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Author: Subject: Moonshiners' 'Thumpers': Myth or Reality?
blogfast25
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[*] posted on 18-2-2015 at 03:06


Quote: Originally posted by Zombie  


It is the interaction of vapor / liquid that strips EtOH from the liquid (beside evaporation).


Again, relatively minor gripe.

In modern fractionating theory, the process is considered just another counter-current separation method like liquid-liquid separations for instance.

Vapour gets sent up by boiling and liquid gets sent down by the refluxer. Mass transfer occurs between the two phases with the more volatile component being enriched in the vapour phase according to the x,y operating diagram.

You want to call that an 'interaction' but that's unnecessarily vague.




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[*] posted on 18-2-2015 at 04:23


Quote: Originally posted by blogfast25  
Quote: Originally posted by deltaH  
Real life is typically twice that , as a very crude rule-of-thumb, because of inefficiencies. It's a really quick way to estimate if you want to go from say 0.05 mole fraction ethanol to say 0.5, how many stages you're going to need.



A minor gripe. That statement is fairly meaningless.

Fractionated columns in industry are designed using fairly accurate design criteria to make them fit-for-purpose.

Actual column performance is then determined mainly as the Number of Theoretical Plates (as well as other parameters) (McCabe Thiele, in essence).


When I say 'real life', I mean real vs ideal, nothing about professional industrial column design. This amateur friendly rule of thumb for distillation does in fact have a theoretical basis... the Gilliland correlation used by professional chemical engineers. As you probably know, but for the benefit of others, Gilland undertook a study of actual commercial distillation over a wide range of types and purposes and plotted them on scales so that an emperical correlation could be drawn between the number of real trays and the real reflux ratios in actual operation versus the theoretical minimum stages and minimum reflux. What he found was this:
gilliland data.gif - 14kB
Now, notice that there is a much larger number of dots near the elbow region. If you take my abovementioned rule of thumb of N = 2N_min, substitute that into his y axis formula and make the assumption that N >> 1, you arrive at an y-axis value of 0.5, which is the upper-bound of that main grouping. That means this is a safe value to pick for most cases to get the job done within reason.

Professional column design, like you rightly say, are done to strict guidelines, but this rule of thumb is very amateur friendly if you're not trained in chemical engineering.




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[*] posted on 18-2-2015 at 04:43


Delta, you are not living up to your tagline very well.
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[*] posted on 18-2-2015 at 05:28



Bart quote.jpg - 11kB




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[*] posted on 18-2-2015 at 05:33


Delta:

That is a very interesting study and new to me. Time allowing, I will look into that with more zeal.

I still prefer (old habits die hard!) the cumbersome calculations needed to design a suitable rectifying system from scratch because it's such a good example of where rationalism, empiricism and historicism blend well and produce real world results.




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[*] posted on 18-2-2015 at 05:53


The Gilliland correlation is old, it's part of what's called the FUG[K] shortcut column design method (stands for Fenske, Underwood, Gilliland, Kirkbride). First you calculate the minimum number of theoretical plates using the Fenske equation, then you calculate Rmin from the Underwood equation, then use those values in the Gilland correlation with your rule of thumb of choice and finally the Kirkbride tells you the best tray to feed on. Easy peasy... kinda :o

It's covered over the net and in many chem. eng. separation texts.

***************************************
The free software Chemsep LITE, for those who are familiar with distillation column, is a very powerful and easy software to simulate equilibrium columns, draw McCabe-Thiele diagrams, phase diagrams and much, much more. It comes with quite an extensive library of components and thermodynamic models and data. For a modest fee, the author will sell you the full version that can do non-equilibrium column design with a very wide range of industrial packings and trays. It's impressive to use. Chemsep LITE also automatically comes when you download COCO (which it integrates with), the free process simulator for multiple unit operations.

Anyhow, I'm digressing from thumpers...

[Edited on 18-2-2015 by deltaH]




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[*] posted on 18-2-2015 at 06:11


Quote: Originally posted by deltaH  
The Gilliland correlation is old, [...]


I'm only 18 so I wouldn't know about that... Nope, 81. Dammit, I'm so old I can't remember when I was born! :o

[Edited on 18-2-2015 by blogfast25]




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[*] posted on 18-2-2015 at 06:17


Quote: Originally posted by blogfast25  
Quote: Originally posted by deltaH  
The Gilliland correlation is old, [...]


I'm only 18 so I wouldn't know about that... Nope, 81. Dammit, I'm so old I can't remember when I was born! :o

[Edited on 18-2-2015 by blogfast25]

You're as young as the woman you feel ;)

[Edited on 18-2-2015 by deltaH]




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[*] posted on 18-2-2015 at 06:53


Question for Zombie:

What method do you use for alcohol determination?




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[*] posted on 18-2-2015 at 09:32


One method that may be of value would be "determination of boiling point." Toggle the diagram below. However, I would not try to use this particular diagram as the axes are not scaled. Surely there are scaled ones available on the internet.



bp-ethanol-water system.gif - 6kB




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[*] posted on 18-2-2015 at 09:50


Magpie:

Accurate BP determinations (e.g. capillary method) aren't easy and are time consuming. We may have to analyse up to 50 samples.


[Edited on 18-2-2015 by blogfast25]




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[*] posted on 18-2-2015 at 10:11


Ethanol and water have strongly differing dielectric constants, so measuring the capacitance of the solution with a multimeter using a small vial and two fixed electrodes should work well. You would need to calibrate of course from a set of alcohol solutions of known strength.

NB: the electrodes would need to be physically well fixed in the vial to not move at all so as to maintain consistency and insulate the electrodes with a thin layer of... whatever :)

Physics is NOT my strong point, so not sure if this can work.

If too small a capacitance is a problem, one could use an open multiplate variable capacitor and immerse it (not sure if immersion would be a problem). The only danger there is that you would need to make sure that no air bubbles trap between the plates as this would introduce an error. Tap it?

[Edited on 18-2-2015 by deltaH]




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[*] posted on 18-2-2015 at 10:17


Whatever method of determining the EtOH concentration won't matter muchly, so long as it's granularity is reasonably fine (e.g. 0.5%), is done with the same equipment, and by the same operator.

It's a Comparison, so the absolute accuracy will not be vital.

Your suggested refractometry thing would be fine for this purpose.

Some calibration would make your data more generally useful of course.




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[*] posted on 18-2-2015 at 10:25


Quote: Originally posted by aga  

Your suggested refractometry thing would be fine for this purpose.

Some calibration would make your data more generally useful of course.


In all likelihood, yes. A rough idea of both accuracy and repeatability would be useful. A simple statistical analysis on the obtained data would give an idea of confidence levels.




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[*] posted on 18-2-2015 at 10:28


Quote: Originally posted by aga  
Whatever method of determining the EtOH concentration won't matter muchly, so long as it's granularity is reasonably fine (e.g. 0.5%), is done with the same equipment, and by the same operator.

It's a Comparison, so the absolute accuracy will not be vital.

Your suggested refractometry thing would be fine for this purpose.

Some calibration would make your data more generally useful of course.


The refractive indices of water and ethanol vary by only 0.027. So increments of 0.5% would mean increments in refraction index measurements down to 0.000135 :o Is that typical of these instruments (never worked with one, so wouldn't know)?

[Edited on 18-2-2015 by deltaH]




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[*] posted on 18-2-2015 at 10:46


Quote: Originally posted by deltaH  

The refractive indices of water and ethanol vary by only 0.027. So increments of 0.5% would mean increments in refraction index measurements down to 0.000135 :o Is that typical of these instruments (never worked with one, so wouldn't know)?



Yes. There are refractometers that are specifically designed for EtOH/water, in that range of index.




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[*] posted on 18-2-2015 at 10:56


Nice! Cost?



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[*] posted on 18-2-2015 at 11:02


Quote: Originally posted by deltaH  
Nice! Cost?


About £25.

I think 1.0 % will be about the accuracy to be expected but if the overall variation S is good then that will be good enough.

Better than 'billy bubbles'! :D




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[*] posted on 18-2-2015 at 11:40


Yeah, PERFECT!



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[*] posted on 18-2-2015 at 12:11


The thumper serves as a partial takeoff head to drain off water and some of the "fusel oil". It's not as efficient as some of the fractionators built into modern so-called moonshine stills.



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[*] posted on 18-2-2015 at 12:30


There's a Digital refractometer :-

http://www.ebay.co.uk/itm/Refractometro-digital-de-Alcohol-p...




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[*] posted on 18-2-2015 at 13:56


Quote: Originally posted by blogfast25  
Quote: Originally posted by Zombie  


It is the interaction of vapor / liquid that strips EtOH from the liquid (beside evaporation).


Again, relatively minor gripe.

In modern fractionating theory, the process is considered just another counter-current separation method like liquid-liquid separations for instance.

Vapour gets sent up by boiling and liquid gets sent down by the refluxer. Mass transfer occurs between the two phases with the more volatile component being enriched in the vapour phase according to the x,y operating diagram.

You want to call that an 'interaction' but that's unnecessarily vague.



Mass Transfer. Correct. Even when I know the lingo I tend to oversimplify.




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[*] posted on 18-2-2015 at 14:11


Quote: Originally posted by blogfast25  
Question for Zombie:

What method do you use for alcohol determination?


Breathalyzer... :P

No, I have a Chase Inst. hydrometer calibrated at 60*f, and use a Kessler -20*C / +150* C thermometer.

My runs begin @ 80% abv, and I stop @ 20% abv.
Average or final proof @ 100.

[Edited on 18-2-2015 by Zombie]




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[*] posted on 18-2-2015 at 14:14


Quote: Originally posted by Magpie  
One method that may be of value would be "determination of boiling point." Toggle the diagram below. However, I would not try to use this particular diagram as the axes are not scaled. Surely there are scaled ones available on the internet.






I posted one up in the first few pages here.



Vapor-Liquid_Equilibrium_Mixture_of_Ethanol_and_Water.png - 15kB




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[*] posted on 18-2-2015 at 14:22


Quote: Originally posted by chemrox  
The thumper serves as a partial takeoff head to drain off water and some of the "fusel oil". It's not as efficient as some of the fractionators built into modern so-called moonshine stills.



Pretty much on the money there.
A large part of what they do is compress the fractions allowing the lightest to come of cleaner. Same with the desired middle fraction (EtOH), and the less volatile keytones, fuesils last.

[Edited on 18-2-2015 by Zombie]




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