Reflux Splitting

[mash rookie]

Hi Rock. I am having some coffee and am a little more alert. I know you have been following. Please keep in mind the main goal is fractions separation. There are several things I learned with these tests.

I have understood SPP from the first moment I saw it. Wait for it...

First, Yes I used reflux return, centrally from the downcomer tube to mid range of packing. It actually lowered the ABV as compared to running without it.

What you are talking about is exactly opposite of what you want to do. You want to reduce vapor speed in packing and reduce pressure. My tests confirm this. Myles agrees in at least part and has offered additional explanation about vapor speed.

A thumper at the base would work well. After that, vapor needs very slow lingering speeds to achieve equilibrium in the packing.
I stated in LW’s thread to turn his system upside down. I was serious. If he placed it on a thumper and allowed vapor to continuously slow in packing above, greater fraction separation would occur.

I read a very simple statement in one of the links FD provided. “Once equilibrium is established, it is very easily disturbed.”
It reminds me of the distillation definition of the word. Equilibrium is when each partial pressure compound (fraction) is occupying its comfortable little desired space. Additionally, pressure crowds them in the plane and vacuum lets them stretch their legs. Ahhh, Flying first class is comfy.

Consider again what he taught us about fractions being partial pressure compounds. Their positions in the column are not based on weight or temperature.

I was already using a finer, denser packing than everybody using scrubbers with great success. I only worried about collapsing to a point of choking. My obsevation is I can go much tighter than I have done to date.

SPP works because it is a very fine tight medium. It provides maximum surface area for vapor. It does not collapse because of its shape and composition. Remaining consistent, channeling is reduced or eliminated. I can see how it is great stuff.

A reflux return is still a very viable tool for redistillation however, the collection device can not be restrictive to the vapor path. Reflux centering rings should follow this rule as well. After watching the glass column I don’t really see a need for centering rings or redirectors in 36” I think a screen cone directly beneath the reflux condenser might be of some help.

Armed with fresh understanding, I will continue to search for the perfect ballance of packing density and vapor speed.
Mash Rookie

[LWTCS]

Consider again what he taught us about fractions being partial pressure compounds. Their positions in the column are not based on weight or temperature.

Sorry, but this needs to be worded more accurately MR. At present, this seems to be a completely inaccurate statement.

[myles]

MR I think you are inadvertently miss-interpreting the comment about partial pressure compounds and to be honest this can NOT be applied to short columns. IIRC this was in refference to great big fractionating columns. In the shorter columns there is unlikely to be any fractionating at all WITHIN the column, as for most of the time the entire column is going to be filled with a single fraction.

Sort of like a slow escalator. Eventually a transition point will be reached and this will slowly move up the column. You only get true fractionation within the column if it is tall enough to establish the appropriate temperature/pressure/whatever else it needs, gradient from top to bottom.

[Frosteecat]

So at what sizes do we make the jump from no -fractioning to fractioning? The rig at the distillery I toured in Butte was basically a 30 foot column in 10 foot parallel sections and he seemed to have near total control of the process from near neutral to pot still type results, on command.
What's the "low end" of height for this kind of control, generally speaking???

[mash rookie]

It is an absolutely correct statement Larry. I thought FD did a good job of explaining it to you a few weeks back. If you have a different understanding please explain it.

I will try my way of explaining it. Here we go. You aggree that your boiler will boil at a different temp depending on alcohol concentration. Right? You also know that the contents do not contain H20 and Azeotrope (a pure compound) ethanol. Right? Water aside, the alcohol is made up of a wide range of different alcohols we refer to as fractions. Agree?
We also know once boiling that they come of in order. Heads, Hearts and tails. Agree?

To understand why the mixture boils at a given temperature and why the fractions come off in order you have to start with understanding Raoults law and the reality of partial pressure compounds. Each compound has a different molecular vapor pressure. Higher pressure molecules release and come off at lower temperatures. Because the (BP’s) pressures of the various alcohols are so close, they will come off with their closest neighbor. Hence the term “Partial pressure compounds”. Consider them as little office workers punching a clock to leave for the day. The ones with the most seniority get to be at the head of the line. New guys bring up the rear. Because of union concerns this will never change.

Temperature is the janitor. He is controlled by these pesky union guys and is only allowed to rise as the higher seniority guys leave. If you read the links and papers FD offered you will see that nowhere is fraction weight or column temp addressed.

Myles I would beg to differ. Although certainly not as efficient as a very tall column. I think we have long established that there is fractioning happening in shorter columns as shown by our ability to not just remove them in order, but by imperial evidence of the superiority of packing over the same size plated column when it come to flavor separation. While I agree with your escalator analogy, and agree they are coming off in order but argue that the fractions are too mixed and close to only have one in a column at a time. In fact it is more difficult to stabilize a shorter column and keep it stabilized as fractions are removed.
I argue, (and think you agree) that the difficulty is caused by excessive vapor speed. The vapor is not allowed to linger and enjoy multiple evaporation cycles. (partial pressure orgasms)
Keeping a column equilibrium stabile is key for steady consistent removal of fractions as they occur.

I personally believe that a shorter, larger diameter packed column will be as or more affective at fraction separation because of the ability to slow vapor speed.

And to add. One of the papers notes that vacuum can cause as wide as a 10-20 deg C BP range greater than atmospheric. What does that tell you about pressurizing a column?

[myles]

Except for the minor detail that once the boiler is up to temperature the vapour leaving it contains ALL the fractions that currently reside in the boiler in varying quantities. It it the function of the column to split these up as far as is possible, throwing some back down to the boiler and allowing others to get past. Some of these you can not split and some you can.

You can do this with a short column and CM quite effectively, but slowly. The longer column lets you do it at a higher vapour speed because there is more time within the increased length for liquid to vapour interaction.

[mash rookie]

Except for the minor detail that once the boiler is up to temperature the vapour leaving it contains ALL the fractions that currently reside in the boiler in varying quantities.

Is that to say that you can not make cuts on a pot still because vapor is a homogenous mix of all fractions?

Referring back to my post, Alcohol fractions come off in the order of their partial pressures. The taller or more efficient the column the easier the separation, or our ability to separate and collect them separate of each other.

My working theory (ATM) is that a short column can be very effective if diameter is large enough to allow minimum vapor speeds and fast collection speeds. (Total condensed vapor volume)

BTW. I did diluting and sampling before spending the weekend on my boat. Test run A had a larger hearts section and a more pronounced tails than test run B.

Where the hell are you Dutchman when I need backup?? These guys are tough!

Yes Rock.

[myles]

Except for the minor detail that once the boiler is up to temperature the vapour leaving it contains ALL the fractions that currently reside in the boiler in varying quantities.

Is that to say that you can not make cuts on a pot still because vapor is a homogenous mix of all fractions?

Referring back to my post, Alcohol fractions come off in the order of their partial pressures. The taller or more efficient the column the easier the separation, or our ability to separate and collect them separate of each other.

My working theory (ATM) is that a short column can be very effective if diameter is large enough to allow minimum vapor speeds and fast collection speeds. (Total condensed vapor volume)

BTW. I did diluting and sampling before spending the weekend on my boat. Test run A had a larger hearts section and a more pronounced tails than test run B.

Where the hell are you Dutchman when I need backup?? These guys are tough!

Yes Rock.

Let me try to clarify this a bit. The pot still is invariably rut under the system of POWER MANAGEMEN. Most folks probably do this without actually realising it. In any situation where you have a mixture of different liquids being heated, the vapour liberated by that liquid contains ALL the components of the liquid.
However, the proportions of each volatile component in that vapour are variable and are influenced by both the temperature of the liguid and the proportions of the components within that liquid - and by many other factors.

If you use too low a power on the pot still what happens? You get heads being smeared all through the entire product run rendering it useless. What you try to do is apply sufficient power that the early run vapour contains lots of heads and a significant amount of ethanol. With luck by the time the concentration of low boiling point nasties - heads - has been depleted from the boiler, it still contains enough ethanol to make a reasonable hearts cut. The hearts still contain a fraction of "heads" but the concentration is low enough to be acceptable.

If you apply too much power to the pot still boiler you increase the proportion of high boiling point components in the vapour and you smear the tails through the entire run.

If you were to analyse samples of heads, hearts and tails from a correctly run pot still you would find that all the samples contain fractions of ALL of the components in the boiler, BUT in different proportions.

So how can we apply this on the reflux column. We do the early run and stabilisation at as low a power as is practical. The vapour produced by the boiler has a small proportion of ethanol and a high proportion of low boiling point volatiles, and we concentrate the heads as much as is possible. On our scale of columns we will never fractionate completely, but we do the best we can. We then either bleed the heads off slowly, or we use a heads trap and dump the heads etc etc but eventually we get to a situation where we have depleted most of the low boiling point heads out of the boiler. At this point we increase power, re-stabilise the column and take off the hearts, using the column to suppress the tails.

If you were to measure the vapour at the base of the column you would find it behaves EXACTLY the same as the pot still boiler. The vapour contains ALL the components in the boiler, but the proportions of them are variable dependent on running conditions. We can not get the situation where the vapour contains only a single volatile component from a liquid that contains a mixture of volatiles. We are using the column as a filter to re-condense the fractions we don't want at that moment in time and to pass the ones that we do want to collect.

[Bushman]

Let me try to clarify this a bit. The pot still is invariably rut under the system of POWER MANAGEMEN. Most folks probably do this without actually realising it. In any situation where you have a mixture of different liquids being heated, the vapour liberated by that liquid contains ALL the components of the liquid.
However, the proportions of each volatile component in that vapour are variable and are influenced by both the temperature of the liguid and the proportions of the components within that liquid - and by many other factors.

If you use too low a power on the pot still what happens? You get heads being smeared all through the entire product run rendering it useless. What you try to do is apply sufficient power that the early run vapour contains lots of heads and a significant amount of ethanol. With luck by the time the concentration of low boiling point nasties - heads - has been depleted from the boiler, it still contains enough ethanol to make a reasonable hearts cut. The hearts still contain a fraction of "heads" but the concentration is low enough to be acceptable.

If you apply too much power to the pot still boiler you increase the proportion of high boiling point components in the vapour and you smear the tails through the entire run.

If you were to analyse samples of heads, hearts and tails from a correctly run pot still you would find that all the samples contain fractions of ALL of the components in the boiler, BUT in different proportions.

So how can we apply this on the reflux column. We do the early run and stabilisation at as low a power as is practical. The vapour produced by the boiler has a small proportion of ethanol and a high proportion of low boiling point volatiles, and we concentrate the heads as much as is possible. On our scale of columns we will never fractionate completely, but we do the best we can. We then either bleed the heads off slowly, or we use a heads trap and dump the heads etc etc but eventually we get to a situation where we have depleted most of the low boiling point heads out of the boiler. At this point we increase power, re-stabilise the column and take off the hearts, using the column to suppress the tails.

If you were to measure the vapour at the base of the column you would find it behaves EXACTLY the same as the pot still boiler. The vapour contains ALL the components in the boiler, but the proportions of them are variable dependent on running conditions. We can not get the situation where the vapour contains only a single volatile component from a liquid that contains a mixture of volatiles. We are using the column as a filter to re-condense the fractions we don't want at that moment in time and to pass the ones that we do want to collect.

I agree with what you say Myles and it seems so simple in theory but the science is something I am still working on understanding. I have read Mike Nixon's article on "Questions about Distillation" and quite frankly will probably have to read it another couple times. In his article he refers to both the different alcohol, the LHV (latent heats of vaporization), something MR has refered to in early posts. He goes on and talks at the end of the article about taking a small part of the liquid surface anywhere in the column (doesn't matter where) and the liquid surface coming down from higher up the column where the temps are lower, and the vapour now flowing over it from below so it starts to warm up by conduction, and as it gets hotter the rate of evaporation from it's surface increases so the net effect is that it looses heat because the volatiles take with them heat at a faster rate than conduction can replace it. This I imagine is the equalization and then separation into a higher abv. How we do this on a smaller column with similar results to get a higher abv is what I am having trouble grasping.

[mash rookie]

Ahh I see what your getting at and agree with your post. Faster vapor=increased pressure which leads to higher boiling/ evaporation temps, while a vacume decreases boil points in turn helps fractions at lower temps and greater speed.

Sorry Rock, I did not respond clearly to your post.
There are two separate issues here. Vapour speed and pressure. Increased vapour speed reduces “linger time” between vapour and the packing, reducing evaporation cycles thereby lowering ABV. It will only increase pressure if there is a restriction not allowing it to pass freely.
Pressure narrows the Boiling points as compared to vacuum which expands boiling points. My conclusions are that any restriction that creates pressure would be detrimental to fraction separation in our relatively short columns. Vapor speed should be limited to the packing’s ability to reflux it. My recent observations appeared to show that take speed off speeds will be mostly determined by diameter. Increased vapour speed did not increase take off rate, just lowered ABV. I will study that closer as my tests continue. Again my theory ATM, is that a shorter wider column may do better with fraction separation than a tall narrow column. My belief is that with a larger diameter we can slow vapour speed to a minimum allowing for better refluxing within the packing.

In any situation where you have a mixture of different liquids being heated, the vapour liberated by that liquid contains ALL the components of the liquid.

Yes but concentrations of fraction contents will change as a run progresses and lower boiling point alcohols are depleted. Here are some excerpts from the distillation manual link.

As you heat your mixture it boils, and the vapor that comes off this liquid is
richer in the lower boiling component. The vapor moves out of the flask and
condenses, say, on the first centimeter of column packing. Now, the composition
of the liquid still in the flask has changed a bit — it is richer in the higher
boiling component. As more of this liquid boils, more hot vapor comes up,
mixes with the first fraction, and produces a new vapor of different
composition—richer yet in the more volatile (lower-boiling) component. And
guess what? This new vapor condenses in the second centimeter of column
packing. And again, and again, and again.
Now all these are equilibrium steps. It takes some time for the fractions
to move up the column, get comfortable with their surroundings, meet the
neighbors And if you never let any of the liquid-vapor mixture out of the
column, a condition called total reflux, you might get a single pure component
at the top; namely, the lower-boiling, more volatile component all by
itself!

[myles]

OK I think I see where there might be a bit of confusion.

Yes the vapour leaving the BOILER contains a mixture of all of the volatile components in the boiler at that moment in time. And yes the composition of that vapour changes as the various components are depleted. And yes the fractions come off the COLUMN one at a time (but never off the boiler one at a time).

However, I am fairly sure that the fractions leaving the column have been separated on the basis of their boiling points - although perhaps this should be more acurately described as their EVAPOURATION points, since boiling within the column is not actually required at all, and would probably be a bad thing if it ever did occur.

If you compare this to an industrial fractionating column where multiple products are taken off at different points all at the same time, what is being controlled is actually the temperature of the column at each take off point. Well I think that is what is being controlled.

This seems to have diverted a bit off topic - but that happens sometimes and it is all interwoven so it is relevant. loops within loops as it were.

[flyingdutchman]

Wow
Go away for a week and i missed a great discussion! Kind of seems like you guys are basicaly saying the same thing just differently.
Mash seems like at least part of what you are refering to is what my friend calls residence time.
t=V/q
where t is used as the variable for residence time, V is the capacity of the system, and q is the flow for the system.
http://en.wikipedia.org/wiki/Residence_time
That would tie in nicely to the idea that a larger diameter column can handle a greater volume of vapor (reduced vapor speed so more time in contact with the packing/plates). So a 4 inch column could be run at say 4 times the rate of a 2 inch column (generally speaking).

In general I believe the number of available plates (the boiler being the 1st one) would determine how effieciently you can seperate the various volatile components based on their partial pressures. Since with say packing it requires some fixed length

For scrubbers the HETP is about 10cm (4 inches), whereas it is 24-38 cm (10-16 inches) for raschig rings or marbles.

I would think the taller the column the greater the number of Theoretical Plates and the better the seperation. Provided you run the system within its design parameters.

[myles]

And IIRC Dutch, at low vapour speeds and high reflux ratios you can reduce that HETP considerably. I think that was why the short column on the PDA1 worked the way it did. You can get good fractionation with the short column it is just so slow.

This topic was supposed to be about trying to push the performance of the packing to increase the product rate, and we have also seen that there are other ways to achieve simmilar results.

I know of 1 guy that can get from wash to azeo with just 50cm of packing in a 2" column. Not sure how fast though.

[mash rookie]

Provided you run the system within its design parameters.

That is the fun of designing.

The wider column ratio will allow more residence time for greater evaporation cycles.
This should also provide the added bonus of being able to maintaining better equilibrium.
Slower vapor speed will be less disruptive as distillate is taken off. With higher numbers of distillations and less disruption fractioning should be improved.

Taking the position of increasing packing density to maximum I ask, what is maximum density? One, I consider that if too little vapor space/ ratio is provided it will create an opposite reaction of increasing vapor speed and an undesired reaction of compressing vapor. Neither of which are desired. Input vapor speed would have to be slowed to a point that vapor will not reach the top.

The thing that hit me in the head like a sledge hammer on my recent tests was the detrimental affect caused by the perforated top plate. It has completely changed my thinking.
Not being able to provide vacuum, I am still considering it as part of the process. Pressure or lack of it affects distillation. What is vacuum? The absence of pressure.

I am visualizing a changing density packing structure with a steady reducing density as the column rises. The goal is reducing pressures at each step to allow improved fraction separation.

Wait,a new thought!!!
What I really would like to do is build a turbine like distillation machine. Vapor forces past a narrow restriction powering a fan blade at the boiler exit. The fan blade drives a vertical shaft. The shaft runs a larger diameter fan blade at the top of the column that pulls vapor up creating a vacuum. That just poped in to the pumkin. Still on my first cup of coffee.

[flyingdutchman]

The PDA1 must be an interesting column.

at low vapour speeds and high reflux ratios you can reduce that HETP considerably

I am guessing that they reduced the physical length of the column and thus the HETP, if we judge that by measuring linnear distance of packing. I wonder if perhaps by using a high reflux ratio they are cycling a small amount of distillate through the same packing in a sort of continous loop. Then the measured linnear distance of packing material doesnt truly represent the number of theoretical plates the distillate encounters.
The plus side is a short column (cheaper and smaller) with perhaps the added benefit of continually keeping the packing wet through out the run. Since its short the distillate may reach just about the bottom before it cycles again?
The down side may be thermal efficiency. I would think that it would cost a greater amount of energy due to BTU's (extracted) to keep it running. I would think a high reflux ratio means you would be pulling a greater amount of thermal energy out of the system. In fact I wonder if you could somehow rate the thermal efficiency by with something like E= BTU /T.P. ?
I am not saying its good or bad setup, just considering the implications...
It is a different sytem than what we are talking about but maybe does have some relevant implications with respect to the system we are talking about?

[mash rookie]

You always ask questions that are over my head Dutchman. I would think that BTU’s extracted (applied?)would be equal to the total ABV extracted.
What I am doing is applying less BTU’s to a larger diameter than typically applied to smaller, taller columns. (proportionally)

Please correct me where I am wrong. I am going to throw out my understanding and rational.

In an ideal column, held at total reflux with power input not a reflux condenser, fractions find their sweet spot in the gradient. Equilibrium. As product is removed other fractions rise up to take their place disturbing equilibrium. This is where take off speed has a major impact. The faster the take off the more difficulty maintaining a high ratio of equilibrium.
You have taught me that these partial pressure compounds change in composition during a typical batch distillation.
With stills the size typically used at our hobby level equilibrium is never maintained. We can only attempt to maintain a reasonably high equilibrium ratio of fractions as they are removed.

While taller is the typical method for maintaining a higher equilibrium ratio, I argue that time and distance are both factors. In the absence of distance, time can play a larger roll.
With a slower vapor speed and linger time “residence time” evenly distributed heat should be more stabile within the column.

Okay. Don’t hold back.

edit to add;
Slower vapor speeds should allow for denser, finer packing with increased surface area. Greater surface area = greater evaporation cycles. (I think)
Since partial pressure compounds are reacting on a molecular level, I visualize that finer packing is being equivalent to a larger taller column using a standard size packing. I see ghosts too

[flyingdutchman]

Ok I really agree with what you said but just for clarity (so were all on the same page) let me define (as I tend to think of them atleast)
Fractions: If I run a distillation and collect the distillate in say 100 test tubes I would say I have 100 fractions. I dont care what size they are, I divided the whole into 100 parts (hopefully based on thier different vapor pressures). Just beacuse I have 100 test tubes doesnt imply each test tube holds a different compound OR that there are not 2 or more compounds in any given test tube.

Equilbrium: When the variuos compounds are sorted out based upon thier vapor pressures, stacked like in the elevator analogy I would say we have reached equilibrium. Mind you some compounds have vapor pressures so close that we cant really seperate them in our column and thats fine I expect them to occupy the same space BUT overall they should be sorted based on vapor pressure (and of course how they interact with each other).

Equilibrate:When we run either an active or passive reflux sytem in total reflux we are equilbrating the system. Of course that doesnt mean we turn down the heat so low nothing is going through the evaporation/condensation cycle we turn it down just enough that is no longer escaping so that the various compounds can sort themselves out (equilibrate).

Partial Pressure: Any liquid (even a mixture of liquids) will have a vapor pressure which I think of as the pressure that the vapor from the liquid exerts back upon the atmosphere. The total pressure is just the sum of the individual pressures added together (hence partial or part of the whole). The actual partial pressure exerted by 1 compound is function of that compounds vapor pressure AND the mole fraction of the compound (actually you multiply the two to get PP). The GREATER the mole fraction (of that compound) the GREATER the percent it is of that total amount liquid is AND so the higher its partial pressure (a greater part of the whole). If the compound is 99.9% of the total liquid then it is a major contributor to the total pressure (even if it is of a much higher OR lower vapor pressure). How much of the compound escapes the liquid to the vapor depends on its partial pressure. So when distill and go from liquid to vapor back to liquid the compound will now have a new mole fraction and so a new partial pressure.

Thermal efficieny: How much heat I need to put in vs what I get out. Of course we cant compare apples to oranges so it needs to be exactly the same amount of distillate at exactly the same composition. I expect an uninsulated column loses heat to the atmosphere more than an very well insulated one all other things bieng exactly the same. So I would think of the uninsulated on as less efficient if I got the exact same product out of both.

[flyingdutchman]

So..

In an ideal column, held at total reflux with power input not a reflux condenser, fractions find their sweet spot in the gradient. Equilibrium. As product is removed other fractions rise up to take their place disturbing equilibrium. This is where take off speed has a major impact. The faster the take off the more difficulty maintaining a high ratio of equilibrium.

Thats the way I see it atleast.

these partial pressure compounds change in composition during a typical batch distillation

Well the compounds dont change but the partial pressure exterted by them does due to the vaporization condensation cycles changing the mole fractions of the liquid mixture. Not just at the plate above where it condenses but also at the plate below (becasue of what just left). I think what you meant anyways I just restated it.

With stills the size typically used at our hobby level equilibrium is never maintained. We can only attempt to maintain a reasonably high equilibrium ratio of fractions as they are removed.

Yep its a balancing act. Sure if we stay in total reflux we are in equilibrium but thats not our goal here. Indeed we can shoot for a something close to equilibrium (in the column) AS the fractions are collected. Which is again exactly what I believe you meant.

While taller is the typical method for maintaining a higher equilibrium ratio, I argue that time and distance are both factors. In the absence of distance, time can play a larger roll.
With a slower vapor speed and linger time “residence time” evenly distributed heat should be more stabile within the column.

Yep. However I see taller as a way to get a better sepearation and increased volume as a way to hold a greater reservoir of liquid/vapor in equilibrium. The larger the reservoir the more we can draw w/out distrubing the equilibrium too much. There is I believe is a caveat there. Lets talk physical plates just with respect to theory. Its not just residence time its cycles of vaporization and condensation that cause seperations. Lets say we have 2 identical diameter columns and I have 8 plates (ideal plates 100% effiecient) and you have just 2. Now lets say you get the exact same amount of seperation between say water and ethanol then something beyond residence time is going on. I believe you can only attain that by cycling through your plates multiple times to my 1 cycle through my plates. remember its not the volume of the plate its the number of vaporization condensation cycles in series. To do this I suggest your vapor travel from plate A to B to the condensor back to A back to B back to the condensor repeatedly. Now imagine both sets of boilers and columns are perfectly insulated (impossible I know). In my column all the energy going up is utilized almost exclusively to cause the vaporization condensation cycles (for 1 cycle up). Now in your column everytime you get to the top your dephleg is sucking out energy (just feel the water temp change) so that you can return to plate A. Multiply that by the number of required cycles and factor in the execllent ability of water to suck up heat/energy 4.183 joules/gram degree K. Thats not to say its bad its just there is a price to pay, there are no free rides. Thats why I think the multiple cycles and longer run times of the PDA1 is less thermally effiecient.

Slower vapor speeds should allow for denser, finer packing with increased surface area. Greater surface area = greater evaporation cycles. (I think)
Since partial pressure compounds are reacting on a molecular level, I visualize that finer packing is being equivalent to a larger taller column using a standard size packing

Yep i like it. Now thats a different story where you utilize a denser packing material with better surface to volume ratio and you do indeed get a greater number of TP per/linnear foot of column.

PS: I dont know this for a fact but I suspect the ability to break azeotrope under vacuum is more a function of the water ethanol interaction in an azeotope under vacuum rather then a general broadening of the overall BP difference. PM me I will send you a refernce
PSPS:
Shamefully off topic but check out the ethanol ethyl acetate azeotrope here
http://en.wikipedia.org/wiki/Azeotrope_(data)

[mash rookie]

Now lets say you get the exact same amount of seperation between say water and ethanol then something beyond residence time is going on. I believe you can only attain that by cycling through your plates multiple times to my 1 cycle through my plates. remember its not the volume of the plate its the number of vaporization condensation cycles in series.

What you describe is how a flute functions. Using a reflux condenser to recycle distillate has shown that it is easier to separate water from alcohol than fraction components that have closer pressures to ethanol.

I dont know this for a fact but I suspect the ability to break azeotrope under vacuum is more a function of the water ethanol interaction in an azeotope under vacuum rather then a general broadening of the overall BP difference.

It is even easier to separate water under vacuum but I still suspect that fraction separation will be easier as well.

Schnell’s statement is pretty encouraging.

I've been using vacuum stills for years as a chemist. They work great. I think they will make a great improvement in this hobby.
At 95 mm Hg the binary azeotrope is 99.5% ethanol and 0.5% water boiling at 33.4 C. This is trivially accomplished in a laboratory apparatus like shown above in previous pictures. I've done this thousands of times, literally.
At this reduced pressure pure water boils at 51.0 C and pure ethanol boils at 33.5 C. Their combined azeotrope is right under that.
i used to use a 50 C bath when I was in a hurry and a 40 C bath on my glassware when I wanted to be attentive to the seperation.

Believe me, you want this improved seperation. It's better than any other trick you can try with your columns, packing, reflux methods, etc.

Shamefully off topic but check out the ethanol ethyl acetate azeotrope here
http://en.wikipedia.org/wiki/Azeotrope_(data" onclick="window.open(this.href);return false;" rel="nofollow)

Wow. That is confusing. Is that an error? As binary azeotropes the bp is significantly lower. 6+ degrees. Their original BPs are only ½ a degree different. I think you need to explain yourself sir.

Not so shameful. The topic is distallation. Another distillation lesson from the teacher. Thanks.

edit; BTW, I like my new term. “Equilibrium ratio” it sounds cool.

[flyingdutchman]

Hi Mash

What you describe is how a flute functions. Using a reflux condenser to recycle distillate

Yes but it could just as easily be any type of packing and ANY two compounds like hexanes and propanol. The idea is if I pass through 8 vaporization/condensation cycles, in series, I believe you need to do the same to achieve the same degree of seperation.

I've been using vacuum stills for years as a chemist. They work great. I think they will make a great improvement in this hobby.
At 95 mm Hg the binary azeotrope is 99.5% ethanol and 0.5% water boiling at 33.4 C. This is trivially accomplished in a laboratory apparatus like shown above in previous pictures. I've done this thousands of times, literally.
At this reduced pressure pure water boils at 51.0 C and pure ethanol boils at 33.5 C. Their combined azeotrope is right under that.

Yes BUT...
1) Look at how the azeotrope has changed. At 760 mm Hg (1 atmosphere) the azeotrope is ~95% ethanol. At 95 mm Hg (0.13 atmosphere) the azeotrope is 99.5% ethanol. We didnt get a better seperation due to distillation or BP changes we changed the properties of the azeotrope by applying vacuum.

2) At 760 mm Hg water bp 100 C ethanol BP ~78.4 C. The BP difference is ~22.6 C. At 95 mm Hg water bp is 51.0 C ethanol bp is 33.5C the BP difference is 17.5C. They are not further apart they are closer!

3) Any seperation on a column is a result of the interactions between the different compounds (water, ethyl acetate, propanol, methanol, ethanol etc) with each other, and the column material (plates, marbles rocks etc). You didnt effect a better seperation here because of the interaction between the compounds and the packing materials, you changed the azeotrope, the interaction between just two distinct compounds. Yes you have less water in the ethanol but you are going to dilute that anyway (and EtOH is hygroscopic so trying to keep it at 99.5% is going to be rather difficult). Now tell me you can eliminate or greatly reduce the EtOH, EA azeotrope and I am interested.

Wow. That is confusing. Is that an error? As binary azeotropes the bp is significantly lower. 6+ degrees. Their original BPs are only ½ a degree different. I think you need to explain yourself sir.

I wish I knew what to explain. Its physical observation, its an azeotrope. Azeotropes can be positive or negative and its just an interaction between to substances. How they interact effects thier physical properties like BP (or vaporization) Remeber we dont live in an ideal world, things arent perfect (like in theory) so all that talk about ideal liquids was just that (a starting point for discussion). We can get close to ideal liquids (like hexanes and heptane) but that is theory not what really happens.

[myles]

Nicely said Dutch. Spliting the majority of the water out of the ethanol is relatively easy, even with a method as simple as freeze distilation. It is seperating the other alcohols from each other that is more challenging.

The properties of the azeotrope are very different to those of either ethanol or water, and there can be advantages in some applications, for reducing the pressure in the system. IIRC though vacume distillation is only applied to situations where you wish to extract a single fraction. I don't think for example it works very well for production of a multi layered product like a whisky. It is a tool for a specific job.

Perhaps it could be applied as a tool for heads compression on a short column? Never really thought about it before. Pressure Management for different phases of the run?

I cant remember where I saw it, but I believe that for single fraction separation, you can also create other intermediate azeotropes for multi stage distillation. Probably beyond the scope of this discussion though.

[mash rookie]

Im just not sure that vacuum is better so any pressure is bad. I am not saying the statement is wrong its just that I dont know one way or the other?

I am not yet convinced my conclusions are incorrect however I was not able to duplicate my calculations with the torr/temp graph. I think some things have gone over my head. My recent Studies left me somewhat confused with my comprehension. The example of a negative azeotrope adds a layer of complexity. My head is swimming a bit. I am doing the best I can to keep up guys.

I will explain my vacuum pressure conclusions. Three observations.

Working with a graph that does not exactly match with alcohol distillation I used it in a fashion not intended. Working with a fixed vacuum I increased known BP’s and compared to observed BP’s on the graph.
My conclusions were that there was an increasing spread of BP’s (percentage wise) as vacuum was increased. Plus 10% Plus 20% Plus 30% etc. Not taking the time to understand torr conversion formula I think I saw what I wanted to see.

I read in one of the manuals a statement that vacuum could increase BP differential by up to 20 degrees. It may not have any reference to alcohol distillation. Again I heard what I wanted to hear.

Personal observation. My strongest evidence, but yet open to interpretation. Using identical test washes and input power I recorded observations using packing and the same packing with an added perforated plate above the packing. My thoughts were that it would add considerable boiling action or liquid/vapor interaction increasing evaporation cycles.

Results were contrary to what was anticipated. ABV dropped by two points. (93% - 91%) Above 90%, two points is a lot of change in either direction.
Results were confirmed with cuts taste tests. Fraction seperation was reduced. The reason as yet to be proven.

Test batch one had cleaner and larger hearts section and a very distinctive tails onset. Tails were stronger in flavor.
Test batch two had a stronger flavor profile through the hearts and a smeared transition to tails. Tails were not as harsh as test batch one.

My conclusions, (help me out if you see this different)
The only affect I can conceive is the plate produced added pressure below in the packing area. Loosing performance, my thoughts are that the packing was not able to exercise as many evaporation cycles as it did without the added pressure. Alternatively considering a pressure cooker, added pressure possibly caused temp gradient in the column to rise bringing water and tail fractions higher disturbing equilibrium. Both negative affects.

What else but pressure could the plate have changed? This has caused me to conclude that pressure is detrimental to fractional efficiency.

Mash Rookie...... Loose screw test case one.

[Prairiepiss]

I would say that the uppermost packing in a packed column. Does a lot more work then everyone gives it credit for. You removed its interaction with the falling reflux off the condenser. And being the last stage in the process.

We already know packing does a much better job of cleaning the spirits up. By putting a lesser qualified tool at the top. You get a spirit that a plate would provide normally. Not as clean as what a packed section would give.

Not real sure pressure has anything to do with it. It has more to do with the tool used.

Just my two uneducated nickles.

[LWTCS]

I would say that the uppermost packing in a packed column. Does a lot more work then everyone gives it credit for. You removed its interaction with the falling reflux off the condenser. And being the last stage in the process.

We already know packing does a much better job of cleaning the spirits up. By putting a lesser qualified tool at the top. You get a spirit that a plate would provide normally. Not as clean as what a packed section would give.

Not real sure pressure has anything to do with it. It has more to do with the tool used.

Just my two uneducated nickles.

I can see how the physical plate loaded with a more dense amount of liquid at the top could affect the balance of action by virtue of back pressure.....
Back pressure at the lower end of the column evidently produces a more favorable result as has been shown.
Not added pressure as such,,,,just back pressure

[myles]

I would say that the uppermost packing in a packed column. Does a lot more work then everyone gives it credit for. You removed its interaction with the falling reflux off the condenser. And being the last stage in the process.

We already know packing does a much better job of cleaning the spirits up. By putting a lesser qualified tool at the top. You get a spirit that a plate would provide normally. Not as clean as what a packed section would give.

Not real sure pressure has anything to do with it. It has more to do with the tool used.

Just my two uneducated nickles.

I tend to agree with this. If you are going to try and combine plates and packing the logical configuration is packing above the plates. Let the plates do the grunt work. I don't think anyone would disagree that a plated column is a great tool for removing most of the H2O - and producing a quality flavoured product. This can even be a near-neutral flavoured product like some white brandies and grappa.

Use the plated column to get you 3/4 of the way towards azeo and then add a packed section afterwards for a final clean up.

Whether this is better or worse than packed for the whole length is a different issue. Personally, I think there is a lot of potential for a larger dia plated column, topped off with a smaller dia packed column for the final fractionation, for those folks that want a really clean product.

[mash rookie]

PP, I think you make a solid point. Although I did not remove packing I did have the down comer a solid 5”into packing returning distillate. It may not have been pressure as much as defeating the top few inches of packing. Its as good a theory as what I am working with. Combined with not being able to make it work mathematically and the negative azeotrope really has thrown me for a loop.

For some time I have been on the same page of using packing above plates or thumpers. I really want to understand and solidify my packing solutions before giving them a kick start. Once happy with packing designs I will add a base thumper. (Yes Larry. You heard me say that) This theory thread does push the level of comprehension. Hopefully my planned tests will shine more light on things for me.



edit; Just got a PM from the prof with more home work. Damn it. I wish I could quit working for a living and study this crap. I really find it fascinating until it hits me in the head like a brick. Vacation is soon. Maybe I can relax and do a little more reading. I am going to change my handle to crash test dummy.

[rubber duck]

I haven't read this whole thread yet and maybe it's been covered.

Why couldn't you use something like the old duel cross tube column system and throttle back the reflux ratio?

You can hit 90% + with those rigs but if you can control the bottom part of the packing might it not work in a vm application?

[LWTCS]

For some time I have been on the same page of using packing above plates or thumpers. I really want to understand and solidify my packing solutions before giving them a kick start. Once happy with packing designs I will add a base thumper. (Yes Larry. You heard me say that) This theory thread does push the level of comprehension. Hopefully my planned tests will shine more light on things for me.

Was reading a thread then started having chest pains and fell out of my chair and just blacked out. Spent a day having my ticker checked out..........where were we and what were we talking about?
Seems just a dream now?

[rubber duck]

For some time I have been on the same page of using packing above plates or thumpers. I really want to understand and solidify my packing solutions before giving them a kick start. Once happy with packing designs I will add a base thumper. (Yes Larry. You heard me say that) This theory thread does push the level of comprehension. Hopefully my planned tests will shine more light on things for me.

Was reading a thread then started having chest pains and fell out of my chair and just blacked out. Spent a day having my ticker checked out..........where were we and what were we talking about?
Seems just a dream now?

Ya that's been happening a lot around hear as of late.....

[LWTCS]

No,no,no im fine.......sorry.... Was being a smarty pants only... Im fine....

Now please lets get back on topic before MR gets back and sees me fiddle farting round off topic and floggs tbe shit outta me. Hurry hurry now. Sorry.