BrevardBioDiesel Blog

Our friend Elias has made the switch to Potassium Hydroxide (KOH) as a catalyst instead of Sodium Hydroxide (NaOH aka Lye) when making biodiesel. Others note a faster reaction with KOH vs. NaOH, easier mixing with Methanol, and better wash results - although KOH is more expensive than NaOH. The photo shows the separation between biodiesel (top) and glycerol (bottom) layers in a minibatch made using KOH.

Elias made these process notes:

1. Made some titrant concentrate: 10 grams of KOH
   dissolved in 1000 mL (1 liter) of distilled water.
2. Made some titrant solution from the titrant concentrate: pour 50 mL of titrant concentrate into a 1000 mL beaker and then top it off with distilled water up to 500 mL. This solution is what I used to run the titrations.
3. Made some KOH-based Methoxide concentrate:
   dissolved 50 grams of KOH + 10% (5 grams) more because
   the KOH I bought is 90% pure = 55 grams into 1000 mL
   of Methanol.
4. Ran three consecutive titrations and settled on 4.8 titration result. Note that this was the same oil I used when I did the titration for the last NaOH based minibatch which gave a titration result of 3.4. So, KOH resulted in a larger titration result.
5. Catalyst amount formula: 1 liter oil * (4.9g KOH (base) + 4.8g KOH (titration)) = 9.7g KOH needed for minibatch.
6. Added 9.7 x 20 = 194 mL of the Methoxide concentrate and 26 mL of Methanol to reach at a 220 mL methoxide mixture as recommended by girl Mark to add to the heated WVO.
7. Heated 1 liter of the oil to 130 F.
8. Added the 220 mL of Methoxide and Methanol mixture to 1 liter of heated oil and mixed for 15 minutes in mixer.

Here is a good thread with sources of KOH.

Here is a thread on KOH vs. NaOH.