10.3 Pentane/Hexane/Heptane and brine wash

Polishing Extract:

We've discussed how to make pristine museum quality bragging rights concentrates, but what do you do after the fact, when what'cha got is not purdy?

You can remove the fats, lipids, and plant waxes by winterizing (See 8.1.1), but that doesn't work for the more polar elements in solution.

For those we steal the target elements from the polar alcohol using an non polar Alkane and then wash out the polar elements left with saturated brine (salt water).  While it isn't the great panacea, it can make dramatic improvements.  

For instance, back when I/we'uns still smoked cannabis, I saved all the roaches and pipe debris for about six months, as well as the denatured alcohol that I soaked my bud pipes in to keep them clean.  At the end of that time, I broke up the roaches and dumped them and the pipe tailings into the alcohol and after shaking well, decanted into a (1) gallon baggie to use for an improvised separatory funnel, so that I didn't dirty up the good separatory funnel with the ashtray stinking mess.

Here is what it looked like at that point, and the picture following it is what we turned it into:

The good, the bad, and the ugly!

 

The good, the stinky, and the purdy!

Of note, we still had to redissolve in alcohol and carbon filter to rid it of all traces of ashtray odor and flavor, so not recommending reclaiming combusted material, but it makes my point.  Combusting the terpenes and terpenoids creates free radicals and other byproduct of pyrolysis that are carcinogenic.

Here are the properties of three Alkanes under discussion.  Note they all three have low dielectric indexes, and are relatively insoluble in water, but they hold some.  While we prefer to work with Pentane, Hexane has better hydrophobic properties and is easier to subsequently remove than Heptane, so that is what we use here.

No

Alkane

BP

VP

DI

H2O Sol

LEL

HEL

Odor Thresh

1

Pentane

36

420mm/Hg

1.8

40mg/L

1.4%

7.8%

2.2 ppm

2

Hexane

69

120mm/Hg

2.0

9.5mg/L

1.2%

7.4%

6.4 ppm

3

Heptane

98

37.49mm/Hg

1.9

3.4mg/L

1.1%

6.7 %

0.2 ppm

Alkane properties

We use an HPLC grade of n-Hexane in this demonstration, which we purchased from American Scientific.

 

95% Hexane

For equipment, you'll need a separatory funnel, appropriately sized for the volume that you're running.  You will also need something to mix saturated brine in, as well as something to catch the discharge in.  Sadly I don't have a picture of the 2L beaker that we mixed brine in, but below is the Erlenmeyer flask that we used to decant the brine, the separatory funnel, and the 1000 ml beaker we bleed the discharge off into.

 

Add brine

The best starting material is a solution of freshly winterized cannabis concentrate, still dissolved in the ethanol.  If you use unwinterized material, you will end up with plant waxes falling out of solution as well, which will stick to the sides of your separatory funnel, like the one I will use below to demonstrate that phenomena.

If you haven't winterized your material, see 8.1.1 Winterizing. 

First we mix the brine by heating the water to ~38C/100F and mixing as much sodium chloride salt in it as will dissolve, before letting it cool to room temperature.  If you had it saturated at 30C/100F, it will be supersaturated at an ambient of 21C/70F, and some of the salt will have precipitated out of solution.

Decant and use that super saturated brine.

Next pour the winterized Ethanol/cannabis oil solution into a separatory funnel, and add n-Hexane at a 1:1 ratio.

To that mixture, add the same amount of water as you added n-Hexane.

Again

Put the tapered glass stopper in the separatory funnel and verify the stopcock is off and secure.  Place two fingers over the stopper and shake thoroughly.

Hold stopper and shake

Next step is to let it rest and separate.  Note the waxes that I spoke off stuck to the side of this separatory funnel:

 

 After separating a bit.

What we now have is a mixture of alcohol and saturated water on bottom, with the terpenes and terpenoids now in the n-Hexane floating on top.  The alcohol brine mixture has no room for the low polarity terpenes and terpenoids, but the jilted terpenes and terpenoids are in love at first sight and instantly in bed with the non polar n-Hexane anyway.   

Sort of  No Fault divorce and instant shack up on the rebound for both sides.  A marriage made in heaven, no?

Along with the water and alcohol are also the water solubles, and as you can see from the green tint at the bottom, some polar chlorophyll.

In the following picture you can see that at the fine line of separation between the two layers, there is a very thin emulsion layer.  That emulsion layer will take additional washes to remove.

Separated

  Next step is to bleed off the bottom layer, leaving the emulsion layer, and then add more brine, shake again and repeat the rest of the process, until the emulsion layer is gone and the brine at the bottom of the separatory funnel remains

crystal clear.

 

More

Last step is to remove the solvent from the extraction, which can be accomplished through simple evaporation, forced air evaporation, simple distillation, or using a rotary evaporator, followed by a vacuum purge at 115F@ -29.5" Hg.

Polished extract


Pentane and Heptane are Class III solvents with FDA residual solvent limits of 5000 ppm:

Solvents in Class 3 (Table 3) may be regarded as less toxic and of lower risk to human health. Class 3 includes no solvent known as a human health hazard at levels normally accepted in pharmaceuticals. However, there are no long-term toxicity or carcinogenicity studies for many of the solvents in Class 3. Available data indicate that they are less toxic in acute or short-term studies and negative in genotoxicity studies. It is considered that amounts of these residual solvents of 50 mg per day or less (corresponding to 5,000 ppm or 0.5 percent under Option 1) would be acceptable without justification. Higher amounts may also be acceptable provided they are realistic in relation to manufacturing capability and good manufacturing practice (GMP).

Hexane on the other hand is a Class II solvent with limits of 2.9 mg/day and 290 ppm residual.

Solvents in Class 2 (Table 2) should be limited in pharmaceutical products because of their inherent toxicity. PDEs are given to the nearest 0.1 mg/day, and concentrations are given to the nearest 10 ppm. The stated values do not reflect the necessary analytical precision of determination. Precision should be determined as part of the validation of the method.

 

 


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