Extended Rate Constant Distribution Model for Sorption in Heterogeneous Systems: 3. From Batch to Fixed-Bed Application and Predictive Modeling

Abstract

Here, we have demonstrated that the recently developed extended rate constant distribution (RCD) model for sorption on heterogeneous sorbents can be applied to predict the column behavior of the sorbents using parameters determined from the sorption kinetics in batch. The suggested approach has been validated on the batch and fixed-bed experimental data of Cu(II), Cd(II), and Zn(II) ion sorption on a polyethyleneimine (PEI) cryogel. Although the average sorption rate constants decreased in the order Cu(II) > Zn(II) > Cd(II), “fast” and “slow” sorption centers with different affinities have been identified for all investigated ions. This explained why, depending on the experimental conditions (flow rate and metal ion concentrations), one or another ion from the mixture can adsorb preferentially on PEI in fixed-bed applications, while at long equilibration time, the ratio between adsorbed metal ions was determined by the sorbent affinity. We have also shown that sorption rate constants for the PEI cryogel determined from the batch data were ∼0.6 log units lower than those determined from fixed-bed experiments that proved higher sorption efficiency for this type of sorbent under dynamic conditions. The column efficiency coefficient introduced to the RCD model for the fixed-bed application allowed us to reveal intrinsic and operational defects in soft monolith sorbents materials, which originated from imperfection of fabrication or destruction of the porous structure at high flow rates, respectively.