Written by Rickdatech

Water in the WVO 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 can't 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 quantative 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, a micowave, a thermometer, and a stir stick. A tripple beam scale is great because it measures up to 2.6kg in increments of 0.1g.  A candy thermometer will work, anything that will measure the temperature up to about 125C.  If you use a microwave, a plastic container will work. If you use a hot plate, you'll need a sauce pan for your container. I have and use a hot plate stirrer with a pyrex beaker.

Now to explain the dangerous part. When the oil reaches 212°F, the boiling point of water, it can boil violently throwing boiling hot oil dozens of feet in every direction. The water in the bottom of the pan will be pressurized by the weight of the oil on top of it. As we heat it under pressure it becomes superheated. Superheated water only needs a little jar or bump and it all becomes steam in a flash. That sudden expansion of the water under the oil is like a little explosion. It will send the hot oil everywhere. So keep the oil stirred up to prevent water from collecting on the bottom and keep the pan covered when not stirring.

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