How to titrate vegetable oils before making biodiesel

When vegetable oil is heated extensively during the cooking process it causes the formation of free fatty acids (FFA's). These FFA's when combined with a base catalyst such as Potassium Hydroxide (KOH) or Sodium Hydroxide (NaOH) will form soaps. This process reduces the amount of KOH or NaOH available to perform the Biodiesel reaction, thus it is often the case with waste vegetable oil, that additional KOH or NaOH will need to be added. The following titration will determine this amount. The basic principle involves adding KOH or NaOH (a strong base) to the oil to determine the exact amount required to neutralise the FFA's (weak acid).

1) Using a graduated 1mL syringe measure 1mL of used vegetable oil into a clean container.

2) With a 10mL syringe measure 10mL of Isopropanol and add to the 1mL of oil.

CAUTION: Isopropanol is flammable. Please read the safety label before use. Keep away from sources of ignition.

3) Carefully swirl the flask until the oil has fully dissolved.

4) Now add 3 drops of 1% Phenolpthalein solution.

5) Prepare the "titration solution" by adding a 1.0g of KOH or NaOH to a 1000mL beaker and fill to the 1000mL mark with water (preferably distilled). Make sure all of the solids dissolve.

6) With a 5mL graduated syringe withdraw the "titration solution" to exactly the 5mL mark.

7) Carefully add single drops of the "titration solution" to the beaker. After every few drops swirl and allow to properly mix.

8) You are looking for the colour of the solution to turn light pink indicating neutralisation of the FFA's with the "titration solution". Keep adding drops and swirling the beaker to ensure proper mixing occurs. If you require more than the 5mL of "titration solution", record the amount used and refill the syringe as before. When the solution changes colour to pink for 15 -30 seconds while stirring the titration is complete and all of the FFA's in the oil have been neutralised.

8) Record the total amount of "titration solution" used.

9) The number of mL's of "titration solution" required equates exactly to the additional number of grams of KOH that is needed to be added to the Biodiesel reaction per 1L of oil. In the table below look up your purity of KOH or NaOH used and the volume of "titration solution" used. This will give you the total amount of KOH or NaOH to add per litre of oil.

Titration Table

Volume (mL)

99% NaOH (g)

95% NaOH (g)

99% KOH (g)

95% KOH (g)

90% KOH (g)

85% KOH (g)

0.0

3.5

3.7

4.9

5.2

5.5

5.8

0.2

3.7

3.9

5.1

5.4

5.7

6.0

0.4

3.9

4.1

5.3

5.6

5.9

6.2

0.6

4.1

4.3

5.5

5.8

6.1

6.4

0.8

4.3

4.5

5.7

6.0

6.3

6.6

1.0

4.5

4.7

5.9

6.2

6.5

6.8

1.2

4.7

4.9

6.1

6.4

6.7

7.0

1.4

4.9

5.1

6.3

6.6

6.9

7.2

1.6

5.1

5.3

6.5

6.8

7.1

7.4

1.8

5.3

5.5

6.7

7.0

7.3

7.6

2.0

5.5

5.7

6.9

7.2

7.5

7.8

2.2

5.7

5.9

7.1

7.4

7.7

8.0

2.4

5.9

6.1

7.3

7.6

7.9

8.2

2.6

6.1

6.3

7.5

7.8

8.1

8.4

2.8

6.3

6.5

7.7

8.0

8.3

8.6

3.0

6.5

6.7

7.9

8.2

8.5

8.8

3.2

6.7

6.9

8.1

8.4

8.7

9.0

3.4

6.9

7.1

8.3

8.6

8.9

9.2

3.6

7.1

7.3

8.5

8.8

9.1

9.4

3.8

7.3

7.5

8.7

9.0

9.3

9.6

4.0

7.5

7.7

8.9

9.2

9.5

9.8

4.2

7.7

7.9

9.1

9.4

9.7

10.0

4.4

7.9

8.1

9.3

9.6

9.9

10.2

4.6

8.1

8.3

9.5

9.8

10.1

10.4

4.8

8.3

8.5

9.7

10.0

10.3

10.6

5.0

8.5

8.7

9.9

10.2

10.5

10.8

5.2

8.7

8.9

10.1

10.4

10.7

11.0

5.4

8.9

9.1

10.3

10.6

10.9

11.2

5.6

9.1

9.3

10.5

10.8

11.1

11.4

5.8

9.3

9.5

10.7

11.0

11.3

11.6

6.0

9.5

9.7

10.9

11.2

11.5

11.8

6.2

9.7

9.9

11.1

11.4

11.7

12.0

6.4

9.9

10.1

11.3

11.6

11.9

12.2

6.6

10.1

10.3

11.5

11.8

12.1

12.4

6.8

10.3

10.5

11.7

12.0

12.3

12.6

7.0

10.5

10.7

11.9

12.2

12.5

12.8

7.2

10.7

10.9

12.1

12.4

12.7

13.0

7.4

10.9

11.1

12.3

12.6

12.9

13.2

7.6

11.1

11.3

12.5

12.8

13.1

13.4

7.8

11.3

11.5

12.7

13.0

13.3

13.6

8.0

11.5

11.7

12.9

13.2

13.5

13.8

8.2

11.7

11.9

13.1

13.4

13.7

14.0

8.4

11.9

12.1

13.3

13.6

13.9

14.2

8.6

12.1

12.3

13.5

13.8

14.1

14.4

8.8

12.3

12.5

13.7

14.0

14.3

14.6

9.0

12.5

12.7

13.9

14.2

14.5

14.8

9.5

13.0

13.2

14.4

14.7

15.0

15.3

10.0

13.5

13.7

14.9

15.2

15.5

15.8

 

1300 246 406