Whenever Biodiesel is made the amount of Free Fatty Acids (FFA) in the oil sample must first be determined so that the correct amount of catalyst is used in the reaction. Although this may sound complicated it is a relatively simple process! The method that we use is very accurate and can be done in easily in the lab. Soon we hope to move all the testing materials to the new facility at Cherry Crossings, but for now the testing is done in the Biosystems Research Complex, seen below.
We use a method of base titration to determine the amount of acid in the sample. Here are the steps that we use:
1. Get an oil sample of 100 mL
2. Weigh the oil sample and record in grams
3. Add color indicator, Phenolphthalein and 50 mL of isopropyl alcohol
3. One drop at a time, add KOH solution to the oil solution
4. When the color changes to bright pink stop and record the amount of KOH added
These are all the steps of the titration! Now all that is left to figure out is a little math to be able to know what the amount of KOH used in titration means for us in the reaction!
The formula is simple: ___ Mol KOH * (56.1g/mol KOH) = Amt of Catalyst need to neutralize the FFA
Where the blank is filled in with molarity of the KOH that you are using! This tells you the amount of catalyst needed just to neutralize the FFA, but it is important to remember to add the amount of base catalyst that would be needed if the oil contained no FFA.
Final amount of required catalyst = Amt of Catalyst need to neutralize the FFA + 7g of catalyst / L of oil
It is important when doing this test to run the test 3 times and then take the average of all the similar results. Leaving off any extraneous results, which probably are a result of poor lab techniques.
After determining the amount of catalyst that needs to be used it is a good idea to run a small sample batch to make sure your results are accurate. The steps for that procedure are:
1. Measure out 22 mL of methanol
2. Measure and then carefully add the calculated amount of catalyst. Screw cap on then stir.
3. Heat up a 100 mL sample of oil to 130 ºF, this can be done in a microwave or on a hot plate.
4. Add the methoxide solution to the oil and quickly add cork.
5. Agitate for 10 minutes and then let in under fume hood.
If this small batch of biodiesel is successful then you know that your calculations were correct and you can apply this to your entire batch.
Below are some of the pictures from the CI’s determination of the amount of catalyst to be used. All of the batches were successful!