Which refrigerant (s) must be recovered before opening or disposing of appliances?

Older appliances and automobiles used Freon (R-12) as a refrigerant. In the many years after it's introduction - scientists discovered that Freon is actually a greenhouse gas. It's a Hydrocarbon responsible for destroying the earths atmosphere.

However, this is not limited to just R-12, but R-12 is the main gas that needs to be disposed of. All refrigerants should be properly withdrawn from appliances and automobiles so that it may be recycled or contained. This prevents unwanted chemical reactions at landfills (Imagine if someone threw away a sodium block that came into contact with rain water - boom!) and to protect the environment if future Scientists discover the current refrigerant we use is harmful.