Report detailing that biodiesel fuels produced to meet or exceed current standards can still precipitate insoluble glycerin when cooled or when blended with ULSD, creating huge challenge for filtration
- One of biggest challenges related to filtration resulting from increased biodiesel post-Energy Policy Act of 2005 is removal of glycerin from neat and blended biodiesel
- Glycerin is byproduct of transesterification process used to treat biodiesel feedstocks and is partially removed from fuel through coalescence, centrifugation and water washing
- Over last 10 years, Donaldson has investigated several hundred filters that exhibited premature plugging due to extensive buildup of insoluble free glycerin
- Report details how biodiesel produced to meet or exceed current standards can still precipitate insoluble glycerin when cooled or when blended with ULSD, which significantly reduces filter life
- ASTM D6751-12 limits glycerin level in B100 to 0.02% by weight (200 PPM)
- Using ASTM D6584 (analytical method to determine glycerin in fuel), equilibrium solubility of glycerin in commercially available B100 at room temperature (22 ºC) yields result of 285 PPM – well above allowable amount; however, when temperature is reduced to 6.5 ºC, maximum solubility drops to only 146 PPM – meaning if biodiesel is produced containing maximum allowable glycerin and cooled to 6.5 ºC it will lose 56 PPM of glycerin to insoluble particles (equivalent of 4 lbs (0.38 gallons) in 10,000 gallon tank)
- Glycerin is even less soluble in biodiesel because fatty-acid methyl esters (FAME) have relatively higher polarity compared to ULSD (mostly paraffin compounds), and glycerin is a relatively small polar molecule
- B10 blend at room temperature has glycerin solubility limit of 12 PPM, so to avoid precipitation initial B100 used to make the blend should contain no more than 120 PPM of glycerin – if biodiesel is produced with maximum allowable amount of glycerin and blended with ULSD to create B10, blend will lose at least 40% of its glycerin to insoluble particles (0.5 pounds (3/4 cup) in 10,000 gallon tank)
- Maximum allowable glycerin content of 200 PPM as outlined by ASTM D6751-12 is not adequate for biodiesel blends or B100 at reduced temperatures
- To test glycerin effect on high efficiency filters, B100 with max amount of glycerin was blended with ULSD and passed through filter – recirculating 2 liters of B50 solution through 13.8 cm2 filter produced pressure increase of almost 3.5 PSI (equivalent to full size filter treating only 400 gallons of fuel) – pressure drop was confirmed to be caused by glycerin particles through microscope
- Solution – initial free glycerin level should be no more than 50 PPM
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