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Handling issues and cautions

  1. Sulfuric acid is dangerous. Take necessary handling precautions. Gloves and goggles.
  2. Adding the sulfuric acid to the methanol is violent exothermic reaction. It’ll boil like mad.. Make sure your mixing container has lots of head room.
  3. For the base side of the process. If the methanol is not cold( < 50F) adding the required amount of caustic to less than 1/2 the normal amount of methanol create a violent mixing boiling action( it will get very hot!!) so mix outdoors and after adding the KOH!! stay away for a while. It might be good to mix in 1/2 the KOH then let the mix cool before mixing in the rest of the KOH.

What is esterification?
from Wikipedia:
Esterification is the general name for a chemical reaction in which two chemicals (typically an alcohol and an acid) form an ester as the reaction product. Esters are common in organic chemistry and biological materials, and often have a characteristic pleasant, fruity odor. This leads to their extensive use in the fragrance and flavour industry. Esterification is a reversible reaction.

In our case we are using methanol, sulfuric acid and Free Fatty Acid( FFA, bad vegetable oil ).

Why use esterification?
In theory esterification followed by transesterification yields the highest amount of biodiesel per oil volume. Some technical issues prevent this from happening in practice espically for homebrewers. First any water in the process slows/stops the acid stage. Water is a byproduct of the esterification. Second any water left in the mix while transesterifing will result in soap. Also for real world oils the transesterification process may result in too much soap and poor yields.

When to use Esterification
I typically use esterification when the titration, using KOH, is 7 or more. If the titration is less than 7 KOH I find the time and effort doesn’t justify the extra cost trying to use esterification. If the titration si over 7 KOH the yeild increase helps offsest the additional processing and cost.

Acid/Base processing – DKenny’s Method
The purpose is to provide and easy way to deal with the real world WVO that BD makers find.

Sulfuric Acid – 93% or stronger
Vegetable oil titration 7 or higher KOH, IE bad oil, BUT dry( <0.5% water)
Methanol – 99% pure. the standard stuff used to make boidiesel
0.1% KOH solution
a PH indicator. I use tumeric.
standard homebrew titration equipment.


  1. Heat the oil to 130F or higher, sometimes I start at 150F. This makes titrating easier and helps with processing.
  2. Titrate the oil. This is the Starting Titration. Let’s say 14.
  3. Determine the amount of H2SO4 needed. (Starting Titration – 3 ) * 0.2ml/L = ml or H2SO4 needed. if the starting titration is 14 then 14-3 = 11 * 0.2 = 2.2ml/L of H2SO4
  4. Determine the amount of methanol for the Acid stage. Oil in Liters * 0.12 = Liters of methanol(12% by volume)
  5. Add the Acid to the methanol. Slower the better. wear goggles and a long sleeve clothes. When the Acid hits the methanol it’ll boil violently. I mix mine in a 15 gallon plastic drum.
  6. Add the methanol/Acid to the oil. this is done just like adding the methanol/caustic mix for normal base processing. Entry rate isn’t critical as with the base stage.
  7. Wait. Depending on the Starting Titration the process takes many hours!
  8. When the Titration stops dropping. Hopefully this will be 3 or less the Acid stage is done. Note the curve like a exponential decay curve. Drops fast at first and slows down. If you titration right after adding the methanol/aicd mix don’t be alarmed if titration goes up.
  9. If the starting titration was over 18KOH then you must allow the mix to settle and drain about 1/2 of the starting methanol volume. For tiration less than 14, I don’t bother with draining. In fact I the acid/water/methanol mix will float on top for titration less than 14KOH.
  10. Process with the normal base processing using 8% (oil volume) of methanol. If you drained the mix remember to add that quantity of methanol to the 8%.

Chart indicates acid required based on the titration value.
Don’t be alarmed if the titration starts to rise shortly after adding the acid/method mix. This is normal. Soon the tiration will fall. Just rememeber the acid esterification process is SLOW. If the mix is allowed to settle and drained ( amount is about 1/2 of the initial volume of methanol used in the acid stage). Recheck the titration after draining as it might be done. I typically see a drop in titration of 4ml after draining.

Instead of draining it possible to use another Acid stage. I would suggest 1 gallon methanol and recalculate the amount of Acid based on step 3. If too much acid is used the ending titration will be higher than the minimum. Sorry I have yet to figure out if/when this occurs.

To Be Determined
Acid purity? Ideally this would require diluting the H2SO4 in water. Say 100ml Acid into 500ml of water. Then using the standard home brew KOH solution to determine the number of mls required to neutralize the acid. This number should relate to the purity of the acid. The formula in step would then require a purity adjustment.

As for determining purity of an unknown acid solution (such as drain cleaner), that should be relatively simple. Proceed with color-indicator titration as per usual, then calculate percent acid based on the molecular weight of the particular acid compound. If the solution is comprised of sulfuric acid (and other unidentifiables- blue beads or silver sparkles or magic beans), then use the molecular weight of sulfuric acid- 98.08 g/mol. The process is much the same for determination of FFA%.

Here’s the formula:
% Acid = (v – b) x N x M / w
v = volume of titrant (mL)
b = blank (mL)
N = normality of titrant (mol/L)
M = molecular weight of acid (g/mol)
w = weight of sample (g)