This thread is hugely confusing to me, but that's probably because of my own ignorance; first off, the use of a fractional distillation column implies that this is not a pot still. A pot still, from my understanding, is a boiler with a corner on the top for vapors to move down. A fractional distillation column is a hollow cylinder, typically made of glass, with indented bits of glass called trays (or hollow and packed with copper/broken glass/stainless steel) for the vapor to condense upon. The theory of operation is slightly different from running a reflux column, but not by much. As someone pointed out earlier in this thread, distillation is high school chemistry stuff, or at least it used to be back in the day. I am a more recent graduate, but I experienced using a fractional distillation column in my organic chemistry lab at university where we used it to extract alcohols from a mixture; actually the fist of these labs was to chemically synthesize alcohol and distill it out of the mixture. I distinctly remember the smell of tequila in the lab (maybe from the chemical process we used) and that the best (highest ABV) distillations were from the students who went the slowest and best monitored the temperature at the top of the column. The ABV was measured by a grad assistant who was familiar with how to use a refractometer. That is a lab grade one; not one of those $20 ones you get on ebay.
In the FDC, the vapor condenses on a tray, then another bit of warm vapor passes by; if the condensed liquid contains some bits which are able to evaporate under this influx of heat, they will evaporate and continue climbing the column. The more indentations, the higher your theoretical plates and the better your separation. If you were to run your boiler at maximum temperature, then this wouldn't really work because you would keep increasing the temperature of the column and you would just spit out whatever you boil at the bottom; when you run these slowly you can watch the liquid creep up the column. In fact, it is remarkable to see the difference of ethanol climbing vs water; the water's high surface tension allows the water stay stuck to the walls of the FDC while any of the liquid with a bit of ethanol in it will continue flowing down the column. Think of stepping out of a hot shower and looking at the mirror; that is about what the inside of the column looked like when water vapor was creeping up. The temperature at the top of the column would go from ~78.5 C to very quickly ~100 C as the water made it to the top of the column. I haven't run my FDC in a few years, but this thread is making me want to get it set up again to take some pics to elaborate on these effects.
With the reflux column, you're running your boiler at full power, but you're chilling the column. So as long as you make sure that you have water running through the column at the correct temperature, you will get out whatever high ABV, and it will probably run quicker than the FDC setup; my problem with it is having to readjust the water the whole time to get the same product. The principle of operation is the same; you end up with a gradient of temperature through the refluxing part of the column which provides high ABV at the top and low at the bottom. You do want a metal reflux column because you want to be able to exchange heat from the inside to the chilling water as efficiently as possible; in an FDC, you don't want to transfer heat efficiently as you want that gradient of temperature across the whole length of the column. Reflux is the name of the process given to the condensing-vaporizing cycle that the mixture goes through inside the column.
With the pot still, you don't try to separate any more than the vaporization from the boil is giving you; you're running off at whatever medium ABV, and from what I can tell (I've never run a pot still, so what do I know, though I could if I removed the FDC from my setup and put the corner bit from the top to right on top of the boiler) it seems like through the whole run of hearts you will definitely have some heads left in the mixture because of how vigorously you're producing vapor. There isn't any column for separation, so whatever makes it into the vapor phase at any point will make it into your collection vessel. I assume that there is something I'm missing with the pot still for this to not be the case, but this lack of separation is also the reason that flavors and aromas will survive so readily with the pot still. I would argue that you can run a pot still by temperature, but it is unnecessary as you should be able to tell when you're at tails from the taste of the product. Using the thermometer in the pot still would be more of a binary indicator for whether you should keep going or not as you're dealing with a very complex mixture ie heads, hearts, and tails at the same time so you don't really know what the azeotropic temperature of the mixture is, but again, I've never run one, so wtf do I know, lolol. I guess if you didn't intend on consuming the product then you may want to use the thermometer, but if you're trying to do a separation of oil and alcohol, I would look to a more robust system like a reflux or FDC system as your solvent may pickup scents/flavors if you're not separating them well enough. I guess if you used the same solvent with the same plant, then it wouldn't matter so much, but if you want to get oils out of lavender and orange with the same solvent without mixing the flavors/scents good luck!
I noticed in the discussion of the azeotrope curve that people were talking about the wash composition and temperature, but you need to remember that each time the vapor condenses, it is essentially a new wash at whatever part of the column. So if I had my column set up well, then there would be the wash at the bottom at whatever low ABV, and as you climb the column the ABV of the condensed liquid increases. So each time the vapor condenses, vaporizes and then condenses again, it will be at a slightly higher ABV. This is the reason you can run an FDC by temperature, but you're measuring temperature of the vapor which is condensing and vaporizing again from the thermometer bob where it will pass to your condenser. If you look at the azeotrope curve again, you can see that if you're measuring the temperature of this vapor, you know the ABV of the vapor.
There was a mention in this thread that someone thought copper/stainless steel would work better as packing material in a column as it has better heat transfer; actually that is a negative for this type of system. The faster that the column packing is able to change temperature, the worse your ABV gradient from top to bottom of the column. Consider a metal pot on the stove with metal handles and then consider a glass pot on the stove with glass handles; from my experience, the metal pot handle will quickly heat up and I'll need pot holders in order to safely handle the pot. My glass pot, on the other hand, I am able to hold by the handle even after it has been on the stove for a long time. If I want my whole column to be one temperature, then I would pack it with metal, but I want there to be a significant gradient from the bottom to the top so that only ethanol is vaporizing at the top. This isn't to say that you can't run a FDC with copper packed in (I remember doing this in one of those organic labs, actually), but I would, and do, use a glass indented column for my stated reasons.
Actually, wikipedia does a pretty good job of explaining how a FDC works in small and industrial scales, so if you're super confused about how or why this works, try out their explanation.
https://en.wikipedia.org/wiki/Fractional_distillation" onclick="window.open(this.href);return false;" rel="nofollow
This isn't reinventing the wheel; this is using the peer reviewed, best methods wheel, lolol.
PS: after looking back through the thread, I think maybe my confusion is because I misinterpreted the intention of the thread; was the point of the thread to determine if you can run a pot still by temperature? Was it to determine what process BurntEloi uses? It seems like BurnEloi wants to know about urethane in his product, but that isn't what Pikey wanted to talk about, I think. What is the topic of this thread? A demonstration of confusion? Also, it looks like BurntEloi knows what he is doing as far as using his still; woo chemistry sets!
PPS: WALL. OF. TEXT.
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way to confuse particularly newer guys with horse shit. I don't want to post to much on factional stills as they are off topic for this thread and generally stills more commonly refured to as fractional towers are not used for alcohol distillation but still always use coolant for condensing.
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(Not Proven as yet). It works fine for me at the moment, but one of these days I will make a batch of washes and do some experiments to see what I can see. 