Chemical characterization of condensed phases from waste plastics pyrolysis

Industrial plastic wastes (PE, PP and PET) were pyrolysed in lab scale reactors as well as in Ri.Pla.Id industrial plant in the temperature range 390-450 °C, with and without a zeolite catalyst. The condensed liquids, which appear as oils, were collected in cooled traps and, after thermogravimetic analysis (TGA), were dissolved in organic solvents for further chemical characterization by different techniques. After a screening of different organic solvents, dichloromethane (DCM) was selected as the best solvent for the samples. DCM solutions were analysed by gas chromatography-mass spectrometry (GC-MS) for the determination of alkane, alkene and aromatic content. The results have been compared with the predictions from literature kinetic models. It can be observed that the catalyst causes a decrease in the concentration of aliphatics with a number of C atoms greater than 25 and also of alkenes, thus improving the quality of the liquid products and making them more similar to a typical diesel oil. The total concentration of aromatics is about 5%, with a prevalence of substituted single-ring species (in particular toluene) and does not change much due to the effect of the catalyst. The chromatographic analysis of the samples highlighted a good quality of the pyrolysis liquid products produced at 390 °C, despite, unfortunately, rather low yields. On the contrary, the products obtained at 430 °C were worse and the effects of the catalyst modest, but the yields adequate (about 70%). The analysis of the tars produced has also shown that the effects of the catalyst at 430 °C appear not to be negligible. The results of the TGA tests are in good agreement with those of the GC-MS analyses, confirming the possibility of obtaining a liquid product with characteristics similar to a diesel fuel through catalytic pyrolysis of waste plastics.