Oxidative stability of hydrocarbons produced by pyrolysis of polypropylene

The instability of liquid oils issued from the pyrolysis of plastics usually leads to the degradation and the deterioration of their different properties. In this study, the stability of oils produced from the pyrolysis with and without reflux of polypropylene (PP) was investigated in a standard test device called PetroOxy. This work compares the stability of PP liquid oils with kerosene throughout their induction period and hydroperoxide (ROOH) content, two well-known stability parameters. Moreover, experimental investigations of the impact of a stabilizer (BHT = butylated hydroxytoluene) on the same stability parameters were achieved. A titration method and GC-MS were used to quantify ROOHs and to identify the oxidized liquid compounds, respectively. PetroOxy tests with BHT showed an enormous influence of BHT on the oxidation stability compared to all other oxidative tests. Adding 500 ppm of BHT multiplied the induction period by 5.9, 4.3, 10.7 and 6.7 for reflux liquid oils, no-reflux liquid oils mixed with kerosene, reflux liquid oils mixed with kerosene and pure kerosene respectively. The ROOH concentration was divided by up to 16.9 for reflux liquid oil when BHT was used. Based on the results, it can be concluded that the liquid oils obtained by pyrolysis with reflux are less stable than without reflux, and both of them are less stable than kerosene used as reference model. But using kerosene as solvent mixed with liquid oils obtained by pyrolysis with and without reflux increases their oxidative stability. The use of BHT as an antioxidant contributes to make these oils compatible for use as fuels.