Modeling of Multicomponent Trace Contaminant Adsorption on Activated Carbon

Modeling of multicomponent trace contaminant adsorption on activated carbon for spacecraft life support applications presents challenges due to the very low contaminant concentrations in cabin air coupled with very strong adsorption of heavier components such as cyclic polydimethylsiloxanes. Both external gas phase and internal micropore mass transfer resistances can be important, and competitive interactions between adsorbed components can result in roll-up behavior in which lighter components become concentrated in the effluent as a result of dynamic displacement by heavier components. Detailed mass transfer modeling and the ability to predict roll-up behavior are particularly important in designing high velocity, low aspect ratio adsorption processes. These capabilities are not available in the heritage NASA TCCS-CP computer program. This paper describes the further development of a dynamic trace contaminant adsorption model based on Ideal Adsorbed Solution Theory (IAST). A new approach to extending a generic potential-theory-based adsorption isotherm to the Henry’s Law region is described and compared with literature data. Optimization of conservation equations and solution methods for speed and stability is also described, along with initial efforts at implementing the model in an alternative software platform for wider access. Based on preliminary estimates of model parameters, predictions of multicomponent cabin trace contaminant buildup are compared with those of the heritage NASA model. Finally, recommended testing needed to evaluate model parameters and to validate or refine IAST predictions is discussed.