Pyrolysis and combustion of waste lubricant oil from diesel cars: Decomposition and pollutants

Pyrolysis and combustion of waste lubricant oil were studied due to its important potential value as a fuel. A thermogravimetric analysis in nitrogen atmosphere conditions and with different proportions of nitrogen:oxygen (N2, N2:O2 mixtures at 4:1 and 9:1 ratios), different weights (1, 2.5 and 5 mg) and different heating rates (5, 10 and 15 °C min−1) were carried out to study the thermal decomposition. Both pyrolysis and combustion can be represented in two processes: in the first process, a volatilization of the oil takes place (this depends on the initial mass and the heating rate) and in the second process there is a decomposition, which is a different process in combustion from the process in pyrolysis.The identification of the volatile and semivolatile compounds from pyrolysis and combustion of used diesel oil was carried out in a tubular reactor at 500 and 850 °C. On the one hand, the semivolatile PAH compounds (naphthalene, phenanthrene, anthracene, etc.) were detected as much in pyrolysis as in combustion (850 °C), but the most highly carcinogenic is benzo(a)pyrene which was only found in pyrolysis at 850 °C. On the other hand, the levels of PCDD/Fs and dioxin-like PCBs were estimated after a fuel-rich combustion process at around 113 pg WHO-TEQ g−1 burnt oil (corresponding to 80 pg I-TEQ g−1) and 3 pg WHO-TEQ g−1 burnt oil, respectively. The PCDD/Fs concentration in the raw sample was estimated at around 7–16 pg WHO-TEQ g−1 used oil (or 6–13 pg I-TEQ g−1) and PCBs were not detected.