Research Suggests Biodiesel Blending is Often Inaccurate; New Radiocarbon Analysis Method Directly Quantifies Carbon of Biological Origin in Blends
While sampling blended biodiesel fuels purchased from small-scale retailers, researchers at the Woods Hole Oceanographic Institution (WHOI) found that many of the blends do not contain the advertised amount of biofuel.
Marine chemist Chris Reddy and colleagues sampled pure biodiesel and blends from more than a dozen distributors across the United States. When testing fuels listed as B20, they found that the actual percentage of biofuel ranged from as little as 10% to as much as 74%. Only 10% of samples met the specifications for biofuel blends required for vehicles of the US Department of Defense, one of the leading consumers of the products.
Reddy and colleagues worked with WHOI senior scientist Bill Jenkins and colleagues at the National Ocean Sciences Accelerator Mass Spectrometer facility to develop an extremely precise radiocarbon-based calibration method for determining if the balance of biofuels and petroleum is correct. The new method relies on the fact that petroleum is “radiocarbon dead” (contains no radiocarbon), while biofuels are enriched with radioisotopes that plants absorb from Earth’s atmosphere and soil.
Error propagation analysis demonstrated that this method calculates absolute blend content with ± 1% accuracy, even when real-world variability in the component biodiesel and petrodiesel sources is taken into account. The researchers independently confirmed this accuracy using known endmembers and prepared mixtures. This is the only published method that directly quantifies the carbon of recent biological origin in biodiesel blends, according to the team.
The calibration method accounts for the differences in chemical makeup of different types of oils, such as canola, coconut, soybean, or animal fats. This method also allows for a direct quantification of the amount of renewable carbon that is emitted from vehicles, which will aid researchers in determining the true environmental value of switching to biofuels.
Reddy and colleagues happened upon the discrepancy while studying the potential effects of a biodiesel spill in the marine environment. The new research was published online on 27 February in the journal Environmental Science and Technology.
Biodiesel blends are often made by local distributors through simple “splash blending,” whereby ingredients are poured together into a container in their respective amounts. The intent is that the simple act of pouring will ensure proper mixing.
But biodiesel is naturally thicker and more viscous than petroleum-based diesel, so it may be settling into separate layers within fuel tanks. Reddy and colleagues also pointed to simple human error—poor math, measurement, or stirring—as a possible reason for the inconsistencies.
The United States currently has a voluntary standard for proper preparation of blended fuels, but no enforcement. The nation does have an enforceable standard for B100 biodiesel, and work on a B20 specification are underway.
The new fuel blending research builds on a 2004-2005 study by the National Renewable Energy Laboratory (NREL) that suggested some national-scale manufacturers were having a hard time producing proper blends of biofuel.
Christopher M. Reddy, et. al. Determination of Biodiesel Blending Percentages Using Natural Abundance Radiocarbon Analysis: Testing the Accuracy of Retail Biodiesel Blends. ASAP Environ. Sci. Technol., 10.1021/es071814j Web Release Date: February 27, 2008
R.L. McCormick, et. al., (2005) Survey of the Quality and Stability of Biodiesel and Biodiesel Blends in the United States in 2004 (NREL/TP-540-38836)
R.L. McCormick, et. al., (2006) Stability of Biodiesel and Biodiesel Blends: Interim Report (NREL/TP-540-39721)