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Study of multicomponent adsorption equilibrium and kinetics of hydrocarbons on activated carbon

Authors Qiao, Shizhang
Issue Date 2000
Summary Comprehensive theoretical and experimental study of multicomponent adsorption equilibrium and kinetics of hydrocarbons on activated carbon are carried out in this thesis. The multicomponent adsorption isotherm and kinetics models based on micropore size distribution concept are proposed to identify the competitive adsorption and the intraparticle mass transfer process. The models assume the micropore size distribution as the source of surface heterogeneity. The adsorbate-adsorbent interaction energy is related to the pore size by the Lennard-Jones potential relationship and the energy matching of different species on heterogeneous surfaces is related to their own interaction strength with the local micropore by the adsorbate-pore interaction mechanism. The pore size exclusion is considered on both adsorption equilibrium and kinetics models. The local adsorbed phase concentration is calculated from the extended Langmuir equation or ideal adsorbed solution theory (IAST). In the kinetics model, the diffusions of both free and adsorbed species are considered and the chemical potential gradient is used as the driving force for the diffusion of adsorbed species, so the concentration dependence of the surface diffusivity can be explained. By using only information of single component equilibrium and mass transfer, the proposed models can be used to predict the multicomponent adsorption equilibrium and dynamics. In the experimental study, adsorption equilibrium data of pure component on activated carbon were collected by a high accuracy volumetric measurement rig. The binary adsorption equilibrium and all kinetics data were measured using a differential adsorption bed (DAB) rig. The extensive experimental adsorption equilibrium and dynamics data of methane, ethane, propane and carbon dioxide on Ajax or Norit activated carbons at different temperatures and concentration conditions were utilized to validate the proposed models. The results show that the models developed in this study can correctly predict the single and binary component adsorption equilibria and kinetics. In addition, the model parameters and micropore size distribution shape were demonstrated to play significant roles in affecting the model performance. The potential of the kinetics models are further tested by predicting simultaneous desorption and displacement dynamics of ethane and propane. Comparing the prediction results of adsorption kinetics between the micropore size distribution method and the energy distribution method shows that the model based on adsorbate-adsorbent interaction concept is more fundamental and has clear physical significance and provides better prediction for binary desorption kinetics.
Note Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2000
Language English
Format Thesis
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