Soap tests

Soap can be seen as one of the three contributors to fuel system failures and faults. The other two are methanol still in the fuel and poorly converted fuel. There are two ways of testing:

• the 50/50 shake test
• a titrated test that will give a ppm (parts per million) result

50/50 shake test

Real time settling of 50/50 shake up test (more than 50ml in this case) - source: K.H

The 50/50 test is relatively simple to perform.

Take a sample of dried, finished fuel, e.g. 50ml. Place it into a glass container and add 50ml of deionised water.( I suggest the use of deionised water because there have been concerns and odd results of shake tests due to the varying water quality throughout the UK.)

Then shake the living daylights out of it. This will create an emulsion between the water and the oil.

Allow it to stand. Within a few minutes you should see the fuel and water begin to split. When the fuel/water sample has fully separated you can then determine the results by a simple visual check. For a good pass, indicating little or no soap present, the emulsion should separate quickly (usually within 5 minutes) and the water layer should have the same crystal clear clarity it had before the test began. The fuel layer on top will now be cloudy. This is perfectly normal as the bio has taken on some of the moisture from the water.

• 50/50 water shake up test
• 

  Dried bio, 50ml cylinder, a mayo jar

• 

  50ml of bio and 50ml of water

• 

  Emulsion formed after shaking

• 

  Clear water after separation. Note that the bio layer is now wet and no longer clear

Assessing water clarity

There a few ways to assess the water clarity after a 50/50 test

• Hold it up to the light to look for milkyness
• See if you can read newsprint through it
• Shine a laser through it

Commercial particulate counters measure laser backscatter to assess particle levels. We can use a simple laser pointer to show up any soap particles in a similar way.

• Water clarity tests
• 

  The classic newsprint test - this sample has settled 24 hours in a warm location, so the bio layer has also cleared

• 

  Laser pointer test - visible beam in a sample known to contain about 250ppm soap

• 

  Laser pointer test - much better - a sample from the same batch but after passing through a dry wash tower

Titrated soap test

This test is a more definitive way of assessing your fuel. While the 50/50 shake test gives you an indication of whether soap is present, this test will give you the results in a more scientific way. By performing the test and using a simple formula, we can then determine the parts per million (ppm) of soap within the fuel. Depending on the results, you can look at ways of improving your process or it can give you the satisfaction of telling you that you’re producing fuel of the highest quality.

Required equipment

Some laboratory instruments and lab grade chemicals are needed in order to achieve a distinctive colour change when the sample being tested reaches a known acidity:

• magnetic stirrer.
• 100ml conical flask
• 50ml measuring cylinder
• 10ml pipette
• 0.2ml pipette
• High purity Iso-propyl-alcohol (aka –IPA or isopropanol)
• 0.4% Bromophenol blue indicator
• 0.01N Hydrochloric Acid (HCl)
• A sample of finished biodiesel

Performing the test

Using the cylinder measure out 50ml of IPA. With the 10ml pipette draw up exactly 10ml of biodiesel and add it to the 100ml conical flask. Using the same pipette add the IPA to the conical flask. This will guarantee that the 10ml sample has been transferred to the flask for testing and none has been left behind on the inside of the pipette. Turn on the magnetic stirrer and add 10 drops of the Bromophenol Blue indicator. The solution should now be a green/blue colour. Using the 0.2ml pipette, slowly, (drop wise) add the HCl solution until you reach the yellow end point. (You should be aware that the colour change can be very rapid if the soap content is low and care should be taken when adding the acid so that you do not exceed the point at which the yellow colour is achieved). Note how much HCl has been used and calculate for soap in ppm using the formula below.

For NaOH derived biodiesel:

HCl used X 304 = ppm of soap

For KOH derived biodiesel:

HCl used X 320 = ppm of soap

Understanding the results

Acceptable ASTM Limits For Soap - NaOH Reacted Biodiesel - No more than 41 PPM (0.041%) - KOH Reacted Biodiesel - No more than 66 PPM (0.066%)

Acceptable ASTM ( American Society for Testing And Materials)Limits For Soap - NaOH Reacted Biodiesel - No more than 41 PPM (0.041%) - KOH Reacted Biodiesel - No more than 66 PPM (0.066%)

Reading The Test: - If your fuel tests within the ASTM limits, well done. Your methods are first rate.

• 100-200 PPM, it shouldn't pose any real problems associated with fuel filter clogging.
• 200-300 PPM, you should be looking at ways of improving your process.
• 300-400 PPM, the likelihood of filter clogging may increase and soap content is getting high.
• 400+ PPM, do not use this fuel in a modern CRD (Common Rail Diesel) engine. Your soap and Methanol removal methods should be looked at again.
• 500+ PPM, there's a good chance you'll see cloudy water in a 50/50 shake test.

This information comes from Graydon Blair and his explanation of how these figures were derived is as follows:

The research that I based my figures on was done by Piedmont Biofuels out of Pittsboro, North Carolina. Rachel (the head chemist there) did a bunch of research and was able to extrapolate the approximations for soap ppm in accordance with the ASTM standard for allowable Sodium & Potassium in Biodiesel (EN 14538).

Somewhere buried on infopop is an excellent post where she went through how she figured it out. A couple other chemists also double-checked the work and came up with the same thing.

If I remember right, I believe the difference is due to the different polar ratios of Sodium & Potassium when they make soap.

The ASTM Standard for Sodium & Potassium is no more than 5 PPM. However, when they're bound up in soap, they're just a single component of the soap salts. So, I believe Rachel did the math to figure out Potassium based salts & Sodium based salts & figured out what 5 PPM of each would be and came up with the figures.