Drywashing Biodiesel with Magnesol
By Rick Da Tech
The Dallas Group produces synthetic magnesium silicate for use as a waterless wash for making biodiesel and brands it Magnesol D60. Some restaurants use synthetic magnesium silicate as an extender for vegetable oil. In the restaurant, the oil is passed through a tub of magnesium silicate and then finely filtered. The dry-wash process removes the particulate matter that reduces the FFA content of the oil.
Magnesol was more commonly used around 2006 to purify biodiesel and is not commonly used today for biodiesel.
To purify biodiesel, mix the magnesol with the biodiesel, absorbing the soaps and other contaminants, then you use settling and filtering to remove the magnesol. The process works with or without removing the methanol first. However, if you remove the methanol first, it takes much less magnesium silicate to perform the task. Also, Magnesol is more effective and quicker at removing soaps when the biodiesel is warm.
One of the reoccurring arguments against using magnesol is that it leaves fine abrasive particles behind in the fuel. The fine particles can clog filters or damage fuel systems. If not properly filtered this can be the case. However, if properly settled and filtered, any particles that remain behind are too small to have any effect. The advantage of magnesol is that it cleans biodiesel without using any water.
You may find it difficult to obtain high quality, low titration feedstock oils. Lower quality oil usually means a shift over to KOH as a catalyst and creating lots of soap. Magnesol offers a low cost, low energy method of removing the high concentration of soaps from biodiesel once you remove the methanol.
The biodiesel becomes much easier to filter if it is allowed to settle for an extended period. With longer settling times, more magnesol settles to the bottom, and less magnesol collects in your filter.
The Dallas Group recommends using 1% by weight (of the biodiesel) for every 1000ppm of soap in the biodiesel. Use this test procedure to determine your soap levels in ppm.
Polishing Biodiesel with Magnesol
Bubble washing, active drying, and ION exchange resins can increase the acid number of finished biodiesel. Magnesol has been successfully used to polish acidic biodiesel. As biodiesel ages, it can oxidize, becoming lumpy and acidic. Polishing old biodiesel can bring it back to ASTM spec. Magnesol also bleaches and deodorizes biodiesel, removing the color pigments, making the fuel a lighter color and removing odors. There is some debate as to if it can reduce the titration numbers on new oils.
Dave uses it to polish his fuel after it has been washed and dried to lighten the color and remove FFA. He heats his washed biodiesel to 40°C (~100°F) and adds 700 grams for each 200 Liter batch. He mixes with compressed air rather than pump mixing because he wants to keep the magnesol out of his pump. Once he has stirred it in, he lets it settle for four days and draws all but about 6 liters from the top, taking care not to disturb the settled magnesol. He runs the polished biodiesel through a pressure driven centrifuge to make sure he has no fines left in the fuel. After four days of settling, the centrifuge usually does not collect any magnesol in the rotor.
The pictures show the biodiesel and Magnesol just before draining and while he is draining it out of his tank. The third picture is the wood chip and shop towel filter he uses on the biodiesel decanted from the bucket of sludge.