Simultaneous recovery of H₂-rich syngas and removal of HCN during pyrolytic recycling of polyurethane by Ni/Mg/Al catalysts

Polyurethanes (PUs) such as flexible (cushioning material and sponge) and rigid (different insulators) forms and elastomers (flexible tube and smartphone case) were thermally decomposed at 500 °C. The useless decomposition products were converted into H₂-rich syngas and the toxic HCN in it was removed by Ni/Mg/Al catalysts at 800 °C under 50 vol% steam/He flow. The resultant total gas production was 1411–1623 mL/g (H₂: 794–967 mL/g), which was almost 30 times larger than that obtained from simple pyrolysis of PUs where no H₂ was produced. Meanwhile, there was a drastic reduction of HCN concentration in the product gas from a maximum at 2.8 to 0.2–0.6 vol%. The excellent performance on the removal of HCN and the enhanced H₂-rich syngas production is due to the synergy between Ni, Mg, and Al in the catalysts. This approach has great promise for treating a variety of PU wastes that cannot be recycled effectively otherwise.