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Step by step titration procedure for making Biodiesel

Updated on March 9, 2013

Titration is an indirect test for free fatty acids (FFA) in waste restaurant fryer oil.

Each titration only takes about 30 seconds (after you've made your initial bottle of reference tester solution), although it looks terribly complicated 'on paper'. Titration is done by reacting a small sample of free fatty acid (which happens to be in a ml of waste oil) with a measured amount of lye, and using pH to tell us when the FFA is all used up.

Why We Titrate

The biodiesel reaction needs alkaline lye (NaOH) or KOH, as a catalyst (methanol and vegetable oil wont' react to make biodiesel by themselves) Waste oil contains free fatty acids (FFA), and the free fatty acids will with lye to make soap before the lye has a chance to participate in making biodiesel.

We do a titration to find out how much free fatty acid is present and to find out how much to compensate for it by adding more lye so there's some left for the desired biodiesel reaction.

How To Titrate

The titration performs the lye/free fatty acid reaction on a very small scale, and we use pH to measure it (somebody before us has previously figured out which pH change indicates that this reaction is complete, and it's at pH 8.5, the color change point of phenolpthalein indicator. Phenol red is close enough and is a hardware store item).

How To Use The Information

The titration will give us a number (technically called acid value or acid number).

We know that we can compensate for the fact that the free fatty acid will consume some of our lye, by adding a specific amount of lye to 'sacrifice' to the soap-making side reaction that the FFA forces on us.

The way this particular titration is written, every 1 ml titration result (ie the acid number) will tell us to add an extra 1 gram of lye for each liter of oil/ffa you're using to make biodiesel to compensate for the side reaction caused by the FFA.


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