Average molecular characterization of the soluble organic fraction of mature diesel particulate matter

This work examines the chemical composition and the average structural parameters (ASP) of the soluble organic fraction (SOF) extracted from mature diesel particulate matter (DPM) gathered from a 20 kW diesel power plant operating separately with diesel fuel (containing 10% by vol. of palm oil biodiesel -B10-) and two aromatic-free fuels (crude palm oil -CPO- and crude jatropha oil -CJO-). SOF samples were subjected to SARA test (Saturates-Aromatics-Resins-Asphaltenes), 1H NMR, vapor pressure osmometry (VPO), elemental analysis (CHNOS), FTIR and DRIFT spectroscopy. All SOF samples exhibited higher concentration of resins followed by saturates, while aromatic and asphaltene fractions were small. CHNOS analysis showed that sulfur content was negligible, while nitrogen content was below 0.67% w/w. 1H NMR showed that hydrogen atoms of carbon in α, β and γ positions were lower for CPO compared to B10 and CJO; however, the SOF from CPO exhibited the highest content of H-olefins. The number of fused aromatic rings (Ra) of B10 SOF was higher (four rings -pyrene-) in comparison with CJO (three rings -phenanthrene-) and CPO (two rings -naphthalene-). B10 SOF exhibited the highest average number of branches attached to aromatic rings (seven branches) compared to CJO and CPO (three). The average number of methyl groups per branch was similar in all SOF samples. The combination of these analytical techniques allowed to determine the SOF average molecular structure and additionally, the boiling temperature was calculated using a group contribution method. Therefore, a minimum devolatilization temperature for thermal analysis of 600 °C for B10 and for crude vegetable oils (CVOs) DPM is proposed.