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Author: Subject: What form of Calcium sulfate?
AllanD
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[*] posted on 17-7-2006 at 09:01
What form of Calcium sulfate?


Ok, in a quantity of EtOH and H2O (~90% EtOH) with a distinct smell of sulfur dioxide...

Added a surplus (an 40gms or so to 4 liters EtOH/H2O) Calcium Carbonate and mix thoroughly (to neutralize the dilute acid formed by SO2 in water) then filtered to remove the unreacted CaCO3

This sucessfully removed the odor of SO2
(the intended goal)

Several days later it was noticed that fine needle like crystals of what I take to be calcium sulfate precipitate out of the solution and were removed by additional filtration.

I am reasonably sure that the (supposed) CaSO4 is of the Alpha-Hemihydrate form as the crystals are both sparkly
and prismatic

any errors in my understanding of this?

I vaguely remember that anhydrous CaSO4 is used as a commercially prepared dessicant and secific to dehydrate azeotropic EtOH, but the name of the product escapes me...

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[*] posted on 17-7-2006 at 09:07


Quote:
Ok, in a quantity of EtOH and H2O (~90% EtOH) with a distinct smell of sulfur dioxide...


Eh? Where's the verb in this sentence?

What precisely did you do? SO2 in water? Where did that come from? Did you bubble SO2 into CaCO3?


Please be a bit more concise, and SAY what you've been doing! Your post is nothing but a riddle!




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AllanD
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[*] posted on 17-7-2006 at 09:20


That IS the starting point, an EtOH/H2O solution (a distillate)
that was contaminated with dissolved SO2.

the only "lab instrument" used to verify the presence of SO2 was a Mark 1 human orafactory system and the knowledge that SO2 was very likely in the original mixture (Somewhat oxidized wine) prior to it's concentration via fractional distillation.

the starting mixture was NOT created intentionally, so any riddle is one I also have....


AllanD

[Edited on 17-7-2006 by AllanD]
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[*] posted on 17-7-2006 at 11:34


"Eh? Where's the verb in this sentence?"
In this case it's the work "with" used as a replacement for "having".
Still not going to win any clear English prizes.
"a friend of a friend" tells me that copper sulphate and redistillation will remove SO2, but I wouldn't know because it would be illegal round here.

[Edited on 17-7-2006 by unionised]
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AllanD
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[*] posted on 17-7-2006 at 12:54


Well, I'm not asking HOW to remove SO2 from 95%EtOH, I've got a process that works....

I'm asking for connfirmation from someone more knowledgable to confirm or correct what I THINK I know about WHY it works, and what the resulting waste materials are.

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[*] posted on 17-7-2006 at 13:51


Couldst be's CaSO4.2H2O. There's enough H2O left in that distillate that CaSO4[.1/2H2O] would dehydrate it, no?

I was cooking down a copper sulfate/chloride solution a while ago and found green balls of acicular crystals in the bottom. Not as much or as quickly as I'd expect for it to be copper chloride (which, being very soluble, tends to crystallize a lot for a given amount of evaporation), but nonetheless it was deep green and hairy! So I filtered it out, and gave it a rinse, and it turned blue (the solution hydrolyzing from green to blue) then white! Hey, that's not copper chloride at all! I'll be damned, there was calcium in solution that, for some reason, suddenly decided it would lose solubility and fool me...

CaSO4 isn't very soluble to begin with, and I imagine with EtOH, even less so; but the process and the crystal shape seems likely.

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AllanD
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[*] posted on 17-7-2006 at 14:48


Well, The CaCO3 I added to react with the H2SO3/SO2 isn't very soluble in water, and CaSO4 even less so... but it did react with the (supposed) SO2/H2SO3 liberating CO2....

but to be honest I added several times as much CaCO3 as was needed, knowing I was going to run it through a 0.1Micron filter anyway.
After waiting an hour, I passed it through the filter to get the excess unreacted carbonate along with the expected CaSO4 precipitate out....

then after several days (or possibly a week) I noticed those
additional precipitated crystals and filtered again.

I was just suprised that the bright, clear, apparrently well filtered liquid could precipitate as much (sparingly soluble) CaSO4 as it did....

Dehydrating ethanol fr fuel? have you heard of the cornmeal method? just like a molecular seive.
It's so stupid it's elegant.... if you think it through
and simply use the "wet" cornmeal in the next mash the elegance for an industrial process is a beautiful thing...

And any alcohol carried along in the cornmeal isn't lost either, it's simply recirculated to the next batch.


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[Edited on 17-7-2006 by AllanD]

[Edited on 17-7-2006 by AllanD]
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[*] posted on 17-7-2006 at 15:20


Ya, my thoughts exactly. To the best of my knowledge, that copper solution was clear and well-settled, but alas, it left me with a small pile of calcium sulfate. Saturated solutions are weird.

Tim




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