H2 production by high-temperature pyrolysis of PEEK

摘要

Polyether ether ketone (PEEK) as an emerging engineering plastic has shown a big potential in recent years to produce Hydrogen (H2) for clean energy through high-temperature pyrolysis. This paper investigates the H2 production capacity and mechanism due to the pyrolysis of PEEK at high temperatures. The results revealed that PEEK has two pyrolysis stages in the temperature ranges of 783-905 K and 905-1173 K respectively. In the first stage, approximately 45 mass loss was observed with an activation energy of 210.55 kJ/mol. However, only 0.93 mg/g of H2 was produced. According to fourier transform infrared, the main source which generated that H2 is the small amount of H atoms caused by the C-H bonds cracking. The H atoms were then recombined into H2 in the gas phase. The second stage of pyrolysis predominates the productions of H2, with around 11 mass loss and an activation energy of 411.47 kJ/mol occurred. The H2 yield reaches 9.84 mg/g at 1073 K in this stage. The H2 is mainly generated by dehydrogenation of benzene rings and a small amount of-CH3 and-OH bonds. As the temperature raised, free radicals released by the breakdown of PEEK network recombined, suggesting three potential pathways for H2 production: (1) the dehydrogenation recombination of phenoxybenzene radicals to form dibenzofuran, (2) the recombination of benzene radicals to form biphenyl and naphthalene, and (3) the reaction of phenol and benzene at high temperature to form dibenzofuran, leading to recombination of H atoms into H2. The overall experiment results indicate that the H2 production of PEEK primarily occurs during the high-temperature pyrolysis stages with low mass loss. This finding shed new light on the mechanisms of H2 production and resource utilization of plastics for the future.