Modeling and simulation of isothermal fixed-bed adsorption column: comparison of pore and solid diffusion mass transfer

Abstract

A study of comparative analysis of two intra-particle mechanisms, pore diffusion and solid diffusion, is explained to understand the dynamics of fixed-bed adsorber column. A mathematical model is developed to account for the axial dispersion and both the external and internal mass-transfer resistances in the adsorption of solute. The developed mathematical models of pore diffusion and solid diffusion are solved numerically using the Explicit Finite Difference Technique and the simulations are carried out to obtain the breakthrough curves at different operating conditions. The proposed models are validated with the experimental results reported in the literature. The proposed model with solid diffusion intraparticle mechanism (s.d. = 0.0285) shows a good agreement with the experimental results as compared to the model reported by Vázquez et al. (2006) (s.d. = 0.0542). It is found that the breakpoint time is delayed for solid diffusion compared to pore diffusion under similar conditions. Also the steepness of the breakthrough curve is more for solid diffusion than pore diffusion mechanism. It is also observed that the percentage removal of the solute is more and the unused bed length is less for solid diffusion model which indicates the proper utilization of the bed. To have better understanding of the dynamic behavior of adsorber column, other important and influencing parameters such as flow rate, bed length, particle radius, and external film mass transfer coefficient, are varied and their effect on the breakthrough curve using pore diffusion and solid diffusion models are studied. The other important parameters such as the total amount of solute adsorbed (q^sub t^), the amount of solute sent to the bed (m^sub t^), equilibrium uptake of the bed (q^sub eq^), empty bed residence time (EBRT), percentage removal of solute (S), the adsorbent exhaustion rate (R^sub a^), and the fraction of unused bed length (y) are calculated for better understanding of the adsorption mechanism.