Waste vegetable oil is commonly used for producing biodiesel and becomes degraded during the cooking process into it's constituent fatty acids. This can also happen with new oil if the raw seeds have not been stored properly. The acidity can not be measured with a pH meter or litmus paper as it is not an aqueous solution and so the titration method must be used.
- 50mm conical flask
- 10mm pipette
- Rubber pipette filler
- 10ml syringes
- 1ml syringes
- 10ml pH bromothymol indicator solution
- 500ml 0.025M sodium hydroxide solution (1g/L)
- 500ml Isopropanol
Add 1ml of oil to the flask and then 10ml of Isopropanol using the syringes and then 3 drops of the indicator solution. Whilst stirring the solution add the sodium hydroxide one drop at a time using the pipette until the indicator solution changes from yellow to green. Keep adding the drops until the green colour is maintained for at least 15 seconds. The amount of hydroxide used will be the final reading minus the initial reading, in ml.
If your amount of hydroxide used = x (ml) and the quantity of oil to process is y (litres), then the amount of solid sodium hydroxide required should be:
z = (x + 3.5) * y grams per litre.
For example, if the titration reading was 3.0 ml, then z will be 6.5 grams of sodium hydroxide per litre of oil.
Step 1: Full Biodiesel Production Instructions
For the complete instructions on how to make biodiesel from waste vegetable oil please visit here: