Bubble Washing your Biodiesel

Things you will need.
For this list, we will assume you will be making small batches to start out.

1. A source of compressed air. This could be from a compressor and a good regulator, or from a cheap, small fish tank pump.
2. Some type of soft, flexible tubing.
TIP: not rubber, polyvinyl works well and is inexpensive
3. Some sort of air diffuser, an aquarium air stone works well.
TIP: try to find a white stone. The blue ones are dissolved by the Biodiesel.

Step by step procedure.

1. Put your freshly made Biodiesel into a container that will hold about 3 times as much as you have made.
2. Fill the container with water to mach the amount of Biodiesel in the container. Example, if you made 1 liter of Biodiesel, put in 1 liter of water.
3. Connect your diffuser to your source of compressed air.
4. Drop your diffuser into the mixture, let it sit on the bottom.
5. Turn on the air source. Make sure you don’t use too much air. You want it to just bubble with small fine bubbles.

After just a little while, the water in the bottom will become cloudy and white. This means it's working. The water is washing out anything that’s water soluble, like any left over glycerin, methanol, and lye.
Actually, any remaining methanol will be evaporated by the air bubbles.
Let this run for about 6-7 hours.

6. After this has bubbled, drain off as much of the water as you can get.
TIP: use your little piece of hose to siphon off the water
7. Refill the container with the same amount of water as you did before.
8. Start your bubbles again.
9. Allow this to run for the same period of time.
10. Drain the water again.

This process needs to be repeated at least 3 times to be sure all of the impurities are removed.

Problems you might run across with washing.

Bubble washing kind of serves a “duel purpose” if you will, not only does it do all the things listed above but it is a great test of the quality as well.
If, after washing the last time, your biodiesel easily separates from the water, you have a good quality fuel and have had a successful reaction.

If you now have what looks like tapioca pudding, well, you have problems. You have what is called emulsification. This is most often caused by an incomplete reaction.

It can also be caused by too much sodium hydroxide. This causes the formation of soaps in the biodiesel and this causes the emulsification.

All is not lost. There are several things you can do. First it to let it sit! Eventually, the emulsification will break, and the biodiesel can be re-reacted to remove the mono and diglycerides. Then the process starts over again. With careful measurements, this usually is not a problem.
Other things than can help is adding salt to your wash water. Salt breaks emulsifications and can aid in the separation time. Also applying gentle heat can also do the job. Use and indirect heat source, such as a bright lamp shinning on you container, or an inferred bulb. You don’t want too much heat, just get it back to 100 degrees or so.
The best option is to just be patient, it will separate back out. It might take as ling as a week or longer.

After washing, the next step is to test your product against the ASTM standard.