Pyrolysis of the rejects of a waste packaging separation and classification plant

Plastic wastes coming from a waste packaging separation and classification plant have been pyrolysed in a semibatch nonstirred autoclave, swept by a continuous flow of N2. The plastic waste contains 39.5% PE, 34.2% PP, 16.2% PS and EPS, and some other minor materials. Temperatures in the range 400–600 °C have been explored, and it has been found that over 460 °C total thermal decomposition of the waste plastics takes place. Three catalysts have been tested: HZSM-5, red mud and AlCl3. Solid yields about 5–7%, liquid yields in the range 40–70% and gas yields in the range 12–24% were obtained. The liquid products were a mixture of C5–C20 compounds with a very high proportion of aromatics (>70%). Such liquids contain significant amounts of valuable chemicals such as styrene (20–40%), toluene (9–15%) and ethylbenzene (7–16%) and have rather high GCV (40–43 MJ kg−1). Thermal pyrolysis oils were a wax-like product which solidified at room temperature, whereas the oils obtained with any of the catalysts were less viscous and maintained in liquid state at room temperature. HZSM-5 favoured gas production and, increased the aromaticity and decreased the carbon number of the oils. AlCl3 did not modify pyrolysis yields but gave rise to lighter liquids. Red mud produced higher liquid yields and the liquids were less viscous, but it was not observed a clear effect on the carbon number of the oils.