Development and Validation of a Two-Stage Kinetic Sorption Model for Polymer and Surfactant Transport in Porous Media

Understanding the sorption processes is critical to the successful design and implementation of a variety of technologies in subsurface application. Most transport models assume minimal interactions between adsorbed species and, thus, are unable to accurately describe the formation of adsorbed bilayers. To address this limitation, a two-stage kinetic sorption model is developed and incorporated into a one-dimensional advective-dispersive-reactive transport simulator. The model is evaluated using data obtained from column experiments conducted with a representative polymer [gum arabic (GA)] and a nonionic surfactant [Witconol 2722 (WT)] under a range of experimental conditions. Model simulations demonstrate that the first-stage polymer/surfactant-surface sorption rate is at least 1 order of magnitude greater than the second-stage rate, associated with bilayer formation, indicating that the first-stage reaction is more favorable. The reversibility of the second-stage sorption process is found to be compound-specific, with irreversible sorption observed for GA and prolonged tailing observed for WT. This study demonstrates that the developed two-stage kinetic model is superior to a two-stage equilibrium-based model in its replication of two-leg breakthrough curves observed in core flood experiments; the normalized root-mean-square error between measurement and regressed model simulations was reduced by an average of 41% with the kinetic approach.