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Biodiesel Titration Made Easy

Visit our Video Section for an easy video guide on Biodiesel titration.

A biodiesel titration is needed when producing biodiesel from old used cooking oil. When oil is used in the cooking process the high temperatures involved produce Free Fatty Acids (FFA's) in the oil. It is these FFA's that cause the oil to eventually become unfit for Human or Animal consumption as they are Carcinogenic (cancer producing).


WVO Titration Kit

Titration Kit Picture


Oil consists of two main parts one of which is glycerin. The glycerin in the oil makes it thick and is what makes oil unsuitable for burning in an unmodified engine. All the biodiesel process does is to replace the glycerin in the oil with methanol.

The catalyst   (Sodium Hydroxide - NaOH or Potassium Hydroxide - KOH) used in the process allows this reaction to take place. We start off with some oil, methanol and our catalyst and end up with biodiesel and separated glycerin.

However if any FFA's are present in the oil they must first be converted to soap before the glycerin can be separated.We do this by adding extra Sodium/Potassium Hydroxide. This ensures that we have enough for conversion, or some glycerin will remain in the oil.

Biodiesel Titration

The biodiesel titration process explained here will give you a quick and simple way of determining the FFA content of the oil being tested and will tell you straight away how much extra Potassium Hydroxide or Sodium Hydroxide to add.

Consensus has it that a basic amount of 5g of NaOH or 7g of KOH is necessary as an initial amount when converting virgin oil. We will use this as our initial amount and will add the extra calculated from our titration onto this.

Firstly you will need some basic lab equipment, then we need to prepare our test solution


Doing the Titration

I suggest you use this biodiesel titration form. There is also a titration worked example. Print them out and use them as worksheets.

  • Firstly take a sample of the oil you will be titrating and put it in a large beaker or jar. If you are taking the sample from a biodiesel processor make sure that the oil has been well mixed before you tap it off, draw off 500ml and return it to the input tank, take a second 500ml for testing.
  • Pour some of your isopropyl Alcohol into a small jar or beaker. Use the beaker as the source of the isopropyl in case you contaminate it by accident, in which case you can throw it away.
  • Using a little isopropyl alcohol or distilled water to rinse the three small flasks or jars out. This is to remove any residual chemicals which may be in them.
  • Use your 10ml pipette or syringe and put 10ml of isopropyl alcohol in each of the three Erlenmeyer flasks.
  • Using your eye dropper put three drops of the Phenolphthalein solution into each of the three Erlenmeyer flasks.
  • We now do a blank titration which neutralizes any acidity in our alcohol. To do this fill the 1ml pipette or 10ml syringe with our test solution. While swirling the liquid in the Erlenmeyer flask around slowly add the test solution until the isopropyl alcohol turns pink.   This should take a very small amount, typically less than a ml. Repeat this procedure for all the flasks.
  • Using a clean 1ml pipette or syringe put exactly 1ml of the oil to be titrated in each Erlenmeyer flask.
  • Swirl the oil around until it is dissolved. The oil may not totally dissolve, this is normal.
  • We now do the biodiesel titration. What we are doing is adding our test solution until we get a change of color to purple that lasts for at least 20 seconds. For each of the flasks, using the 1ml pipette or 10ml syringe, add the test solution into the Erlenmeyer flask, slowly, swirling all the time. Keep track of how much solution you add. Do this until you have a change of color that lasts for at least 20 seconds. Write the reading in ml down on the titration worksheet.
  • Have a look at the three biodiesel titration readings. If any one of them is significantly different from the rest then discard it and repeat the sample again from step 2 . The readings should not differ by more than five percent.
  • Average the three readings.
  • Each ml in the result equates to 1g of extra catalyst. Add the average result to the base amount of 7g for KOH or 5g for NaOH.
  • This total can now be multiplied by the number of litres of oil that you are using to give the amount of catalyst to add to your batch of oil.
  • We use a fixed percentage of 22% Methanol in the reaction. Our catalyst is mixed together with the methanol and produces a substance called Methoxide.


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