From: B.Hamilton@irl.cri.nz (Bruce Hamilton)
Subject: Re: freon ccl2f2 process??
Date: Sat, 10 May 1997 20:31:11 GMT
firstname.lastname@example.org (DKelly2716) wrote:
>how is freon, R-12 made, thanks in advance dmk
If you are thinking of making some, forget it. It's not
easy, or economical, on small scales. They are hundreds
of patented processes, the most common involves the
successive vapour phase replacement of chlorine ( on a
molecule such as chloroform or carbon tetrachloride )
with fluorine from gaseous hydrogen fluoride using
chromium oxide or halide, ferric chloride or thorium
tetrafluoride catalysts. Read the precautions for
handling gaseous hydrogen fluoride *very* carefully.
The traditional liquid phase process also used HF, but
with antimony pentafluoride or a mixture of antimony
trifluoride and chlorine as catalysts.
If you read up the history of CFCs, you will find that
existing common refrigerants ( ammonia, methyl chloride, and
sulfer dioxide ) were toxic and some were fire hazards.
Frigidaire asked Thomas Midgley, Jr in 1930, to produce
a safer alternative, and he decided to look at CFCs.
They purchased five 1-oz bottles of the then-rare SbF3,
and made CCl2F2 from one bottle. When they placed a guinea
pig in a bell jar with some of the product it was unharmed,
and they were delighted. However, when they made additional
CCl2F2 from one of the other bottles, the guinea pig died.
When they repeated the experiment, they detected the odour
of toxic phosgene (COCl2). They removed the phosgene with a
simple caustic wash. When tested, all the remaining bottles
of SbF3 had been contaminated with a double salt containing
water of crystallisation, which produced the phosgene. If
they had used any of those bottles first, they would have
concluded that CCl2F2 was toxic and looked elsewhere.
Despite Uncle Al's frequent panic attacks about government
regulators, there is good scientific evidence of the harm
from CFCs, and I highly recommend Robert Parson's superb
Ozone Depletion FAQ that is posted to sci.environment.