Testing Biodiesel Before You Wash

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Testing biodiesel for contaminants before water washing can prevent emulsions. Below you will learn how to test for soap in biodiesel and to check if the oil has been fully converted. If you discover either of these problems, you can take steps to correct them before you wash.

27/3 Test (Methanol Test):

This test is based off Jan Warnqvist's Conversion Test. It tests for unreacted fuel.

Here’s how it works: Triglycerides and diglycerides will not dissolve in the methanol and will settle to the bottom of the jar as an undissolved bubble of oil. Any amount of this oil means your fuel is under-reacted.

In order for this test to work correctly, you must use room temperature biodiesel, and the methanol must be completely dry.

Find a small, clean, dry, clear, sealable container.

Add 3 ml of biodiesel and 27 ml of methanol (both room temp).

Seal the container and shake for a few seconds.

For a highly converted batch of biodiesel the methanol will remain clear and no oil will settle out.

A poorly converted batch of biodiesel will cause the methanol to cloud, and when it eventually settles there will be oil on the bottom.

Bromophenol Blue Soap Test:

Used for testing biodiesel soap content in processed but unwashed fuel. This information is useful to prevent emulsions.

Bromophenol blue turns to yellow (from blue) when it reaches a pH of 4.5. At a pH of 4.5 the hydrochloric acid has neutralized all the soap.

Measure 100 mL of isopropyl alcohol (99% or better) into a clean beaker.

Add 10 mL of your unwashed biodiesel, and mix these together.

Add 15-20 drops of Bromophenol Blue to the beaker and mix.

In a syringe, measure 1 mL of ‘0.01 Normal Hydrochloric Acid’.

Add the acid drop by drop, while stirring, until the mixture turns a bright yellow.

Figure out how many mL of acid you used, and then use this formula:

mL acid you used, multiplied by 304 = ppm of soap present.

A good number will be less than 60 ppm, which means you should use less than 0.2 mL of acid to turn the mixture yellow.

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