engleski

Comparison of methods for determination of biogenic fraction in liquid fuels

A method of direct measurement of14C activity concentration via liquid scintillation counting (LSC) is recognized as good and fast method for determination of biogenic component in liquid fuels. Two laboratories that used this14C technique participated in this survey: Laboratory from University of Novi Sad (UNS), Serbia and Laboratory from Ruđer Bošković Institute (RBI), Croatia. Each laboratory used its own calibration methods on the same set of samples (produced diesel-based bio-fuels and commercially available domestic oils). From the obtained results it can be concluded that each method which uses 14C technique for determination of biogenic component in liquid fuels has its advantages and disadvantages. RBI data evaluation method is based on two calibration curves, for purely biogenic and purely fossil liquids, and the calibration does not depend on the exact chemical composition of the organic liquid. The limits of the method are defined by the SQP(E) of approximately 690. Below this value the count rates of biogenic and fossil liquids become close to each other or even indistinguishable from one another and the obtained results for biogenic fractions are not reliable. In this intercomparison UNS used two different methods, one for produced bio-diesels and the other one for domestic oils. UNS data evaluation method is very dependent on the composition of the examined fuels, so the obtained results with the "two-step" method were relatively good in the case of diesel mixtures with biogenic component. In the case of biogenic oil samples (bought on market), UNS "two-step" method did not give realistic results, and with the "one-step" method the limitation is large quenching in the samples, so for the samples with SQP(E) less than 700 this method could not give expected results. Samples prepared with liquid fuels are usually colored and the main challenge for determination of biogenic component in both laboratories is handling of highly quenched liquids.

LSC ; liquid fuels ; 14C ; biogenic component

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