Valorization of 3D printing filament waste into syngas via CO₂-assisted pyrolysis

Three-dimensional (3D) printing is adopted in manufacturing field due to its ability to rapidly fabricate complex objects. However, a substantial amount of polymeric waste derived from 3D printing process and its limited recyclability have raised environmental concerns. This study proposes a strategic approach for the valorization of 3D printing waste into pyrolytic gas by employing CO₂ as a reaction medium. A commercial 3D printing filament (3DPF) was used as a model compound of 3D printing waste and identified as acrylonitrile-butadiene-styrene (ABS) by FT-IR analysis. Thermo-gravimetric analysis (TGA) suggested that∼98 wt% of 3DPF are volatilized and reallocated into pyrolytic oil and gas. In single-stage pyrolysis, the volatiles from 3DPF predominantly converted into pyrolytic oil, while the gas yield suppressed (<0.5 %) due to insufficient thermal cracking. For enhancement in the yield of pyrolytic gas, experimental configuration was modified into double-stage pyrolysis. Under the CO₂ condition, CO enhancement was observed though 3DPF contains no intrinsic oxygen content. This CO evolution was attributed to the homogeneous reactions between CO₂ and volatiles released from the 3DPF. To accelerate homogeneous gas phase reaction and enhance the yield of pyrolytic gas, a Ni/Al₂O₃ catalyst was adopted in this study. Catalytic pyrolysis enhanced H₂ and CO formations by the catalytically expedited homogeneous reactions, while suppressing the formations of aromatic, nitrogen-containing compounds, and PAHs in pyrolytic oil. These experimental observations suggests that CO₂ can be used as an effective reactant for converting polymeric waste into pyrolytic gas, providing an environmentally benign platform for 3D printing waste management.