So let's assume we are planning to flash off methanol/water (and recover/dry) between acid and base...

Has anyone experimented with determining the LEAST amount of methanol needed in the first acid stage?

I am guessing the amount used to bond with the FFAs to form methylesters is quite small (and a function of the amount of FFA present)..but I assume overdosing ensures more reaction (in less time).
Just as we only need something like 13-14% methanol "on paper" to fully react triglycerides in base reaction..we usually overdose at 17-20+%.

So lets say we had oil with 10%FFA
In this case is seems we would "need" only something like 10% of the total 20% we use for the base reaction...or roughly 20mls methanol per liter of 10%FFA oil.

I am sure that time/temp/agitation all play into it,but has anyone investigated this?

In theroy your thoughts should work, but let me ask. if you are flash evaporating the excess methanol then why are you concerned about limiting the amount you put into the reaction?

Overdosing the methanol above what is therotecially needed does not speed up the reaction. It allows the reaction to go to completion. Without the excess it will not complete the rection.

Logan Vilas

Hi Rob-

The stoichiometric ratio for the esterification reaction is 1:1 (1 mole Methanol : 1 mole FFA). For oil with a 10% FFA content, this would mean roughly 1.3% Methanol, if I did my math right.

Now, this is the 'theoretical minimum' of the reactants. Of course, at this level, the reaction would go no where. Water formation is the main issue to overcome, as it inhibits the reaction (due to hydrolysis re-forming FFA's IIRC?).

I hope that helped get an idea.

-Nick

I have seen plants operating that use a 20:1 stoichiometric ratio of methanol so for every mole of FFA 20 moles of Methanol are used.

I qualify this by stating that typically the oil/ester phase is vacuum stripped to remove all methanol and water and the methanol is then dried in a distillation column.

vegenergy,
i wish I had a good answer for you but I don't use as much methanol as you suggest I only run 12% by oil volume. this is titration upto and including 27KOH(14%FFA).
My thinking is restricting the amount of methanol is not with the recovery later but to force the methanol/water,acid layer down. should one desire to drain. this would leave the BD( acid estrification made) and oil on top and left for the transestrification phase.

I have been looking over my notes and it seems that for values of titration between 14 and 18 my method works without draining.
In a couple of batches ( 25,27 KOH) when I did drain. the titration dropped 4 mls or more. just by draining.


just my 2 cents

-dkenny