Question about refreshing dessicant packs

[Ian]

Typically, silica gel dessicant which has reached its saturation limit can have the water driven back out by heating in an oven for a period of time (X temp at X time, usually several hours). This may or may not be convenient or efficient for small batches such as the little packs some of us save for storing with our bullet moulds.

In the automotive air conditioning world, moisture must be completely eliminated within the system for safety and function, so a deep vacuum is applied to the system to boil the water out where it can be removed. As an added measure, all systems have a dessicant pack located within the system somewhere to absorb any remaining trace amounts of moisture and trap it away from the refrigerant and oil.

So, the question is, how about instead of heat we just dump our saturated dessicant packets in a glass canning jar and use one of those handy-dandy infomercial vacuum pumps to draw down the pressure, and just put it away for a day or a month (as needed)? The water should boil out at room temperature into the space inside the jar and the packs could be removed quickly after taking off the lid to prevent immediate re-absorption of the moisture that would condense inside the jar when opened. Then the dried packs could be transferred to vacuum sealed bags and sucked down tight with no space around them for storage until needed.

Has anyone tried this?

 

[Brad]

Never thought of it?
I have always used heat and time to dry out the desiccant. That is what we did in Chem lab to dry hygroscopic substances so I stuck with it.
Does the vacuum packing pump create enough of a vacuum to remove the water from the desiccant? I don't know.

Biggest advantage to hear is that we pretty much all have a kitchen oven. I don't own a vacuum device with the proper set up to handle dessicants.

To try it I would recommend buying some dessicants crystals at the hobby store with the indicator crystals. This stuff turns blue when it is holding moisture and white when dried out.

 

[S Mac]

As Ian stated, the water boils out at room temp under vacuum the way I understand it. I would say it would work well. I do feel that the purge of the vacuum pump is needed to give the moisture a way out of the container.

 

[Brad]

But how much of a vacuum is required to drive the moisture out? Water is adsorbed by silica gel, not absorbed. This is a weak inter molecular force holding the water not merely water in a pore in a sponge.

Like I said, I don't know. Easy enough to test with one of the indicator gels.

Ian, do you have a home type vacuum sealer for bottles? Can you compare it to an industrial type pump like you have at work? Would be an interesting study.

 

[fiver]

I think I'd rather just store my molds in a Tupperware container packed full of oil soaked sawdust.

 

[Ian]

Water is adsorbed by silica gel, not absorbed. This is a weak inter molecular force holding the water not merely water in a pore in a sponge.

Aha! I didn't know that. So that probably changes the game. Most food storage vacuum pumps don't pull a very deep vacuum (I'd estimate 25 inches of mercury at most) but the hand pump jobbies do a pretty decent job. I just asked Giggle and found a chart that says water boils at 76°F or higher at 29.02" mercury. That is a DEEP vacuum, not likely to be achieved by anything outside of a specialized pump. Guess that sorta answers my own question.

 

[358156 hp]

There are probably a lot of old style AC vacuum pumps stuck away in the corners of repair shops that need a new purpose in life since refrigerant needs to be recycled any more. I don't believe I'd try it with glass though.

 

[JWFilips]

I just take mine and lay them out on a clean baking tray and put in a 170 deg for an hour.
When they come out I put them in a Ball Jar with a new canning lid. By time they cool the lid seals.
Trick is; when you need one only open the jar on a low humidity day!

Ian, my memory fades me, but I think Mr Wizard did an experiment like that in the 1960's

 

[fiver]

I thought the old bell jars were made from glass.
I'm pretty sure that's what they called them.
but they were somewhat bell shaped and were used for placing them over things you wanted to put in a vacuum.
I do know glass will stand up to suction pretty well, we used to use glass faces with a neoprene blanket on the back of them with the air sucked out to hold the frames and screen work when we used to burn the solution for making screen printing screens.
airc [long time ago] the vacuum was only like 10-12 lbs or so though.

 

[Farmerjim]

I vacuum seal all my PC powders in quart jars. The seal a meal pump works well enough, the powders stay dry enough to BBDT in this high humidity Louisiana climate. I have an AC pump if I need a higher vacuum, but have not so far.

 

[Intheshop]

Oven here.

We have a pretty sophisticated dryer system on our "spraying" compressor.The desiccant stage is filled with the cheapest product we've found that works.Mimi Litter from wally world pet department.

Good luck with your project.

 

[Elkins45]

One other thing to remember is that although the water in indeed "boiling" you haven't actually added any kinetic energy to drive it off any faster. They draw a vacuum on AC lines because that's something that differentiates between the water and the fluid. If they could heat it up to drive off the water it would probably work faster.

In this case heat is your friend.