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Author: Subject: Copper sulphate and vacuum question
NEMO-Chemistry
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[*] posted on 13-1-2018 at 09:11
Copper sulphate and vacuum question


I have two VAC pumps, one is really old. Its the type that used to have a glass bell jar on top of the Vac inlet, it has a separate motor belt connected to the vac unit.
I use this for most my dirty vac work, but the spare seals and gaskets are getting harder and harder to get. So i feel like i need to abuse it less.

The other pump is my good one, its a two stage one that sucks like a ' ', well put it this way, it could suck a water melon through a hose pipe.

This pump i normally use with a vacuum chamber, various traps etc and change the oil frequently. the last stage of the line to the pump normally has a wash bottle, in this i put a mix of mineral and veg oil with a emulsifier in.

My hope is this catches at least some the water.

Normally if i put a beaker of cold water (1-2c), in the vac chamber in my cold lab, the pump pulls a vac good enough to boil the water within 15-20 seconds.

So I decided to dry some finely powdered copper sulphate with it, the copper sulphate was anhydrous a month or two back, but over the last few weeks the colour has become more blue as it has picked up water from the damp air.

The powder is normally sealed up, so its not alot of water. Anyway, i put the powder in a thin layer in a beaker and pulled a full vac. I ran the pump for a good 30 mins, after 30mins i couldnt detect a single change in colour!!

I was so sure the pump would pull the water out the copper sulphate! So this has given me an idea.....

My pump is either fecked (no gauge on it), or copper sulphate at a cold room temp dosnt want to give up water easily, if this is the case then maybe i could put anhydrous copper sulphate in the last wash train sandwiched between some filter paper, draw the air through the powder and into the pump.

Given all the above, do you think this would work?
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[*] posted on 15-1-2018 at 17:50


I assume it just doesn't want to give up the water. Perhaps it would in time. Normally I would just say to use something cheaper like magnesium sulfate, but of course copper sulfate opens up the possibility of changing color as it becomes saturated with water.

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[*] posted on 15-1-2018 at 17:58


There is a difference between water in a damp portion of a substance and water of crystallization. I would not expect a vacuum to remove water of crystallization.
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[*] posted on 16-1-2018 at 04:08


Thats a shame. It makes sense when i think about it, the water needs alot of energy when removing from a crystal, so copper sulphate taking up water is not the same as forming a crystal and trapping water.

Or in short...

I am talking bollocks and it wont trap water! Shame though as it would have been an excellent and cheap way to protect the pump, back to the cheap skate methods i use.
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[*] posted on 27-1-2018 at 23:40


You could make a simple plaster plug as plaster of paris is cheap, and lets air through; but being solid won't get sucked into your vacuum pump. Plaster plugs can be made very porous and able stip moisture from the air. This extends the life of the oil in a HVAC pump. Plaster of paris is cheap at a hardware store and can be cooked in an oven below 200C to drive the water out of it, so it becomes a dessicant again. If you cook it at above 200C, it's dessicant properties will end; but there are other strong dessicants like calcium chloride or magneisum chloride that could be soaked into a plaster plug even after it's been made into calcium anhydrite. The combination of a plaster plug and calcium chloride is hard to beat for price and moisture trapping ability. It's amazing how quickly hardened and re-dried plaster soaked in dry-z-air (calcium chloride) will pull moisture out of the air. Pieces I made like dried chalk were damp within hours after being bone dry when exposed to air. Commercial line dryers for HVAC systems sold for $50/cartridge are about the same; They can also usually be cooked to restore their dessicant properties after use. The secret is running silicone or teflon tubing into an oven since they can take heat, and use an aquarium pump outside the oven to run purging air through the tubing into the oven and into the canister while cooking the metal dessicant canister at >350F (>150C). That's why a metal (and not plastic) canister is important to get.

Good luck.




[Edited on 28-1-2018 by semiconductive]
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[*] posted on 28-1-2018 at 01:41


It's important to recognise that a right angle bend in a vacuum pipe will significantly reduce the flow rate.
Putting any sort of "plug" in it will seriously reduce the flow.
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[*] posted on 29-1-2018 at 13:21


Quote: Originally posted by unionised  
It's important to recognise that a right angle bend in a vacuum pipe will significantly reduce the flow rate.
Putting any sort of "plug" in it will seriously reduce the flow.


That's very true; When the heat pump was built at my house, I was told to use two 45 degree bends in the pipe in preference to a 90 and to leave a little straight line between the two joints. Also, the diameter of the desiccant canister is on the order of 5 inches, for a 1/4 pipe; the massive diameter change is to try and compensate for the plugging effect. I've never disassembled one, though, to see if the dissonant has through holes of visible diameter which would effectively let water through but absorb it during multiple passes of circulation on the surface of the desiccant.

The design of a water trap or desiccant depends on how critical it is to stop water on the first pass through, or not.

In the case of evaporation of water for crystals, the rate of removal of moisture and the lifespan of the pump are things that only the O.P. will be able to decide what is more important.

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[*] posted on 29-1-2018 at 13:26


Heat it up a lot.

Turns from blue to almost-white

Stick it in a bag with a ton of conc sulphuric for a month and it'll go white, right up until you take it out of the bag.




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[*] posted on 29-1-2018 at 13:43


I got a tiny lab oven now :D its in the pic on another thread, as a bonus I can hook a vac to it.
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