Biodiesel Titrations

The Science Company sells chemicals used in tests commonly performed in producing biodiesel fuel from new or used cooking oils.

To produce biodiesel requires an alkaline catalyst, lye (sodium hydroxide or potassium hydroxide) to enable the reaction of methanol (methyl alcohol) and vegetable oil. Virgin oil of any type requires an amount of lye equal to about 1.0% by weight of the vegetable oil. This amounts to 3.5 grams of lye per liter of vegetable oil.

In waste oil, free fatty acids (FFA) are typically present that will interfere with the biodiesel reaction by “using up” some of the lye before all of the vegetable oil can react to form biodiesel. To determine how much additional lye is required, a titration is needed to be performed. This will determine how much FFA is present and how much extra lye is required to drive the biodiesel reaction to completion. This titration utilizes a 0.1% sodium hydroxide water solution.

The titration is performed by dripping the sodium hydroxide solution into a mixture of isopropyl alcohol and waste vegetable oil. This is typically 1 milliliter of vegetable oil into 10 milliliters of isopropyl alcohol). The reaction is complete when all the FFA have been neutralized.

Phenolphthalein pH indicator will show a color change when the end point is reached. Other methods of pH determination employ pH paper (not as accurate as phenolphthalein) or a pH meter (more accurate than phenolphthalein). The amount of sodium hydroxide solution (in milliliters) used in the titration represents the amount of extra lye (in grams of lye per liter of vegetable oil) to be added in the biodiesel reaction in addition to the 3.5 grams per liter required for the reaction of virgin oil. For example, if it takes 3 milliliters of 0.1% lye solution to complete the oil / isopropyl alcohol solution titration, you will need to add 3 grams of sodium hydroxide to the 3.5 grams for new oil, or 6.5 grams total per liter of waste oil.

After a quantity of biodiesel fuel is produced it will require washing or some other treatment to remove soap contamination. It can be tested for soap content by performing the Soap Test Titration. This test can help predict how a given batch of biodiesel will wash. It is also employed by those who use magnasol or synthetic magnesium silicate instead of water washing to determine how much magnasol to add.

The soap test titration uses hydrochloric acid, 0.01N solution, as a reagent, bromphenol blue, 0.4% aqueous, as a pH indicator, and acetone or isopropyl alcohol as a solvent. Bromphenol blue turns yellow at about 4.5. The yellow end point is the point at which all the soap in a test sample has been neutralized by the hydrochloric acid titrant. By knowing the volume of .01N HCl used in the soap test titration, it is possible to calculate the amount of soap in the biodiesel test sample.

Use the following formula:

Soap content (in ppm) = (ml of .01N HCL solution) / weight of sample x 30.44