In-situ sulfur fixation using aluminum-based sorbents during the pyrolysis of sulfur-containing waste polymers

Hazardous sulfur species (H₂S, thiophenes, etc.) are released during pyrolysis of sulfur-containing plastics (PPS, etc.), challenging their recycling. Aluminum-based sorbents (M-Al-O, where M = Ca, Zn, Cu, Fe) were evaluated for in-situ sulfur capture performance. Results showed that all sorbents increased sulfur in char to 71.09-79.67%, compared to 48.56% without sorbent. The overall sulfur regulation performance followed the order: Cu-Al-O > Fe-Al-O > Ca-Al-O > Zn-Al-O. Ca-Al-O minimized sulfur in tar (6.71%) by inhibiting oligomer/thiophene formation. Zn-Al-O promoted PPS depolymerization but showed limited cracking activity, raising tar sulfur (8.19%). Cu-Al-O and Fe-Al-O achieved high H₂S fixation (>92.40%). Cu-Al-O facilitated decomposition of dimers and trimers while promoting polycyclic thiophenes. Fe-Al-O exhibited limited tar sulfur suppression (7.45%) due to ineffective oligomer cracking. Based on these complementary mechanisms, a synergistic Ca-Cu-Al-O composite sorbent was designed. Sulfur fixation efficiency increased with sorbent loading (74.18-93.67%). At a 1:1 ratio, sulfur fixation efficiency reached 86.24%, and the tar sulfur concentration was reduced to 44,480 ppm, below the calculated additive value of 48,458 ppm. In this system, CuAl₂O₄ promoted the cracking of oligomers, reducing trimer content by 61.51-94.66%, while Ca₃Al₂O₆ suppressed thiophene formation, decreasing benzodibenzothiophene intensity by 2.33-52.3%. Sulfur was fixed as CaS, which mitigated poisoning of copper active sites and preserved their catalytic activity for oligomer cracking. This work elucidates the role of aluminum-based sorbents in regulating sulfur transformation and provides a viable strategy for clean recycling of sulfur-containing plastics.