Hello all
I’m new to this group as well as to biodiesel synthesis so excuse me if my question has already been answered.
The complete transesterification reaction produces glycerol and free fatty acids. But I assume the reaction rarely runs to completion. That means there would probably be varying amounts of mono and biglycerides. I have done several reactions with different amounts of methanol and/or NaOH. I have seen similar amounts of BD produced but different amounts of glycerol. My explanation was that the more complete the reaction the more glycerol that would be produced. But the BD level will stay the same no matter how incomplete the reaction.
Which leads to my question. Does anyone know a way to measure the amount of mono, bi and triglycerides produced? I think TLC might be one way but thought I would ask before I tried anything.

I would think either GC or GC/MS would be a better way to go, use 4 standards for calibration(one each for the mono, bi and tri-glyceride's and the forth an internal standard that is uncommon and comes off the column in between the other standards). Then toss the internal standard into your raw sample for processing.

UV/Vis might also work, probably have some wacked out peak broading that would complicate things.

I would think it'd be more effective to merely consider some of the physical properties rather than result to such level of testing (unless your producing this commercially and have the monies for a chemist); consider comparing the viscosities, densities, cloud/gel points, pH, etc. These later are low cost solutions to determining quality.

Then there are the bold among us (some times I'm equally brisant) that flirt with disaster running ad-hoc mixtures knowing the weather is relatively the biggest factor once the glycerin is drained off and the BD is in the tank.

Not sure if I've helped or hindered. Best of luck,

Ralph.

TB,

quote:

The complete transesterification reaction produces glycerol and free fatty acids.

No, it produces fatty acid methyl ester, glycerol and soap, in an unavoidable side reaction.

quote:

But I assume the reaction rarely runs to completion. That means there would probably be varying amounts of mono and biglycerides.

Yes, the reaction can't go to "completion" (if you mean 100% reacted) since each of the three reactions is an equilibrium reaction.

quote:

That means there would probably be varying amounts of mono and biglycerides. I have done several reactions with different amounts of methanol and/or NaOH. I have seen similar amounts of BD produced but different amounts of glycerol. My explanation was that the more complete the reaction the more glycerol that would be produced. But the BD level will stay the same no matter how incomplete the reaction.

Yes, there are various levels of Tri Glyceride, Di Glyceride and Mono Glyceride. You can see some GC test results here: GC TEST or search for GC.

The amount of byproduct is not a perfect indicator of the degree of completion, since it's volume is affected by the soap production, along with the BD the soap traps, and the amount of excess methanol.

As a simple test for conversion check out 3/27 test article or the original thread .

The test will not tell you much about mono and di glycerides, but it will tell you clearly if you have more than a trace of unreacted tri glyceride.