Modelling the dynamic behavior of fixed bed adsorbers by tank-in-series

FASCE, L. A.; SEOANE, I.T.; CONTRERAS, E.

Ciudad Autónoma de Buenos Aires

Congreso; 11th World Congress of Chemical Engineering, WCCE 11; 2023

The Bohart-Adams (B-A) model is still widely used to represent the breakthrough curves of fixed bed adsorbers. In fact, the B-A model can be found in almost every water and wastewater treatment textbook. Typically, the B-A model is employed to fit lab-scale breakthrough curves to extract kinetic and adsorption capacity parameters for design purposes. The B-A model assumes that the adsorbate is adsorbed irreversibly, the adsorption rate is proportional to both the residual capacity of the adsorbent and the adsorbate concentration, plug flow and, negligible diffusion limitations. Unfortunately, most of these assumptions are not achieved in real fixed bed absorption columns, so B-A predictive capability is limited to very idealized situations. In this work, a tank-in-series model (TIS) is presented as a versatile tool to simulate the dynamic operation of fixed-bed absorption columns. The TIS model was implemented in GEPASI 3.30 and MATLAB software packages. Despite its simplicity, the appealing feature of TIS model is that it can be tailored to account for reversible adsorption rates, mass transfer resistance and non-ideal flow conditions. First, the effect of the number of tanks (N) was analyzed by comparing breakthrough curves obtained from the B-A model with TIS model predictions for typical sets of experimental operation conditions considering irreversible adsorption rates. Results demonstrate that TIS curves practically overlapped B-A model for N ≥ 10. Then, the better simulation capability of TIS model over the B-A equation was demonstrated for several experimental data sets reported in literature. For example, Figure 1 shows the better performance of the TIS model over the B-A equation in fitting the experimental data for Congo Red removal in a fixed-bed column [2]. The TIS model could be easily expanded to simulate the transient behavior of another reactor types, including fixed bed heterogeneous reactors in which adsorption is followed by surface reaction and fixed bed enzymatic reactors.