Thermo-catalytic pyrolysis of biomass and plastic mixtures using HZSM-5

The catalytic effect of HZSM-5 zeolite was studied on the thermal decomposition of model waste mixtures of plastics (composed of PE, PP, and PET) and biomass (composed of newspaper, cardboard, and pine sawdust). The influence of temperature and catalyst ratio as well as the hindering effect of cellulose and lignin on the catalytic decomposition of plastic waste were studied applying analytical pyrolysis at low and high heating rate by thermogravimetry/mass spectrometry (TG/MS) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), respectively. The products of laboratory scale batch pyrolysis and thermo-catalytic pyrolysis were analyzed in details and compared. HZSM-5 catalyst reduced the thermal stability of plastic waste, but the catalytic effect was blocked when 50% cellulose or 10% lignin were mixed in the plastic waste. Principal component analysis (PCA) has been applied to reveal correlations between the composition of pyrolysis products, pyrolysis temperature and proportion of the applied catalyst. It was established that the hindering effect of biomass could be compensated by applying higher catalyst ratio. In a batch reactor, the use of HZSM-5 catalyst led to a significant increase in the yields of volatiles (both gases and pyrolysis oil); moreover aromatization or isomerization effects have been observed. Aromatic compounds were produced to a reduced extent by thermo-catalytic pyrolysis of biomass-containing plastic waste compared to that of plastic waste indicating that the cellulose and lignin components of the waste lower the HZSM-5 catalyst activity.