Hydrogen Production by Three-Stage (i) Pyrolysis, (ii) Catalytic Steam Reforming, and (iii) Water Gas Shift...

The three-stage (i) pyrolysis, (ii) catalytic steam reforming, and (iii) water gas shift processing of waste plastic for the production of hydrogen have been investigated. The (i) pyrolysis and (ii) catalytic steam reforming process conditions were maintained throughout, and the experimental program investigated the influence of process conditions in the (iii) water gas shift reactor in terms of catalyst type (metal-alumina), catalyst temperature, steam/carbon ratio, and catalyst support material. The metal-alumina catalysts investigated in the (iii) water gas shift stage showed distinct maximization of hydrogen yield, which was dependent on the catalyst type at either higher temperature (550 °C) (Fe/Al₂O₃, Zn/Al₂O₃, Mn/Al₂O₃) or lower temperature (350 °C) (Cu/Al₂O₃, Co/Al₂O₃). The highest hydrogen yield was found with the Fe/Al₂O₃ catalyst; also, increased catalyst Fe metal loading resulted in improved catalytic performance, with hydrogen yield increasing from 107 mmol g_plastic ^-1 at 5 wt % Fe loading to 122 mmol g_plastic ^-1 at 40 wt % Fe/Al₂O₃ Fe loading. Increased addition of steam to the (iii) water gas shift reactor in the presence of the Fe/Al₂O₃ catalyst resulted in higher hydrogen yield; however, as further steam was added, the hydrogen yield decreased due to catalyst saturation. The Fe-based catalyst support materials investigated alumina (Al₂O₃), dolomite, MCM-41, silica (SiO₂), and Y-zeolite; all showed similar hydrogen yields of ∼118 mmol g_plastic ^-1, except for the Fe/MCM-41 catalyst, which produced only 88 mmol g_plastic ^-1 of hydrogen yield.