chemical hand warmers as oxygen absorbers

Posted by: LesSnyder

chemical hand warmers as oxygen absorbers - 05/12/11 07:11 PM

a month or so ago, I decided to put some staple food goods into 5 gal buckets for some long term storage, primarily just to see what process worked, and at what cost...most of the videos I viewed showed the use of mylar bags to block light, and dedicated oxygen absorbers sealed in the bags, but seems like the quantity packaging of the O2 absorbers almost necessitate a 10 bucket string, not a few packages at a time I wanted to try (I know you can store the unused O2 absorbers in glass jars, but there was not a local vendor for the mylar/O2 absorbers outside of the internet) ....I picked up a couple of the gray opaque buckets from Lowes and lids from Home Depot (the Lowes lids did not have a gasket) I recently purchased a vacuum food sealer, and set about to repackage an earlier bucket into which I had dropped an iron powder hand warmer... when I removed the handwarmer it was cold...I vacuum sealed the contents, and when I went to throw the hand warmer away, it was warm again...evidently it had worked, and the reaction stopped when the oxygen in the bucket had been used up....I repackaged the two buckets, added a warmer to each of the buckets... today when I looked at them, the lids are concave, and a slight concave crease in the side of the bucket where the air pressure inside is less than outside...I didn't check the barometric pressure the day I sealed the buckets,but looks like the handwarmers work to remove O2... just thought I would pass on an observation
Posted by: Art_in_FL

Re: chemical hand warmers as oxygen absorbers - 05/12/11 11:02 PM

On the face of it it doesn't sound like a bad idea. Save some money and double-down on the utility of hand warmers. I loves me some cheap utility.

But I don't know as how I would use hand warmers for oxygen removal in long term storage situations. The ones that might sequester oxygen either burn something, charcoal or lighter fluid, or react oxygen with iron using salt water to speed it up.

I'm not sure that water in a sealed container is the way you want to go. It also has to be pointed out that one of the main products of combustion is water. Doesn't sound like a good idea.
Posted by: adam2

Re: chemical hand warmers as oxygen absorbers - 05/13/11 07:12 AM

The burning of any common fuel does indeed produce water, which is about the last thing wanted in sealed storage.
Common fuels are all mixtures or compounds of hydrogen and carbon, when burnt they produce water and carbon dioxide.

Chemical hand warmers come in various types, some slowly burn small amounts of lighter fuel or charcoal, these would not be suitable.
Other types contain iron powder in a sealed pouch or other container. These should be suitable, they react iron with oxygen to produce iron oxide, no water is produced.
Iron oxide can be corrosive in the long term, I would be inclined to place the handwarmer in a peforated rigid plastic container in order that it may not contact the stored goods.

One drawback of any oxygen absorber is that the removing of the oxygen from the air in the container reduces the volume of the air by about 20%.
This causes stress on the walls and lid of the container and in the long term may lead to cracks, fractures, leaks or distortion.
It might be worth briefly and slightly opening the container after a few days in order to eqaulise the pressures. This will of course admit more air containing more oxygen, but a large enough oxygen absorber should absorb this as well as the first lot.
After the second and final sealing of the container, the pressure within will again drop as the oxygen is absorbed, but this time by only about 4% rather than by about 20%.
The effects of this may be minimised by finally sealing the container on a very cold day, or after storage in a refrigerator.
Posted by: LesSnyder

Re: chemical hand warmers as oxygen absorbers - 05/13/11 12:35 PM

adam2... I equalized the pressure when I noticed the differential(there was a definite air rush into the buckets), will check them again in a day or so... the goods were vacuum packaged inside the buckets...I'm going to reduce the amount of iron powder to decrease the volume of O2 consumed for future attempts (due to the irregular shape of the vacuum packs its difficult to determine the exact internal volume, or I could use the PV =nRT gas law formula to determine the amount of iron needed).. for future reference I'll try a bag and 1/2 bag on an empty bucket to satisfy my curiosity
Posted by: LesSnyder

Re: chemical hand warmers as oxygen absorbers - 05/13/11 04:49 PM

If I did the calculations correctly... a 5gal bucket has about 3.8liters of oxygen contained in the 19L of volume of the air(O2 is about 20% of air)...corrected to 25C and 1 ATM that is .16mol of O2... assuming a mix of +2 and +3 oxidation state for the iron it needs about 15g of iron powder, assuming 100% reaction rate
Posted by: Aussie

Re: chemical hand warmers as oxygen absorbers - 05/16/11 01:08 AM

Originally Posted By: adam2

It might be worth briefly and slightly opening the container after a few days in order to eqaulise the pressures. This will of course admit more air containing more oxygen, but a large enough oxygen absorber should absorb this as well as the first lot.
After the second and final sealing of the container, the pressure within will again drop as the oxygen is absorbed, but this time by only about 4% rather than by about 20%.
The effects of this may be minimised by finally sealing the container on a very cold day, or after storage in a refrigerator.


Perhaps set off the heat pack and let it run for a while before you put in into the container ? If you let it run for (say) 2/3 of its rated hours before you seal it in, you may get less pressure.
Posted by: adam2

Re: chemical hand warmers as oxygen absorbers - 05/16/11 02:44 PM

[quote=Aussie
Perhaps set off the heat pack and let it run for a while before you put in into the container ? If you let it run for (say) 2/3 of its rated hours before you seal it in, you may get less pressure.
[/quote]

Dont think that would help.
The idea is to remove all the oxygen, or it at least as much of it as possible.
Since air contains about 20% oxygen, the removal of this will unavoidably reduce the volume of the remaining gas to about 80%.

To avoid a partial vacuum in the container, more air must be admited, and the oxygen in this additional air must also be absorbed.

If the handwarmer is partialy expended before the container is sealed, then it might still have sufficient capacity to absorb all the remaining oxygen, and produce a partial vaccuum as above.
Alternatively the partialy expended handwarmer might be able to only remove part of the oxygen, this would reduce the degree of vaccuum produced, but would be a bit pointless since the object of the exercise is to remove all/as much as possible of the oxygen.
Posted by: Aussie

Re: chemical hand warmers as oxygen absorbers - 05/16/11 11:05 PM

Adam2 - Good point.

In winemaking we pump CO2 into tanks to exclude air and prevent oxidation, but generally we have special valves to allow the CO2 in and air out. Potentially you could mount a valve(s) on the lid of the container and pump CO2 in, air out ?

Seems a bit messy, but it depends what you want to do.

- Just a thought ...
Posted by: Susan

Re: chemical hand warmers as oxygen absorbers - 05/16/11 11:48 PM

I thought that when you used CO2, it was heavier than regular air and would settle to the bottom of the container, gradually expelling the oxygen? Would you really need to pump it out?

Sue
Posted by: Aussie

Re: chemical hand warmers as oxygen absorbers - 05/16/11 11:59 PM

Yes you're correct, the CO2 is liquefied under pressure so it just flows in, its not actually "pumped".
It does settle to the bottom of the tank (or sits on top of the wine), which displaces the lighter air mix. Because there is a venting valve at the top of the tank, the air is pushed out and eventually the entire volume is filled with CO2.

A fancy setup can actually monitor the gas pressure and automatically top it up as needed.

Probably a bit fancy for a 5gal bucket, but I have heard of people using soda siphon bulbs to inject CO2 into smaller wine vessels, but I’m not sure exactly how.
Posted by: LesSnyder

Re: chemical hand warmers as oxygen absorbers - 05/17/11 02:34 AM

traditionally dry ice(solid state of CO2) has been used in the "redneck" long term storage process from at least back in the 60's... I probably fit the term, even though I went to a reputable school in the South... does anybody have a technique for doing a single bucket at a time storage?...pruging with nitrogen or CO2 from a gas cylinder?...I'd like to do a full bucket of popcorn after I freeze the corn to kill off any weevil eggs...using the vacuum sealer is not volume efficient..
Posted by: Susan

Re: chemical hand warmers as oxygen absorbers - 05/17/11 07:44 PM

Why not just use dry ice?

Put a fist-sized lump in the center bottom of the bucket, add your popcorn to within an inch or so of the top, put the lid on put slightly ajar to vent. After 20-30 minutes, feel the center bottom of the bucket for cold. If it's still cold, some ice is still there. Continue to feel it until the center isn't cold, then seal the lid. Watch the bucket for several minutes -- if it starts to bulge, release the lid on one side for a few minutes. Seal and watch again. When no bulging occurs, you're done.

Sue
Posted by: LesSnyder

Re: chemical hand warmers as oxygen absorbers - 05/17/11 10:14 PM

Sue... that will probably be my solution...my local source of dry ice has a minimum purchase anyway
Posted by: Aussie

Re: chemical hand warmers as oxygen absorbers - 05/17/11 10:58 PM

Originally Posted By: Susan

Watch the bucket for several minutes -- if it starts to bulge, release the lid on one side for a few minutes. Sue


That lid will release its self if the dry ice is still in there ! POP ! I can see a comedy skit in that (Ha Ha)!

You may need to check that the dry ice doesn't "burn" any food that it is in contact with. When I've used it in the past, mostly for meat storage, we always wrapped it in paper to stop this happening.

But dry ice would be an interesting comparison to the hand warmers. By the way, you can store dry ice for a few days in foam box in a domestic deep freeze – it won’t keep too long, but if you don’t use it all immediately you can prolong its life a little.
Posted by: Art_in_FL

Re: chemical hand warmers as oxygen absorbers - 05/18/11 01:13 AM

I'm not so sure about using dry-ice. The intense cold might trap moisture by converting it to ice or liquid that can't be pushed out by the sublimating CO2.

Dry ice is pretty easy to get. You can buy it here by the pound at many grocery stores. But, you can also get CO2 from most any welding supply house. It is pretty cheap. A simple rig with a rented tank, regulator, and hose would be easy to use.
Posted by: Aussie

Re: chemical hand warmers as oxygen absorbers - 05/18/11 01:23 AM

You are right about the dry ice, it may cause condensation. If you do use CO2 and blast it in, the expanding gas can absorb heat from the environment and cause freezing too, so you need to go slow when adding liquefied gases.
Posted by: Susan

Re: chemical hand warmers as oxygen absorbers - 05/18/11 02:13 AM

Quote:
The intense cold might trap moisture by converting it to ice or liquid that can't be pushed out by the sublimating CO2.


I understood that dry ice sublimates directly from -100°F to a gas, and doesn't go through a moist stage. Is this incorrect?

It's been used for food storage for a long time. You'd think the word would have gotten out if it caused dampness and mold.

Sue
Posted by: Art_in_FL

Re: chemical hand warmers as oxygen absorbers - 05/18/11 03:31 AM

Originally Posted By: Susan
I understood that dry ice sublimates directly from -100°F to a gas, and doesn't go through a moist stage. Is this incorrect?

It's been used for food storage for a long time. You'd think the word would have gotten out if it caused dampness and mold.

Sue


You are correct saying that CO2 in the form of dry ice doesn't usually have a liquid phase. Not that that matters much because dry ice does not contain any water and does not speed of support decomposition.

But the air already in the contained certainly has some percentage of water. And when dry ice is introduced the temperature into the air around the dry ice drops, which causes the moisture in that air to fall out and form condensation. This condensation isn't going to be forced out by the CO2 liberated as the Dry ice sublimates.

If you could introduce the CO2 into the container without markedly dropping temperature, you would better remove both oxygen and moisture.

Is that a desirable goal; depends. If you are packaging food in a low humidity location, a northern state in the winter, it might not make any difference because there isn't enough humidity to worry about. On the other hand, if you are packaging food in the south in summer, with humidity pushing 100%, it may make a big difference in how long the food lasts.

That dry ice has been used for years like this isn't much of an argument in my book. So far most people using this technique are reporting they get 'good' results. After a few years the food comes out in good shape. The question is whether this is as good as it gets. If they get good results at five years who is to say they might not get ten years if they used gaseous CO2 instead of solid CO2.

It also has to be noted, based on informal search on my part, that many of those using dry ice are in states with presumed lower relative humidity. Methods that work well in Arizona might not work so well in semi-tropical south Florida.
Posted by: Susan

Re: chemical hand warmers as oxygen absorbers - 05/18/11 05:34 AM

Okay, I see. Thanks for the explanation.

Sue
Posted by: EMPnotImplyNuclear

much ado about nothing (not enough water) - 05/18/11 08:33 AM

Its much ado about nothing, there is not enough water in the air in the bucket to affect the wheat (increase the moisture past 10%)
I'll leave the calculation for the skeptic.