collection rate

Putting older posts here. Going to try to keep the novice forum pruned about 90 days work. The 'good' old stuff is going to be put into appropriate forums.

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Straight_Ehs
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Post by Straight_Ehs »

I know a little about distillation theory so i can throw in a little info...

When you turn up the heat, like you were saying, you basically disrupt the entire effect that the column has in purifying the product coming over.

A column's efficiency is rated by its number of 'theoretical distillations'. As vapour comes up through the column, some of it condenses on its internal surfaces. These internal surfaces then heat up, and the condensate coating them releases vapour, except with a higher percentage of the lower-boiling point fractions of the mixture. Each of these 'theoretical distillations' is roughly equivalent to doing a run through a pot-still; the more times you do it, the higher proof you get.

The reason why turning up the heat messes things up is that, in order for a theoretical distillation to 'count', you have to have both a liquid and vapour phase (or else youre not distilling, are ya?) in equilibrium. When you turn up the temp, the lower portions of your column basically 'dry out' with respect to the lower boiling point fractions because its too hot for them to condense. Ideally, you want the length of your column not to exceed the boiling temp of what you're trying to purify (while youre collecting) in order to maximize the amount of times the vapour condenses and gets turned back into vapour again.

So my opinion is, not only are you getting propanol by turning up the temp, but youre limiting the purity of the distillate across the board (more water, more stankness, more everything bad) and cutting down the effective length of your column to almost nothing.

It does depend where the thermometer is, of course, but you want the temp of the vapour just peeking over the top of your column to be as close to 78.6c (or whatever it is exactly) as possible. The temp of your column shouldnt stray too much from this either, if you think about it, because the liquid that's ideally coating all the internal surface area is alcohol and you cant have liquid alcohol at a temp above its boiling point.

Of course, i mean at the point where you start collecting it should be steady at that exact temp. Towards the end of a perfect reflux distillation, it should suddenly increase in temp as the last bit of alcohol evaporates off the surfaces of the column, but in my experience its never that sudden.
firefly
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Post by firefly »

Straight_Ehs, very nice explanation.....
I must be doing something wrong cause im way far of the 10-15ml/min as claimed by the manufacturer...
1st run I was steady at 78C and barely collected 3L out of a 25L batch(92%)...but the rate was at 3-4ml/min......seems a bit too long to me... :D

Anyway...im still reading and I just might figure out what im doing wrong or if my distiller really can't handle the 10-15 ml rate......cheers :D
birdwatcher
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collection rate

Post by birdwatcher »

Interesting stuff gentlemen,

I have 36" of ss packing in a 2" column. The column is insulated.

With my latest setup I can monitor the temperature at the top of my boiler
and at the top of my column. I heat my boiler with a 750 watt immersion heater. Very slow.

After equilibrium, I gather ethanol at 4ml per minute, about 3 drips per second.

On my last run the steam at the top of my boiler was 85C-86C and at the top of my column 77.9

G
Last edited by birdwatcher on Sun Dec 09, 2007 5:02 am, edited 2 times in total.
My sugar wash for ethanol is under the Tried and true recipes forum.
Straight_Ehs
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Post by Straight_Ehs »

I would go by purity of your final product, rather than manufacturer claims.

The rate that you'll be able to fractionally distill is also (somewhat) dependent on the alcohol concentration of your wash. Its possible that they got those numbers by distilling something that was already 70%, for example.

Your collection rate seems about right to me. Just as a reference, all of my organic chem texts say to collect at MOST 2 drops per second (of course this is with a smaller and less effective column) but generally you want to distill as slow as possible/bearable.
firefly
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Post by firefly »

Well....i've read that some people collect at a rate of 3-4L in 5-7 hours (90-92%) with a similar distiller but with a 3" column.....where as I have a 2" column.....

I "googeld" the 2 drops per second and it should equate to about 6ml/min...and im still under par.... :D
Straight_Ehs
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Post by Straight_Ehs »

well a drop isnt really a standard volume; it depends on the purity of the distillate and the surface area/material of what the drop is falling from as well as the temperature.

I'm not sure what kind of a column youre using but you could certainly boost its capacity by increasing its surface area by packing it with marbles, ceramic chips, pyrex wool, pretty much anything that conducts heat relatively well and wont leach any grossness into your brew.

If youre gonna be packing it with something that has a lot of heat capacity (like marbles or ceramic chips) you should insulate your column.
firefly
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Location: Canada

Post by firefly »

I have the PSII from brewhaus and I always throw some copper pieces in the boiler before I distill....

As for the insulation.....I was told to remove it cause that's what might be slowing it down.....and im distilling indoors....so that was gonna be my next step...remove my 30$ insulation..... :D
Straight_Ehs
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Post by Straight_Ehs »

yeah, I'd certainly listen to the old timers over me :)

I'm new to these active reflux stills, and actually incorrectly labeled mine as such; i'm using a straight fractional distillation rig.

My theory tells me that cooling a column down just to increase reflux is a little backwards though. I get the idea of it, but in terms of a puritanical view of fractional distillation, its a little counter-productive, isnt it?

I guess if youre sure that the alcohol is the lowest boiling point fraction of your mixture then its a good idea... something about it seems like cheating somehow, though :D
firefly
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Location: Canada

Post by firefly »

Straight_Ehs....I sure appreciate you taking the time to help.....Im also new to distilling so im open to any suggestion.....
cheers buddy :D

..
mtnwalker2
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Post by mtnwalker2 »

There is a great difference in the manipulations of 2 types i think of VM and LM. With the ps II you control the head temp. vapor takeoff. You can give it as much heat as allowed as long as you can supply enough cooling to keep temp. at head withing proper perameters. Not enough to puke into your column, or exceed your condensors capacity, but a balance to keep temperature steady for quality. It take many runs to learn the ropes with this one, but when you do, you can almost set and forget for the hearts run. It is a balance of the heat input, water flow to reflux section and temp. and what the condensor can handle. Also, the diameter of the column for speed, and heigth for purity. Again, somewhat unique for this particular column.

Firefly, give your setup a chance. I have both the psII pro, and the HC unit. Both work well within their limits. You have not run enough runs with posted responses to yet enjoy your still. Practice a bit, and use the dozen or so posts you have received to better the outcome.
> "You are what you repeatedly do. Excellence is not an event - it is a
>habit" Aristotle
birdwatcher
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Joined: Mon Oct 09, 2006 7:27 am
Location: Ontario

collection rate

Post by birdwatcher »

Straight_Ehs wrote:I would go by purity of your final product, rather than manufacturer claims.

The rate that you'll be able to fractionally distill is also (somewhat) dependent on the alcohol concentration of your wash. Its possible that they got those numbers by distilling something that was already 70%, for example.

Your collection rate seems about right to me. Just as a reference, all of my organic chem texts say to collect at MOST 2 drops per second (of course this is with a smaller and less effective column) but generally you want to distill as slow as possible/bearable.
I appreciate your comments. I added above that my column is insulated.

And, a drip or drop is hardly a scientific term. I do aim for a collection rate with my particular setup of 4ml. per minute, but always slower rather than faster.

All I can say, is I've been drinking great vodka martinis for the last 12 or so years.

Merci encore and have a great day.

G
My sugar wash for ethanol is under the Tried and true recipes forum.
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