Distilling 90% ethanol

[hobojoe00]

Hi guys I use ethanol to extract essential oils from plants. After the extraction I need to place the solution into a boiler and recover it. My problem is since I'm at 90% ethanol. As it boils the cooling effect from evaporation drops the temperature of my boiler faster than I can raise it. Does anybody know the mathematical equation I would need to do in order to figure out how much energy will be required to maintain a boil?

[Kareltje]

Are you sure you do know how to handle 90 % alcohol? 90 % alcohol already burns at 17 dgr C!
The explosion limits in air are 3.4 and 19 % by volume!

The heat of evaporation of alcohol is about 850 kJ/kg, much lower than that of water: 2,260 kJ/kg.
I suppose you can cook water, so it seems strange to me that you can not cook alcohol.

[still_stirrin]

...I use ethanol to extract essential oils from plants....

As it boils the cooling effect from evaporation drops the temperature of my boiler faster than I can raise it.

Does anybody know the mathematical equation I would need to do in order to figure out how much energy will be required to maintain a boil?

Your question sounds a bit unbalanced...once the solute is boiling, you need enough heat to maintain the boil. And as Kareltje pointed out, the heat of vaporization of pure ethanol is much lower than that of water. So, it should be easy to maintain the boil....unless you're pulling out much more heat in the reflux condenser than you put into the boiler. If the refluxing alcohol is much cooler than it's saturation temperature (the temperature at which both phases exist, liquid and gaseous), then you should reduce the coolant flow to the reflux condenser.

But, for all things "essential oil"...post your questions in the proper forum. We have a dedicated forum exactly for these types of scenarios. You'll have much more response and input if you take it there. Here...it's out of place.

Good luck hobojoe...and be safe. Remember, high proof alcohol is highly flammable and explosive. Be careful when using it to extract essential oils. And, always keep a fire extinguisher nearby.
ss

[hobojoe00]

I didn't want to say this in the initial response because I worried it would confuse things. It's a vacuum distillation system. Once under vacuum the ethanol boils so incredibly fast it drops the temp faster then it can be added.

I'm going to try and have this moved to the essential oil thread like you suggested.

[hobojoe00]

Are you sure you do know how to handle 90 % alcohol? 90 % alcohol already burns at 17 dgr C!
The explosion limits in air are 3.4 and 19 % by volume!

The heat of evaporation of alcohol is about 850 kJ/kg, much lower than that of water: 2,260 kJ/kg.
I suppose you can cook water, so it seems strange to me that you can not cook alcohol.

Thank you for your response, I did the math previously to determine how many kilojoules I will need to maintain a boil but I could not find anywhere the equation you would use to add in the variable of vacuum. It should drop the amount of kilojoules needed significantly.

[Kareltje]

I still do not understand. Shouldn't some equilibrium be established? When the boiling takes to much heat and the temperature gets lower, the boiling would slow down until the temperature rises again etc. ?

[hobojoe00]

I still do not understand. Shouldn't some equilibrium be established? When the boiling takes to much heat and the temperature gets lower, the boiling would slow down until the temperature rises again etc. ?

Yes you are correct and that is the problem the vacuum is powerful enough to make it come over at the speed of a garden hose. 6 gallons in 10 minutes but then it slows down because my temp went from 120 to 70 and now there is no heat and the vacuume pump is doing all the work and a lot is making it past my condensers and into my cold trap , or into my pump and I have to replace the oil.

[hobojoe00]

I'm currently using a 1000 watt heat blanket that wraps around the entire vessel and on the bottom I have 2000 Watts heating from a mantle. If I run the vacuum at like 5% it will find the equilibrium you were talking about but I want to redesign the system so I can go full speed.

[hobojoe00]

I have a 10 liter rotovap that is able to have the vacuum running full speed , full depth and the hot water bath is able to add heat back fast enough. I'm sure I could do a hot water bath and just keeps adding heating elements until I find that sweet spot but I would like to just know the mathematical equation so I could buy a jacketed reactor and a oil heater.

[hobojoe00]

I figured it out. Im posting the answer here in case anybody else is ever trying to figure this out. You do not need a different equation. The basic kilojoules per kilogram equation will work. Its the same if your at -30 or -5 inhg. Even though vacuum allows ethanol to boil at a lower temperature. You still need the same amount of energy put back into maintain that boil. Yes you will be boiling at a much lower temperature but the energy required is the same. The only difference is at -30 the ethanol is boiling at such a low temperature now the environment is considered a heating source and is helping a small amount but I would still make sure my heating source is powerful enough to match the kilojoules per kilogram equation.

Thanks everyone

[Kareltje]

Thanks for sharing the soluion!
But than you have a problem with the speed: 6 gallons in 10 minutes!

[Pikey]

Thanks for sharing the soluion!
But than you have a problem with the speed: 6 gallons in 10 minutes!

Yes - Ss's advice to keep a fire extinguisher handy might be a little "underkill"

[MrFish]

You might already have fixed this but it appears really clear that your product condenser is underpowered.

It's just a guess but is seems like when you pull your vacuum and the boil starts (at whatever temperature), ethanol partial pressure rises quickly and if you can't condense it back, it goes straight to your pump and screws it up, dropping vacuum until your pump can get rid of the gas. Then it starts over, pretty quickly destroying your pump! Ever heard of cavitation? [WINKING FACE]

I would think that in your present configuration, if you add a heat source, you'll just make things worst for your pump and eventually blow it.

If you haven't fixed this yet, try bleeding your vacuum a little and work progressively so that no vapor goes past you trap. Increase your condenser fluid flow rate and/or get a more efficient condenser.

Hope that helps!

Fish