Diffusivities Of Benzene In Mfi Zeolites And Metal-Organic Framework Cu-BTC Determined By The ZLC Technique

Zeolites, due to their regularly shaped channels, high specific surface area, and shape-selective catalysis and adsorption, are widely used in the fields of petroleum, fine chemicals, and pharmaceutical industries. In shape-selective catalysis and adsorption, the intracrystalline diffusion of target molecules within zeolites is a key process. In addition, prior to investigating the intrinsic kinetics of heterogeneous reactions as well as to designing reactors, an intracrystalline diffusivity should be determined. Therefore, the intracrystalline diffusivity is considered as an important parameter in studying mass transfer processes and kinetics in zeolites.The measurement of intracrystalline diffusivity is a very challenging subject. Up to now, many different techniques have been developed to measure intracrystalline diffusivities in zeolites. Among them, the ZLC (zero-length column) technique, a kind of macroscopic technique, has been widely applied in determining zeolite diffusivities.In this thesis, the intracrystalline diffusivities of benzene in MFI-type zeolites and the metal-organic framework Cu-BTC were determined using the ZLC technique. The main results are summarized as follows:1) Fe-ZSM-5, H-ZSM-5, and silicalite-1were hydrothermally synthesized using tetrapropyl ammonium bromide (TPABr) as template, sodium silicate as silicon source, Al2(SO4)3as aluminum source, and Fe(NO3)3as iron source. The synthesized samples were characterized by XRD, N2adsorption-desorption, and SEM techniques and ICP-AES analysis. The characterization results show that the synthesized zeolites are of MFI-type with uniform crystal size. The diffusion processes of benzene in the three zeolites were investigated using the ZLC technique and the diffusivities and activated energies were determined. The results show that the presence of the extra-framework H+and Fe species can affect the diffusion limitation and the Fe species can more significantly limit the diffusion of benzene in FeZSM-5.2) The metal-organic framework Cu-BTC was synthesized by a hydrothermal method using H3BTC and Cu(NO3)2-3H2O as reactants and the mixture of DMF, alcohol, and water as solvent. The synthesized Cu-BTC was characterized by XRD, N2adsorption-desorption, and SEM techniques. The characterization results confirm that the sample has a high crystallinity and a typical cubic crystalline structure and their morphology and crystal size are uniform. The diffusivities of benzene in Cu-BTC were determined using the ZLC technique and the results show that there is a less diffusion limitation for benzene in Cu-BTC, compared to that in MFI-type zeolite.