How To Calculate And Determine The Amount Of Free Fatty Acid In Biodiesel Oil
You can calculate the free fatty acid (FFA) content of a small sample of your oil and use the result to determine the amount in the total volume of oil intended to make the Bio-diesel. The process is a mimicry of acid-base-titration neutralisation reaction in elementary chemistry except that the base is titrated against the oil, instead of an acid against the base. The implication is that, the Burette will contain the base, while the oil will be in the conical flask.
The materials (Apparatus) required to carry out the titration of the base against the oil are as follows:
Retort Stand with Clamp
This refers to the chemicals required for the reaction. In neutralisation reaction, reagents are usually the acid, base, and the indicator. The choice of the indicator is dictated by the strength of the acid and the base used. We are using KOH lye as our base, implying that the base is a strong base. Because it is to be titrated against the fatty acid content of the oil which is a weak acid, we are choosing phenolphthalein as our indicator. Hence, the reagents needed for the reaction are:
Potassium hydroxide lye (eg extracted from plantain peel)
Oil sample (eg Rubber seed oil)
Before commencing with the titration of the base against the oil, it is essential that certain precautions are adopted. Abiding with the rules will ensure that an accurate result is obtained at the completion of the process. The precautions are as follows:
1. You must wash and dry all the materials to be used to carry out the experiment. The Burette must be well washed clean and clamped upside down on the retort stand to drain out the water. The beaker, conical flask and the pipette must all be clean and dry.
2. The base of the retort stand must be covered with a white back-ground so as to be able to detect any slight change in colour.
3. Enough light should be available in the room to be able to observe clearly
4. There should also be aeration since you are dealing with chemicals
5. You should remember that towards the end of the titration, the base should be added to the oil in drops so as be able to detect any slight change in colour.
We must know that, before the titration reaction, the molarity in Moldm-3of the base must be know. Let's work with 1Moldm-3 KOH ,
1. Use the pipette to measure 25cm3 of the oil into the conical flask.
2. Add two or three drops of Phenolphthalein to the the oil, and you should see that the colour of the oil remains colourless.
3. Use the Beaker to fill the Burette with the base to the convex mark.
4. Place the conical flask at the base of the retort stand, open the burette tap and begin to titrate the base against the oil, gently shaking the Flask in a swirling manner.
5. Begin to add the base in drops at any slight change in colour of the oil from colourless to pink.
6. Observe the point at which the colour of the oil just turn to pink and take down the volume of the base used.
7. Repeat the experiment once or two more times and calculate the average which is the final volume of the base used VB
Calculation of amount of free fatty acid in oil
Before calculating the amount of FFA in the oil, we should write down the equation of the reaction. You should also know that the general formulae for a fatty acid chain is represented as RCOOH. Where R is an alkyl group. Hence,
Mole ratio of FFA to base=1:1
This implies that, 1Moldm-3 of FFA requires 1Moldm-3 of KOH for complete neutralization. Which also means that, 1cm3 of FFA requires 1cm3 of KOH.
Therefore, VBcm3 KOH reacted with VBcm3 of the oil.
The volume of free fatty acid (FFA) in the oil sample is equivalent to the volume of the base titrated against the oil if the base is 1 molar. You can use this value to calculate the total amount of free fatty acid in the bulk of oil intended to make your Bio-diesel.