Modeling of Adsorbers Containing Core-Shell Adsorbents with Various Morphologies by Shrinking Core Model - The Effects of Adsorber Types and Adsorption Kinetics

Modeling of adsorption phenomena was carried out for core-shell adsorbents with spherical, cylindrical, and slab-type morphologies. Numerical solutions of adsorbates in the adsorber could be obtained as a function of time by solving coupled diffusion equations to take account of the inert-core thickness (x'). Transient responses of batch and continuous adsorbers containing core-shell adsorbents were predicted, assuming rectangular or Langmuir-type adsorption isotherms. In batch adsorber, the removal rate of adsorbates increased with increasing Biot number (Bi), and the decaying rate of the adsorbate concentration increased in the order of sphere > cylinder > slab. The equilibrium concentration of adsorbate in batch adsorber decreased with decreasing value of x' due to the increased volume of active shell in the adsorbents. In continuous adsorber with suspended adsorbents, the adsorbate concentration was affected by feed rate and initial concentration of adsorbate, and the breakthrough curve was saturated more slowly by cascade connection. In fixed bed adsorber, the adsorbate concentration increased more rapidly with increasing x' for insufficient active volume for adsorption. The breakthrough curve was also affected by Bi and Peclet number (Pe) as well as adsorbent shape, implying that external resistance and axial dispersion, as well as interfacial area, are an important factor for adsorber design. Estimations of effective diffusivity and Pe were possible from experimental data of organic dye by macroporous silica microspheres or micro-fibers as adsorbents.