PNNL

The Science

Accurately measuring biofuel when biofuel and fossil fuel are mixed is essential for coprocessing facilities. It’s possible to detect even small amounts of biofuel by measuring the amount of carbon-14 in a sample, but gold-standard measurement techniques require expensive equipment with complicated, time-consuming sample preparation.

A simpler process called direct liquid scintillation counting (LSC) uses light produced by carbon-14 emissions in a prepared sample to measure carbon-14. However, the colors biofuels retain from their various biological sources can interfere with LSC measurements when they extinguish or “quench” light detected by the LSC.

Pacific Northwest National Laboratory researchers compared three procedures to correct for this quenching effect. They determined the procedure that had the easiest sample preparation and that quantified carbon-14 in fuel samples containing as little as 1–2% biofuel as reliably as gold-standard measurement techniques without requiring specialized laboratory space and handling.

The Impact

The researchers confirmed a cheaper, faster, and easier-to-prepare LSC method to monitor biofuel in mixed fuels. This method is as accurate as more expensive methods and can be more easily implemented by commercial, analytical, and industrial laboratories to verify the composition of mixed fuels.

Summary

Using color quench curves, chemical quench curves, and an internal carbon-14 spike, the researchers performed LSC analyses on samples containing low-level amounts of biogenic gasoline, jet fuel, and diesel blended with fossil fuel. They analyzed the samples using the gold standard—accelerator mass spectrometry—for comparison. In addition, they used optical spectroscopy to investigate potential diagnostic information related to LSC color quenching.

The researchers found both color quench curves and internal carbon-14 spiking reliably quantified biogenic carbon in fuel samples with LSC. Both approaches had essentially the same results within limits of error when analyzed on the Tri-Carb LSC. While the internal carbon-14 spiking method and color quench curve methods were found to be accurate, using color quench curves provides easier sample preparation by eliminating the need to add a radioactive carbon spike, which requires specialized laboratory space and handling. They determined that quench correction was essential for measuring colored samples and that longer count times increased the accuracy and precision of the measurement for all fuels when using the internal spike or color quench methods.

PNNL Contact

Charles G. Doll, Pacific Northwest National Laboratory, charles.doll@pnnl.gov

Andrew E. Plymale, Pacific Northwest National Laboratory, plymale@pnnl.gov

Mariefel V. Olarte, Pacific Northwest National Laboratory, mariefel.olarte@pnnl.gov

Funding

This research was funded by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office under DEAC0576RL0-1830. We are grateful to Dr. Jonathan Male for his insights. The researchers thank Mr. Igor Kutnyakov, Ms. Marie Swita, and Dr. Teresa Lemmon for assistance with the chemistry analyses. The upgraded oils were prepared by Dr. Douglas C. Elliott, Mr. Gary G. Neuenschwander, Mr. Leslie J. Rotness, Mr. Alan H. Zacher, Mr. Todd Hart and Dr. Mariefel V. Olarte, and the diesel fossil fuel oils were provided by Engr. Daniel M. Santosa.