If one extracts with heptane denatured ethanol and residual solvent tests shows the presence of ethanol, would that imply that there is still heptane in the oil? A friend shows me lab results that had 50,000 ppm or something like that of ethanol, but was below the limit for heptane. Is the lab wrong? Shouldn’t there still be some heptane with that much ethanol?
depends on your recovery temperature/vac level. you may have recovered that volatile heptane down to an acceptable level.
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But heptane has a higher boiling point, so wouldn’t all of the ethanol be removed first?
was it tested for residual heptane as well? what ppm? that is the only way to know the answer to this.
get a second independent test if you’re doubtful
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It was, yes. It was “below the limit” which I believe is 600ppm or so.
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Shit, 50,000ppm is 5% ethanol, That extract is about as strong as a Coors Banquet as far as ABV. Although 5% of that should come out to 2,500ppm of heptane, heptane evaporates faster than ethanol. Just because the boiling point is higher doesn’t mean it won’t evaporate until all of the ethanol is gone. Though I know heptane and ethanol do form an azeotrope 
… Yea, this question is above my pay grade. I tried, hopefully someone else can explain that.
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Depends on how you ran your experiment
Ethanol forms an azeotrope, and there’s a lot more ethanol than heptane- the azeotrope by definition has a lower boiling point than either compound that make it up so it will evaporate the azeotrope first, followed by the ethanol that remains- think of the azeotrope as a unique entity that is neither heptane nor ethanol in the way it behaves physically- so the azeotrope is the first fraction of your distillation that works on a constantly changing curve rather than a series of set compounds coming off at specific temperatures-
When I equilibrate a fractionating column I am moving the first azeotrope fraction to the top and holding it there until it stabilizes
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Wrong. All of you. Not to worry though. If isaac newton was wrong, you (and I, constantly it seems) can be too.
Ethanol water and heptane form a low boiling ternary azeotrope. You cant distill off or leave behind water, ethanol is the last thing leaving the flask. What stays behind depends on the composition of what you put in there, but if theres a low concentration of heptane and water then ethanol will be the last thing that leaves.
The larger implications for this are that you can’t distill denatured ethanol to remove water. Water doesn’t stay behind, ethanol does, which sounds great until you realize that what’s coming off the top cant be more concentrated in water than the azeotrope or any other place on that side of the distillation boundary.
Yikes.
Also, do you think denatured ethanol salesman know this or tell anybody this. They dont.
Welcome to solvent recovery hell.
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Oh. So to answer your question, you would 100% expect to find ethanol and no heptane unless there was way way more water or heptane in your starting solution.
Didn’t I just sort of say the same thing? How am I wrong? My understanding may need to be adjusted
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Actually you’re right, but theres water which makes the situation even worse. I’m pissed off at denatured ethanol vendors. It’s basically a scam. They’re playing ignorant to all these problems imho.
The ethanol azeotropes thread mentioned above is great. I just left a post there too.
No, @limitbreaker, it is possible to evaporate heptane (as the top layer of the ethanol:water:heptane ternary azeotrope), and achieve very low heptane leftover in the bottom layer ethanol. If heating and boiling, the continuously-mixing mixture will have a single averaged b.p. and vapor composition ratio, but if gently evaporated without stirring, the top layer (which has 98% heptane) will evaporate with its azeotropic ratio and relatively high vapor pressure. Read my article to which @downtheterphole posted a link here here for you, then the comments of that thread. It is a very confusing issue, but suffice it to say I trust your friend’s results within a conservatively high margin of error… I wouldn’t drink that tincture, iow.
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