[Stoves] Vegetable oil or biodiesel?

[ajheggie at gmail.com]

On Wednesday 09 November 2011 21:44:09 Crispin Pemberton-Pigott wrote:
> I think if you want to make a fuel you will have to avoid
> saponification and I had not given it any thought, but if you add the
> lye directly to the oil it will turn some of it into soap immediately
> so they must have a method of keeping it pretty thin to avoid that.

That's why the caustic is added to dry methanol, to keep the water out, 
the mixture of pure methanol and caustic makes sodium methoxide which 
splits the triglyceride and the methyl radical immediately attaches to 
each of the three fatty acid strings to make a single chain fatty acid 
ester which is similar to diesel. Plainly the methanol contributes about 
10% of the energy in the biodiesel.

If water is present it catalyses the splitting and a sodium salt combines 
with the ester instead.

AJH