I am writing this to help those of you performing alcohol-based cannabis extractions, and especially for those playing around with n-heptane-denatured ethanol, isopropanol, and other less expensive alternatives to 190 proof potable ethanol.
Please understand that drinkable 190 proof ethanol, isopropanol, and n-heptane denatured ethanol are very different animals. I strongly advise people to reclaim and reuse solvent as much as possible, rather than just buy cheaper solvent.
190 proof potable ethanol is “perfect”, as long as you treat it with effectively cold temperatures (below -40°C/F) and commensurately brief biomass contact (residence) times to achieve selective resin extraction. It can be your enemy at higher temperatures and higher residence times, but it will be your best friend at -67°C or lower, at which point residence time without extracting green pigments increases to practically infinity.
Isopropanol, isopropyl alcohol (IPA), rubbing alcohol must be used at least 99% pure in order to make it work right, but that still has much higher capacity to pull vegetable oil (fatty acid triglycerides) and epicuticular wax than using ethanol, at even 200 proof, but especially at 190 proof, as seen in the excerpt below:
It makes a world of difference to use and reuse potable 190 proof, compared to trying to re-use heptane-denatured ethanol after it starts forming the ternary (3-component) azeotrope with water… and it WILL form that ternary azeotrope, changing over time until your extraction yields drop too dramatically to ignore!
I used to advise folks to “weather” their n-heptane-denatured solvent with a bit of water prior to using it, since it will end up with water in it anyway, just so the solvent won’t keep changing during and after every extraction, but even that fails to avoid changes or reduced extraction efficiency. Here’s why:
A. The ternary (3-part) azeotrope of [n-heptane : ethanol : water] forms at least a binary (2-layer) set of solutions, each with different ratios of all 3 components, and thereby different densities (which generates 2 totally different layers of solvent, each comprising about 50% of the total volume).
B. The heptane in the azeotrope not only screws with the consistency of the solution, but also extracts more undesirable stuff from the plant matter… both on its own, and in the variable ratios with ethanol and the inevitable water.
C. Excessive (read: not strongly hydrogen bonded) water in your extraction solvent will diminish your extraction efficiency (lowering yields) and selectivity for cannabinoids and terpenes (increasing undesirable content); be it the 12.3% water in the isopropanol:water azeotrope, any water in excess of 4.5% in the ethanol:water azeotrope, the 15% water in the lower layer of the ethanol:water:n-heptane azeotrope, or any other “water overloaded” mixture with solvent!
I would like to add this cobbled Wikipedia table for reference values on the water:ethanol:n-heptane ternary azeotrope (top line of values are percentages of each component in the boiled vapor, aka the “complete azeotrope”) and the 3 different component concentrations in each of the 2 liquid layers (Upper and Lower) of its binary solution system when it is or returns to liquid form:
I included the n-hexane ternary, also, for reference.
Here is an abbreviated binary azeotrope table for water with various alcohols, just to show that even some binary azeotropic mixtures can separate into 2 layers when in liquid state:
And finally, here are some binary azeotropes of ethanol… mostly to show its behaviors with the n-alkanes:
Please feel free to ask questions, comment, and provide input & your personal experiences! All comers welcome!