CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: How Safe is Rotablation?   Next in Forum: Human Rate Of Freezing In A "Waterless" Place
Close
Close
Close
11 comments
Participant

Join Date: Mar 2017
Posts: 4

Dehumidification with Nafion Membrane for Oxygen Concentrator

03/28/2017 3:38 PM

As a Junior Biomedical Engineering student, I am working on developing an oxygen concentrator suitable for the developing world. A major is issue is that the lifespan of oxygen concentrators is significantly reduced due to water vapor contaminants in the Zeolite material due to incomplete dehumidification of the inlet air.

We are looking into alternative methods for dehumidification and are curious about Nafion membranes (or any other alternatives - suggestions?) for this, as they would provide an excellent method for both removing the water vapor from inlet air and would also provide a method for re-humidifying the air at the outlet (this must happen before the outlet air is inhaled by the patient). Is this a feasible idea? How would we go about this?

I would assume that running both the inlet and outlet air through the same "box" but just separated by the membrane would be the place to start. This would create the necessary partial pressure gradient across the membrane and the flow would help increase the diffusivity??

I am open to any advice on this topic as it is completely a preliminary idea at this point.

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18343
Good Answers: 1065
#1

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/28/2017 3:57 PM

Sounds a little pricey for 3rd world application....maybe powdered rice could be used....then eaten...In any case I think a desiccant might be cheaper for removal of moisture, and a combination of compression and desiccant would be even better....

https://en.wikipedia.org/wiki/List_of_desiccants

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply Score 1 for Good Answer
Participant

Join Date: Mar 2017
Posts: 4
#2
In reply to #1

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/28/2017 4:08 PM

The price is certainly a concern. However, use of a membrane as opposed to a desiccant would require less maintenance, which is a major concern for the facilities and technicians that we surveyed. Some of the desiccants we have explored saturate FAR too early under continuous use.

At this point we are just trying to explore all of our avenues - the silica gel beds already in the units are obviously not enough to adequately dehumidify. Although cost is a concern, a few people "on the ground" are adamant that it is more important to have a device that meets their needs than another unit that doesn't work (saving $100 is pointless if what they purchase is out of service in less than a month).

Register to Reply Off Topic (Score 4)
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11601
Good Answers: 137
#3

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/28/2017 4:31 PM

Why Nafion? Because these have been published on so much in conjunction with PEM fuel cells?

You should consider the effect humidity has on the relative permeability of your material if using PSA or if using a separation membrane for oxygen and nitrogen. Since you may not be interested (I have no assumptions about that) in pure oxygen, you might want a method that is highly permeable to nitrogen and water vapor, such that a relatively dry oxygen stream is left in process. Then it is simple to rehumidify.

Common Zeolites as molecular sieves are not the most efficient materials. Zeolite analogues are used as molecular sieves, and I have seen these materials used in drying process air to upgrade to instrument air.

I think you should keep searching for better ways. I seem to recall a new "re-breather" technology, that actually emits oxygen and allows very light weight dive gear, and does not rely on carbon dioxide absorption (but my old mind is a bit cloudy with a chance of rain).

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Participant

Join Date: Mar 2017
Posts: 4
#7
In reply to #3

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/29/2017 12:05 PM

Nafion, although it is not its main use, has been reported to be very effective in dehumidification processes (particularly in microfluidics). We are using a PSA technique for the project, and this is why we are focusing on removing humidity before passing it through the zeolite (as the water will bind tightly to the zeolite and not desorb when the pressure drops).

Although we looked into membrane concentration techniques, we decided that a traditional PSA process is more robust for this application. I will be looking into the tech used in rebreather systems though! Thanks!

Register to Reply
Guru

Join Date: Apr 2010
Posts: 5380
Good Answers: 522
#4

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/28/2017 7:12 PM

This article doesn't mention any problem with water vapor in oxygen concentrators.

The oxygen concentrator uses zeolite to absorb nitrogen from air under pressure. When the remaining air is removed (mostly oxygen), under reduced pressure, the zeolite gives back the nitrogen, which is then vented to the atmosphere.

https://en.wikipedia.org/wiki/Pressure_swing_adsorption

Is this the same process you are using?

Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 18343
Good Answers: 1065
#5

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/28/2017 10:02 PM

I think I might look at incorporating a regeneration cycle into the concentrator, have it regenerate automatically, perhaps include rotating zeolite capsules, one cooks while one works....

http://www.sciencedirect.com/science/article/pii/S1387181109003357

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply
Guru

Join Date: Oct 2009
Posts: 1170
Good Answers: 22
#6

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/29/2017 10:22 AM

You understand that you will not be the first with concerns about using oxygen concentrators in the developing world, and that others have already addressed some of the issues. I do note that they did not mention your problem of a shortened lifespan of the zeolite. However, CR4 has already run a thread on refilling zeolite cartridges so maybe the users out there are truly having problems the manufacturers are not willing to admit to.

The idea of humidifying the outgoing oxygen with the water from the dehumidification of the incoming air is superficially attractive and new technology (Nafion) may be the ultimate answer. However, as a former medical professional, I may point out that humidifying the oxygen is not always essential. When it is necessary the required kit is cheap. Old technology (a series of silica gel cartridges on the oxygen concentrator inlet, dried out in turns) may still be a simple and cost-effective solution.

Register to Reply
Participant

Join Date: Mar 2017
Posts: 4
#8
In reply to #6

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/29/2017 12:10 PM

I certainly agree that a cheap bottle method for re-humidification would be cheaper and easier (although less novel) but this is probably best for the project.

I have been looking for information on the silica gel beds used, with absolutely no luck. Would you be able to provide a list of references for this so I can investigate it further?

The "dried out in turns" aspect is critically important for this project and it would be incredibly helpful to have more background on this. It seems that there are VERY few sources online that provide information about silica gel or other desiccants being used in standard concentrators (even in searching through service manuals).

Register to Reply
Guru

Join Date: Oct 2009
Posts: 1170
Good Answers: 22
#10
In reply to #8

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/30/2017 6:01 AM

I was thinking of using the canisters used for soda lime in the rebreathing circuit of an anaesthetic machine (see fig). They are designed to be easily removed and replaced with a freshly filled one. Silica gel is available in bulk on Amazon, so I would not foresee a difficulty in finding an industrial source. Equally, drying out a wet canister-full should not be too awkward.

Register to Reply
Guru

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 11601
Good Answers: 137
#11
In reply to #10

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/31/2017 11:54 AM

I was hoping there could be an application for the new cobalt based material.

See this article:

oxygen storing substance - based on cobalt. This material certainly has a higher capacity than anything we have dealt with before. The molecule does not appear to difficult to make.

It would be ideal for situations where one does not require nitrogen in the flow, or can add air to the flow if pure oxygen is undesirable.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Power-User

Join Date: Jan 2007
Location: spain N38 39' E 00 3' and uk N52 14' W 00 54'
Posts: 204
Good Answers: 2
#9
In reply to #6

Re: Dehumidification with Nafion Membrane for Oxygen Concentrator

03/29/2017 5:15 PM

Nafion is hardly new technology.

I looked at developing this concept some 20 years ago. The use of the nafion was normally to produce nitrogen.

I met with complete obstruction by the distributors/manufacturers and I eventually threw in the towel. I would have used a primary dessicant to treat the inflow. Perhaps I should have kept the towel

__________________
duikerbok
Register to Reply
Register to Reply 11 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

BMEO2 (3); duikerbok (1); James Stewart (2); phph001 (2); Rixter (1); SolarEagle (2)

Previous in Forum: How Safe is Rotablation?   Next in Forum: Human Rate Of Freezing In A "Waterless" Place

Advertisement