So subzero ethanol extractions r becoming increasingly popular recently and is probably where large scale processing is going right now. and I’ve been researching co2 expanded solvents (CXS) and realized how easily i could modify my machine for this process method. I have a jacket pressure vessels and large tanks of co2; all i think i would need is a large condenser, a cheap vac pump and the liters of high proof ethanol i would need (which is expensive here in cali but fortunately part of my design is a large vacuum still lol).
Let me explain my idea without all the minutia first;
Take ethanol that has been chilled(x) and add to my main vessel which has been prechilled to the same temperature (x) then dissolve co2 in cold ethanol (x) then add plant matter to the mixture (x) then filter into 2nd vessel (x) and distill most solvent under moderate vacuum (x) yielding a concentrated ethanol cannabinoid solution (x)
ill end the abridged version there cause the final steps depend on what product ur going for and the exact parameters of the extraction. but almost always include purging of all the solvent at some point.
Take ethanol that has been chilled(as much as u can) and add to my main vessel which has been prechilled to the same temperature (I could use solid or pressurized liquid co2 do this by pressurizing-depressurizing cycles or I could make a cryo-liquid coolant out of iso or acetone and dry ice and pump thru the jacket) fill only ~40% full to leave room for both expansion and plant matter. Then dissolve co2 in cold ethanol (I would add dry ice to ethanol then seal chamber and let the pressure build to start then i can also add co2 gas into the system from the bottom of the vessel. co2 gas becomes more soluble in ethanol as it gets colder so this has to be done till all the ethanol is at lowest temp) then depressurize the system and add plant matter to the mixture (after addition reseal vessel and wait 30-45 mins) this is where the real unknowns start so ill be general. then filter into 2nd vessel (piping co2 gas into to top pushes ethanol thru filter and into next vessel or using the built up pressure) let solution warm to room temp then slowly raise to 40c to drive off co2 and distill most solvent under moderate vacuum (apply at least enough vacuum so that ethanol can be distilled with hot water pumped thru the jacket and in addition to a condenser an ice trap with dry ice cryofluid i also us a pusedo capilary tube action to prevent bumping) yielding a concentrated ethanol cannabinoid solution (stronger vacuum can be applied to the vessel and left on low heat to fully purge or may be collected then purged in a vac oven) from what ive read u could also grow thca crystal from this if ur starting material is high quality.
i might be able to do this all at atmospheric pressure when at -75c but if thats not true i hav 2 options, i could experiment with pressure and i hav good resources on the properties of the co2+ethanol mixture from 0f+ at pressures up to 1100psi just not for extracting cannabinoids. or i can just do a cryogenic ethanol extraction
One of the biggest benefits of this process over co2sfe is crystallizing of thca from freshly harvested and frozen (wet) cannabis recently given the term “live” extractions or thru the well documented liquid-liquid extraction of the thca. ive also seen this referred to as the Polar-NonPolar (Pnp) or acid/base (A/B) extraction of thca. similar techniques r know for co2 but r much harder to adapt to my machine.
Other potential benefits are yield and purity. and the yield is almost guaranteed to be better from what i understand its just if that yield is worth the decreased purity and process cost.
The biggest absolute negative is reduction batch size. i am basically making the solvent in situ and adding the plant matter to that so the material and the solvent both hav to fit. instead of just packing the with as much as can fit lik co2sfe.
This process might also be limited by how much can be dissolved it that volume of solvent which depends on the ratio of co2 to ethanol to water.
Another big negative is purging. i use to make bho so i know how fucking annoying purging oil is and how much time and overhead it adds. with co2 i dont ever hav to purge and i can always say my oil is solvent free.
and the setup cost is minimal and is for the same stuff i would need to buy to winterize my oil.