Wheat straw/HDPE co-reaction synergy and enriched production of aromatics and light olefins via catalytic co-pyrolysis over Mn, Ni, and Zn metal modified HZSM-5

The co-reaction synergy of wheat straw (WS) and high-density polyethylene (HDPE) plastic waste with varying mass ratios were evaluated at 550 °C in a fixed bed pyrolyzer reactor. Ex-situ catalytic co-pyrolysis of WS and HDPE feed mix (3:1) at a high feed to catalyst ratio (10:1) was performed over Mn, Ni, and Zn (1, 5, and 10 wt%) metal-modified HZSM-5 at 550 °C to study the effect of metal promotors variations on the production of aromatics and light olefins. The prepared catalysts were characterized by employing XRD, N2 physisorption, NH3-TPD, H2-TPR, and UV-Vis analytical techniques. The results obtained in the present work indicated that 1%-Zn modified HZSM-5 produced a more relative proportion of aromatics (25.12%) in the co-pyrolysis oil organic phase, followed by 5% Ni and 5%-Zn-loaded HZSM-5 at 16.22% and 15.76% respectively. Furthermore, 5% Ni-HZSM-5 has shown higher deoxygenation ability (58.43%) in reducing the oxygenates formed, followed by 5% Mn (40.96%) and 1% Zn (35.37%) respectively. While, 5% Mn-HZSM-5 generated pyrolytic gases with higher volumetric compositions of (C2-C4) light olefins at 15.84%, followed by 1% Mn (13.97%) and 10% Ni (13.61%) respectively and these volumetric yields were strongly correlated with intermediate acidity of catalysts. The physical properties (e.g. HHV ~ 41–43 MJ/kg) of the resultant organic fraction of catalytic co-pyrolysis bio-oil are almost analogous to conventional fuels such as diesel and light fuel oil (LFO). Additionally, the resultant catalytic pyrolytic gases possessed excellent calorific value (LHV ~ 30–31 MJ/Nm3) and are comparable to natural gas. Overall, the present study has successfully demonstrated the promising nature of the catalytic co-pyrolysis process for the conversion of biomass and waste plastic into useful chemicals and fuels.