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 must be tested to evaluate its acidity. Titration is a common method used to determine the appropriate amount of lye (base) needed for a particular batch of WVO.
- an electronic scale or beam balance
- 2 beakers or jars
- a graduated dropper
- litmus test strips or electronic pH meter
- isopropyl alcohol
- distilled water
- Measure 1 gram of lye on a scale.
- Measure 1 liter of distilled water into a beaker.
- Thoroughly mix the gram of lye with the liter of water until it’s dissolved.
- Measure 10 milliliters of isopropyl alcohol into a separate beaker.
- Thoroughly mix 1 milliliter of used vegetable oil into the alcohol.
- With a graduated eyedropper, put a 1 milliliter drop of the lye/water mix into the oil/alcohol mix.
- Immediately check the pH level of the oil/alcohol mix with a piece of litmus paper or an electronic pH meter.
- Repeat step 7, keeping track of the number of drops used, until the oil/alcohol mix has reached a pH level of between 8 and 9--normally no more than 4 drops.
- Calculate the amount of lye needed for the biodiesel reaction by adding 3.5 (amount of lye used for virgin oil) to the number of drops from step 7. For example: suppose a titration uses 3 drops of lye/water. Adding 3.0 plus 3.5 = 6.5. This hypothetical batch of oil requires 6.5 grams of lye per liter of oil.