"Blair P. Houghton" wrote:
>
> Until you can prove that the aromatics settle out of the
> liquid propane, and then that they don't burn, I'm just
> not going to worry about it. You've done neither, and
> the links you've posted haven't even mentioned those
> processes.

Here's what the warning says on a 14.1 oz container
of Bernzomatic brand propane, Model TX9:

"This container and byproducts of the combustion
of its contents contain chemicals known to the
state of California to cause cancer, birth defects,
or other reproductive harm."

So at least Bernzomatic is aware that not all
of the hydrocarbons are completely combusted
to harmless carbon dioxide and water.

In the supply chain, propane is handled as
a liquid. However, your tank is a "converter",
that is to say conversion from liquid to gas
occurs in your tank. That's why heavy ends
(hydrocarbons with higher molecular weight than
propane) accumulate in the tank.

Here's what PetroCanada said to a guy inquiring
about accumulation of impurities in propane-
powered vehicles.

Quoting from:
http://cars.rasoenterprises.com/Propane-Residuals.htm

Most propane as it is produced at a gas plant
(the majority of product in Western Canada) or
refineries is very clean. However, during
distribution it can pick up contaminants such
as traces of gasoline or diesel fuel (if pipelined
through a common products pipe line, or in storage
caverns) or extract some plasticizers from hoses
and gaskets. Some of these contaminants,
particularly diesel fuel and lube oil range
materials, have low volatility - so as propane
is evaporated in a converter (changing from a
liquid to a gas), the contaminants remain behind
at a low point in the system - which can be the
bottom of the converter, or a low-lying loop
in a fuel pipe delivering propane vapours to
the carburetor. So there is no 'conversion' or
'breakdown' of propane into oily residues in
a converter - the residues are contaminants
left behind when the propane evaporates.
Unfortunately, the current propane specification
allows rather a lot of oily residues - up to
500 ppm. I've seen instances of 6 - 12 ppm
oily contaminants (6 - 12 litres of oil from a
million litres of propane used in a high volume
heating situation) being enough to cause problems
with build-up of the oil in the bottom of large
converters.

While instances of contaminants in propane have
been on-going for decades, and appear in different
forms (oily materials, 'grease-like', 'black
shoe-polish', and waxy deposits), they are usually
sporadic, even seasonal, and we (the industry)
have not been successful in finding the sources
of all the contaminants. It is clear that potential
future uses of propane, such as fuel cells, will
require very clean product, and current
contaminants will be totally unacceptable.