Skrinkle - 23-6-2008 at 14:04
http://www.autobloggreen.com/2008/05/24/got-some-biodiesel-y...
Any speculation as to what this additive might be?
Saying one constituent is an alcohol and the other a volatile chemical is awfully vague. 
Any ideas would be appreciated.
not_important - 23-6-2008 at 15:04
Looks to be a large glop of PR (public relations)
In the video, the product is at least as much of the additives as the biodiesel. I'd bet it's organic to reduce the viscosity, boost the octane
rating, and perhaps help protects seals from solvent action.
A mix of alcohols and lower boiling hydrocarbons would do it. Both would reduce viscosity, alcohol helps with anti-knock as would branched alkanes or
aromatics. Low boiling hydrocarbons help with cool weather starting.
Good trick to get the prices they talk about. Biodiesel is twice that cost, light petroleum ether shouldn't be much less expensive than gasoline
itself.
Note that running something like a lawnmower engine for a few minutes is a long ways from a fuel that would work properly in an automobile for months
or years. Also note that if the lawnmower had been running just before the video was shot, it would still be hot enough that you could possibly run
it on straight vegetable oil.
Skrinkle - 23-6-2008 at 20:06
So, it's probably just ethanol and a petroleum hydrocarbon of some sort? I should have guessed it. I feel silly about believing the hype but I guess
I kind of lust after a home made gas substitute. Making it from biodiesel is all the more attractive as ethanol is foolishness when you consider
production costs and butanol is smelly and you have to separate it from the acetone. So pretty much just an alcohol plus naphtha or something
similar, huh?
P.S.
Wouldn't biodiesel actually be cheaper than that if you make it from used cooking oil or some other free/low cost feedstock?
not_important - 23-6-2008 at 20:24
I'm guessing on what's in the additives, based on the properties of diesel, biodiesel, and gasoline. Anti-knock, lower viscosity, and higher vapour
pressure are what seems to be the significant differences.
A lot of people do make biodiesel from used fats and oils. The bigger players get their's from large scale producers, plants that use the oils in
cooking foods and so on. The small time guys go around to restaurants and get that. Apparently waste oil has gone from "we'll pay you to haul it
away" to "pay us and we'll let you take it"; while it will remain cheaper than virgin plant oils the cost of waste oils is likely to continue to rise.
One problem with used oils is the the free fatty acid content is fairly high. When used in an alkali catalised transersterfication this increases
consumption of alkali, plus the soap formed increases the difficulty of separating biodiesel esters from the glycerol and other wastes. Acid
catalysts don't have that problem, but need more forcing of the equilibrium to get decent yields. Reactive distillation does a good job, gives high
quality glycerol, and doesn't consume alkali or acid.
By the way, the typical backyard alkaline catalyst biodiesel is rather wasteful. To force the transesterfication enough in the direction of the methyl
esters, a 100% excess of methanol is used; that excess ends up in the wash water. It also consumes alkali, again ending up in the wash water.
It has been estimated that if the USA were to collect all the waste fats and oils and convert those into biodiesel, the result would equal about 1/20
to 1/25 of the US gasoline plus diesel needs.