Standards and the homebrewer
"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.
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