Oxygen

I saw another episode of Top Gear the other day. This time the challenge was to buy a used car sight unseen over the internet in Bolivia and drive it over the Andes to the Pacific Ocean. Each of the three guys picked a different 4x4 vehicle. The show's producers arranged to have them delivered via barge to a river bank on the Amazon River. When they had successfully gotten their cars off the barge and onto dry land, the producers rewarded them with a care package, which included a winch, a chain saw, and a package each of condoms, Tampax and Viagra.

After many trials and tribulations, they successfully escaped the rain forest, negotiated the Road Of Death, and reached the Andes mountains. Here they began making use of cocaine in the form of leaves and tea. This sufficed until they got up to about 15,000 feet (of elevation). That's when the Viagra got put to use.

Now they have a choice: take the short way over the volcano or the long way around. They have been slogging along for days now and are ready to be done with this, so they opt for the short route. The show makes a big deal about it being an active volcano, but they don't even consider that it might cause a problem, and in fact it doesn't. However, the part about going OVER the volcano does. They get up to 17,000 feet and call it quits. There just isn't enough air. I am surprised they made it that far. I've hiked up to 10,000 feet a couple of times and there isn't any air at that elevation. I found it interesting that there is a road there. Who the devil built the road? And who drives on it? Anyway, the cars are still running, but there isn't enough air for the drivers. They turn back and end up taking the long way around.

I was talking to my friends about this and we got to thinking about how you could get oxygen and somebody mentioned the little machines used by people who need oxygen for medical reasons. It used to be that people would carry a small bottle of oxygen around with them (on a little cart, even the little ones are heavy), but now we have these little machines that make oxygen out of thin air. So naturally we want to know how they do it. No one knows, so I volunteer to look it up, and here's what I found:

From Wikipedia:

The simplest oxygen concentrator is capable of continuous delivery of oxygen and has internal functions based around two cylinders, filled with a zeolite material, which selectively adsorbs the nitrogen in the air. In each cycle, air flows through one cylinder at a pressure of around 20 lbf/in² (138 kPa, or 1.36 atmospheres) where the nitrogen molecules are captured by the zeolite, while the other cylinder is vented off to ambient atmospheric pressure allowing the captured nitrogen to dissipate.

Typical units have cycles of around 20 seconds, and allow for a continuous supply of oxygen at a flow rate of up to approximately five liters per minute (LPM) at concentrations anywhere from 50 to 95 %. This process is called pressure swing adsorption (PSA).^[1] Since 1999, concentrators providing up to 10 LPM have been available for high flow patients, in sizes not much larger or heavier than 5 LPM concentrators.

and Zeolite:

Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents.^[1] The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that had been adsorbed by the material. Based on this, he called the material zeolite, from the Greek ζέω (zeō), meaning "boil" and λίθος (lithos), meaning "stone".^[2]

As of January 2008, 175 unique zeolite frameworks have been identified, and over 40 naturally occurring zeolite frameworks are known

So we pump air into a container filled with this funny, probably custom made, rock. The Nitrogen creeps into the rock, which means the remaining air has a higher concentration of oxygen. It does this for 20 seconds and then it switches to the other cylinder, and the first cylinder is vented to the air. The pressure is now lower, so the nitrogen flows back out of the rock.

Zeolites are used for all kinds of things, from kitty litter to gasoline refineries to oxygen supplies for aircraft (here's what they used to use). It is basically a porous rock, but it is not like pumice or other lightweight volcanic rock. I suspect it is more like your run of the mill granite. I mean the pores are sub-microscopic. I don't know what these tiny pores do to the density.

You wouldn't be able to tell it was porous by looking at it, unless you maybe had a scanning electron microscope, and even them I'm not sure you could tell. Only by observing the disappearance of a liquid of gas and then it's reappearance under heat could you be sure of what you had.

I am disappointed. I was really hoping for a micro-cryogenic-fractional-distillation technique.

P.S. The Tampax and condoms were used to waterproof some critical parts of the cars when they had to ford a river.