WHW Test for Water

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The Weigh Heat Weigh test for water in oilWater in the oil is the biggest cause of problems when making biodiesel. Having the dryest oil possible is the biggest key to being able to make quality biodiesel from high titration oils. You cannot assume that just because the oil is clear, that it is water free. As a result, there have been many tests developed to determine water content both qualitatively and quantitatively.

One simple way to test WVO and biodiesel for water content is to use the Weigh / Heat / Weigh method (WHW). It is good for giving quantitative water content measurements down to about 1000-2000 ppm. Below that, you want to use either the Sandy Brae test kit, the Carbide Manometer, or send it off to a lab for the Karl Fisher water test.

You need a good scale, a container for the oil, a microwave, a thermometer, and a stir stick. A triple beam scale is great because it measures up to 2.6kg in increments of 0.1g. A candy thermometer is a good choice, anything that measures the temperature up to about 125°C (260°F). If you use a microwave, a plastic container is sufficient for the task. If you use a hot plate, a saucepan for your container is a better choice. I have and use a hot plate stirrer with a pyrex beaker.

warningNow to explain the dangerous part. As we heat the oil, beads of water settle to the bottom of the container. The weight of the oil on top of the water pressurizes the water in the bottom of the pan. The added pressure on the water raises its boiling point a little, becoming superheated. The superheated water only needs a little jar or bump to release the pressure, and it all becomes steam in a flash. That sudden expansion of the water under the oil is like a little explosion. It throws the hot oil everywhere. To prevent the water on the bottom of the container from becoming superheated, stir the oil vigorously as it approaches the boiling point of water.

The procedure:

Weigh your container and record the weight as the tare weight.

Add WVO to the container, about 1kg and record the weight as the wet weight.

Heat the oil to above 120C STIRRING constantly.

Weigh again and record the weight as the dry weight.

The calculation:

Subtract the dry weight from the wet weight and record as the water weight.

Subtract the tare weight from the wet weight and record as the oil weight.

Divide the oil weight into the water weight and multiply by 100 for the percent water content.

Example:

Empty beaker weighs 150g for tare weight

Beaker plus oil weighs 1150g for wet weight

Beaker plus dry oil weighs 980g for dry weight

Water weight = 1150g - 1127g = 23g

Oil weight = 1150g - 150g = 1000g

Percent water content = 23 / 1000 x 100 = 2.3%

Convert Percent Water Content to ppm:

ppm = percent water content x 10,000

In the example 2.3% = 23,000 ppm