How to Titrate Oil Prior to Making Biodiesel
When doing a titration, the solution in your beaker should be constantly and gently stirred. Always avoid contamination by keeping your lab area clean and lids on all your containers.
- Mix together a solution of about 1 gram of NaOH per liter of water. This will be your basic solution.
- Put 10 ml of 99% isopropyl alcohol in a small beaker.
- Add two drops of phenolphthalein Ph indicator.
- Slowly add drop by drop, some of your basic solution until the mixture in the beaker just barely turns and then stays fuchsia. This helps to assure that there are no acidic contaminants.
- Add exactly 10 ml of 0.01N HCL.
- Slowly add your basic solution until the mixture in the beaker turns back to fuchsia.
- Calculate the following: ( 4.0 )/ (# of ml of basic solution) = (True grams of NaOH/ liter) in basic solution.
To accurately determine the acidity (FFA content) of your oil, you need to accurately know the strength of your base solution. It is nearly impossible to measure out a small amount of the base (like sodium hydroxide) to mix into a solution with a high degree of accuracy. One of the problems encountered in trying to do this, is the fact that NaOH quickly absorbs water and CO2 out of the air. This makes the compound both heavier and weaker. Steps 2–6 (above) have allowed you to determine the strength of the basic solution that you are using to titrate your oil. To double check the strength of your base solution, repeat steps 2 through 6 to make sure the results compare.
Because a basic solution will lose strength over time, whenever, you have a day that you plan to titrate some oil or fuel, start by employing steps 2 through 6 to find the strength of your base solution. If it has degraded somewhat, there is no need to worry. Simply use the new number that you have for “true grams of NaOH/liter” in step 5 below.
Now to actually titrate your oil (or finished biodiesel if you are testing for TAN):
To process this in the BioPro™ 190, you should have less than 5% FFA. To pass TAN test for finished fuel you should have less than .28% FFA.
For greater accuracy on the TAN test you can use 50ml of isopropyl (step 1), 10 ml of fuel (step 3), and divide by 12.8 instead of 1.28 (step 5).
- Add 15 ml of isopropyl and two drops of PH indicator to a beaker.
- Add your basic solution drop by drop until the mixture in the beaker just barely turns and stays fuchsia. This helps to ensure that there are no acid contaminants in the beaker.
- Add 1 ml of the oil in question to the beaker.
- Now slowly add your basic solution into the beaker until the solution turns and stays fuchsia.
- Calculate ((true grams of NaOH/liter) * (number of ml of basic solution)) 1.28 = %FFA
Frequently asked questions
How do I titrate used cooking oil to measure free fatty acids?
Put 15 ml of 99% isopropyl alcohol and two drops of phenolphthalein indicator in a beaker. Add your standardized NaOH solution drop by drop until the liquid just turns fuchsia and stays that color. Then add exactly 1 ml of oil.
Slowly add more NaOH solution, stirring gently, until the mixture turns fuchsia again and holds. Multiply the true grams of NaOH per liter by the milliliters of solution used, and divide by 1.28 to get percent FFA. For a BioPro 190, the result should be under 5% FFA.
Why do I need to standardize my NaOH solution before titrating oil?
Standardizing tells you the true strength of your sodium hydroxide solution, which an accurate FFA result depends on. NaOH quickly absorbs water and CO2 from the air, making it heavier and weaker. That makes it nearly impossible to weigh out a small amount accurately.
To standardize, neutralize 10 ml of 99% isopropyl alcohol with indicator, add exactly 10 ml of 0.01N HCl, and titrate back to fuchsia. Then 4.0 divided by the milliliters used equals true grams of NaOH per liter. The solution loses strength over time, so repeat this each day you titrate.
What supplies do I need to titrate oil for biodiesel production?
A basic titration setup needs only a few supplies:
- Sodium hydroxide (NaOH), mixed at about 1 gram per liter of water
- 99% isopropyl alcohol
- Phenolphthalein pH indicator
- 0.01N hydrochloric acid (HCl), for checking the NaOH solution's strength
- Small beakers and tools for measuring milliliters accurately
Keep the work area clean and lids on all containers to avoid contamination. Stir the solution constantly and gently during each titration. Wear eye and skin protection when handling NaOH and acid.
How do I test finished biodiesel for acid number (TAN) with titration?
Use the same procedure as for oil, with finished biodiesel as the sample. To pass the total acid number (TAN) test, the fuel should measure below 0.28% FFA.
For greater accuracy, scale up the sample. Use 50 ml of isopropyl alcohol and 10 ml of fuel, then divide by 12.8 instead of 1.28 in the final calculation. As with any titration, standardize your NaOH solution first and neutralize the alcohol and indicator before adding the sample.
What color change marks the endpoint of a biodiesel oil titration?
With phenolphthalein indicator, the endpoint is reached when the solution turns fuchsia (pink-purple) and stays that color while stirring. Add the NaOH solution slowly, drop by drop, as you approach the endpoint so you do not overshoot.
Before adding the oil sample, bring the isopropyl alcohol and indicator to that same faint, lasting fuchsia. This neutralizes any acidic contaminants in the beaker, so the second color change reflects only the acids in your oil.
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