bandil64 - 28-4-2017 at 07:36
Hi All!
Long time since i've been doing any chemistry, so good to be back :-)
I am constructing an automated soxhlet unit for recreational use and one of the machine parts causes me some concern.
I have built an evaporation chamber out of spun aluminum that leads the vapour using a brass fitting to an electrically powered condensor. My concern
is the brass / aluminium interface. In marine environments brass / alu interfaces are a nogo because of galvanic corrosion.
My system will however solely be used to distill ethanol and other alcohols and will not get close to salt water.
To test worst case conditions i have milled out and assembled a brass / stainless steel / aluminium system and submerged it into saturated salt water
with a small amount of detergent in i. As seen in the attached image there is a slight evolution of hydrogen. I have repeated the experiment with the
same metal system submerged in 90% isopropylalcohol. No results from the second experiment yet, but i will post it once it has had a little time.
My question is:
Do you think i can get away with using this metal interface when the machine solely is used for vapours with high alcohol content solvents? I need a
5-10 years lifetime of the machine.
Thank you greatly for any input!
Best regards
Bandil
[Edited on 28-4-2017 by bandil64]
JJay - 28-4-2017 at 08:02
Why don't you use all stainless steel?
bandil64 - 28-4-2017 at 08:12
Hi, and thanks for reply!
Cost! Unit cost is quite critical and stainless steel will definately ruin it.
Also, we are extruding and moulding several parts, so alu brass are preferable.
Regards
Bandil
JJay - 28-4-2017 at 09:12
I wouldn't recommend using brass in case someone decides to run vinegar through the Soxhlet or extracts an acidic material, although you could
probably get away with it.
bandil64 - 28-4-2017 at 10:50
Good pont, altough the system is designed for ethanol and ipa extractions alone. I could however very well see the risk that people will experiment
with acidic solvents.
What about a stainless steel / brass combination? Most pro coffee makers are made of these alloys. The element are pretty close in the reactivity
system.
Ill conduct experiments on elevated temperatures with slightly acidic ethanol and see how the brass / alu system behaves and post results here. Alu
and brass are awesome for manufacturing so it would be nice to get a stable and reliable system with.
Regards Bandil
Microtek - 4-5-2017 at 23:17
As long as the part made out of the more reactive metal (the aluminum) is bigger than the other one, you should be fine. Particularly if running an
anhydrous mix through it.
This is also why you shouldn't use iron rivets in a copper pot, but can do it the other way round without much trouble (at least from a corrosion
point of view).