Effect of diffusion on the conceptual design of a fixed-bed adsorber

Abstract This work studies the effect of intraparticle diffusion phenomena on the conceptual design of an industrial fixed-bed adsorber for the removal of Rhodamine B (RhB) basic dye by using an abundant low-cost natural zeolite. Initially, equilibrium and transient observations obtained from independent experiments at laboratory scale are fitted by means of Langmuir isotherm model and two kinetic models, i.e., intrinsic Langmuir model and apparent pseudo-second-order model, respectively. Furthermore, effective diffusion coefficient is estimated from independent experiments using particles of the natural zeolite that are supposed to be packed in the fixed-bed adsorber. Then, all this information is used to develop three pseudo-heterogeneous models with and without accounting explicitly for intraparticle diffusion to predict the performance of a fixed-bed adsorber: (i) Linear Driving Force model (LDF-M); (ii) Apparent Kinetic Approach model (AkA-M); and (iii) Kinetic-Diffusion model (kD-M). The three fixed-bed adsorber models lead to different tendencies related to their breakthrough curves and breakthrough points, indicating significant resistance to diffusional mass transfer. Even though three fixed-bed adsorber models accounts for adsorbent diffusion, kD-M approach is found to be a complex yet necessary approach to carry out the conceptual design of a fixed-bed adsorber packed with a natural zeolite since diffusion characteristic time and, hence, resistances to mass transport by diffusion are significant to be lumped in equilibrium or kinetic models via LDF-M or AkA-M, respectively.