To my understanding, Boeing and Airbus will go for rather simple devices; you will litterally press bleed air through ceramic filters with catalytic properties, which will strip a fair amount of oxygen off the bleed air. Sorry if some of the words aren`t proper english - but I`ve missed all "english for chemical engineers" courses so far...
In the presentations I have seen, there were almost no moving parts (except for valves of course!). The key issue however seems to be to stay in a tight temperature/pressure/flow area...
Unfortunately (or: Fortunately ;-) ) I have the papers at work, not here.
Keep in mind that at least the retrofit solutions (if the FAA really pushes us into that!) must be ... well... retrofitable (in terms of space, consumption, cost etc.).
Cheers,
JV
