  We investigate a system related to a particular isothermal gas-solid
chromatography process, called ?Pressure Swing Adsorption?, with two species
and instantaneous exchange kinetics. This system presents the particularity to
have a linearly degenerate eigenvalue: this allows the velocity of the gaseous
mixture to propagate high frequency waves. In case of smooth concentrations
with a general isotherm, we prove L1 stability for concentrations with respect
to weak limits of the inlet boundary velocity. Using the Front Tracking
Algorithm (FTA), we prove a similar result for concentrations with bounded
variation (BV) under some convex assumptions on the isotherms. In both cases we
show that high frequency oscillations with large amplitude of the inlet
velocity can propagate without affecting the concentrations.
