Pore and solid diffusion models for fixed‐bed adsorbers
Tóm tắt
Most models for fixed bed adsorbers have used either the homogeneoussolid or pore diffusion model for the pellets. When the adsorption isotherm is linear, the two models can lead to identical breakthrough curves. The conditions for this equivalence are presented here. It is shown that one of the bulk flow factors that was included in the formulation of one pore diffusion model will be significant only for feedstreams containing a relatively high concentration of adsorbate. The prosity factor of the pore model is shown to be very important, especially as the porosity decreases. The importance of the two diffusional models with respect to the predicted breakthrough curves is demonstrated. For comparable beds, it is shown that the breakthrough curve based on the homogeneous model is delayed with respect to that based on the pore model at early times, regardless of the shape of the isotherm. Finally, the various possible solutions for an irreverisble isotherm are reviewed for each of the models, and a solution is presented for the general case of a pore model with an outside film resistance.
Từ khóa
Tài liệu tham khảo
Allen P. W.“Unsteady‐State Diffusion in Porous Media ” Ph.D. thesis Univ. of Colorado Boulder (1968).
Brecher L. E., 1967, Combined Diffusion in Batch Adsorpation Systems Displaying B.E.T. Isotherms: Part I, AIChE Symp. Ser., no. 74, 64, 18
Brecher L. E., 1967, Combined Diffusion in Batch Adsorption Systems Displaying B.E.T. Isotherms, Part II, ATChE Symp. Ser. No. 74, 63, 25
Carter J. W., 1966, A Numerical Method for Prediction of Adiabatic Adsorption in Fixed Beds, Trans. Instn. Chem. Engr., 44, T253
Damköhler G., 1935, Uber die Adsorptiongeschwindigkeit von Gasen an porösen Adsorbention, Z. Physik. Chem., 174, 222, 10.1515/zpch-1935-17421
Dedrick R. L., 1967, Kinetics of Adsorption by Activated Carbon from Dilute Aqueous Solution, AIChE Symp. Ser. No. 74, 63, 68
Hsieh J. S., 1971, Batch Adsorption Kinetics in Sewage‐Activated Carbon, Proc. Am. Soc. Civil Eng. J. Sant. Eng. Div., 4, 505
Kondis E. F., 1971, Nonisothermal Sorption of Ethane by 4A Molecular Sieves, AIChE Symp. Ser., No. 117, 67, 25
Lee H., 1971, Carbon Dioxide Remooval from Air by Sodium‐X Molecular Sieve Under Nonisothermal Conditions, AIChE Sypmp. Ser., No. 117, 67, 84
Lee R. G., 1969, Interpretation of Methdane Adsorption on Activated Carbon by Nonisothermal and Isothermal Calculations, Can. J. Chem. Eng., 60
Masamune S., 1965, Adsorption of Ethyl Alcohol on Silica Gel, AIChE J., 41
Smith S. B., 1959, Kinetics of Batch Adsorption of Dichlorophenol on Activated Carbon, AIChE Symp. Ser., No. 24, 55, 25
Testin R. F., 1967, Diffusion Coeffecients Measured from Gas‐Solid Adsorption Rate Experiments, AIChE Symp. Ser. No. 74, 63, 10
Vermeulen T., 1958, Advances in Chemical Engineering, 147