Effects of phosphorus-modified HZSM-5 on distribution of hydrocarbon compounds from wood–plastic composite pyrolysis using Py-GC/MS

• Waste WPC was converted into reusable hydrocarbons by catalytic pyrolysis.
• Hydrocarbon selectivity was strongly influenced by reaction conditions in pyrolysis.
• Phosphorus-modified HZSM-5 favored light aliphatics (C4-C12) formation.
• Aliphatics selectivity increased with the increasing P content in modified HZSM-5.

ZSM-5 zeolite is an efficient catalyst for both biomass deoxygenation and polyolefins cracking in pyrolysis process. In this study, wood–plastic composite (WPC), composed mainly of woody materials and thermoplastic polymers, was pyrolyzed using Py-GC/MS over phosphorus-modified HZSM-5 (P-HZSM-5) with varying P loadings (from 0 to 10 wt.%). The catalysts were prepared by wet impregnation method and characterized by XRF, XRD and NH3-TPD. The effects of pyrolysis temperature, time, heating rate, catalyst to WPC ratio and P loadings on the hydrocarbon distribution of WPC pyrolysis were studied. Pyrolysis conditions have significant effects on hydrocarbon distribution. Parent HZSM-5 facilitated aromatics formation, while P-HZSM-5 favored the formation of light aliphatic hydrocarbons (C4-C12). The yields of C4-C12 increased first with rising pyrolysis temperature from 450 to 550 °C, then decreased over 550 °C. Similarly, C4-C12 yields increased during the pyrolysis time from 15 to 30 s and decreased with the further prolonged time. A low heating rate (0.002 °C/ms) favored the formation of light aliphatic hydrocarbons, while high heating rates (>0.2 °C/ms) favored the formation of aromatics. Increasing catalyst to WPC ratio augmented aromatic selectivity. Hydrocarbon distribution strongly depended on the catalyst’s acidity, adjusted by varying P loading in P-HZSM-5. The highest yield of C4-C12 was obtained while using P-HZSM-5 with P loading of 3.5 wt.%.