Demonstration of low-level biogenic fuel content using quench curve and direct liquid scintillation counting (LSC) methods

Abstract

An investigation into the direct method for liquid scintillation counting (LSC) quantification of biogenic fuel content in fuel blendstock is presented. This method development intentionally used a colored matrix (∼99 wt%), fossil diesel fraction, and low-level biogenic fractions (∼1 wt%) to determine the applicability of the LSC technique in colored blend mixtures. LSC procedures for quench correction, includingtheuse ofan instrument internal standard (QuantulusSQP values), color quench curves,andaninternal14C standardspike on samples containing low-level amounts of biogenic gasoline, jet, and diesel mixed with fossil fuel, were compared.Samples were analyzed on both Perkin-ElmerQuantulusand Tri-Carb instruments, and the 14C contents were compared with those determined by accelerator mass spectrometry (AMS). Results from the Tri-Carb instrument showed that percent differences of <10 % compared to AMS-reported values are achievable at 5-hour count times despite colored samples. A comparison between the impact of chemical and color quenching in the fuel samples showed that color quenching in highly colored samples reduces efficiency significantly more than chemical quenching, indicating that chemical quench curves are not appropriate for highly colored biofuel/fossil-fuel blended samples. Results indicate that both the direct method with internal spike quench correction and the use of a color-quench curve provide accurate results for 1 % biogenic fuel blends.Additionally, we have explored the use of Fourier transform infrared (FTIR) spectroscopy in measuring the biogenic content of the colored blended fuel samples. Preliminary results show the presence of biogenic carbon-derived fingerprints that are absent in fossil-derived sample. However, further work is needed to develop an FTIR-based quantitative method.