Latest biodiesel quality results show a record 97 percent on spec

By Ron Kotrba | February 06, 2013

Teresa Alleman, a senior chemist with the fuels performance group at the National Renewable Energy Laboratory in Golden, Colo., shared the latest biodiesel fuel quality survey results with attendees at the National Biodiesel Conference & Expo in Las Vegas.

NREL obtained B100 samples from 53 producers and 14 terminals from August 2011 through February 2012. Alleman said the samples collected represent 94 percent of the biodiesel volume in the marketplace today, and 97 percent of those samples met requirements in the latest iteration of ASTM D6751, the biodiesel fuel quality specification.

“This is a huge improvement over previous years,” she said. In 2006, only 40 percent of samples in the survey were on spec, a major drop from the 2004 results that showed 85 percent met the then-current ASTM spec. In 2004, however, there were far fewer producers with only a fraction of productive capacity in operation compared to 2006. The ’06 samples showed massive failures for total glycerin, which Alleman said led to quality issues and fuel filter clogging experienced in Minnesota shortly after its B2 mandate went into effect, spurring balloting and passage of the Cold Soak Filtration Test, what Alleman called one of the best improvements to the specification and to biodiesel quality.

Since 2004 there have been 15 modifications to D6751, evidence that the industry is driven to continually improve itself.

All of the latest samples were on spec for total and free glycerin, and the average oxidative stability was measured at an impressive 9.5 hours. For metals, most samples were below the detectable limits with only one failure; the same sample also failed in other areas. CSFT times were also noteworthy, with all but one sample coming in below 200 seconds, with the remaining sample still within spec below 360 seconds.

Even though cloud point is not regulated in D6751, Alleman noted that there was a wide range in the samples, with the average at 2 degrees Celsius (35.6 degrees F). “Diesel fuel has the same range,” she said.

While the recently implemented No.1-B grade voluntary specification, which calls for a 0.4 percent monoglyceride limit and a year-round 200-second CSFT time limit, was not in effect at the time the samples were taken, Alleman said her scientific curiosity drove her to test how the latest samples would measure against it. About 90 percent of the biodiesel volume on the market today would pass the 0.4 percent mono limit and 200-second CSFT time in the No.1-B grade voluntary spec.

She spoke of the ultra performance liquid chromatography (UPLC) method to analyze mono content versus the gas chromatography method, and how UPLC speciates the various unsaturated monos whereas the GC method shows them all as a conglomerate blob. For saturated monos, however, there’s not a really good correlation yet, so the UPLC method “needs to be fine-tuned,” she said. 


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