Comment by logfromblammo

It depends on whether the propellant is used to increase or decrease the orbital velocity of the vessel.

Acceleration propellant would have to be ejected at the orbital velocity of the vessel plus escape velocity to escape. Deceleration propellant would just have to be ejected at escape velocity minus orbital velocity.

As deceleration near atmosphere is almost free just by dipping into it, or by using some form of sea anchor to pull on the atmosphere or magnetic field, it is more likely that propellant would be used preferentially for attitude control and acceleration.

It isn't impossible, but imparting enough velocity to propellant for it to escape Earth orbit--while accelerating a vessel in the opposite direction--seems unlikely for orbital station-keeping. You need at least 12000 m/s for escape velocity plus at least 8000 m/s to counteract the orbit you were already in, so the propellant would have to leave the vessel at more than 20000 m/s. That's a specific impulse of about 2000 s. Ion drives and VASIMR could do it, but the propellant is very likely to experience its own atmospheric drag and electromagnetic interactions, and the probability that any particular atom of propellant would actually escape with the minimum velocity-relative-to-vessel is very low. The propellant would spread out to a larger volume as quickly as it could, too. It's far more likely that one of those xenon ions would collide with a hydrogen atom in the upper atmosphere and randomly bounce it out, like a bowling ball hitting a billiard ball.