Converting polyolefin mixtures into fuels via a closed-system pyrolysis process

This work examined the effects of the experimental conditions in an oxygen-free closed system on the pyrolysis process of a polyolefin mixture (PO) composed of 40 % medium-density polyethylene (MDPE), 35 % low-density polyethylene (LDPE), and 25 % polypropylene (PP). The goal was to get the best yields and quality of gasoline and diesel-type fuels. The effect of the autogenic pressure was studied by varying the temperature (400, 425, and 450 °C) and reaction time (1, 5, 15, 30, and 45 minutes). The effect of the initial pressure (10, 20, 30, 40, and 50 bar) was studied at 425 °C and 60 minutes. The products obtained were gas, oil, and wax. The presence of coke was not observed. The preferred product for fuel production was oil. The temperature of the pyrolysis process decreased to 400–450 °C in an oxygen-free closed system from a usual 550 °C when the procedure was conducted in an open system. Gas and liquid chemical composition and simulated distillation behaviors were also studied in both processes. In the autogenic pressure process, the optimal variables for higher yield and quality of the fuel-like products were 425 °C, 30–45 min, and up to 33 bar. The effect of the initial pressure showed that higher pressures did not present an advantage in the PO cracking process. While the autogenic pressure was the result of an increasing gas formation and therefore presented an important effect on the products obtained, higher initial pressures (above 10 bar) seemed not to be required for the increment in the yield or quality of the products.