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Author: Subject: Simple Distilling Questions
LiveWire
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[*] posted on 6-3-2006 at 00:14
Simple Distilling Questions


Just a couple quick questions about distilling:

1. I got a simple distillation setup dirt-cheap (I think it was used, but for the price, I really don't care). I was wondering how cold the water that gets pumped through it needs to be. Would ice-cold water break it? It says borosilicate glass, so it's heat/cold resistant, but does that mean I can have huge temperature differences like that?

2. I'm trying to make nitric acid by distilling sulfuric acid+potassium nitrate. I was wondering how hot I can get the acid before it breaks down and starts producing NO2 gas. I'm thinking of putting it in a hot water bath at around 60 degrees, so that I don't have to deal with the NO2. (I don't have vacuum apparatus.) But I don't want it to take all night, so I'm wondering just how hot I can get it.

Thanks in advance.
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mantis
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[*] posted on 6-3-2006 at 06:15


Quote:

Would ice-cold water break it?

You will have no problems with strong temperature-changes and borosilicate.


Quote:

I was wondering how hot I can get the acid before it breaks down and starts producing NO2 gas.

The nitro-oxides are only an by-product during HNO3-destillation. Conc. nitric acid destills off at a temperature about 380K.
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LiveWire
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[*] posted on 6-3-2006 at 06:45


Thank you for your reply.

Quote:

You will have no problems with strong temperature-changes and borosilicate.

Well, I've broken laboratory glass pipes by heating them and dunking them into water; isn't that a little similar to the distillation setup?

Quote:

The nitro-oxides are only an by-product during HNO3-destillation. Conc. nitric acid destills off at a temperature about 380K.

I thought nitric acid breaks down if it gets too hot, so I figured I could avoid the problem if I stayed at a lower temperature, perhaps even lower than the boiling point. Have I been thinking wrong?
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DrP
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[*] posted on 6-3-2006 at 07:11


QUOTE:
'Well, I've broken laboratory glass pipes by heating them and dunking them into water; isn't that a little similar to the distillation setup?'

This is not the same - you don't quench hot glassware by dunking it into cold water during a distillation - the water is constantly flowing through the condenser keeping it cool. At worst there is a temperature gradiant from the condenser to the flask being heated but nothing to worry about.
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[*] posted on 9-3-2006 at 00:46


OK, thanks. I just wanted to make sure.

What about the nitric acid question, can anyone help me out?
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riisa
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[*] posted on 8-3-2008 at 20:17


So I just tried distilling ethyl alcohol from denatured alcohol and ended up with some results I don't understand. As I remember, I came out as about three sections: A little at about 69 degrees C, a lot at 72 degrees C (much lower then the water-ethanol azeotrope BP of 78.1) and just a tiny bit at 75-80. My apparatus consists of a 500ml Boiling flask, a vigreux column, 3-way w/thermometer adapter, liebig condenser, vacuum adapter (not using vacuum for this distillation) and I used a few 100ml beakers to collect. The bulb of the thermometer was seated all the way below the arm of the 3-way, just as it should be. Heat provided by Hot Plate + Stirrer and an oil bath. I have heard this this is, indeed, a difficult distillation...
Is it safe to assume that the large amount of distillate that came over at 72 degrees is ethanol?
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[*] posted on 8-3-2008 at 21:02


The temperature of the water depends on the vapor temperature of the distillate.

Borosilicate glass will withstand a differential of more than 100 C.

A condensing water temperature of 20-30 C colder tha the vapor temperature concerned is quite adequate.

So, suppose your condenser water is 25 C. If so, the maximum vapor temperature you put through that condenser is 125 C. And, water at ANY temperature, even close to boiling, would condense vapor at 125 C.

I am not advising you to heat your cooling water.

If you are distilling something with a vapor temperature >150 C, use an air condenser. Or, reduce the vapor temperature by reducing the pressure in the system (vacuum distillation).

Too high a differential between coolant and vapor and you run the risk of cracking the condenser at the jacket.




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[*] posted on 21-3-2008 at 22:34


Did riisa get an answer?
What is it denatured with?
I'm only curious about the motivation for procuring pure ethanol with your method.
My route was to distill vodka to the azeotrope, and then clean it up from there with calcium oxide or benzene, but unfortunately I shared the distillate with my friends, and started over.

[Edited on 21-3-2008 by shadow]
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[*] posted on 21-3-2008 at 22:52


No he didn't get an answer. Chances are his denatured alcohol is about 90% ethanol and 10% methanol. The methanol is the denaturant used to prevent dumbasses from drinking it. If one of these people gets the bright idea to distill it and get cheap booze they run into the same problem as riisa. The boiling point of methanol is only about 14C more than ethanol and most likely you are getting a mixture of the two.


Also you say "Is it safe to assume that the large amount of distillate that came over at 72 degrees is ethanol?"

Well no because ethanol boils at 78.4 °C. so in short if your goal is azetropic ethanol or higher either

A. buy absoloute ethanol

B. Buy everclear/vodka or something without a denaturant with a boiling point within 10 degrees of ethanol.

Honestly if It was that easy don’t you think someone would have done it?




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[*] posted on 18-6-2008 at 19:07


riisa,

Is your column insulated? The easiest thing to do is to redistill the 72C fraction as slowly as possible with a column insulated as well as possible. Also calibrate your thermometer by holding it just above some very very gently boiling water or better still run some water through the still to see if the thermometer reads bang on 100 while its distilling. If it does and the re-distillation gives you the same result then you're fucked and i don't know what the hell that 72C fraction is. It is odd though and i'm sorry you hit a shitty snag straight away.

Also i never read anything in your post about drinking ethanol from this denatured alcohol distillation, you just said you wanted ethanol.

wait i just had a thought

yes there is a ternary azeotrope between ethanol, methyl ethyl ketone (often used as denaturant) and water boiling at 73.2 but it only is supposed to contain 14% ethanol, this does not explain your observations. oh well




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