| Popis: |
An increased level of CO2 concentration in the atmosphere is a direct consequence of intense fossil-fuel combustion over a last century. Search for alternative energy sources and reduction of emission of CO2 from fossil fuels by production of energy from biogenic material are topics of intense current studies. European Union stimulates the production and use of biofuels by lower excise and income tax relief. In this context there is a need for control of producers and dealers of various types of fuels and independent determination of the biogenic fraction in fuel. Here, the term “biogenic” refers to a compound produced in natural processes by living organisms but not fossilized or derived from fossil resources. The fraction of the biogenic component can be determined by measuring the 14C content (EN 15440:2011) since bio-fuels reflect the 14C activity of atmospheric CO2 during the plants’ growth period, while fossil fuels do not contain 14C. Therefore, a simple linear mixing curve with well-defined end members is obtained. Any measuring technique for 14C content, widely used in the radiocarbon dating laboratories, may be used for determining the bio-based content. All these techniques are accurate and precise, but are also time-consuming and expensive, so there is a need for simple, fast, reliable, sensitive, accurate, and not expensive technique. When liquid fuel is concerned, a direct measurement of fuel mixed with an appropriate scintillator by LSC is possible. However, various types of fuel matrices and various blends show different quenching properties (due to different colours) resulting in rather complicated data evaluation procedure which depends on the type of the matrix/blend mixture. To avoid this problem we have developed a novel technique for direct measurement of any liquid fuel by liquid scintillation counting. The idea is to use various purely biogenic compounds of different colours and quenching properties to construct the “modern calibration curve”, as well as various purely fossil liquids to construct the “background calibration curve”. The fraction of the biogenic component in an unknown sample is then determined as the ratio of net count rates of the sample and the biogenic sample having the same quenching properties. The proposed technique has been validated by preparing various mixtures of modern and fossil samples, and the satisfactory agreement between the expected and measured biogenic fractions has been achieved. |
