The Glycerin Treatment
By Rick Da Tech
You can lower the titration number and FFA of your raw WVO by using a technique I'm calling Glycerin Stripping. It's really simple, you add the raw glycerin from a previous batch to your WVO, heat, stir, settle, and decant. The technique was introduced to infopop several years ago by a semi commercial British producer with the forum handle HighCompressionII. After several years, the technique is beginning to catch on with back yard biodiesel brewers. Here is what I think is the best infopop thread on Glycerin Stripping.
There is no set recipe yet, results also vary. It's this variation in the results that have caused it to be slow to be adopted. Even with the variation in results it almost always improves the WVO making processing easier. Most often reported results are a lowering of FFA or titration numbers, dehydrating the WVO, removal of small particles and trash in the oil, an increase in yield and a lowering of the gel point. There may also be a transfer of methanol from the glycerin to the oil.
Basically, the excess caustics in the glycerin is combining with the FFA and water soluble acids to make soap and salt in much the same way as Caustic Stripping with Soda Ash. Since you are not buying anything this technique does not add any cost to the fuel, and there are no acids involved like in the acid/base recipes.
There is usually a thickening with high titration oils, probably due to soaps staying with the oil. There is usually a 2% to 10% increase in the volume of the oil after it is treated. This is probably due mostly to biodiesel being released from the glycerin. The glycerin will usually thicken up, sometimes dramatically, and often get darker. This is probably due to the process grabbing the trash and junk from the oil as well as an increase in soap levels in the glycerin. (Caustic stripping is used in the refining of oils primarily to clean the oils). Finally there was testing by Girl Mark that shows it reduces water content of the oil to super dry levels.
To summarize, this technique is a cheap and easy way to reduce FFA levels. Typically titration will go down by half, while it dries and cleans the oil. If you have some high titration oil, give this technique a try.
Glycerin Prewash on vegetableoildiesel.co.uk