KINETICS OF ADSORPTION ON BIPOROUS SOLIDS - FOR A SYSTEM WITH RECTANGULAR EQUILIBRIUM - REANALYZED

Mass transfer equations describing the rate of adsorption for rectangu lar equilibrium on biporous solids were solved numerically by finite d ifference technique. Values of parameters affecting the rate of adsorp tion were varied over wide ranges. It was observed that at a given ins tant, the microspheres constituting a single biporous solid particle c ould be classified into three distinct categories: (a) outermost shell of microspheres which are completely (or almost completely) saturated , (b) the middle adsorption shell of microspheres, where adsorption is taking place, and (c) the inner core of microspheres which is yet to be exposed to the adsorbate. A dimensionless parameter beta has been d efined. The thickness of the adsorption shell goes on reducing as the value of beta increases. It was found that at large values of beta rat e of adsorption is much higher than that predicted by macropore diffus ion control. An alternate rate model, incorporating accumulation in ad sorption shell, is proposed. Experimental observations of kinetics of adsorption on biporous spherical absorbent particles (molecular sieves and macroporous ion exchange resins) have been analysed. The results indicate that more than one model can correlate data leading to differ ent interpretations.