Clean fuel is essential to avoid problems with engine performance later on. Washing biodiesel, can be done through various methods, all which will remove soaps and other contaminates.
Water washing is the traditional way of purifying biodiesel and the safest. No harmful gases are emitted like during the dry wash methods that require evaporation. Methanol, containing polar impurities, is left in the biodiesel folloing its production. Washing the crude biodiesel removes the methanol which holds the impurities in the biodiesel. Biodiesel must be washed several times before it is pure enough to be used as a fuel source. Water washing is flexible enough to be used to at varying levels of agitation (from static to aggressive) to satisfactorily “clean” the biodiesel.
Dry washing is becoming the more desired method of purification over water washing because of the decreased production time, lowered cost, requiring less plant space, and in some cases the dry washing agent (magestrol) is reusable. Dry washing also prevents the chances of forming emulsions upon production of a bad batch. When a dry wash is done properly a higher quality biodiesel can be produced. In the dry washing method containments (soaps and glycerins) stick to the magnesol (magnesium silicate), silica gel, or saw dust as they are filtered through. The impurities are suspended in the methanol which is polar and is absorbed into or sticks to the various media.
Other forms of dry washing use evaporation to drive off the methanol along with the impurities. This method of purification can be dangerous since methanol vapors are highly flammable. Vapors of methanol are slightly heavier than air and may travel some distance to a source of ignition and flash back. If these vapors accumulate in a confined space they have the potential to explode if ignited.
• Ion-exchange resin
• Bubble washing
• High heat (vacuum) drying
• Base/base processing
This purification technique is very dangerous and should only be used under strict supervision. Electrostatic field separation is used to separate the glycerol from biodiesel by passing a high voltage DC current through the crude fuel. It works particularly well, except there is the risk of igniting the methanol fumes if a the electrical current gives off a spark. http://www.graham-laming.com/bd/nr.htm