engleski

Limitation and comparison of two methods for determination of biogenic fraction in liquid fuels by 14C

European Union’s promotion of the use of sustainable and renewable resources requires use of at least 10 % of synthesized biodiesel in liquid fuels by the year 2020. This legislation has stimulated various types of petrodiesel and bio-based component blends production, and development of methods for exact, effective and reliable quantification of biodiesel content. The method for determination of the biogenic fraction in liquid fuels by direct measurement of the 14C activity concentration via liquid scintillation counting (LSC) technique was developed in few laboratories worldwide. It is based on different 14C signatures of the two components: the biogenic component reflects the modern atmospheric 14C activity, and no 14C is present in fossil fuels. The quantity of 14C in the fuel is the criterion for bio-fuel presence. This method is regarded as fast, simple, accurate and sensitive determination procedure for the mass assessment of biogenic fraction in biofuels. Laboratory for low radioactivity at the Department of Physics, University of Novi Sad (UNS), Serbia, and Laboratory for low-level radioactivities of the Ruđer Bošković Institute (RBI) in Zagreb, Croatia have developed two different methods for biogenic fraction determination in liquid fuels [1, 2]. Both laboratories tested the stability of prepared samples by measuring the same samples after some period of time and used the same set of mixtures with the known fractions of the biogenic component, i.e. FAME produced from either sunflower oil or lard fat. The comparison revealed in general good agreement of the results and also indicated some constraints of the methods used, The RBI evaluation technique is limited by the SQP(E) values lower than 600 where the count rates of the biogenic and the fossil samples become indistinguishable. The lower the SQP(E), the larger the relative differences between the measured and the expected biogenic fraction for 600 < SQP(E) < 700. The biogenic fraction can be successfully determined at SQP(E) > 700. The two-step calibration procedure that UNS used implements quench correction and therefore offers more reliable 14C determination in fuels in comparison to one-step calibration method. The application of these calibration curves is limited to samples with chemically identical bio and fossil components. It can be used for precise biogenic fraction determination in examined fuel samples if the components of the fuel mixture are well known in advance. The obtained results showed very important limitation of used methods as the samples have to be analyzed as soon as possible after preparation in order to obtain reliable results.

14C ; liquid fuels ; biogenic fraction ; intercomparison

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