-53?Al?hardly adsorb H₂S due to the weak interactions?OH...S?and fewer adsorption sites between H₂S and the MOFs.Compared with the desulfurization performance of various metal organic framework materials,it is considered that MOF-199 is an ideal modified base material.2.Modification of MOF-199 by benzoic acid?BA?is researched.It is found that,adding a certain amount of BA to MOF-199 can accelerate the nucleation of MOF-199 and form small and irregulation MOFs crystallization.It makes the Cu²⁺of MOF-199 convert to Cu⁺ions due to the lack of linkage of the carboxylate oxygen atoms after BA added.As the amount of BA added increases,a loss of copper metal center occurs,resulting in an increase in the mesoporous volume of MOF-199 at 20-50 nm.Fixed bed experiments show that the removal performances of H₂S and CH₃SCH₃ are improved by BA modification.And BA-MOF-199 has good regeneration performance for CH₃SCH₃.The increase of unsaturated metal sites in BA-MOF-199 and the increase in sulfide diffusion rate are the main reasons for the increase in sulfur capacity of BA-MOF-199.3.MOF-199 is modified by series of organic amines.The physical and chemical properties of MOF-199 before and after modification are analyzed by means of XRD,SEM,XPS and N₂ adsorption-desorption and so on.Grafting of primary amine monoethanolamine?MEA?and secondary amine diethanolamine?DEA?into MOF-199 can destroy the structure of MOF-199 due to strong interaction between them and makes the low sulfur capacities for respectively2.65%and 1.87%.The structure of MOF-199 can be maintained by the modification of moderate tertiary amine triethanolamine?TEA?due to steric hindrance.The H₂S working capacity of the TEA functionalized MOF-199 is up to 8.78%,increase by 65%of MOF-199.The DFT calculation reveals that the binding energies of H₂S adsorption on the TEA/MOF-199 are larger than that H₂S on purified MOF-199,which is considered to contribute to the improved adsorption.The strong interaction between hydroxyl of loaded TEA and H₂S improves the binding energies of H₂S on the TEA/MOF-199.