Biodiesel Distillation


Biodiesel quality continues to be a concern for diesel engine makers, fleet managers, and the public in general. Variability in the quality of biodiesel, coupled with the high cloud point of biodiesel produced from certain feedstocks, has resulted in the ASTM adopting more stringent biodiesel standards. In October 2008, the ASTM revised the ASTM D7501 standard, requiring all finished biodiesel to pass a cold soak filtration test. This new testing requirement was designed to improve the cold weather performance of biodiesel.

The test to determine cold soak properties is now ASTM D 7501. This is a standard test method for determination of fuel filter blocking potential of biodiesel (B100) blend stock by cold soak filtration test (CSFT)


The answer is…it depends. It depends on the feedstocks currently being used, and on the process technology used to convert those feedstocks into biodiesel. The new ASTM D6751 cold soak filterability test is a measure of how well biodiesel flows when chilled then poured through a filter. Biodiesel that may have passed the previous ASTM tests may fail this test because biodiesel produced from feedstocks with high gel-points inherit this attribute from their feedstocks. Worse yet, homogenized oils, or feedstocks that are blended from many sources, can have gel points that vary from sample to sample. Yellow grease, white grease, and waste vegetable oil (WVO) all fall into this category.

So what can be done to help ensure feedstocks with high FFA can be made to pass the cold soak filterability test? There are really three approaches to addressing cold filterability:

  • Select feedstocks that have low gel-points (Soy for instance)
  • Use fuel additives to lower the gel-point of existing feedstocks
  • Improve the cold filterability by distilling your biodiesel

Switching to soy can be an expensive proposition. Using fuel additives can help, but adds significant and recurring costs to your production. Distilling your biodiesel produces the purest form of biodiesel possible and dramatically reduces cold filterability of most feedstocks (see photos above). Another advantage of distilled biodiesel is that no further washing is required, so dry washing Ion Exchange or Magnesol is unnecessary.

Advantages of Biodiesel Distillation:

  • Creates product homogeneity
  • Creates a superior biodiesel when using both virgin and animal feedstocks
  • Market differentiation by creating the purest biodiesel possible
  • Takes sulfur out of high sulfur feedstocks like beef tallow and chicken fat (up to 80 PPM)
  • Meets ASTM specifications

Are you concerned about passing Cold Flow Filtration? SRS International has the answer to your problem with our ASVB-Series Distillation System which distills your biodiesel, creating the purest biodiesel possible. By distilling your biodiesel you can be back in business in no time with ASTM compliant biodiesel. And, you don’t have to worry about losing the $1/gallon tax credit!

Not sure if your biodiesel will pass? Perform this quick test: Put a jar of your biodiesel in the refrigerator for a few hours, then check:

  • Clarity – does the fuel get hazy or cloudy?
  • Solids – do you see solids forming or crystallization?
  • Viscosity change – Is your chilled biodiesel noticeably thick and slow pouring?

If any or all of these are present, you may be in trouble.

For information on cold soak filtration and biodiesel distillation, call us today at (800)497-5841 or email us

 To View Printable PDF Version of this Page 

Biodiesel Distillation
Left – Finished Biodiesel
Right – Distilled Biodiesel
Both samples came from the same batch

Need More Help ? Contact Us
Translate »