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How To: Biodiesel Titration Tests

Free fatty acid (FFA) content is a quality parameter you need to monitor when making biodiesel. If you're trying to burn straight vegetable oil (SVO), oil with high FFA content can damage your engine, and if you're trying to make biodiesel, you need to take FFA content into account when figuring out how much catalyst to use. You can measure the FFA content by doing a chemistry test called a titration. Titration is pretty simple, but you have to be careful about how you do it to make sure you get good results.

Things You'll Need

Eye protection
Scale accurate to at least the nearest ~0.1 gm
Sodium hydroxide
Distilled water
Graduated cylinder or measurement beaker
Stirring rod (glass, wood or similar)
Glass bottle or plastic HDPE bottle and cap
2 - 50 mL beakers
2 small bowls half full of warm water
Isopropyl alcohol
3 graduated syringes
Phenolphthalein

Instructions

- 1
  Put on eye protection first. You'll be working with a chemical called sodium hydroxide, which is very caustic; it can burn your skin and it will make you go blind if you get it in your eyes. Gloves would be a good idea if you have them.
- 2
  Measure out 500 mL of distilled water. Weigh out and add exactly 5 gm of sodium hydroxide.
- 3
  Stir the distilled water until the sodium hydroxide dissolves. You can use a glass or a wooden stirring rod or a clean wooden spoon; wooden chopsticks will work too if you have them.
- 4
  Pour the glass and sodium hydroxide solution into your glass jar or HDPE bottle. It should be a bottle that has a tight-fitting cap. Label the jar clearly. When you're done with the titration, make sure you store this out of reach of children, preferably in a tub so that even if it leaks, the tub will collect the liquid and keep it from flowing everywhere. You can use this material for future titrations as well.
- 5
  Measure out 5 mL of the sodium hydroxide solution and add it to one of the 50 mL beakers. Add another 45 mL of distilled water and put the beaker into one of the two bowls with warm water in it.
- 6
  Add ~10 mL of isopropanol to the other small beaker. Use a graduated syringe to suck up and add exactly 1 mL of the vegetable oil you want to test.
- 7
  Place this second beaker in a bowl half-full of hot water. You want to warm up the contents to help the fats dissolve. Allow the mix to warm up for a couple minutes, then stir until the fats have dissolved.
- 8
  Use a different graduated syringe to add 2 or 3 drops of phenolphthalein to the alcohol-fat solution. Stir to mix.
- 9
  Use the last of your three graduated syringes to suck up some of the sodium hydroxide solution. Note that you'll need to track how much sodium hydroxide solution you add, so record the starting volume on a piece of paper.
- 10
  Slowly add sodium hydroxide to the alcohol-fat solution while stirring. You will see a faint burst of pink color as each drop of sodium hydroxide hits the solution and this pink color will dissipate as you stir. Stop when the solution turns pink and stays pink for 15 seconds or more. This change will happen very suddenly, so don't add sodium hydroxide too quickly.
- 11
  Record how much sodium hydroxide you added in total. If the amount added exceeds 3 mL, your vegetable oil may be too acidic to use as-is. Keep in mind that even if the FFA content is low, however, your vegetable oil may contain other contaminants like particulate matter. If you are making biodiesel from your vegetable oil, you can use the results from this titration later on when determining what amount of catalyst you need.

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