lower vapor temp on a second run?

junkyard dawg · Post by **junkyard dawg** » Sun Nov 20, 2005 11:41 am

anyone ever seen this before, I am running a second distillation of the distillate collected from 4 earlier stripping runs of corn mash. I run a stillmaker type reflux still. It seems that the thermometer reads 75.5 C. When running a wash as opposed to a distillate the temp sits at 78.5. Why is this?

junkyard dawg · Post by **junkyard dawg** » Sun Nov 20, 2005 12:17 pm

oh, I'm not offended... no, I'm not offended... no.. but I hate that kind of response.

You know, I read that part just before posting this question. I didn't understand what I read I guess. So on your suggestion I re read it and still it doesn't seem clear.

If I'm distilling a wash at 10% abv my reflux still sits at 78.

If I have a distillate that I'm distilling the second time, why does the temp sit lower than 78?

here I go to re re read it...

junkyard dawg · Post by **junkyard dawg** » Sun Nov 20, 2005 12:50 pm

just so we're on the same page... "The temperature at any point is governed solely by the boiling point of that liquid mix, " If I'm drawing off 90% ethanol when Im distilling the 10% wash and the thermometer reads 78.4+ or -

Why would there be a lower temperature when I'm drawing off 90% ethanol from a 40% wash? At the top of the still is the same 90% vapor in each case.?... How can I be seeing a vapor temp that is lower than the boiling point of the ethanol alone, and certainly lower than that of an ETOH/H2O mixture?

hope this doesn't come across as a stupid question... and no frustration, just trying to learn.

junkyard dawg · Post by **junkyard dawg** » Sun Nov 20, 2005 1:48 pm

so now you see why I'm confused...

I think the thermometer is ok... as far as massive methanol content, I'm not sure... I ran 4 washes to get the low wines, if I turned on the reflux the temp would settle out at 78.5 or so, since I just wanted to strip them, I would turn it off most of the time and let it rip. now, running these four batches together, with reflux the temp settles out at 75.5. No reflux, 78.5. Distillate burns blue, smell clean and corny. Is it possible to get that much Methanol in a grain wash?

Post by **Grayson_Stewart** » Sun Nov 20, 2005 2:02 pm

. Have you calibrated your thermometer in boiling water to see if it reads 212 F?

junkyard dawg · Post by **junkyard dawg** » Sun Nov 20, 2005 2:10 pm

I took off about 100 ml of fores from each batch of low wines after a period of reflux and equilibration. At no point did I suspect anything funky with any of the early runs. The only strange thing was the low temp observed today. what I wouldn't give for my very own gas chromatograph...

I appreciate the explanation, tho I think I had a pretty good grasp of the theory. It was todays real world results that make no sense.

Post by **Grayson_Stewart** » Sun Nov 20, 2005 2:24 pm

if I turned on the reflux the temp would settle out at 78.5 or so

Sounds about right to me.

I would turn it off most of the time and let it rip.

I assume you saw a temperature rise when you did this, correct?

now, running these four batches together, with reflux the temp settles out at 75.5. No reflux, 78.5.

All this makes me think your thermometer is off by about 4 or 5 degrees F. The numbers seem to be working the way they should be, you're just a few degrees off.

junkyard dawg · Post by **junkyard dawg** » Sun Nov 20, 2005 2:25 pm

Yes Grayson, I just rechecked it. It is right on at both ends. 0 in crushed ice and RO water, and 100 in boiling RO water. I'm lost now, this was the culmination of much work. I hate to toss this, but don't like the uncertainty. I'm really fond of vision...

Post by **Grayson_Stewart** » Sun Nov 20, 2005 2:56 pm

Everything Holy told you was correct. I would be a little baffled myself. My first thought would be you never removed all the forshots and my second thought would be the column never reached full equilibrium. How were you operating the column 10 minutes before and during the time (each time) when you were removing the foreshots? How were you operating the column when you were making the second run? Did it sit in full reflux mode for an extended time, say thirty minutes? What was the take-off rate after allowing the column to reach full equilibrium?

junkyard dawg · Post by **junkyard dawg** » Sun Nov 20, 2005 3:45 pm

I am baffled. I run the same every time. High power to heat up. When the column temp starts to climb I back off the gas and run the column under full reflux for about 45 min to an hour then take the fores slowly. today I took the fores very slowly after over an hour of total reflux. It took about 2 hours for the fores after the head came up to temp. I didn't measure the rate the distillate ran without reflux, but it was fast. A steady full stream with out reflux, but I only did this to see how fast it was running. I estimate I returned about 75%. I collected about 1 liter/hour. There was a clear change in smell after about 750 ml, The temp was steady the entire run, until I started this conversation and turned off the reflux. no reflux the temp went to 78.5. with the reflux it was rock steady at 75.5. Just like usual, just 3 degrees low.

Thanks for trying to help.

linw · Post by **linw** » Sun Nov 20, 2005 6:12 pm

Can anyone play?

I agree with everyone here! Like Grayson, I thought your thermometer must be reading low. But you checked the calibration. But the laws of physics can't be broken. Your vapour WILL NOT sit steady under reflux at a true 75.5 - just won't happen.

So, where does that lead us? The only question remaining IMVeryHO, is the placement and environment of the thermometer. Please explain your head workings and the placement of the thermo. Is it possible that the bulb/tip has liquid reflux pouring over it??

Nothing like a good mystery

Guest · Post by **Guest** » Sun Nov 20, 2005 6:31 pm

does sea level play any part in this?

linw · Post by **linw** » Mon Nov 21, 2005 12:00 am

Anonymous wrote:does sea level play any part in this?

No, because he tested the calibration at 0 and 100 deg C.

junkyard dawg · Post by **junkyard dawg** » Thu Nov 24, 2005 7:25 am

Ok everyone, thanks for playing along...here are some background details. The column is 40 inches to the lyne arm. reflux is controlled by a valve and is returned to the column 3 inches below the lyne arm. There was no packing above the reflux return, and the thermometer is centered with the bulb at the bottom of the lyne arm. The water flowing through the condensor was pretty cold. Can't quite wrap my head around how the reflux could change the thermometer reading unless the distillate boiling point was 75.5. (bad azeotrope)

With no reflux the temp would go back to 78.5. This seemed ok because the stuff in the boiler was already at about 90 proof. All of the previous stripping runs also ran under reflux at 78.5. so is it safe to rule out an abundance of lower boiling point compounds and chalk it up to an unruly mob of unaccounted for kilocalories?

linw · Post by **linw** » Tue Nov 29, 2005 12:52 pm

I notice your condenser cooling water is pretty cold. Maybe this, below, might help?? Came from this site.

Cooling Rate - Minimum & Maximum The heat removed from the column has to be the same as that put in to it. This means that for any given heat input, there is a minimum rate at which you should cool it (total of condensor heat loss and extra losses). If you go below the minimum, not all the vapour will get condensed (the "subcooling" value will be negative (eg hotter than its dew point)) and will be lost as a vapour (good for setting fire to the place). If the cooling rate is too great (eg 1400 W vs 1200 W) the distillate gets too cold, and ends up affecting the top couple of plates. This is because there isn't enough heat in the rising vapour to both heat the down-coming liquid (because its now so cold) and extract the most ethanol from it. So in practice don't run your cooling water too fast - keep the distillate fairly warm.