Standards
and the home brewer
"Most
of the standards can be met simply by preparing and washing the fuel
well," says Todd Swearingen of Appal
Energy.
From a message to the Biofuel
mailing list, Thursday, 10 Oct 2002
Looking at the US ASTM
D-6751 standards as the benchmark for home brewers, most of the
standards can be met simply by preparing and washing the fuel well.
A) Flash point (130 deg C minimum) will be relatively
consistent for all feedstocks, presuming reaction completion and the
alcohol is removed. If the alcohol is distilled or washed out this is
a non-problem.
B) Water and sediment (0.050 maximum % by volume) are
non-problems with adequate settling times, filtration and fuel
reheating to about 120 deg F (48 deg C). (I don't suggest adding any
acid to clear fuel haze, as this will increase the acid number.)
C) Free glycerin (0.020 maximum % by mass) is removed
and is a non-problem with adequate settling time and washing.
D) Total glycerin (0.240 maximum % by mass) is
reduced to nil and is a non-problem if sufficient reaction time is
permitted (mono-, di- and tri-glycerides are all cracked), sufficient
caustic is used (not excess, as this can raise the acid number by
cracking methyl esters back to FFAs) and sufficient settling time is
given.
E) Kinematic viscosity (1.9 - 6.0 mm2/s at 40 deg C)
will also be a non-problem if the total glycerin content (Items C
& D) has been resolved and the acid number is not elevated by
imprudent use of caustic, causing back cracking of esters to FFAs
(higher viscosity than B-100).
F) Sulfated ash (0.020 % by mass) is a
non-controllable when using straight base (single-stage base
transesterification), as the only sulfur in the equation is derived
from the parent feedstock. When using an acid/base process the
sulfuric acid used in the esterification step is neutralized by the
base. The resulting salt is soluble in the water wash and should be a
non-problem with proper washing.
G) Sulfur (0.05% maximum by mass) -- see Item F.
B-100 is essentially sulfur free.
H) Phosphorus content (0.001% maximum by mass) is a
non-controllable relative to the parent animal or plant feedstock and
is a non-problem as long as phosphoric acid is not used to clear fuel
haze. Phosphoric acid can also increase the acid number (acid + FFAs).
This is why either adequate settling times, and slightly warmed fuel
are the better options for clearing fuel.
I) Acid number (0.80 maximum milligrams of KOH per
gram of fuel) will remain low if acids are not added to the fuel
either pre, post or during washes (either to "ease washing"
(?) or clear fuel haze) and if caustic is not used in excess, which
causes higher numbers of esters to break down to FFAs.
Other standards, such as distillation temperature, copper strip
corrosion, cetane number and cloud point are for all practical intents
and purposes properties that will fall within the ASTM standard if the
fuel is prepared and washes are conducted properly.
As for a poor person's method of checking acid number... It can be
conducted in the exact same manner as the titration of the original
feedstock, save for the substitution of biodiesel for oil. Keep in
mind that the assay of the KOH being used will need to be taken into
consideration. If the assay is 90% for example, the number of
milligrams of KOH per gram of oil should be multiplied by the %
purity.
One can also assay the KOH with an acid titration. But that's a bit
out of the realm of probability for most shadetree biodieselers.
The in-house chemist (Ph.D. in chemistry) suggests that a careful
titration using the same method as the original feedstock titration
should get you within + or - 10%, perhaps + or - 5% if one is really
precise.
You could also use other indicators such as phenolphthalein to titrate
the fuel. This would reduce the margin for error from the "pH
method," as pH is really designed for aqueous solutions.
Hope this helps.
Todd
Swearingen
Appal Energy
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