Testing for Water in WVO
Written by John Galt
Water in vegetable oil and biodiesel exists in three phases, Dissolved, Emulsified, and Free. The jar on the left contains biodiesel with only dissolved water and is transparent. The jar on the right has both dissolved and emulsified water and is turbid or cloudy.
Dissolved water is characterized by individual water molecules dispersed throughout the oil. It is similar to humidity in the air - the water is there, but it is too small to see because it is dispersed molecule-by-molecule. Thus VO or BD can hold a significant concentration of dissolved water and still appear clear. Most vegetable oils can hold 200 to 1000 PPM of water (0.02 to 0.10 percent) in the dissolved state depending on the temperature and age of the oil. Used oils can hold three to five times more water in the dissolved state than new oil.
Oil becomes saturated with moisture when the amount of water exceeds the maximum concentration for it to remain dissolved. In this second phase, the water is suspended in the oil in microscopic droplets known as an emulsion. This is like fog on a cool, spring day. In that case, the amount of moisture in the air is greater than the saturation point, and a suspension of small droplets of moisture or fog results. In VO or BD, this “fog” is often referred to as haze and the fuel is called 'cloudy' or 'hazy'. Haze usually indicates moisture above 1500 PPM [0.15%] at 'room' temperature. Therefore VO or BD that appears clear may not necessairly be dry enough for use as motor fuel.
Adding more water to an emulsified mixture will cause a separation of phases to produce a third phase of free water as well as the dissolved and suspended water. This is similar to rain falling when the amount of moisture in the air exceeds the dew point. This free water is usually found on the bottom of containers of used VO, where it's mixed in with the fatty sludge and food particles. If free water is evident then it's likely that dissolved and suspended water is also present in the VO or BD.
When testing VO feedstock for making BD, 1000 PPM is usually sufficient and up to 3000 PPM will work, however soap contamination in the finished BD can present a problem with increased water contamination of the feedstock. The generally acceptable amount of water in VO or BD fuel is 500 PPM or 0.05 percent.
Tests for Water in Vegetable Oil or Biodiesel:
The Crackle Test or Hot Pan Test
Heat a pan to 320°F (130°C), then add a drop of oil in the center. Moisture in the oil is indicated by the number of bubbles seen when the water boils off. A few small bubbles is about 500 to 1,000 ppm (0.05 to 0.1 percent) water. More bubbles of a larger size show approximately 1,000 to 2,000 ppm water, and a crackling sound is evident if moisture levels are in excess of 2,000 ppm. The Crackle Test is reportedly only sensitive to free and emulsified water.
Related Link:Visual Crackle Test - Machinery Lubrication Magazine
The Hot Spoon Test.
It's quicker, uses much less oil and is much easier to clean up while producing the same results. It uses a teaspoon, a tablespoon, a plumbers propane torch and paper towel over the sink. Smear a little oil on the tablespoon and heat it over the propane flame till it begins to smoke. Use the teaspoon to scoop 1/2 a teaspoon of oil to test and pour it into the hot tablespoon. Look for bubbles as per the hot pan test. Dump the hot oil on the paper towel, rinse in water to cool. Wipe the spoon with paper towel and it's ready for the next test. The same limitations as the HPT apply.
It works to quantify the percent moisture in a sample of fuel. The larger the sample the more accurate the test, 250ml is the minimum amount for a common 1/10 gram scale. This is a standard moisture test commonly used in the agriculture industry. It can be used for VO, diesel fuel, or mixes of the two, but won't work with mixes containing volatile solvents.
The Vapor Test
A water test that's repeatable and easy to set up is the water vapor condensation on glass test. Use a cup with a handle (a short and big diameter one is better than a tall and small diameter for more surface area). Fill the cup with a 1/4" of VO/BD to test. Put a piece of glass that completely covers the cup [a glass lid works] then heat in a microwave till the suspended water boils and rises as vapor and condense on the glass. In most microwave ovens it takes 1 to 2 minutes. The condensation starts near the rim of the cup (where it's coolest) and grows inward depending on the amount of moisture present. By measuring the diameter of the condensed vapor ring, a correlation to the Sandy Brae test could be made.
The Karl Fischer Titration Test
The recognized industrial standard is: ASTM E203 - 01 Standard Test Method for Water Using Volumetric Karl Fischer Titration
Many oil analysis labs offer this test.