Abstract
Sorptive liquid-phase diffusion of three solutes, dissolved in cyclohexane, onto pore surfaces of three NiMoγ-Al 2O 3 adsorbents at ambient, nonreactive conditions was studied to assess multicomponent diffusion and competitive adsorption effects. Single- and binary-solute adsorption isotherms were well modeled by Freundlich and extended Langmuir equations, respectively. The diffusion rate for single-solute systems was characterized by effective diffusivity under the influence of restrictive diffusion. For the binary-solute systems, deviations were observed between measured concentration-decay curves and curves calculated from a model using the effective diffusivity obtained from the single-solute systems when differences in adsorption uptake and/or the restrictive diffusion effect were relatively large. Two possible mechanisms are offered to explain the deviation, viz. importance of cross-term diffusivity effects, and effect of restrictive diffusion effects on main-term diffusivities. Based on the latter mechanism, lower diffusivity values were obtained for the binary-solute systems, possibly due to a slow displacement rate of weakly-adsorbed solute in the pores of the adsorbents by strongly adsorbed solute and counterdiffusion of individual solutes.
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