[lockjaw]

Hi forum members,

I have been trying my damnedest to find the answer.  I am interested in botanical extraction using pure n-butane as the extraction solvent.  Am I correct in my understanding the under low vacuum all n-butane will be removed from the extracted 'oil'?  If not is boiling the n-butane off at room temperature a viable option?

If not please point me in the right direction.

Thank you for your consideration, and I apologize for my rather simplistic question, Lukia

[Heisenberg]

Hi there. I have performed extractions using this method before and although I do not have access to equipment which would allow me to analyse the extract to see how much residual butane there is, in theory the butane should evaporate off under normal conditions.

Butane boils at -0.5 degrees C, so at room temperature it should evaporate off your product. If you are worried about some butane getting 'stuck' in your extract then you could try heating the extract gently or dissolving the extract in a suitable solvent and then evaporating off the solvent. Don't think it should really be much of a problem though, I would be more worried about impurities left behind by the butane (unless you know it is pure).

[lockjaw]

Hi,

Thank you very much.  I thought as much in terms of general ease in removing n-butane.  I may have access to a MS but not for a while.  Could you possibly suggest a solvent one could use to remove remaining butane if one believes there is indeed n-butane remaining?  (And am I wrong in thinking that using a solvent to remove a solvent is less than ideal?)

I have access to pure n-butane and the extraction apparatus I am interested in operates under low pressure (IIRC 300psi) with working temperature at ambient room temperature and light vacuum to remove the butane.

Again, thank you for your time, Lukia

[Heisenberg]

I'm just playing around with ideas here really.

I think if you were going to give the solvent idea a try, you would use one which will dissolve all of your extracted chemicals so solvent choice depends on the extract. Butane is non polar, often produces a very oily, sticky 'tar' like extract from plant material. Because of the nature of the extract residual butane becomes a worry. I think that it extracts polar compounds too. You could try using a solvent with a higher density than butane, so that when the extract has dissolved in the second solvent, the 'trapped' butane is released and rises to the surface. If it has a lower boiling point (which it will if your other solvent is liquid under standard conditions) then it should evaporate off first.

I suppose that using a solvent to remove another solvent might be a bad idea, the second solvent in the idea I stated would probably be even harder to remove than the butane because of it's higher boiling point. Considering your using a partial vacuum to remove the butane anyway, I wouldn't even bother.

Like I said I'm just throwing some ideas about. I reckon that when you get access to the MS you will find that the amount of butane left in the sample is minimal if at all. It would be interesting to hear what the results are though when you analyse it.

What are the properties of the extract? What botanicals are you extracting from?

[lockjaw]

Hi again,

Thanks so much for your help.

I am making extracts of C. indica Spontania, hopefully for medical application, but that depends upon the extracts purity (eg. no residual solvents or other impurities).

After the initial extraction with pure butane, I think I will use your idea of a second solvent to redissolve the extract.  I think I will use pure food grade ethanol, err, that is the azeotrope of pure ethanol (95.63%) and water (4.37%).  The second solvent (ethanol) will 'un-trap' any butane and most other higher hydrocarbons 'stuck' in the extract.  A concern I have is the chemical cannabinol (a major fraction of the extract) has strong affinity to butane.  From my understanding it is difficult to separate all butane from cannabinol even with vacuum while exceeding the bp of butane.

The bp of the azeotrope of pure ethanol (95.63%) and water (4.37%) is lower than the bp of either ethanol or water. The bp of that positive azeotrope is 78.2°C, which is also above atmospheric vapor pressure.

This is my thinking:

After I redissolve the extract with ethanol I will put the solution into a very cold freezer (-20°C; lab quality freezer) for 12-24 hours so the impurities can precipitate into the solution, out of the extract.    After the freezer stage I am thinking of placing in a microcentrifuge for 10-20 minutes, ensuring total precipitation of impurities from the extract.  Then I am thinking of aspirating and/or filtering the solution from the extract.  Would it be wise to rinse filtered extract with distilled water?  And finally I am considering using a glass or pyrex vacuum desicator in a non-sparking incubator at 175°F to boil off any remaining ethanol.

Open question I have:  Is it necessary to both chill and spin the solution to get total impurity precipitation out of extract?  Could I just use a microcentrifuge?  Or just a freezer?

How dangerous would it be to put the vacuum desiccator with the filtered extract in an oven at 79°C (175°F)?  I wonder if the little remaining ethanol would be a flammable concern?  Ethanol flash point is ~13°C (closed-up method) and ignition temperature is ~422°C and vapor pressure is ~44mm @ 20°C.
 
Please let me know of any errors of misunderstandings, Thank you 


BTW, I want to pre-wash the raw plant material in alkaline water (pH =>10 using caustic soda), and then clean the raw plant matter with multiple washes of pure water.  Would this cause problems with the initial n-butane extraction (under pressure) of raw plant matter?  Or would it cause other types of impurities I would need to later remove?

[tamisium]

Hello Lockjaw
I hold the patent on the Tamisium Extractor and can shed some basic light on the fundamental of removing a volatile solvent like butane.
The key is to keep the extract in a liquid state so that the butane vapor can travel to the surface and evaporate away. When using heat is not a good idea you can supplement that process of evaporation using a 25-30 hg vacuum. Vac combined with heat expedites the process. As little as 2 ppm has been achieved and that is with a very waxy extraction.
You can add another solvent that lowers the viscosity as a way around the heat.
Remember that adding heat can create cold so be aware that you have to stop the heat when that cooling process stops if you want to avoid a specific temp.