Adsorption And Diffusion Properties Of Porous Materials:Case Studies

Phenomena of adsorption and diffusion in porous materials have not only attracted great attention in science, but also have been widely applied in industry. This MSc research has been focused on adsorption and diffusion models. The applications of generalized Maxwell-Stefan (GMS) in the field of modeling multi-component adsorption and diffusion in porous materials are presented. The synthesis methods to prepare silicalite-1membranes and their application in the separation of alkane isomers are also reviewed in detail. The desorption curves of benzene in FDU-16and MFI-type zeolite crystals were measured by the ZLC technique and fitted by different models to extract their diffusion properties. The main results consist of four parts as follows:1) The applications of generalized Maxwell-Stefan (GMS) in modeling multi-component adsorption and diffusion in porous materials are presented. The emphasis is placed on the proper handling of the cross terms and the proper selecting of multi-component adsorption models. If the experimental results confirm that both ideal adsorbed solution theory (IAST) and extended Langmuir model cannot describe multi-component adsorption in porous materials, a new adsorption model must be proposed in order to interpret the multi-component diffusion mechanisms of porous materials correctly.2) Three synthesis methods for preparing silicalite-1membrane, i.e., in-situ hydrothermal synthesis, secondary growth, and template-free methods, are comprehensively reviewed. The template-free method takes advantage over the in-situ hydrothermal synthesis and secondary growth methods, because the organic template-free during the synthesis can avoid the crucial calcination, minimizing the risk of membrane cracks. Additionally, the applications of silicalite-1membranes in the separation of alkane isomers are reviewed. The results show that the separation properties are controlled by both adsorption and diffusion properties of alkane isomers in silicalite-1.3) Mesoporous carbon FDU-16was synthesized by an organic-organic self-assembly method, and the synthesized sample was characterized by XRD, SEM, TEM, and N2-adsorption-desorption techniques in detail. For the first time, a ZLC technique was applied to the investigation on the intracrystalline diffusion of benzene as probe in the synthesized FDU-16crystals. The results show that the synthesized FDU-16possesses micropores and mesopores simultaneously while its microporosity is dominant. Although FDU-16contains some mesoporosity, the mass-transfer limitations of benzene in FDU-16are mainly in its diffusion in the micropores, resulting in low diffusivities and a high activation energy for diffusion.4) Three MFI-type zeolites (Fe-ZSM-5, H-ZSM-5, and silicalite-1) were characterized by XRD, N2adsorption-desorption, SEM techniques and ICP-AES analysis. The characterization results show that the synthesized zeolites are of MFI-type with uniform crystal size. And then, the desorption curves of benzene in MFI-type zeolites were measured by the ZLC technique and fitted by the middle-range method to extract the diffusion properties of benzene in MFI-type zeolite crystals. The results show that the presence of extra-framework H+in H-ZSM-5and the Fe species in Fe-ZSM-5channels can slow down the diffusion of benzene while the Fe species more significantly limit the diffusion of benzene in Fe-ZSM-5.