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Antoine Equation vs Homedistiller.org calculators

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Antoine Equation vs Homedistiller.org calculators

Postby Harry » Fri Oct 22, 2010 3:57 am

Mike Nixon (co-author of The Complete Distiller) has discovered an anomaly in the calculations of the Homedistiller.org site. After comparing the calculator figures to results derived using the Antoine Equation, Mike has written this paper to bring the error into focus and correct the tables.

Reviews and comments are welcome.

http://distillers.tastylime.net/library ... ine_nixon/
.


Slainte!
regards Harry
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Re: Antoine Equation vs Homedistiller.org calculators

Postby Tracker » Fri Oct 22, 2010 4:46 am

I just wish that I had the time, inclination and desire to read all that because I'm sure it would have a benefit to my hobby but the only drawback is that after I did all that, I would still not understand it. :cry:
Sadly I will have to leave that for the more technically minded amongst us.

I will just have to stick to the principle that I do this 'cos I know it works for me.


Just wish I was younger some times.
Cheers.
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Re: Antoine Equation vs Homedistiller.org calculators

Postby stillton » Fri Oct 22, 2010 11:23 am

im totally stupid when it comes to math.. but there was some logical reasoning in there that i believe i can grasp.

why is the data on page 4 not compared with two plates of the Antoine Equation? makes it a bit confusing to compare the numbers. or will that value differ depending on what kind of still you run? if so, what are the compensations you might want to use on different kind of stills?
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Re: Antoine Equation vs Homedistiller.org calculators

Postby loneswinger » Fri Oct 22, 2010 1:49 pm

Antoine's equation is an approximation, and in the case of ethanol and water, not the greatest, at least not with a single set of coefficients. There are higher order extensions to Antoines' equations that will give more accurate values if you really wanted to do it this way. Clearly the approximation used by Nixon is in error since there is no longer an azeotrope of ethanol and water with this approximation.

Also, Mike was a little careless with his use of both mole fractions and ABV, a conversion which is not straight forward and requires an additional calculation. For example a 49.6% ABV solution has 391.1 g/L of ethanol in it. This is 42% alcohol by weight and has a mole fraction of 20.1%. (since volumes are not additive it make the conversions tricky) (From CRC) I think that this is where the largest deviations come from when comparing Nixon's Antoine equation numbers with other calculators out there.

-Loneswinger

Edit: I checked the tabulated data on http://homedistiller.org/calc.htm and it's consistent with the measurements in Perry. The calculator on that page is based on a polynomial fit to the VLE data. However, I got slightly different conversions than what is on there going from %mass to %volume. The %molar to %mass conversion appears to be correct though (the Perry data is listed as mole fraction). The differences between mine and what is on the site are less than 2% so I am not sure where the difference is coming from. The calculator on this page http://homedistiller.org/ under the theory tab, gives slightly different values from the other also, so there are some inconsistencies but all less than ~ 2%.

There are probably updated VLE data that should be used for more up to date calculators. But, I think the ones on the HD site are sufficient for our purposes.
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Re: Antoine Equation vs Homedistiller.org calculators

Postby Harry » Sat Oct 23, 2010 2:41 am

Forwarding Mike's reply to Loneswinger...
And if there's anything you take umbrage at, I suggest you communicate with the man personally via email (found at the end of this communique), rather than have this thread descend into a pissing contest.

Here 'tis...

Oh dear ... someone is really having a bad hair day!

What made me smile was the statement that I was being a bit careless with my use of both mole (mol?) fractions and ABV, and then saying that it's a conversion that's not straightforward.. I never said that an additional calculation wasn't required, but for those who don't like maths, I simply put down the simple conversion calcs you need to go either way (derivation below, for those interested). For one who is doubtless stringent in his definitions, I was also surprised he didn't draw the distinction between ABV as being a dimensionless ratio (vol/vol) and that number expressed as a percentage. Forgetting to multiply or divide by 100 make a wee bit of a difference to the results of an equation. That became evident when he stated that a 49%abv solution has a mole fraction of 20.1% ... a fraction is a percentage?? I also presume he was being a bit picky when using a value of 0.7885 gm/ml (at what temperature?) instead of the accepted 0.791 gm/ml at 16 deg.C, the STP value for temperature. Using that, as I did, I was clearly guilty of being 0.0025 gm/ml out. I wonder if the International Standards Committee knows that it's made such a grave error, or is it perhaps that some regard the domestic American standard temperature of 20 degC as sacrosanct?

So by all means use the On-Line calculator as your gospel if you believe that boiling a 7% mix will yield a 47.4%abv vapour. This will mean such a lot to Scottish whisky distillers who's incompetence results in producing just 25%abv from their wash stills. Such a pity too that poor old Jules Antoine Lissajous got it so horribly wrong when he came up with an equation that he blissfully thought would give more accurate results than the Clausius-Clapeyron geezers whose equation was based on an ideal gas. Of course, he did know that his equation would require more constants if you wished to refine the results you get in different temperature ranges, but the usual three seemed adequate enough for me in a short paper ... if only to save time and ink. I look forward to the next edition of Perry's when they discredit those three old frauds!

Now for the promised conversion from %abv to mol fraction of Ethanol (Xe), and back again.
Let me start by telling you up front what values I'll be using:

Ethanol: 1 mol = 46.068 gm
Density of liquid ethanol at 16 deg.C = 0.791 gm/ml
Volume of 1 mol of pure liquid ethanol = 46.068 / 0.791 = 58.24 ml
Me = mols of Ethanol in mix
Xe = mol fraction of Ethanol in mix

Water: 1 mol = 18.016 gm
Density of liquid water at 16 degC = 1.000 gm/ml
Volume of 1 mol of pure liquid water = 18.016 ml
Mw = mols of water in mix
Xm = mol fraction of Water in mix

Now Xe = . Me .
(Me + Mw)

so Me = . Xe .
(Me + Mw)

and Mw = Me x (1 – Xe)
Xe

Now %abv = . 100 x volume of Ethanol in mix .
volume of both Ethanol and Water

%abv = . 5824 x Me .
(58.24 x Me) + (18.016 x Mw)

%abv = . 5824 x Me .
(58.24 x Me) + .18.016 x Me x (1 – Xe).
Xe

%abv = . 5824 x Me x Xe .
(58.24 x Me x Xe) + (18.016 x Me) – (18.016 x Me x Xe)

%abv = . 5824 x Xe . RELATION 1
(40.224 x Xe) + (18.016)


So Xe = . 18.016 x (%abv) . RELATION 2
(5824 – 40.224 x (%abv)

Now that wasn't quite as bad as having a tooth pulled out, was it?

If anyone still finds it difficult to understand, then I urge you do a bit of a brush up on your basic maths before tackling a big-boys book like Perry's. Please don't take your frustration out on everyone else. I'd always supposed this to be an adult forum for exchange of knowledge and mature debate, not a political dog-eat-dog slanging match.

And before some idiot says I'm claiming to "know it all", I've said it before and will say it again ... I don't, and firmly believe there is no such thing as a "Guru". If I'm wrong in anything I've written, then please do me the courtesy of showing me exactly where and why, and back it up with more than just vague references to "a higher authority". Correction and guidance I welcome ... I just can't abide personal attacks from people who seem to have an axe to grind.

Cheers!
Mike Nixon
mike@silverkey.co.nz
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Re: Antoine Equation vs Homedistiller.org calculators

Postby Harry » Sat Oct 23, 2010 5:14 am

Just to clarify some things here...

Tony Ackland (author of original homedistiller site) and Mike Nixon, are old friends and colleagues. Mike has lost touch with Tony and therefore would not have even let out these findings to the public if he (Mike) could have resolved the issue in private. However as we all know from recent events, Tony no longer has control of his own content on homedistiller, and therefore cannot rectify any erroneous calculations, even if he (Tony) had a desire to.
Hence the reason Mike chose to publish his findings in the paper in my Library.
.


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Re: Antoine Equation vs Homedistiller.org calculators

Postby stillton » Sat Oct 23, 2010 10:49 am

Nixon wrote:
Oh dear ... someone is really having a bad hair day!

What made me smile was the statement that I was being a bit careless with my use of both mole (mol?) fractions and ABV, and then saying that it's a conversion that's not straightforward..

....


Now that wasn't quite as bad as having a tooth pulled out, was it?

If anyone still finds it difficult to understand, then I urge you do a bit of a brush up on your basic maths before tackling a big-boys book like Perry's. Please don't take your frustration out on everyone else. I'd always supposed this to be an adult forum for exchange of knowledge and mature debate, not a political dog-eat-dog slanging match.

Then please dont turn it into one.. theres no use in fighting fire with fire if you really mean that.
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Re: Antoine Equation vs Homedistiller.org calculators

Postby punkin » Sat Oct 23, 2010 1:06 pm

I understand that both loneswinger and Mike have a lot invested in this. Loneswinger because he's actuallly trying to develop revised calcs to produce a better app, and Mike because that is his proffesional field.

I would second the motion that it is taken to email in a collaborative, rather than destructive vein and that you may both end up with a better understanding of each other at the very least, and the subject too hopefully. :8)


Until that happens i would be loathe to see this degenerate into a third person shitfight, and would probably go so far as to remove the posts or the thread from view. I'm sure that there's plenty here who don't want that to happen even if there's one or two who don't give a fuck.
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Re: Antoine Equation vs Homedistiller.org calculators

Postby loneswinger » Sat Oct 23, 2010 2:35 pm

Wow. Sorry Harry for you being a 3rd party to this. For Punkin, the only stake I have in this argument is to not spread misinformation. I don't really care what anyone thinks of me personally.

I will address this line by line as best I can. I am not real keen on dealing by email with the man after reading what he has posted here lately via Harry.

I am going bald so every day is a bad hair day. That said, I had no ill feelings and was quite joyful while writing my previous post. Not so much this one (more joyless now)

Not sure what I said to piss him off. I was advocating the use of experimental data over theoretical. That is all. Perry is not the only experimental measurements, I will link some more a little later. Doesn't anyone think that someone in the entire field of chemical engineers and world wide distilleries would have noticed these glaring errors in the VLE diagram?

He put ABV in place of mole fractions within the Antoine equations, there is a large difference between these two measurements of alcohol content is all I was pointing out.

I don't care about fraction to % is multiply by 100, thanks Mr. O!! I doubt anyone on here was confused by my carelessness there.

I am not picky about small changes in density, I had a CRC book handy so I could just use a single line out of convenience. Everything was STP which I believe is how ABV is normally measured but I could be wrong. This is why VLE tables like to list mass fractions or mole fractions since they are not temperature dependent, g/L or ABV are both temp dependent.

Scottish distilleries are collecting ~ 47% alcohol when there is 7% in the wash. But the collected ABV goes down as the wash ABV goes down. When it is 2% they are collecting ~ 17%. They keep collecting until the distillate ABV is something like ~ 1%, and the boiler ABV is ~ 0.1%. All the distillate goes into the same container and the resulting mix is that 25-30% low wines you mentioned.

In Mike's rebuttal he conveniently forgot to address the lack of the azeotrope, which by the way (in case somehow everyone in this community didn't already know this) boils at a lower temp than pure ethanol. Something you are not going to get with Antoine's equation. Which is why the equation clearly does not apply to our needs.

This whole thing is so silly that I can't believe I have to argue my case at all.

Please don't lock this thread yet. I want to link some experimental VLE data which I will do by editing this message. After that I promise not to post on this thread again. The rest of you can make up your own mind.

-Loneswinger
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