| Résumé | Plastic pollution has become one of the main environmental problems that afflict land, waterways and oceans. Currently, about 141 megatonnes (Mt) of plastic wastes are produced annually in the world, while only about 13% of those are recycled. The great majority of plastic wastes are incinerated or dumped, which pollutes the environment. Remanufacturing or recycling is a way to reduce plastic waste, but plastics cannot be recycled endlessly. Forty percent of plastic wastes have a short life time and are contaminated with residues or contain an abundance of water. However, these contaminated plastic wastes can be converted to energy. As plastics are petrochemicals, conversion of plastic wastes to carbon free hydrogen (H₂) and other solid chemicals will not only protect the environment but also reduce greenhouse gas (GHG) emissions compared to converting plastic wastes to liquid fuel. Catalysts help to improve the product selectivity toward hydrogen or other chemicals. In this project, an experimental investigation on catalytic hydrothermal conversion of plastics to hydrogen under a supercritical water condition was carried out. Hydrothermal conversion is suitable for feedstocks with high water content, and supercritical water is able to dissolve organics. The effect of catalysts that have high selectivity toward hydrogen production was investigated. The results reveal that without a catalyst, only CO₂ was observed in the produced gas. Alkaline metals NaOH and KOH yielded gas with H₂ selectivity of 74.4% and 44.3%, respectively. More CO than H₂ vol% was formed when Raney®-Nickel 2800 was used as catalyst. Liquid selectivity also varied significantly with changing the catalyst. |
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