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

Abstract

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 gplastic -1 at 5 wt % Fe loading to 122 mmol gplastic -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 gplastic -1, except for the Fe/MCM-41 catalyst, which produced only 88 mmol gplastic -1 of hydrogen yield.