[ece421]

How does one calculate catalyst amounts needed to drive a reaction?

Since catalysts are not consumed in the reaction, their molecular weights shouldn't matter?

Say you have a reaction of triglycerides to methyl esters, and you need either KOH or NaOH as catalysts to convert it.
       
       O
       ''
C-O-C-CH2CH3                                 
'      O                             NaOH or       O              CH2OH
'      ''                              KOH             ''               '
C-O-C-CH2CH3   + 3CH2OH  3CH2-OC-CH2CH3 +  CH2OH
'      O                                                                '
'      ''                                                                CH2OH
C-O-C-CH2CH3

TGs = triglycerides (above)

How would you determine how much KOH to add or how much NaOH to add?  One manufacturer is telling me 1.5 % NaOH wt% of TG's is required for this reaction, and one manufacturer is telling me 0.5% NaOH wt % of TG's of the same exact NaOH.  Can I calculate this amount myself empirically?  Or do I need to run some kinetic trials to determine this qualitatively by varying the amount of catalyst until I get the desired conversion?

One of the manufacturer's is also telling me that the amount of KOH to add is different from the amount of NaOH to add because of the molecular weights, but I don't understand how this can be possible, because they are not consumed or generated in the reaction.  They are when neutralizing free fatty acids that are sometimes broken off from the triglyceride chain, but I already know how to calculate the amount to compensate for neutralization by titration.  What I don't understand is how much to add for just the tranesterification reaction, and how I determine it.

If I am in the wrong forum, I apologize.

[Rabn]

Personally, I would prefer to build a calibration curve. I'd start at 0.1% NaOH wt% and measure the activity with a spectrophotometer; then I'd increase the percentage until I reach a mixture that exhibits the kind of activity profile that you're looking for, then go another 5 or so measurements beyond. it wouldn't take long for you to characterize the catalyst as long as you had the right equipment.