Pyrolysis and in-line catalytic steam reforming of polystyrene through a two-step reaction system

•Pyrolysis and in-line reforming strategy efficiently produces H2 from PS.•Full conversion of PS pyrolysis products is attained in the reforming step.•A H2 yield of 82.5% and a production of 291 g kgPS−1 are obtained.•Catalyst deactivation reduces conversion to 85.6% after 96 min.•Deactivation rate feeding PS is faster than previously reported for HDPE.

Hydrogen production from polystyrene (PS) has been studied following continuous pyrolysis and in-line steam reforming. The first step was carried out at 500 °C in a conical spouted bed reactor and the subsequent reforming one was performed in a fluidized bed reactor on a commercial Ni catalyst at 700 °C. The effect space time and time on stream have on the reaction indexes (reforming conversion, yields of H2, CO2, CO, CH4 and hydrocarbons, and H2 production) has been determined. Furthermore, the process performance has been compared with the results obtained in a previous study conducted by feeding HDPE under the same conditions. Full reforming of PS derived volatiles and high H2 production of 29.1  wt% were attained at zero time on stream. However, a significantly poorer performance of the catalyst was observed after 100 min continuous operation, with the decrease in activity being more acute than that observed for HDPE in a previous study. This deactivating behaviour has been related to the aromatic nature of PS thermal degradation products. The cokes deposited in the degradation of PS and HDPE have been analysed by means of temperature programmed oxidation (TPO) and electron microscopy, and the higher deactivation rate observed in the case of PS has been related to the condensed and encapsulating nature of the coke formed from aromatic hydrocarbons.