This thread is intended to compile and summarize the possibilities for the employment of super-critical carbon dioxide as a solvent for general extraction purposes. The potential advantage of using SC-CO2 is that it is nontoxic and evaporates cleanly and instantly under normal pressure. It was originally proposed on the forums as an eco-friendly means of extracting limonene:
Extraction and Purification of Limonene - Advanced/Enhanced chemistry - Welcome to the DMT-Nexus
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http://www.anoniem.org/?http://facweb.northseattle.edu/kowens/che122web/wordPDF/chem122_Limonene.pdf
and was later proposed for the extraction of DMT:
Welcome to the DMT-Nexus
The difficulty presented is that SC-CO2 only exists under fairly extreme pressure that most common and household equipment simply is not capable of withstanding. While SC-CO2 is commonly used for the commercial extraction of essential oils, the equipment used to do so is well beyond the means of most hobbyists.
One way that SWIM has proposed to accomplish a fairly large scale extraction is by loading an empty CO2 tank with the material to be extracted from, inserting a filtered siphon tube of some sort, and simply performing a CO2 transfer between tanks:
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The potential problems SWIM sees with this proposal is that dry ice may form if the tube is blocked or filtered in any way, thus plugging the tube and stopping the flow of SC-CO2, so this method may not be safe or viable--likely one would just end up with a broken siphon tube, though.
However, a much more safe and viable method would be to pack a tube with the material to be extracted, and lock it into a pressurized system with a CO2 tank containing a siphon tube--such as a CO2 fire extinguisher or a modified soda club (often used for paintball)--allow the tube to fill, then expel onto a dish or into a smoking device using a valve and nozzle.
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With a system like this, the SC-CO2 would be forced to percolate through the material in the tube by the pressure of its release into the tube, and in theory, the pressure of being released from the tube would force out the extract.
While this may only be viable for extremely small-scale extractions (instant extraction of individual doses), it's possible that a longer tube could be packed and perhaps coiled to facilitate the extraction of larger amounts of material.
SWIM believes that the cheapest way to go about this would be to use a CO2 fire extinguisher in the manner documented here:
Bulk-fill: Part 3 | Pyramyd AIR Blog
Working with bulk-fill CO2 guns | Pyramyd AIR Blog
Alternatively, practically any regular CO2 tank (with an antisiphon tube) could be turned upside down to expel liquid CO2.
The goal for DMT extraction would be to retrieved an instantly crystallized (or at least oily) freebase product, but if one were to extract from cactus, it may be possible to retrieve mescaline carbonate by bubbling through water. This may also work for other extractions, such as the extraction of harmaloids. SWIM's hope for this would be the development of a universal extraction rig using a nontoxic and efficient solvent.
While such a method may eliminate the need for limonene in extraction, most people consume oranges and have some use for limonene, so occasionally packing a tube with orange peels and extracting limonene with a CO2 tank would be a fairly practical habit to get into. Aside from that, there are plenty of other practical applications for having a larger CO2 tank, capable of filling smaller ones.