Pyrolysis is a promising way of waste transformation into new valuable products. Pyrolytic oil is a mixture of hundreds of compounds and it requires detailed and accurate characterization for future applications. One of the most widely used techniques is mass spectrometry in combination with electron ionization. Tuneable ionization provides benefits including additional structural information and validation of molecular ion due to limited fragmentation at lower energies compared to conventional 70 eV, which provides spectral matches towards libraries. This approach was applied to the compounds identification and group characterization of virgin plastics polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), high-density polyethylene (HDPE), low-density polyethylene (LDPE) and their mixture. The use of lower ionization energy was beneficial for distinction of alkanes, iso-alkanes and aromatics. On the contrary to 70 eV, significantly higher fragmentation in branching of iso-alkanes at 12 eV was observed with higher yield of molecular ion also for n-alkane. More than 50 % of detected peaks were identified up to the retention time of icosane. The main analytes of produced pyrolysis oil were monoaromatic (from PVC and PS), alkene/cycloalkane (from PP and mixture). In the case of HDPE and LDPE the main compounds were 1-n-alkenes and n-alkanes. The applied methodology reveals compound group, carbon chain length and degree of unsaturation with higher confidence and success rate compared to traditional nominal mass 70 eV datasets.
Keywords: Compound identification; GC-HRMS; Group characterization; Low energy electron ionization; Pyrolysis oil; Virgin plastic (PVC, PP, PS, HDPE, LDPE).
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