Just remember we used to do it by the book for years then we found out that a base of 3.5 NaOH wasn't enough ,
Paul
Catch up Paul.......
And then we started 2 stage no titration and found out actually 3.5g NaOH base is enough... so long as your oil is DRY. lol.
Even bone dry oil won't give complete conversion single stage without 5g+ base. The Acetone paper seems to suggest that complete conversion is possible with much less than 3.5g.
Hypothetically, you should only need a tiny bit of catalyst, because it's a catalyst and not consumed by the process where no water and FFAs are present, so you could get away with 0.1g/l if the process was right!
I'm guessing 5g/l and 3.5g/l all comes down to Glycerol byproduct retarding the catalyst in some way.