I've read articles about using hydrocarbons as extraction methods for plant materials such as cannabis, root barks, coffee for decaf processing, canola seeds, etc. Some of the main solvents used in these processes are butane, propane, supercritical CO2, or ethanol which have been graded as food safe for the final product. I've also read about extraction methods that use Naptha, benzene, heptane, DMC, petroleum ether, or other light distillates that can cause serious effects.
What I'm trying to understand is once a specific substance is extracted from the plant material, do hydrocarbons end up leaving any residue once it is evaporated or precipitated then dried? To connect this further, when these applications are applied to essential oils or cannabis or other areas where inhalation is concerned, is it safe at the end of the day? Or are the amounts so negligible that it doesn't cause any long term effects? Do the higher hazard light distillates such as benzene or Naptha pose a higher risk to this process and should be avoided at all cost?
Thank you for taking the time to reach out, feel free to send me links to any sources that possibly explain this better as I've been searching the internet and cannot find conclusive answers to these questions.
Removing solvents entirely from a mixture is difficult (if not impossible) to do. Because of this, I would avoid using benzene and naphtha since benzene is a carcinogen and naphtha may contain benzene. Benzene has an allowable limit of 2 ppm in tablets and capsules.
Hexane has a limit of 290 ppm and / or 2.9 mg/day. Cyclohexane is better at 3880 ppm and / or 38.8 mg/day.
It would be more difficult to remove hexane from oil than it would be from water due to similar molecules.
I would suggest that you stick to food grade solvents so you won't have problems with the FDA.