Titration Test for Homemade Biodiesel

Test waste vegetable oil with titration

Chemistry equipment

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.

How to Perform a Titration Test

Equipment Needed

  • an electronic scale or beam balance
  • 2 beakers or jars
  • a graduated dropper
  • litmus test strips or electronic pH meter
  • lye
  • isopropyl alcohol
  • distilled water

Steps to Complete a Titration Test

  1. Measure 1 gram of lye on a scale.
  2. Measure 1 liter of distilled water into a beaker.
  3. Thoroughly mix the gram of lye with the liter of water until it’s dissolved.
  4. Measure 10 milliliters of isopropyl alcohol into a separate beaker.
  5. Thoroughly mix 1 milliliter of used vegetable oil into the alcohol.
  6. With a graduated eyedropper, put a 1-milliliter drop of the lye/water mix into the oil/alcohol mix.
  7. Immediately check the pH level of the oil/alcohol mix with a piece of litmus paper or an electronic pH meter.
  8. 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.
  9. 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.