Determination of 14C content in co-processing feedstocks and products provides quantitative assessment on biogenic carbon apportionments in fuel products. While accelerator mass spectrometry (AMS) 14C analysis is the “gold standard” for determining biogenic carbon content, it is not readily available as a tool for rapid, in-house assessment of co-processing experiments. Analysis of 14C by liquid scintillation counting (LSC) through CO2-amine reaction has been studied by many researchers and was once listed as a ASTM method. Here, we have explored this CO2-amine method by developing a biogenic carbon (aka, 14C in pMC) calibration curve using AMS-calibrated CO2 gas. A closed CO2-amine absorption system was constructed to facilitate quantitative CO2 capture. Significant correlation between CO2 mass and LSC 14C counting rate (counts per minute, CPM) was achieved in the range of CO2 mass from 0.25 g to 2.49 g. The counting efficiency varied, ranging from ~40% to ~60%, depending on the CO2 saturation rate. The biogenic carbon calibration curve was verified by AMS-calibrated CO2 gas and solid biomass sample (IAEA-C3 cellulose, 14C=129.41 pMC). CO2 gas samples with biogenic carbon contents ranging from 2.7% to 96.2% were analyzed by the LSC CO2-amine method and show excellent consistency with AMS measurements. This study has demonstrated the feasibility of using LSC through the CO2-amine approach for determining biogenic C content in solid biomass and feedstocks with low bio-oil/petroleum blending levels.

Determining low 14C content in co-processing feedstocks and products by LSC through CO2-amine complex approach

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