BioDiesel-Soap Test

Testing Biodiesel For Soap Content

When Biodiesel is made, one of the by-products that gets produced along with the Biodiesel is soap. Typically, the amount of soap produced can be directly tied to how high the titration was, how wet the oil was to start with, or how much extra catalyst was used. Soap in Biodiesel is a contaminant and something that should be measured for each time you make a batch.

Why Is Soap Bad?
Soap in Biodiesel isn’t good for your diesel on many counts. The main problem we see is plugged fuel filters. This is because it tends to congeal up on the fuel filter fibers which leads to reduced throughput which leads to a plugged fuel filter…and down time for your diesel. Next in line is that when soap is burned in a diesel engine it leaves behind an ash residue. This residue can manifest itself as higher levels of soot out the tailpipe or even build up on fuel injectors and in the combustion chamber.

How Soap Is Formed
Soap is formed when free fatty acids in oils mix with water and catalyst (Sodium Hydroxide–NaOH or Potassium Hydroxide–KOH). Typically, the higher the free fatty acid level in oil leads to higher soap content in the Biodiesel. It’s why we titrate waste vegetable oil–so that we can add enough extra catalyst to react the majority of the free fatty acids into soap and still have enough left over to react the remaining oil into Biodiesel.

How To Test For It
There’s two popular tests for checking soap levels in Biodiesel. One, called The Shake Em Up Test, is a subjective test that can give you a good approximation of the soap content in Biodiesel. The other test, called The Soap Titration Test, is an extremely accurate objective test that will tell you exactly how many parts per million are in your Biodiesel sample.

Test #1: The “Shake-Em Up” Test
This test is a subjective test that will give you a good approximation if the soap content in Biodiesel is almost gone. It’s a great test for checking to see if you’re “getting close” to getting all the soap out of your Biodiesel. However, it is not an exact test and should only be used to give a “close approximation” of the level of soap in Biodiesel. Passing this test doesn’t necessarily guarantee that soap is at ASTM levels. A pass simply indicates that soap levels are significantly reduced.

How The Test Works
Distilled water is mixed into Biodiesel and then allowed to settle out. If soap is present in large amounts, it will cloud the water that settles out of the Biodiesel. If soap is present in high quantities, it will readily dissolve into the water. As the water settles out the soap will cloud the water making it hazy and somewhat opaque. The test relies on being able to see the difference between fresh, clear water and water that may have absorbed soap. It is a highly subjective test and only gives an indicator that soap may be present. It does not indicate the “amount” of soap present in the Biodiesel.

0080514456503_500X500Items Needed:
– Clean Glass Jar (at least 500 mL capacity)
– Distilled Water
– Biodiesel To Test

How To Perform The Test:
1) Fill a clean glass jar half-way full of Biodiesel
2) Fill the rest of the jar with distilled water
3) Cap the jar and shake it vigorously for about 10 seconds
4) Set the jar down and allow the water and Biodiesel to sit for about 30 min to 1 hour
5) Return and look at the water that has settled to the bottom.

Reading The Test:
If the water that settles out isn’t as clear as the water that went in, then
soap levels are still fairly high and the Biodiesel should continue to be washed further.
If the water is as crystal clear as it was going in, there’s a good chance that soap levels are low. It’s now a good time to test with the Soap Titration Test to see what exact soap levels are.

Test #2: The Soap Titration Test
This test is an objective test that when properly performed will allow you to measure soap levels in Parts Per Million (PPM). It can be used to successfully identify exactly how much soap is present in your Biodiesel and is an excellent test to use to ensure that the soap levels in your fuel are low enough to run in a diesel engine.

How The Test Works
The test works very close to how an oil titration test works except in reverse. Biodiesel is diluted in highly pure isopropyl alcohol, a pH indicated called Bromophenol Blue is added and everything is mixed up well causing the mixture to usually take on a bluish green tint. Once mixed, small amounts of a very weak solution of Hydrochloric Acid (HCL) are added in measured amounts. If soap is present in the Biodiesel, the acid will neutralize the soap and the pH indicator will change from a greenish blue to a yellow color. The amount of HCL used to neutralize the soaps in the Biodiesel is recorded and used to calcuate the soap levels in Biodiesel in parts per million (PPM).

Items Needed:
– Bromophenol Blue pH Indicator
– 99% Pure Isopropyl Alcohol
– Hydrochloric Acid 0.01 Normal (HCL)
– Magnetic Stirrer
– Graduated Glass Beaker Capable Of Holding 150 mL Liquid
– 2 Glass Pipettes (1 mL or 10 mL works best)
– Biodiesel To Test

The Biodiesel Soap Test Kits and get all the items needed to perform soap tests in a handy kit!
Basic Biodiesel Soap Test Kit | Deluxe Soap Test Kit | Ultimate Biodiesel Soap Test Kit

soaptestingkitultimateTest Biodiesel for soap with our soap test kit

How To Perform The Test:
1) Measure 100 mL 99% Pure Isopropyl Alcohol into glass beaker
2) Place beaker on magnetic stirrer and begin stirring
2) Dissolve 12 mL (or 10 grams) of Biodiesel into the alcohol
2) Add 10-20 drops of Bromophenol Blue to tint the mixture and continue to mix
— This may tint it to a greenish blue, completely blue, or even just a light green
3) Using a glass pipette, add measured amounts of HCL until the mixture turns yellow
4) Record the amount of HCL used to turn mixture yellow
5) Calculate soap content

Calculating Soap Content:

Soap Calculation Multiplier:
NaOH Reacted Biodiesel – 304
KOH Reacted Biodiesel – 320
Times the amount of HCL required to turn yellow added to the multiplier
Example: 0.05 mL x 304 = 15.2 PPM

Acceptable ASTM Limits For Soap
– NaOH Reacted Biodiesel – No more than 41 PPM (0.0041%)
– KOH Reacted Biodiesel – No more than 66 PPM (0.0066%)

Reading The Test:
If your fuel tests within the ASTM limits, congratulations!
If your fuel is 100-200 PPM or less, it shouldn’t pose any real risks to plugging fuel filters or to diesel engines.
If your fuel is 200-300 PPM, it’s really right on the edge of what you should be using
If your fuel is 300-400 PPM, filter clogging may occur and soap content is getting high
If your fuel is above 400 PPM, it really should be washed again to lower the soap content
If your fuel is above 500, there’s a good chance you’ll see cloudy water in The Shake-Em Up Test