Get your cinnamon out (using supercritical CO2!)

I love DIY chemistry, and this one ranks up there with the best of them.  I earlier presented some ways to make your own thin layer chromatography columns to do separation of dyes, amino acids (maybe) and other useful compounds. In this set of videos, Ben Krasnow demonstrates how to fabricate a supercritical CO2 chamber for extracting a variety of natural products, including those from cinnamon, coffee, and vanilla bean.  But what is supercritical CO2, and how did he achieve this?

Supercritical fluids

A supercritical fluid is a state of matter with properties mid-way between those of a liquid and those of a gas.  It is called supercritical because the material has been forced beyond its critical point, a combination of pressure and temperature at which distinct boundaries between these phases cease to exist.  For CO2, this critical point is at relatively easily achievable conditions, namely 31 degrees Celsius and a bit more than 1000 psi.  Although the pressure sounds quite high, it’s not when you consider that most pressurized gas containers operate in the 3000-4000 psi pressure range, and as you’ll see in the video, you can also achieve these pressures fairly easily just by constraining the volume and heating dry ice appropriately.

Phase diagram for carbon dioxide

Phase diagram for carbon dioxide.  Source:  Wikipedia

Why is this useful?

Supercritical CO2 is currently used as a solvent to extract a large number of different essential oils and compounds from natural products.  This works because supercritical fluids have some properties of a fluid (such as density), but have other properties closer to those of a gas (like zero surface tension and high diffusivity, meaning they move through other materials well).

SCF_prop

Properties of a supercritical fluid. From “Natural Extracts using Supercritical Carbon Dioxide”, Mamata Mukhopadhyay, p. 12.

How do I make it go?

This is where Karsnow’s videos come in.  His videos show two useful DIY techniques.  First, he demonstrates how to fabricate a supercritical CO2 extraction chamber out of aluminum and acrylic using ordinary machining techniques.  Second, he demonstrates how to generate supercritical CO2 by heating dry ice using a propane torch.  By combining these two techniques, Krasnow is able to achieve small (5% yield) quantities of extracts from each of these natural products.  Although commercial yields are higher, Krasnow does not add any cosolvents to his CO2 that would alter the polarity and thus make extraction more efficient, so it’s certainly possible to imagine implementing this improvement in a future iteration.  Krasnow also mentions that the acrylic itself (or more likely, the unreacted monomers or polymerization promoters left over in the acrylic) actually get extracted along with the desired products – yech.  However, as he points out, this is easily solved by fabricating a metal extraction chamber.  The only disadvantage is that then you can’t see the awesomeness that is supercritical CO2 at work.  There are also two other supporting videos by Kransow in which he lays the foundation of his current extraction technique.  These are linked from the main video here:

If you are a teacher of chemistry or physics and want to teach supercritical fluids, phase diagrams, chemical extraction, or natural products on the cheap, I recommend this set of videos as a good place to start.

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