In what way? The reading I have done left the impression that hexane fumes were far more harmful than heptane fumes.
A google search yielded this from pubs.rcm.org.
It should be stated that both hexane and heptane are toxic . However, hexane is more volatile, can cause peripheral neuropathy and is more neurotoxic than heptane
Honestly, looking at the literature, your claim is justified. It may be old “wisdom” I am judging by. I was taught that odd numbered alkanes were more toxic than even numbered alkanes, but pentane is seemingly less toxic than hexane or heptane so I’m not sure now if that really works. I was taught that hexane was used as an extraction solvent more than heptane industrially not only bc of the lower bp but also bc odd numbered alkanes were very toxic by inhalation by the liver. Reading now for a minute makes me question that as well as oral ingestion should be worse for the liver and inhalation more neurotoxic.
Interesting to hear that, perhaps it’s a sort of “old wife’s tale” amongst chemists of the past.
If I remember correctly, heptane is considered a “green solvent” in the sense that it’s impact on the environment is less significant than many other solvents as well.
Yeah “old wives tale” probably; I’m sorry to (almost) pass it on… I saw a paper from a European pentane lobby which (not surprisingly) shows pentane as being really safe to use.
@Photon_noir @Cryo13 definitely seen this cloudyness when cleaning glassware with heptane denatured ethanol. And as well with boiling points (temp vs vacuum depth) in our rotos.
We split 55gal drums between smaller runs and ive noticed the last 15gals if split into its own material; that said drum/keg will evap at way lower temps and not as deep of a vac. And the top layers of the drums need more heat and deeper vac depth
Well, I cannot go back and edit the original post now, but I meant to explain WHY ethanol becomes more selective as temperatures decrease! Although it is still a hypothesis because I cannot easily obtain direct evidence of the facts, according to my observations, I sincerely believe ethanol selectivity at low temperatures is more physical/mechanical than chemical:
In order to make sense of both of the following systems, one must understand a bit of cellular biology and think microscopically.
At higher low temperatures, selectivity has to do with decreased solubility of undesirables in the plant; namely epicuticular wax (water-resistant protective layer on outer surfaces of leaves and plant parts, which inhibits passive evaporation of water in warm growing conditions) and the vegetable oil (e.g. food grade hemp oil and any other large-molecule fatty acid triglyceride compounds… similar to coconut LCT and MCT oils… which often coexist with free fatty acids, phosphatides, and other lipid components).
Other undesirable compounds with decreased solubility in ethanol at lower temperatures include sugars and more complex carbohydrates (sugar polymers), free amino acids and proteins (amino acid polymers), and other intracellular materials, which brings us to the concepts of the secondary effects of decreasing temperature…
At lower low temperatures, decreased uptake of undesirables by solvent has to do with the density & viscosity of the solvent, and the permeability & cellular mechanics of the plant material.
This is similar to the conceptual difference between chopping/cutting/grinding the biomass, which breaks and opens many individual cells, and shredding/hand-breaking biomass, which mostly splits it up along the cell walls, leaving cells mostly closed and intact. In the case of cannabis, the latter (unopened cells) improves selectivity in the same way super low temperatures improve selectivity, if that makes sense.
*1. Ethanol at -40°C/F:
Temperatures at or below this point render the epicuticular wax on the plant material relatively insoluble, most especially in 190 proof potable ethanol (aka ethanol:water azeotrope)… and although the wax is less soluble at this temperature, it is still much more soluble in 200 proof pure or denatured ethanol. The same rule applies to vegetable oil and other non-polar intracellular compounds that are accessible to the ethanol due to open cells. This also applies to more polar compounds like sugars, but the prevailing belief is that said intracellular sugars are slightly more soluble in 190 proof than in 200 proof and denatured… the key words here are “intracellular” and “slightly”, though. Ultimately, proper shredding minimizes access to these compounds… as does lower temperature, described in *2.
*2. Ethanol at -70°C:
Temperatures at or below this point render most undesirables almost completely insoluble AND cause the ethanol to become so dense & viscous that it is less able to penetrate stomata, other pores, and even torn openings in the cells, which are surrounded by insoluble waxy cell walls and which are now minimized in size due to thermal shrinking! In other words (as usual, most especially 190 proof) ethanol is physically less able and less likely to penetrate into (and therefore less likely to wash back out of) cell interiors, where almost all of the undesirable compounds reside!
How resin extraction occurs:
Thinking this way, it is vital to also comprehend the nature of the glandular trichome membrane and the state of the material inside those trichome “heads” when starting the extraction process. Along with an understanding of the low heat capacity of very dry biomass, this should also help explain why it is better to leave dry plant matter at room temperature and hit it with cold solvent than it is to freeze said dry plant matter…
Only a thin part of the combined outermost cell membrane (cuticle) of the secretory disc cells expands like a balloon as it fills with cannabinoid acid rich terpene resin. These disc cells are specialized to create this elastic membrane, which becomes thinner and more (molecularly) porous as it expands, just like any elastic material. When this “stretched skin” (membrane) is exposed to alcohol or other solvents, the solvent can rapidly diffuse into the resin through the pores in the membrane, causing the gland to rapidly swell and rupture, releasing the already-partially-dissolved liquid resin into the wash of bulk solvent.
Naturally, small particles and even molecules of the exploded membrane can enter the solvent when this occurs, which is one reason there is always some phosphatide and other impurities in the resin.
Also, the disc cell plasma membranes (which keep their disc cell contents from spilling out into the resin) are more vulnerable to solvent attack than the wax-covered hard cell walls on the rest of the plant, which is one reason why relatively brief solvent/plant contact time is always preferred over extended solvent residence time in cannabis extractions.
So say I use methanol. And distill is down to oil then add ethanol and then purge again? How much ethanol do I add per oz of oil?
So, I assume that you have a mostly purged methanol hash oil. Just add enough ethanol that you can see it’s a viscous solution and purge again. The remaining methanol will be gone very quickly and once the ethanol is purging well the methanol is gone.
I can give more specific advice if that’s my good enough, but it’s the sort of thing that’s not too hard and if I was to give very specific advice I’d have to think about what techniques are being used etc. The boiling point of methanol is lower than ethanol and they don’t form an azeotrope. Methanol is formed naturally in many alcohol preparations and this is the head they really don’t want. So when you have a touch of methanol left and then solvate it all again in ethanol, the methanol isn’t trapped in crystals or goop or anything. So as you heat it, pretty much the very first thing that comes off is all the methanol. Your ethanol is still solvating the material and at elevated temperature / reduced pressure so there isnt the issue of a wax trapping fluids. In the end you will be left with ethanol contamination determined by your operating procedure for an ethanol purge.
Alcohols and terpenes form azeotropes - not as a class but as each individual pair or not… but I urge you to use enough ethanol, but not to go crazy and loose more
So like mix it to a 5:1?
@Lewis_Bronsted is just explaining the physical concept of how viscosity and dissolved solids of a solution affects evaporation of any solvent. As the mixture becomes more viscous or solid, the volatiles have a harder and harder time physically escaping the mixture… so evaporation slows way down.
Therefore, if you want to remove a lower boiling point solvent from a mixture completely, it is best to mix in some higher boiling point solvent to loosen up the fluid, allowing all traces of the lower b.p. solvent to escape freely.
You may be familiar with people using this method on BHO, for example. Instead of purging the BHO into a hard slab over several days in a vacuum oven, and then dissolving the slab in ethanol to Winterize, many choose to simply add ethanol to the gooey butane:resin mixture. This serves the purpose of both loosening the mixture, allowing butane to more rapidly evaporate, and also allowing the resin to dissolve more rapidly in the ethanol. It’s two sides of the same coin.
The same procedure can be done when methanol or some other lower-boiling (and possibly toxic), non-azeotroping solvent needs to be completely removed from your resin.
Don’t let this confuse you, but it could also work with 2 solvents that DO form an azeotrope, as long as that azeotrope is lower-boiling and thereby easy to completely evaporate from the mixture… but this will always take longer to completely remove the toxic/undesirable solvent, since it effectively gives you a single b.p. evaporating solvent (azeotrope) composed of both solvents, instead of letting one totally evaporate while the other mostly stays behind to keep the mixture loose.
“What he said!”
100
@Photon_noir I’m wrapping my head around this before presenting it to the owners. If our heptane denatured 200 proof has 4.5% heptane, which if im reading correctly can azeotrope to around 15% water, isnt that a composition of roughly only 1 percent water overall? Does that really make a huge difference? I’m planning to buy a LOT of molecular seives to try to dry our denatured ethanol and heptane (liq/liq use).
I’m also curious of how terps affect proof/introduce additional water azeotropes as well. Up until last night I didn’t think inmiscible liquids formed azeotropes. Thank you for waking me up to this.
Appreciate any thoughts you have.
Alex
I’m wondering, what’s wrong with removing most of the heptane from denatured alcohol? Seems like nobody has given much attention to that question, unless there’s a different thread about it that I haven’t seen?
Fractionating columns are not exactly high tech or expensive to build from tri-clamp fittings. Nor would you need a large column that can distill many gallons per hour, either the binary or ternary azeotrope has a lot of heptane after all. With a decent reflux ratio and stainless scrubbers as packing in a 4-5’ long by 3" dia column, collecting maybe 1/2 to 3/4 gal/hr, I see no reason that wouldn’t pull out near azeotropic 60% heptane leaving very little behind. I’d add just slightly more water than is needed to satisfy the ternary azeotrope, but it would work without water.
Alternatively, maybe force it to separate into two phases and decant the upper phase? The problem here is then you’ll have a bunch of water ethanol mixture that needs to be reconcentrated, so it wouldn’t avoid the need for a column, and the whole volume of ethanol would need to run thru it rather than just the heptane rich fraction, so I see no advantage to this method.
But…
It may be possible to use something other than lots of water to cause phase separation, allowing one to use a normal recovery still to reclaim the ethanol after decanting the heptane. The only nonpolar extractant possibility I know of is silicone oil. Even heavy mineral oil is a bit too soluble to alcohol. From a manufacturer:
“Silicone fluid is highly soluble in hydrocarbon solvents such as toluene, xylene, ligroin, and mineral spirits as well as in chlorinated hydrocarbons. However, it is insoluble in ethanol , methanol, and water.”
It could be easily reused too. No doubt the cleaned up ethanol would need to be run thru a normal pot still, or rotovap to eliminate however much oil that did dissolve into it.
More commonly mentioned in literature is polar solvents (they’re working with much higher % heptane mixtures) and I found papers that show how a nontoxic deep eutectic solvent choline chloride+propylene glycol/glycerin and potentially a little water can work wonderfully for separating ethanol and heptane. Bulk livestock feed grade choline chloride is quite inexpensive too. It won’t let me post links yet, but if you’re interested you can piece these together. researchgate . net/publication/255771075_Deep_eutectic_solvents_as_extraction_media_for_azeotropic_mixtures
researchgate . net/publication/325221289_Effect_of_water_addition_on_extraction_ability_of_eutectic_solvent_choline_chloride_12-propanediol_for_separation_of_hexaneheptaneethanol_systems/amp
The liquid/liquid extraction style technique would also be even more useful to break the ternary azeotrope that’s collected from a fractionating still, in order to recover the heptane and little bit of ethanol as usable solvents. Much smaller volumes of deep eutectic solvent needed that way. Fractionation and then separate the azeotrope is probably how I’d go about it.
If one could find grades of denatured ethanol with methanol or some other less problematic solvents thatd be great but they don’t seem nearly as common or readily available. Nonetheless, buying heptane denatured stuff and fractionating off the heptane looks potentially much easier than fermenting and producing many gallons of azeotropic ethanol. I do have some experience with that… Its not a bad option either. If you do it, my recommendation is find some bulk wine in IBC totes for as cheap as possible and build stills (as many as you need) with beer kegs and 3" tri-clamp spools, packed with scrubbers. Don’t expect over 1 gal/hr of near 95% etoh from a still that size. They don’t have to cost too much, but you better insulate them and have an efficient fuel burning heat source (with a heat tranfer fluid hopefully) or cheap electricity. Its helpful to initially run the wine thru a pot still cranked up as fast as it will go, to “strip” the ethanol out as 40-60% before feeding it into the fractionating still. I’m assuming many of you are reasonably near wine country… 
If you’re lucky enough to find super cheap or free wine like I did, it won’t cost much more to produce the 'shine than denatured alcohol costs. Unless you value your time much. Having the equipment to produce drinkable spirits has its own set of risks and benefits though. I know of a guy down the road who got all the way thru the process of pressing/fermenting apples, building the still, producing the alcohol and then said “screw it, this stuff tastes too good to ruin with a bunch terpenes from trim”
Be aware it can be difficult to avoid some flavor from home made ethanol getting into the extract, whether that’s a problem depends on many factors.
I haven’t used it, but methanol is also intriguing in my opinion. Particularly if you’re already set up to perform extractions below -60 or your post processing steps can handle some extra hydrophilic contaminates.
P.S. I’ve been lurking and sometimes posting in forums on a wide range of subjects since around 2006, but this forum really stands head and shoulders above the rest! I’m really loving it and learning lots, so BIG kudos/congrats/all the rest to everyone who keeps this thing running and the folks contributing their experience and providing real usable high quality information.
Edit:
In regards to measuring the water content of heptane denatured ethanol. Seems like it would be feasible to use a hydrometer (although it would need to be able to read a bit lower SG than a normal 0-200 proof hydrometer) to get the SG of the fresh denatured 200 proof. Then take a sample, add a measured amount of water, record the new specifc gravity, maybe repeat that again just to be sure. At least until the phases separate.
I’d try it myself but I don’t have the right hydrometer. Maybe measuring the SG at freezer temperature could cancel out the lower density of the heptane to allow the normal hydrometer to work. Hmmm…
Edit 2:
Cool, that works. 95% EtOH 5% n-heptane measures exactly 190 proof (aka 0.8156-0.8160 SG) on my hydrometer, at -32°C. It was syphoned out of a freshly opened barrel and put directly in the freezer two days ago so there shouldn’t be much water.
So that’s a start. I’ll try adding some water to small amount and remeasure once its cooled off.
No, @alex.at.biosphere, 15% water means 15% water.
The problem isn’t even the amount of water, though, because the max total water (at least in the azeotrope) is only about 6%.
The problem is the fact that essentially ANY water in the mixture causes the whole azeotrope (of which there is a continuum of ratios for all 3 components) to separate into 2 distinct layers… each of which have different percentages of all 3 compounds: upper layer has about 2/3rds heptane, very little water, and 1/3rd ethanol… the lower layer has up to 15% water, mostly ethanol, and about 5% heptane!
So if you have 6% water in the mixture (which it naturally pulls from air and plant matter), then that 6% water still causes ALL of the liquid to separate into 2 distinct layers which have the ratios mentioned above! Even if you only have 3% water, it still ALL separates into 2 distinct layers which have slightly different ethanol:heptane ratios, and only half the usual rations of water (i.e. top layer is 0.1% water instead of 0.2%, and bottom layer is 7.5% water instead of 15%)!
These layers obviously have very different extraction properties!
Yes, terpenes and other solutes may very well form azeotropes with one or more of each of the 3 solvent components, which would wreak all sorts of havoc on any calculations… but I can verify that the bilayer system still exists after solvent recovery!
@back2thefuture The point of denaturing is to make azeotropes that are very difficult to separate. Sure, one could probably make secondary azeotropes and fractionally distill the ethanol:heptane apart, but something is going to stay azeotroped with something else.
So agitation makes this less of an issue?
Maybe, but not really… the layers separate pretty rapidly. Agitation (when cold, so I can see the difference between the phases) appears to make a heterogeneous matrix of the bottom (more dense) phase with little bubbles of the top (less dense) phase in it, which rapidly climb to the top.
Front load washing machine it is!
thanks @Photon_noir! I hope someday I will be able to help as many people as you do.
An old washer, perhaps… the new HE washers stop and start and generally don’t agitate enough to keep it homogenized. Honestly, the only time the azeotrope is truly homogeneous is when it is in vapor phase!
Rising film heptane extraction and filtration?
Ps: i think the edibles kicked in
Filtering a rising film would be a feat, but interesting idea… vapor phase extraction can be a thing, much like supercritical fluid extraction!