Model Forum / Radio Controlled / Air Models / May 2009

Molecular sieves work by having a hole in the chemical structure that
water fits nicely.  Bigger molecules like oils or alcohols are too big
to fit into the hole in 3A so are not absorbed.

Regeneration by driving the water out with heat is easy enough.  Put
them on a tray on your kitchen oven and heat to 450 or 500 deg F for a
couple of hours.  Be sure to rinse them well with alcohol to get rid
of all the oils and nitro first.  Then dry them in air spread thinnly
on a tray for 48 hours or so to get rid of the methanol before you put
them in the oven.  If you skip the rinse and dry be prepared for a lot
of bad odor in the kitchen and perhaps a fire.  With a little luck you
might even be able to blow the door off the oven if you do it wrong.
If that happens you will probably blow out every window in the kitchen
too.

Drying ethanol and methanol are two entirely different issues.
Ethanol (95%) and water (5%) form something called an azeotrope.  An
azeotrope is simply the mixture of two compounds that boils at some
minimum temperature below the boiling points of any of the
ingredients.  The result is you can only purify ethanol to about 95%
by simple distillation.  There are a variety of tricks you can pull to
get that last 5% of water out of ethanol by distillation.  One is to
add benzene as benzene, ethanol and water form a tertiary azeotrope
that boils below the ethanol-water azeotrope.  But that leaves you
with ethanol containing small amounts of benzene and the benzene is
not always an acceptable ingredient.  So if you want pure ethanol mole
sieves is a decent way to dry out that last 5% of water without adding
any other organic compounds to your final ethanol.

Methanol on the other hand does not form an azeotrope with water so
you can simply distill it in a good still with 20 or 30 theoretical
plates and get dry methanol right from the still.

Either methanol or ethanol will tend to pick up water vapor from the
atmosphere.  However, the amount of water you pick up is so small it
is irrelevant for a model engine if you take the slightest care to at
least keep a loose lid on the containers.  If the containers are
sealed well enough that you do not see significant evaporation of the
fuel over a six month period you have them more than adequately sealed
to prevent significant water absorbtion.  After all 1 or 2% water in
your fuel does no harm at all in terms of engine performance.  If the
oil is staying in solution and the fuel is not becoming cloudy or
forming a separate layer due to oil being forced out of solution by
large amounts of water you are just fine.  All the fuss about a small
amount of water in fuel by a few in the model community is simply
mindless drivel by those who have no clue.  In fact there was a
published report in one of the model mags several years ago that
showed that a few % of water in fuel actually upped the RPMs in static
tests.  Water injection systems have even been installed on a variety
of internal combustion engines over the years to enhance power output.

If you buy a decent grade of methanol to start with it will not have
enough water in it to wrorry about.  With the most modest efforts to
keep it sealed it will never pick up enough water to cause a problem.
Thus there really is no reason to bother fooling around drying it to
some super dry condition with Mole Sieves.  On the other hand if you
want to burn ethanol, which if legally sold without all of the
government subsidies for fuel ethanol for on the road fuels, you will
pay more than you pay for methanol unless it is 95% stuff.  If it is
95% stuff you probably do need to dry it to get something that will
allow the oil to stay in solution.