Abstract
The parallel transport of an organic acid by solid-phase and macropore diffusion within a porous ion exchanger was studied by measuring equilibrium isotherms and uptake curves for adsorption of acetic acid and lactic acid on a weakly basic ion exchanger, DIAION WA30. Experimental adsorption isotherms were correlated by the Langmuir equation. The Langmuir equilibrium constant of acetic acid was close to that of lactic acid, and the saturation capacity of acetic acid was about 84% that of lactic acid. Intraparticle effective diffusivity Deff was determined using the homogeneous Fickian diffusion model. The value of Deff for acetic acid was about 1.5 times lactic acid. Because Deff increased with linearly increasing bulk phase concentration C0, Deff was separated to the solid-phase diffusivity DS and the macropore diffusivity DP by applying the parallel diffusion model. The model agreed well with the experimental curves. The values of DS and DP for acetic acid were about 2 and 1.5 times those of lactic acid, respectively. The acetic acid and the lactic acid may be separated by the difference of the diffusion rates.
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