Composite waste recycling: Predictive simulation of the pyrolysis vapours and gases upgrading process in Aspen plus

Waste generation is one of the greatest problems of present times, and the recycling of carbon fibre reinforced composites one big challenge to face. Currently, no resin valorisation is done in thermal fibre recycling methods. However, when pyrolysis is used, additional valuable compounds (syngas or H₂-rich gas) could be obtained by upgrading the generated vapours and gases. This work presents the thermodynamic and kinetic multi-reaction modelling of the pyrolysis vapours and gases upgrading process in Aspen Plus software. These models forecast the theoretical and in-between scenario of a thermal upgrading process of an experimentally characterised vapours and gases stream (a blend of thirty-five compounds). Indeed, the influence of temperature (500 °C-1200 °C) and pressure (ΔP = 0, 1 and 2 bar) operating parameters are analysed in the outlet composition, residence time and possible reaction mechanisms occurring. Validation of the kinetic model has been done comparing predicted outlet composition with experimental data (at 700 °C and 900 °C with ΔP = 0 bar) for H₂ (g), CO (g), CO₂ (g), CH₄ (g), H₂O (v) and C (s). Kinetic and experimental results show the same tendency with temperature, validating the model for further research. Good kinetic fit is obtained for H₂ (g) (absolute error: 0.5 wt% at constant temperature and 0.3 wt% at variable temperature) and H₂O (v) shows the highest error at variable T (8.8 wt%). Both simulation and experimental results evolve towards simpler, less toxic and higher generation of hydrogen-rich gas with increasing operating temperature and pressure.