A (likely) unsolvable problem with ethanol extraction (keep them terps!)


Nah the terp Will be heated either way


So the real issue here would be viscosity.
.44 -.5nm pore size and water+etoh passes through.
Everything else channels outside pathway.
Pressure are acceptable up to 500psi I believe with that manufacturers specs for solvent stable membranes.
Possibly heated N2 gas would work well??
This would eliminate falling film etc evaporators.
Etoh and water could be heat swung mol sieve applies to take water out of etoh.
Thoughts? Maybe I don’t need to go to Dow chemicals for this :thinking:


But just keeping the boiling point at 45c or so to have less degredation issues.

I guess the main point of the membrane is for less energy use though.

I was curious if having the ethanol vaporized so you’re only using the membrane to separate the ethanol from azeotropic terpenes would need significantly less membrane area/pumped pressure.


Man in Theory If the still can makepressure it Could work but i guess You have to try


Terps water and etoh
Crude with little to none of color / heavies

Removes need for sub temps and heat evap (solvent recovery)

Also pumps and high pressures like 300-800psi
Gonna give this r&d

If anyone wants to join it’s gonna be around 40-80$k


You have a design. I imagine ?


There’s a few designs out there right now and a couple companies.

Ive got some high pressure vessels… I’ve got a 16hp compressor with 100cfm @120 that could drive a pneumatic liquid pump. Could probably run a pilot project on a 3" wide tube. Buy like 5-10 filters from 1micron down to 0.5nm. should cover all the bases that way.

Other companies use racks of cartridge style for surface area. Probably much more efficient that way.


Plate and frame.
Ya that might work for stage one for wax and chlorophyll.
PSI I think is gonna be more like 300 and 800psi


The problem is more about solvent resistance etc
RO style is what I’m setting up


This is for tweedledew’s question 21 days ago about how to separate ethanol from other solvents, that wasn’t really addressed. Since terps and nonpolar/moderately polar solvents are not very different I think the following applies to both.

Silicone oil is supposedly “insoluble” in ethanol, but I haven’t dug up any solubility data and it would be complicated by the various grades of silicone oil available. Not too hard to test that for yourself though. If silicone oil turns out to have low affinity for terps theres probably other options. I’m talking stuff like PEG 400 but much less polar. Liquid polyester or polyacrylate oligomers could be worth a look, there has to be some nonpolar enough to not dissolve in ethanol. Shouldn’t be hard to find them with low enough vapor pressures to easily vacuum distill or gas strip the terps out of the polymer oil.

Deep eutectic solvents aka DES or polar ionic liquids will pull ethanol and leave behind nonpolars. My favorite cheap nontoxic one I’ve seen is 1 mol choline chloride with 2 mol PG/glycerin and 2 mol water. They don’t have to be expensive or toxic like imidazole based ionic liquids. See my post in the ethanol/heptane azeotropes thread for more on that, and references. I think it basically raises the polarity of the ethanol a ton, so it could be just as useful for separating the terps as it is for separating out alkanes. In either application not having to reproof the ethanol back out of a bunch of water seems like big advantage. Something like a small amount of DCM, diethyl or dimethyl ether, might be useful to facilitate the full terp extraction from ethanol/DES mixture.

I’ll have to check into it but I have a strong suspicion there are ionic liquids (basically 0 vapor pressure) that are inoluble in ethanol and could be used to directly extract the terps from azeotropic ethanol. Would they be insoluble enough to use the de-terped ethanol directly for another extraction? I kinda doubt it. Pretty much no matter what I think the ethanol is going to have to be distilled after any liquid/liquid process. I don’t see that as a problem if whatever you’re distilling it out of has a miniscule vapor pressure, or in the case of a DES, the only components with any vapor pressure are glycerin/ PG and tightly held water. Tiny traces of that carrying over in the ethanol would not bother me.

To avoid a liquid/liquid and subsequent distillation, why not use a solid sorbent that terps can be reclaimed efficiently from? I assume people have tried to recover they terps from AC after using that to clean the ethanol? This seems viable to me, we’re not talking about huge masses of terpenes here and the sorbent should be reusable… If carbon (maybe with some microwaves to get things moving) for some reason can’t be made to work, I would bet there’s a different less aggressive fairly nonpolar sorbent that could be used (resins?) Then recover terps from it either by N2 or CO2 flushing the sorbent with heat/vacuum or by redissolving them out of the sorbent with a different (hopefully lower boiling) solvent, like the ones I mentioned above for extracting terps from ethanol/DES solution.
Fluorinated refrigerants anyone?? :stuck_out_tongue:

Pervaporation with membranes has been mentioned above, and that’s certainly an interesting direction to look into. I have a feeling that a nonporous polar polymeric membrane could effectively separate ethanol and water from terps, alkanes, etc. Those shouldn’t be that hard to manufacture on small scale with fairly simple tech. Impregnate some paper/cloth with the appropriate polymer perhaps. There’s a lot of scientific lit and patents out there about this for other applications. It doesn’t need to have super high ethanol flux per square inch if the membrane is cheap enough…

I do wonder if something as simple as inert gas stripping of the ethanol/terp solution might carry away the ethanol more selectively than distillation? Anyone tried it? Not particularly complex or difficult. Recirculate the inert gas after a fraction of the ethanol has been dropped out in a condenser. For recirculating, there might even be a decently affordable ethanol resistant gas pump/blower considering just a couple psi should be sufficient to bubble the gas thru the ethanol… or if you happened to have a liquid ethanol pump that can make >10-20psi and decent volume, then inert gas could also be recirced by using a venturi to pull it into the ethanol, the bonus here is you get great mixing of the gas and liquid phase. It would be interesting to try. Might even be able to do double duty as the first stage in ethanol recovery to reduce the volume before a rotovap. I assume gas stripping ethanol from extract has been discussed somewhere here but I wonder if anyone tried running just terp laden ethanol that way? Seems like that might be a way to at least get an idea of whether gas stripping loses less terps than distilling. But lab tests comparing gas stripped extract to rotovaped extract might also answer that.


I know somewhere I was talking about N2 gas in the roto for that with someone in here but definitely never thought about the application in terms of increasing solvent recovery and recirculating…that’s brilliant.
Aside from the “louche game”, would be nice to get a solid sop down for terp capture


Yeah a once thru gas stripping arrangement would require a boatload of gas and cooling for the cold trap.


I have a hvac recovery unit atached to a cls collection pot and iT circulates pure oxigen at 60 psi treu my ethanol solution
For days on end i think iT should be able dooing iT at far higher psi s


Okay, so the issue with loosing the terps can be saved by crashing them out with water, yay, except use brine it will push the oils out more.

But both alcohol and water protonate terpenes, making some amount, small as it may be with standing procedures, change. Alpha pinene becomes beta (maybe racematizes also) or maybe even terpinolene, etc. linalool shocks and becomes geraniol/nerol … this is not an exhaustive list.

Considering the plant produces a fair amount of acetic, it’s worse than just alcohol and water in the mix!

The issue with alcohol isn’t just azeotropes it is that it is the perfect medium for altering the spectrum of the plant.

Process for the isomerization of alpha-pinene

“As the protonating agent, there can, for example, be named the following proton-yielding compounds: dilute mineral acids such as dilute (e.g. 2-N) hydrochloric acid, sulphuric acid, phosphoric acid; sulphonic acids (e.g. ptoluenesulphonic acid); carboxylic acids (e.g. alkanecarboxylic acids such as acetic acid or aromatic carboxylic acid); alcohols (for example, alkanols such as methanol, ethanol); phenols; amines and ammonium compounds having at least one available hydrogen atom, for example, ammonia (liquid or gaseous), primary or secondary amines such as monoor dialkyl amines, ammonium halides (e.g. chlorides or bromides; solid or as aqueous solution), pyridine hydrohalides; and finally water.”

Not only does the plant produce acetic/formic, which are extractable with alcohol/water, but it also makes pyridine salts; likely not a hydrohalide salt, but I think I’ve made my point well enough. This is not to call into question the quality of the work y’all are doing with ethanol, but to show it’s a slippery slope and why a slight deviation from the formula can carry such problems.



The novel compounds of this invention are prepared by reacting a terpene alcohol, which undergoes dehydration or rearrangement in the presence of acid, such as certain bicyclic terpene alcohols, with an organic acid halide or acid anhydride in the presence of a slight excess of a suitable base or with an ester of an organic acid and a lower alcohol, preferably methanol, in the presence of a neutral or basic catalyst.

“Bicyclic terpene alcohols that undergo dehydration or rearrangement in the presence of acid” (there will always be acids in plants) “lower alcohol” etc


Maybe the best way to do gas stripping would be a countercurrent falling film. I think you’ll want to increase the surface area by using a packed column. Would be the least demanding on the gas recirculating blower. The bigger the column diameter, the better the thermal conductivity of the column packing needs to be to avoid excessive temperature drop from evaporation.

If one were recirculating the ethanol thru the column, consider using a gas operated bubble lift or “geyser pump” to lift the ethanol solution back to the top of the column to avoid the solvent pump. But I’d try to get it to work without recirculation of the liquid phase, with a big enough column. I think you’d only need to concentrate the terps (or crude) to a solution with little enough ethanol to finish in a rotovap, to avoid serious terp losses and a giant rotovap…

After some quick calculations I figure 3 cubic meters of 35°C inert gas at 1 atm pressure will carry 1 liter of 190 proof ethanol. So a 10 cfm recirculating blower could strip a little over 4 gallons per hour if the gas is cycled between 5° in the condenser 35° in the column. I like the sounds of that. Need to have a sizeable condenser to handle the gas flow. Nothing a stainless pool heat exchanger can’t handle.

That’s interesting stuff about the terpene isomerization. Certainly worth considering. I remain a little skeptical that the acids are concentrated enough to cause it to occur at normal ethanol recovery temps…

On further thought, with the relatively short residence time in a falling film, it might be just fine to run it up to 45° which doubles the ethanol carrying capacity of the gas.


“ Conditions for the isomerization of linalool into geraniol and vice versa were studied in detail by Rivkin and Meerzon.44 They found that the reaction was reversible in the presence of water at high temperatures and pressures and in the absence of catalysts. Weak acids caused dehydration, whereas certain salts had catalytic influence on the reaction. In all cases. the rearrangement took place only to a small extent. A thorough study of the mechanism of this type of reaction has been made by Prevost.45

“Since the rearrangement is a reversible reaction, it is possible to convert geraniol to linalool although with greater difficulty and in smaller yields. Heating geraniol with water in an autoclave at 200° is reported to cause partial conversion to linaloo1.46 A similar rearrangement is brought about when sodium geranyl phthalate is subjected to steam distillation.47 Many studies of allylic rearrangements have been carried out through the halide compound, the transformation taking place with greater ease with the halide than with the hydroxyl radical.”

I’m not saying it messes them up too badly, but see, even steam distillation causes some changes in some terpenes.

My whole point is just whatever you can do with aprotic solvents, do :D. It’s not that you are doing anything wrong, it’s just maybe you can find a better way one day, properly armed with knowledge


Point taken. It would be very interesting to actaully quantify the changes in terpenes under different conditions.

I’d sure love for a barrel of pentane to be sitting next to my barrel of ethanol.

I guess acetone is about the only really cheap aprotic solvent around without a high boiling point. At least without running a catalytic dehydration reactor to make dimetyl ether from methanol… I think that would be an interesting project.

Running liquid CO2 and recirculating it thru a bed of sorbent or maybe a column of a second immiscible solvent might be another way to grab the terps before the main extraction while avoiding the having to evaporate and recondense large volumes of CO2.


Polar aprotic:

Ethyl acetate
DMSO (High bp so you would crash with water)
Propylene carbonate (High bp miscible with water)


This is just a crude list of options; I’m not telling anyone to switch to any of these lol. However, most of the polar options would likely have to be cold.


Haha well the key word was cheap…

And I’m not so sure DME and dioxane are much less polar than the likes of ethyl acetate, thf, acetone.


Ethyl acetate is very non polar yeah that’s wrong apologies.l, but thf is in between and pretty polar (water miscible). Acetone is weird it’s polar for sure but oddly nonpolar sometimes.


Nitromethane hash oil sounds bomb sorry for the pun.

For cheapness, I think the ability to reclaim it is key. Dcm and ethyl ether (not as hard to get as you have been told) are so volatile you would loose a lot every time you did anything. Chloroform needs to be stabilized after you distil it btw like ether but bc of phosgene not peroxides

I found a quote about nitro which I will leave you all to ponder. Now it’s very polar so at rt I imagine youd have green black shit for sure but:

“ As crystallization solvents, nitroalkanes have shown the ability to drive polymorph selectivity. The combination of high polarity and low water solubility can also provide a number of advantages in solvent-extraction systems.”