Catalytic Pyrolysis of Polyurethane Waste over SiO2/Cu for Selective Production of Aniline

This study investigated the effects of silica (SiO2) and copper-modified silica (SiO2/Cu) catalysts on the pyrolysis behavior and product distribution of polyurethane waste (PUW), focusing on the selective recovery of aniline, a valuable chemical intermediate. PUW pyrolysis was evaluated using thermogravimetric analysis (TGA) and a laboratory-scale batch reactor. Thermal degradation kinetics were analyzed using the Coats–Redfern method with four kinetic models: F1, A2, R3, and D3. TGA revealed two distinct degradation stages, with the F1 model providing the best fit for both stages. Both catalysts facilitated urethane hard-segment degradation during the first stage while promoting thermal stability and char formation during the second stage. Catalytic pyrolysis substantially increased aniline selectivity from 12.36 wt% for PUW to 29.66 wt% for PUW/SiO2 and 42.38 wt% for PUW/SiO2/Cu, attributed to the additional acidic sites introduced by Cu species. The estimated nitrogen balance showed that nitrogen recovered as aniline increased from 11.9% to 19.0% and 30.1% of the initial PUW nitrogen, respectively, while the unaccounted nitrogen fraction decreased from 64.7% to 47.2% and 38.1%. These findings suggest that SiO2/Cu selectively directs nitrogen-containing intermediates toward recoverable aniline and may potentially reduce pathways leading to harmful nitrogenous emissions, providing a promising approach for value-added and environmentally sustainable PUW recycling.