Water Washing Biodiesel

Washing removes contaminates by an osmosis type of action. Contaminates more readily dissolve in water than in biodiesel. Methanol and glycerin are suspended in the biodiesel and when a water droplet touches methanol or glycerin the droplets will merge and become larger and settle out of the biodiesel quickly. The soap molecule becomes connected to the water also forming large droplets of water surrounded by soap that fall out quickly. Multiple washes are needed to remove the soap. Once all the soap has been removed, biodiesel will no longer be able to hold significant quantities of water and settling out the water only takes a couple of days. More active drying techniques are also available.

We will explain the different ways to wash and include some tips and tricks for each type of washing. Differences in water, weather, ambient temperature, feedstock oil quality, processing technique, and a number of other factors all converge to make it difficult to prescribe a step by step instructions that works for everyone. There is a basic starting point that you can use in washing.

How fast you need the biodiesel also plays a major role in how you wash. If you are using low titration oil and use the 5% prewash it is possible to wash using hot water with the stir method. The other end of the spectrum is to not wash at all. If you leave your unwashed biodiesel in a vented drum for six months, the contaminates will fall out to the bottom.

Time can be your friend. The longer you wait between steps, the easier the wash. Letting your biodiesel settle in the processor for three or four days instead of the typical overnight will force more of the methanol, soaps and glycerine into the byproduct layer, making washing easier. If you leave your biodiesel sitting on top of water that is not completely saturated with soap for a few days, more soap will migrate to the water making subsequent washes easier. Time is good for homebrew biodiesel. If you’re getting frustrated with emulsions, walk away for a couple of days and things will get better.

How to Know When to STOP Washing

On the Internet the general consensus is that washing is finished when the wash water is clear. However, if you have soft water you may find that you can wash forever and the wash water never gets clear. The ASTM standards for biodiesel do not include a test for soap. We want to wash our biodiesel until it no longer has enough soap to create an emulsion in our vehicle’s fuel tank. We also want to be able to easily dry our biodiesel. If we wash it long enough to dry easily, then it is unlikely to create an emulsion in our tank.

Another better test is the ’Dry Test’, put about a cup of biodiesel in an open jar and see how long it takes for the biodiesel to clear. If it haziness goes away in two or three hours then your done washing, and your biodiesel will dry easily. Another indicator is that when settling after the last wash, the biodiesel will turn darker in color as the water settles out.

Basic Washing Instructions - a starting point

1.Add the unwashed biodiesel through the standpipe on top of the water from the last batch.
2.Let settle overnight.
3.Drain the old water and mist wash until you have collected an amount of water in the bottom of the wash tank approximately equal to 1/3 of the biodiesel
4.Let settle overnight.
5.Replace the water with fresh water and bubble wash 8 hours
6.Let settle overnight.
7.Repeat steps 5 and 6 until the Dry Test passes.
8.Pump the washed biodiesel into another drum for drying.

Water Washing Tips

• Orange Juice is good. When washing the biodiesel will become cloudy and change colors, it is often referred to as ”orange juice” in appearance.
• Fewer emulsion and faster cycles can be the result of heating your wash tank.
• Hard water creates fewer emulsions and washes faster but leaves white stuff in the biodiesel that needs to be settled out and possibly filtered out. The white stuff is magnesium and calcium soap that do not dissolve in either biodiesel or water.
• In a steel drum it can be difficult to judge the thickness of the various layers. One solution is to ”dip” it by sticking a tube or pipe all the way to the bottom then putting your thumb over the opening on top and drawing out a sample. Put the sample in a clear container to see the condition of the wash water and how thick any emulsion layer might be.
• The 5% pre-wash can dramatically reduce soaps and make washing easier.
• The longer you let the biodiesel settle between washes the easier it is to wash.