Characterization of adsorption uptake curves for both intraparticle diffusion and liquid film mass transfer controlling systems

In general, the adsorption uptake curve (AUC) can be easily determined in either intraparticle diffusion or liquid film mass transfer dominating systems. However, for both intraparticle diffusion and liquid film mass transfer controlling systems, the characterization of AUC is much more complicated, for example, when relatively small adsorbent particles are employed. In addition, there is no analytical solution available for both intraparticle diffusion and liquid film mass transfer controlling systems. Therefore, this paper is trying to characterize AUC for both intraparticle diffusion and liquid film mass transfer controlling adsorption systems using the shallow bed reactor technique. Typical parameters influencing AUC include liquid film mass transfer coefficient (kF), effective intraparticle diffusivity (DS), influent concentration (c0) and equilibrium parameters (such as Freundlich isotherm constants k and 1/n). These parameters were investigated in this research and the simulated results indicated that the ratio of kF/DS and Freundlich constant 1/n had impact on AUC. Biot number (Bi) was used to replace the ratio of kF/DS in this study. Bi represents the ratio of the rate of transport across the liquid layer to the rate of intraparticle diffusion. Furthermore, Bi is much more significant than that of 1/n for AUC. Therefore, AUC can be characterized by Bi. In addition, the obtained Bi could be used to determine DS and kF simultaneously. Both parameters (DS and kF) are important for designing and operating fixed bed reactors.