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

[EN] 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 (DeltaP=0, 1 and 2bar) 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 DeltaP=0bar) 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: 0.5wt% at constant temperature and 0.3wt% at variable temperature) and H2O (v) shows the highest error at variable T (8.8wt%). Both simulation and experimental results evolve towards simpler, less toxic and higher generation of hydrogen-rich gas with increasing operating temperature and pressure. The authors want to thank the Ministry of Science and Innovation of Spain (Ref. PID2019-110770RB-I00) and the Basque Government (Ref. KK-2020/00107, ELKARTEK program) for the funding to carry out the investigation. The authors also thank the financing granted to the “Sustainable Process Engineering” research group for the 2016–2021 period (Basque Government, Ref. IT993-16) and are grateful to Iñaki Múgica from Su Medioambiente (SUMA Soluciones Medioambientales, S.L.) for the technical support provided.