炭材料复合金属有机框架化合物（MOFs）常温脱硫性能研究

发布时间：2018-05-19 15:09

本文选题：MOFs + 改性　；参考：《太原理工大学》2017年硕士论文

【摘要】：天然气中含有一定量硫化物,不仅对其工艺使用中的催化剂造成毒害,一旦燃烧排放入大气,还会对环境造成严重污染。因此,必须将硫化物脱除。其中,吸附脱硫因其具有操作简便、工艺条件温和等优点成为一项非常有竞争力的脱硫技术。金属有机框架化合物(MOFs)是由含氧、氮的有机配体和过渡金属离子通过配位键自组装形成的微孔网络结构晶体。与传统的多孔材料相比,MOFs具有大的比表面积和孔隙,结构多样性和孔尺寸可调的特点,在气体存储、分离、催化等方面都显示了巨大的应用前景。同时,MOFs作为吸附脱硫剂在脱硫领域也表现出了优于活性炭和分子筛的良好性能,引起了研究者的极大关注。然而,MOFs也存在一些问题,其大的比表面积和发达的孔隙结构说明材料的色散力较弱,当吸附小分子时,吸附质容易从骨架逸出。因此,为了提高MOFs吸附性能,将MOFs进行适当改性。本文采用活性炭(AC)和氧化石墨(GO)对MOF-199进行改性,通过水热法将获得改性后产物,即复合材料MAC和MGO。采用固定床评价其对硫化氢、甲硫醚以及乙硫醇气体的动态吸附行为。运用XRD、FTIR、氮气吸附-脱附、Py-IR、SEM、TG-MS和XPS表征硫化前后样品,并将样品结构和脱硫性能进行关联。与MOF-199相比,复合材料MAC形貌没有明显改变,但晶体结构更为有序、比表面积提高、孔径减小以及金属不饱和位增多。而MOF-199经与石墨烯复合后形貌发生了明显的变化,形成的是方形薄片以一种有组织的方式叠在一起类似于层状结构的一种新材料,并且比表面积提高。固定床实验显示,与MOF-199相比,MAC和MGO对三种硫化物吸附效果有显著提高。这是因为AC可能会包裹进MGO-199空腔,引起孔径减少和比表面积提高,GO表面的含氧官能团和MOF-199的金属中心结合导致形成额外的孔,这些性质的提高都有利于提高材料的物理吸附性能。此外,MAC不饱和金属中心的增加也对吸附硫化物做出贡献。实验考察吸附温度对MAC脱除三种硫化物的影响,发现吸附温度会影响硫化物的吸附,研究还发现,水汽对于MAC脱除硫化氢有促进作用。制备的复合材料MAC的吸附性能优于MGO,主要是因为前者的比表面积和孔容比后者高,MAC孔径的减小和不饱和金属位点的增加也有利于脱硫效果的提高。复合材料对三种硫化物的吸附机理不同,这是由于三种硫化物在MOFs结构中产生的空间位阻效应不同。硫化氢分子直径最小,可与金属中心直接接触并发生化学反应,生成CuS。乙硫醇虽然分子直径较大,但是分子一端为-SH,也能与金属中心产生不可逆吸附反应。甲硫醚分子直径最大且两端连有甲基,在MOFs骨架中产生的空间位阻最大,因此与金属中心不发生反应,而以弱配位形式吸附。而正是由于甲硫醚以弱作用力与复合材料结合,产生的吸附是可逆的。研究表明,MAC和MGO经3次循环后,其穿透硫容仍可达到初始硫容94%,是理想的硫醚吸附剂。
[Abstract]:Natural gas contains a certain amount of sulfides, which not only poisons the catalysts used in the process, but also causes serious pollution to the environment once the combustion is discharged into the atmosphere. Sulphides must therefore be removed. Among them, adsorption desulfurization has become a very competitive desulfurization technology because of its advantages of simple operation and mild process conditions. Organometallic frame compound (MOF) is a microporous network crystal composed of organic ligands containing oxygen, nitrogen and transition metal ions, which are self-assembled by coordination bonds. Compared with the traditional porous materials, MOFs have the characteristics of large specific surface area and pore size, structural diversity and adjustable pore size. They have shown great application prospects in gas storage, separation, catalysis and so on. At the same time, as adsorptive desulfurizers, MOFs also show better performance than activated carbon and molecular sieve in the field of desulfurization, which has attracted great attention of researchers. However, there are some problems in MOFs. Their large specific surface area and developed pore structure indicate that the dispersive force of the material is weak, and when adsorbing small molecules, the adsorbate is easy to escape from the skeleton. Therefore, in order to improve the adsorption properties of MOFs, MOFs was modified appropriately. In this paper, MOF-199 was modified by activated carbon (AC) and graphite oxide (GOO). The modified products, that is, MAC and MGO, were obtained by hydrothermal method. The dynamic adsorption behavior of hydrogen sulfide, methyl sulfide and ethanethiol was evaluated in a fixed bed. The samples before and after vulcanization were characterized by XRDX FTIR, nitrogen adsorption-desorption (Py-IRM) TG-MS and XPS, and the structure and desulfurization properties of the samples were correlated. Compared with MOF-199, the morphology of MAC has no obvious change, but the crystal structure is more orderly, the specific surface area is increased, the pore size is decreased and the unsaturated potential of metal is increased. However, the morphology of MOF-199 was obviously changed after composite with graphene, and the square sheet was stacked together in an organized manner similar to the lamellar structure, and the specific surface area was increased. Fixed-bed experiments showed that the adsorption of sulfides by MOF-199 and MGO was significantly improved. This is because AC may wrap into the MGO-199 cavity, resulting in reduced pore size and increased specific surface area, resulting in the combination of oxygenated functional groups on the go surface and the metal center of MOF-199 to form additional pores. The improvement of these properties is beneficial to the improvement of the physical adsorption properties of the materials. In addition, the increase of unsaturated metal centers also contributes to the adsorption of sulfides. The effect of adsorption temperature on the removal of three sulfides by MAC was investigated. It was found that the adsorption temperature would affect the adsorption of sulfides. It was also found that water vapor could promote the removal of hydrogen sulfide by MAC. The adsorption performance of the composite MAC is better than that of MGO.The main reason is that the reduction of pore size and the increase of unsaturated metal sites in the former are also beneficial to the improvement of desulphurization efficiency. The adsorption mechanism of the three sulfides in the composite is different, which is due to the different steric resistance effect of the three sulfides in the MOFs structure. The molecular diameter of hydrogen sulfide is the smallest, which can be directly contacted with the metal center and react with the metal center to form CuSs. Although the molecular diameter of ethanethiol is large, one end of the molecule is -SH, which can also produce irreversible adsorption reaction with the metal center. The methyl sulfide molecule has the largest diameter and methyl at both ends, which results in the largest steric resistance in the MOFs skeleton, so it does not react with the metal center and is adsorbed in the form of weak coordination. It is precisely because methyl sulfide binds to the composite by weak force that the adsorption is reversible. The results show that after three cycles, the penetrating sulfur capacity of MGO can still reach the initial sulfur capacity of 94. It is an ideal sorbent for sulfides.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O647.33

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