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Understanding Distillation

This topic can be found at:
http://biodiesel.infopop.cc/eve/forums/a/tpc/f/4441089311/m/5237023763

February 07, 2013, 10:58 AM
Legal Eagle
Understanding Distillation
While the link I am providing is a detailed methodology on Moonshine stills it goes into specifics about how distillation works, and what type of distilling apparatus works best under what conditions.
It is essentially an education in distilling ... anything. Ok, here is the link: Moonshine Still

For most people a simple pot still will suffice, but if you start getting into serious volumes per batch to be recovered then considering a reflux column style distiller might be best.

You know your needs, so act accordingly. Enjoy.



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February 07, 2013, 09:28 PM
WesleyB
Why do you suggest a reflux column condenser? As far as I know, if I can get it to evaporate, vaporise or boil out of my biodiesel then I want to remove it and condense it. I'm not trying to increase the percentage of methanol in the distillate. If the distillate has water in it fine, then I've removed some water from the biodiesel by vacuum distillation in demething. I do test batch size quantities. Maybe I'm misunderstanding what you suggest. A simple reflux condenser would drop the water back into the still pot. Distilling out ethanol from fermented liquid is a completely different goal when compared to demething. Its concentrating on the distillate, not trying to improve the quality of what's in the still pot (backwards). Maybe its just for academic study, even though its backwards. Thanks
February 08, 2013, 03:09 AM
taralec
quote:
Originally posted by WesleyB:
Why do you suggest a reflux column condenser? As far as I know, if I can get it to evaporate, vaporise or boil out of my biodiesel then I want to remove it and condense it. I'm not trying to increase the percentage of methanol in the distillate. If the distillate has water in it fine, then I've removed some water from the biodiesel by vacuum distillation in demething. I do test batch size quantities. Maybe I'm misunderstanding what you suggest. A simple reflux condenser would drop the water back into the still pot. Distilling out ethanol from fermented liquid is a completely different goal when compared to demething. Its concentrating on the distillate, not trying to improve the quality of what's in the still pot (backwards). Maybe its just for academic study, even though its backwards. Thanks


Remember water present in the distillate is counter productive for re using the methanol,as water makes excess soap.Basically need the methanol as pure as possible if it is to be re used for brewing.
February 09, 2013, 10:53 PM
Legal Eagle
For small batch demething a simple pot still is fine, but if you are dealing with large quantities then a reflux will do the job more efficiently.

Both types are discussed in the link I posted.

Personally I use a pot still as I only do about 30L per batch and so far it has worked well, but if I were to up that to 100L+ then I would definitely look at a reflux set up.



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February 10, 2013, 01:05 AM
Johann Cape Town
Surely a pot still is the best way to de meth bio. Reflux just slows it down and leaves water behind.
If purity is paramount, then re distil the recovered product using reflux.
February 10, 2013, 06:21 AM
Franklin Westaway
Pot stills give an incomplete separation of water and alcohol. If there is water in the pot some of it will be present in the output of a pot still. That is the way pot stills work.

For maximum purity you want to use a reflux still.
February 10, 2013, 10:43 AM
Johann Cape Town
FW surely you would want to remove water and methanol from bio. Reflux on bio is silly unless you want to add a step after relux to remove water, be it air drying or distilling.
February 10, 2013, 11:14 AM
Legal Eagle
In a dry wash system the bio is distilled to get the residual methanol out so the soaps can, with settling, fall out of solution.

Only unless the little bit of methanol recoverable from biodiesel distillation is crucial then the pot still is the way to go and any water present isn't going to be much of an issue. Recovered methanol should only be reintroduced into a follow up batches incrementally anyway. I use an 80/20 ratio and it works great. (80% fresh, 20% recovered)



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February 10, 2013, 04:14 PM
WesleyB
I tried to distill methyl biodiesel under about a 280 millimeter pressure vacuum years ago. I got the hot oil bath that was heating the still pot up to about 170-180 degrees centigrade. The biodiesel didn't exactly boil, but it was smoking, as was the hot oil bath. Don't try this! Its probably dangerous, especially in large quantities. Well, I got about one large drop of distillate in the condenser that was white semi-solid. I think what happened was the water present in the boiling flask/still pot hydrolysed the methyl biodiesel due to the heat and maybe partly due to the pH. My point is in part, heating wet biodiesel with water probably produces free fatty acids and methanol at some unknown rate. That's part of why I wouldn't reflux water back into the hot biodiesel during demething. At the lower temperature maybe its no big deal, I'm not sure. The vacuum pressure I used was too low. But I've never heard of anyone successfully distilling biodiesel to purify it. Its too hot for me, maybe it could be done industrially.
February 10, 2013, 05:22 PM
Franklin Westaway
Johann,
I have only provided information about how stills work. I make no recommendations as to how or if you should distill biodiesel.

I have always thought that people distill biodiesel to recover the methanol and re-use it.
If all you want to do is dry your biodiesel I can think of easier, more cost effective methods than distillation.

If you look at my original statement I said "If there is water in the pot some of it will be present in the output of a pot still." That is a true statement.
If there is no water or very little water in the pot then there will be no water or very little water present in the output of a a pot still.

For maximum purity you need to use a reflux still. If you are satisfied with the purity you can achieve with a potstill then you do not need to go to the added expense of a reflux still.

quote:
Originally posted by Johann Cape Town:
FW surely you would want to remove water and methanol from bio. Reflux on bio is silly unless you want to add a step after relux to remove water, be it air drying or distilling.

February 10, 2013, 09:43 PM
WesleyB
Maybe this has no bearing on the subject. If you have pure free fatty acids in a still pot under vacuum with no water, and someone heats it enough, then it makes water plus the free fatty acid anhydrides. Two carboxlic acids loose one water molecule and bond to each other. At lower temperature concentrated sulfuric acid acts as a catalyst for this reaction. Say you've got wet crude biodiesel with excess methanol and heat it,the methanol distills out then the water hydrolyses the methyl ester and you distill out the methanol leaving the free fatty acids. Continue to heat the free fatty acids and it makes water and the free fatty acid anhydride, the water boils out, leaving fatty acid anhydrides. After that I'm not sure what continued heating under vacuum produces. There's a lot to consider when demething crude biodiesel.
February 11, 2013, 06:10 AM
Johann Cape Town
OK let me try again. Methanol Recovery.

Reflux on bio is silly....pot still wins.
Reflux on glycerol is first prize......pot still can do.
April 07, 2013, 09:13 PM
dkenny
a pot still without reflux..

is a waste of time..
end of story..

if you want purity in the output..
a reflux setup is the only way to get it. and control the temp at the top. forget the pot temp.

a moonshine still..
doesn't get the purity needed..for methanol nor ethanol
for ethanol..its not possible!!96% is the limit..PERIOD!..so don't believe me..google it..

for methanol..with a reflux setup its possible to get 99+% pure..


WesleyB..
using a vacuum make the solution to higher purity require 2 variables instead of 1. so its more complex. possible..but harder..variables..boiling point of methanol vs pressure..
sure lower the pressure.lower the boiling point...hum 2 points instead of temperature only??

2nd..if you heating biodiesel that hot..my guess is its a bad idea..( you 2/10/13 post)

ok..so fame me I late..but I run a business and don't be much free time to comment on posts..and I miss everyone.

so I'll ask what's pure enough?
can you use your distillate for 27/3 testing?
what about using it for A/E processing..water is a killer this type of processing?

fyi..I use mine for 27/3 testing and A/E processing.

-dkenny


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May 23, 2014, 10:28 PM
Yuka
Bro
Im new at recovering methanol, i always evaporate it.
I saw your methanol recovery unit. And i was amazed..
I want to build two stainless steel units for demething bio, and other one for recovering from glyc.

The bio demeth unit is for 1,000 liters.

The tank is gonna be 100 cm diameter and 155 cm tall. So its a 1,200 liters tank.
I wanted to ask you.
What diameter and height size would you recommend for the column.
How much KW for heating?
Should i pump the liquid, bubble air or just let the element heat until evaporates?

The glyc unit is for 400 liters of glyc (i use KOH).
The tank is gonna be 80 cm diameter and 100 cm tall si its a 500 liters tank.
I wanted to ask you.
What diameter and height size would you recommend for the column.
How much KW for heating?
Should i pump the liquid, bubble air or just let the element heat until evaporates?

Marbles is the best option for higher purity?

Whats the best type of tank? taller thiner tanks, conical, box type tank, horizontal tank?

Would you recommend whole batch demeth instead in one larger tank?
I dont like mixing things, and trying to avoid stechiometric point is gonna leave small amounts of methanol on biodisel after WBD, same case for glyc.

Any advice would be really helpful.

Thanks.
May 24, 2014, 11:06 AM
Jon Heron
For the fastest, most efficient and IMO most convenient way to recover your methanol is with WBD using vacuum. You need to continually circulate the batch when doing WBD, its best to pump from the bottom of your reactor tank into the headspace of the reactor, that way the methanol can flash out of the bio and ever thickening glycerin into the headspace.
You dont really need a reflux column for methanol as there is no azeotrope with water and methanol like there is with ethanol. You can achieve 100% purity methanol without a giant reflux column.
To get 100% methanol you would need a temperature controlled pipe angled off the top of your processor where the water can separate from the methanol and then drip back into the processor or you could make a trap at the bottom of the pipe to catch the water too but for the small amount of water we are talking about I doubt it would be worth the trouble of making a trap.
Off the top of my head (bad memory Wink ) I think the sweet spot was 140F, at that temp the methanol will be evaporating but the water will be condensing.
I bought a big peltier bridge unit years ago so I could make a device to cool or heat the pipe off the top of my reactor to get 100% methanol recovered (like I used to on my small 100L reactor) but I find the 98% methanol I am currently recovering has been working just fine as is...
An easier way may be to just have a line teed into your condenser water feed thats wrapped around the pipe on the top of the reactor, you could keep it in the sweet spot by controlling a solenoid with a PID to control the water flowing over the pipe. After observing how mine operates (using vacuum) my pipe is generally too hot (155 ~ 160F throughout much of the recovery process) so only cooling would be needed to bring up the purity.
When I make a bigger condenser later this year I am going to revisit this, I will post the results and setup here if it works as I expect...
Cheers,
Jon
In this pic you can sort of see my angled pipe (white insulation) leading to the top of my condenser plumbing, I have a heat tape around the pipe and a TC hose clamped on the top of the pipe under the insulation. When I am dewatering I heat the pipe up to 175F to help with removing the water, now if I could just cool it to 140F (IIRC) I could be recovering 100% purity methanol. Stay tuned...



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Simple schematic for a pump and heater control with a high limit
Sensor for the biodiesel/glycerin layer