One hundred percent virgin or lightly used waste vegetable oil (WVO) requires 3.5 grams of lye per liter of oil to cause a biodiesel reaction. Heavily used oil can require significantly more, and requires testing to evaluate its acidity. Mini test batches is the method we use to find the correct amount of lye to add to the waste vegetable oil (WVO) to create a successful biodiesel reaction—some people prefer titration, but we actually find the test batch method simpler.
Mini Test Batches
Equipment:- an electronic scale or beam balance
- old blender (no longer used for food processing)
- half-pint mason jars
- lye
- methanol
- Measure 0.35 grams of lye on a scale.
- Measure 20 milliliters of methanol into a half-pint mason jar.
- Thoroughly mix the 0.35 grams of lye with the 20 milliliters of methanol until it’s dissolved.
- Measure 100 milliliters of WVO into a separate ½ pint mason jar.
- Add the dissolved lye/methanol (sodium methoxide) to the jar of oil.
- Place the blender agitator over the jar opening and screw on the cap ring.
- Flip the jar upside down and place on the blender motor housing.
- Turn the blender on medium and mix for 10 to 15 minutes.
- Turn the blender off, remove and flip the jar right side up.
- Let the jar sit undisturbed for 30 to 60 minutes while waiting for the reaction.
If there is a distinct separation (light thin biodiesel at the top of the jar and dark thick glycerin at the bottom), the reaction was successful. If the mixture remains a homogenous liquid (no separation), then the reaction failed because of insufficient lye. Repeat the process with a new batch of oil, increasing the lye amount by 0.1 grams. (the second test will be .45 grams) until a successful separation occurs.
Calculate the amount of lye needed for the biodiesel reaction by multiplying the final amount from the mini test batch by 10. For example: a successful mini test batch requires 0.55 grams of lye multiplied by 10 = 5.5. This hypothetical batch of WVO requires 5.5 grams of lye per liter of oil.