| Carbon nanofibers (CNFs) have great application potentials in the catalysis field for their novel structural and chemical properties. However, the small dimensions of CNFs inhibite their use as catalyst support directly in the form of powders in chemical reactors. In order to overcome this drawback, CNFs are synthesized on the surface of graphite fibers with catalytical chemical vapour deposition (CCVD) method to realize the immobilization of CNFs. The synthesized CNF/graphite-felt composite combines the properties of CNFs and graphite felt with high porosity, high geometric specific surface area and high BET specific surface area, which is a type of structured catalysts. In the thesis, the structured CNF composite was synthesized using Ni as catalyst and ethane as carbon source. The structural properties of the CNF composite were characterized by means of SEM, N2 adsorption-desorption, mercury porosimetry and so on. Pressure drop of the CNF composite for single gas and liquid phase flow was tested and correlated to the structural properties of the composite. Moreover, the pressure drop and total liquid holdup of the composite for gas-liquid two-phase flow was studied and correlated to the velocity of gas and liquid phases with slit model. The flow behavior of liquid phase in the composite was characterized by the residence time distribution (RTD) measurement, and the liquid flow through the porous CNF layers was simulated with Comsol Multiphysics. Finally, the as-synthesized CNF composite was tested for two applications:one was used directly as catalyst for the decomposition of ammonia to hydrogen, and the other was used as sorbent and coalescencer for the removal of oil from water. The mian results of the work are summarized as follows:(1) The pores in the CNF composite can be divided into two categories including large pores derived from the intertexture of graphite fibers and small pores derived from the intertwist of the grown CNFs which located within the CNF layers. The pressure drop of the composite was derived from the convective flow of the fluid in the large pores, while the fluid in the small pores was stagnant and had no influence on the pressure drop. After the composite was wetted by cyclohexane and dried in air, the CNF layers shrank due to capillary effect, which induced the decrease of fiber diameter and the increase of the volume fraction of large pores, as a result the pressure drop of the composite decreased drastically. The pressure drop of the CNF composite for single-phase flow was described by an extended Ergun equation, which showed excellent prediction to the experimental results.(2) Due to strong hydrophobicity of CNFs, permeability of the CNF composite for liquid is dependent on the surface tension of the flowing liquid. As the surface tension of liquid increased, wettability of the CNF composite decreased, as a result the effective porosity of the composite decreased, and the permeability decreased. On the other hand, the decrease of wettability of the composite resulted in the increase of slip flow of the liquid on the surface of CNFs, which is favorable for the increase of permeability. Under these two conflicting effects, CNF composite showed highest permeability when the surface tension of the liquid is 26.2 mN/m.(3) When gas and liquid flew downward cocurrently through the CNF composite, the pressure drop increased with gas and liquid velocities; the total liquid holdup increased with liquid velocity and decreased with gas velocity; and the static liquid holdup was independent of the velocity of gas and liquid. The pressure drop and total liquid holdup of the composite for two-phase flow could be correlated to the velocity of gas and liquid by the slit model, which showed excellent simulation to the experimental data.(4) Flow behavior of liquid phase in CNF composite was obtained through the fitting of PDE model to the RTD curves. For single liquid phase flow, the model parameters were independent of liquid velocity, but strongly influenced by the loading of CNFs. As CNF loadings increased, the thickness of CNF layers increased, as a result the Peclet number decreased; the fraction of dynamic liquid decreased; and the number of mass transfer units increased. Flow behavior of the liquid was also dependent on the wettability of the CNF composite. When water flowed through the composite, CNFs could not be wetted, as a result, the Peclet number in water was higher; the fraction of dynamic liquid was higher; and the number of mass transfer units was lower than that in cyclohexane. For gas-liquid two-phase flow, Peclet number is independent of the velocity of gas and liquid; the fraction of dynamic liquid increased with liquid velocity and decreased with gas velocity; and the number of mass transfer units increased with gas velocity and decreased with liquid velocity.(5) Flow behavior of liquid in the CNF layers was modeled using Comsol Multiphysics, which was strongly influenced by the permeability of the CNF layers. Mass transfer between liquid in the bulk flow and the liquid in the CNF layers could be enhanced through the convective flow in the CNF layers by increasing the permeability of the CNF layers.(6) The as-synthesized CNF composite was applied as catalyst for the decomposition of ammonia to hydrogen, which exhibited quite high reactivity with high H2 production. Compared with CNF powders, CNF composite showed much lower pressure drop and better catalytical reactivity.(7) The sorption capacity of CNF composite is quite high due to the hydrophobic and oleophilic properties of CNFs. CNF composite showed excellent oil absorption and coalescence efficiency for the dispersed oil. When the CNF loading was 1.09 and the flow rate of oil/water suspersion was 10 mL/min, the oil separation efficiency was as high as 99.2%.
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