Characterization of chemical composition of fuel biofractions by different analytical techniques

The increased use of liquid biofuels has created a need for an accurate and a reliable technique for determining blend ratios of biofuel and fossil fuel due to technical reasons related to car engines and due to legislative reasons. The true portion of biological carbon in a fuel can be determined reliably only by radiocarbon measurement. Radiocarbon is created in upper atmosphere by cosmic radiation and is transferred to flora and fauna via photosynthesis. When an organism dies, the radiocarbon in its body starts do decay. Because the half-life of radiocarbon is very long and because biofuels are manufactured from relatively young feedstock materials, it is possible to calculate the biofraction of a fuel sample by determining its radiocarbon contents. The most popular techniques for determining this are, to date, accelerator mass spectrometry and liquid scintillation counting. Liquid scintillation counting is cheaper and easier to use, but in low concentrations the accuracy is not as good. In addition, the technique has the drawback of quenching effects. Accelerator mass spectrometry is the most accurate method, but the disadvantages are the price and size of the equipment and labor-intensive sample preparation process, which can take several days. In addition to the radioanalytical techniques, the biofractions of biofuels have been determined by infrared, Raman, nuclear magnetic resonance, X-ray and fluorescence spectroscopy and by gas and liquid chromatography, but these techniques have more limited applicability. In these techniques, the determination is usually based on direct or indirect detection of fatty acid methyl ester groups. However, the newer generation biofuels do not anymore contain these groups and their chemical composition is similar to fossil fuels. In addition, by using these techniques one cannot determine e.g. whether the ethanol in petrol blend is in fact manufactured from biological or fossil sources. In the experimental section of the thesis an elemental analyzer -based sample preparation method was developed, by which the time spent on sample preparation for accelerator mass spectrometer was decreased when compared to previous method, described by standard ASTM D6866-10. The biodiesel samples were combusted in the elemental analyzer and the carbon dioxide collected cryogenically. The carbon dioxide was reduced to graphite and their radiocarbon contents was measured by accelerator mass spectrometry. In addition, the results from elemental analyzer method were compared to previous results by closed-tube-combustion method. It was noticed that the elemental analyzer method was more accurate, faster and easier to use.