Recovery of carbon fibres and production of high quality fuel gas from the chemical recycling of carbon fibre reinforced plastic wastes

• Ethylene glycol is effective in the recovery of carbon fibres from composite waste.
• Depolymerisation of the resin support was up to 98%.
• Recovered carbon fibres had similar mechanical properties to virgin carbon fibre.
• Residual liquid was hydrothermally gasified using two different types of catalyst.
• Hydrothermal gasification of the liquid product yields a H2 or CH4-rich fuel gas.

A solvolysis process to depolymerize the resin fraction of carbon fibre reinforced plastic waste to recover carbon fibre, followed by hydrothermal gasification of the liquid residual product to produce fuel gas was investigated using batch reactors. The depolymerisation reactions were carried out in ethylene glycol and ethylene glycol/water mixtures at near-critical conditions of the two solvents. With ethylene glycol alone the highest resin removal of 92.1% was achieved at 400 °C. The addition of water to ethylene glycol led to higher resin removals compared to ethylene glycol alone. With an ethylene glycol/water ratio of 5, at 400 °C, resin removal was 97.6%, whereas it was 95.2% when this ratio was 3, at the same temperature. The mechanical properties of the recovered carbon fibre were tested and showed minimal difference in strength compared to the virgin carbon fibre. The product liquid, containing organic resin degradation products was then subjected to catalytic supercritical water gasification at 500 °C and 24 MPa in the presence of NaOH and Ru/Al2O3 as catalysts, respectively. Up to 60 mol.% of H2 gas was produced with NaOH as catalyst, and 53.7 mol.% CH4 gas was produced in the presence of Ru/Al2O3.

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