Radiocarbon Analysis for Biofuel Quantification in Fuel Blends

Abstract

Fuel blends, particularly those composed of a mixture of biobase and fossil sources, are comparatively new in the energy marketplace relative to pure fossil fuels such as gasoline or pure biobase fuels such as sugarcane‐derived ethanol. A developing market exists for these blends of biobase and fossil fuels and accompanying this is the need for accurate assessment of each source's contribution in the mixture. In the United States, the Energy Independence and Security Act of 2007 mandates that specific levels of renewable fuel be established by 2022. Currently, this requirement is met by the 10% ethanol, derived primarily from corn, which is added to most gasoline sold in the United States. This mandate requires that the accurate determination of this addition of renewable fuel be provided. The well‐developed technology of radiocarbon dating, measuring the abundance of the 14 C atoms in a material, can determine the source material based on the abundance or absence of 14 C, similar to but distinct from age determination in radiocarbon dating. Relative to other analytical techniques, 14 C determination is the only one able to unambiguously determine a fossil‐fuel‐derived product. The use of radiocarbon, as a determinant of a biobase product, stems from the natural occurrence of 14 C in plants as a result of 14 CO 2 uptake during photosynthesis along with the far more abundant stable isotopes of carbon 13 CO 2 and 12 CO 2 . Once harvested, the biobase source material such as corn or sugarcane will no longer take up 14 CO 2 and will retain the majority of the 14 C absorbed with only a minor loss through the continuous process of radioactive decay. 14 C has a half‐life of 5730 years, the time required to halve the 14 C content, and becomes undetectable, or indiscernible from background activity, after approximately 10 half‐lives or 57 000 years. Carbon‐containing materials older than this have no measurable 14 C activity and are considered fossil in origin. This is a far shorter time than is required for the maturation of petroleum hydrocarbons or other fossil fuels so they are in essence at or below background 14 C activity by the nature of their long‐term formation. This paper discusses the use of 14 C and stable isotope of carbon to determine the mixing of biobase and fossil fuel‐derived materials.