3D modeling of overall adsorption rate of acetaminophen on activated carbon pellets

- The overall adsorption rate of acetaminophen on activated carbon pellets was studied.
- 3D diffusional model was applied to predict the concentration decay curves.
- Surface and pore volume diffusion are important on the adsorption of acetaminophen.
- Desorption zones of acetaminophen were identified from 3D modeling.

In this work the overall adsorption rate of acetaminophen on activated carbon pellets (ACP) was analyzed in deep. The concentration decay curves were interpreted by a 3D diffusional model because the intraparticle diffusion of acetaminophen inside ACP in radial and axial directions are important in this form of activated carbon. The 3D diffusional model considers the external mass transfer, intraparticle diffusion (pore volume and surface diffusion) and the adsorption on an active site. The results demonstrated that the application of 3D diffusional model based on pore volume diffusion interprets clearly the kinetic curves, however values of effective diffusion coefficient (Dep) higher than molecular diffusivity are obtained indicating superdiffusion phenomenon. On the other hand, the application of a general diffusion model evidenced that during the whole time interval, the acetaminophen diffuses consecutively by surface diffusion followed by pore volume diffusion. In short times the surface flux is higher than the pore volume flux, but at higher intervals of time, the relevance of both fluxes reverts. Finally, from 3D simulation it is clear that at longer times, the solute mainly enters from the solution through the pellet borders, and acetaminophen desorption signs are even evident at the center of the pellet covers, due to the inverse concentration gradient established between the pellet and the solution.

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