Abstract
Catalytic steam reforming of waste high density polyethylene for the production of hydrogen/syngas has been investigated using different zeolite supported nickel catalysts in a two-stage pyrolysis-catalytic steam reforming reactor system. Experiments were conducted into the influence of the type of zeolite where Ni/ZSM5-30, Ni/β-zeolite-25 and the Ni/Y-zeolite-30 catalysts were compared in relation to hydrogen and syngas production. Results showed that the Ni/ZSM5-30 catalyst generated the maximum syngas production of 100.72 mmol g−1plastic, followed by the Ni/β-zeolite-25 and Ni/Y-zeolite-30 catalyst. In addition, the ZSM-5 supported nickel catalyst showed excellent coke resistance and thermal stability. It was found that the Y type zeolite supported nickel catalyst possessed narrower pores than the other catalysts, which in turn, promoted coke deactivation of the catalyst. Large amounts of filamentous carbons were observed on the surface of the Ni/Y-zeolite-30 catalyst from scanning electron microscope images. In addition, the influence of Si:Al molar ratio for the Ni/ZSM-5 catalysts in relation to hydrogen and syngas yield was investigated. The results indicated that hydrogen production was less affected by the Si:Al ratio than the type of zeolite support. Also, the Ni/ZSM5-30 catalyst was further investigated to determine the influence of different process parameters on hydrogen and syngas yield via different reforming temperatures (650, 750, 850 °C) and steam feeding rate (0, 3, 6 g h−1). It was found that increasing both the temperature and steam feeding rate favoured hydrogen production from the pyrolysis-catalytic reforming of waste polyethylene. The optimum catalytic performance in terms of syngas production was achieved when the steam feeding rate was 6 g h−1 and catalyst temperature was 850 °C in the presence of Ni/ZSM5-30 catalyst, with production of 66.09 mmol H2 g−1plastic and 34.63 mmol CO g−1plastic.
Highlights
Hydrogen is an environmentally-friendly and efficient clean energy with the attraction that its combustion only releases water and energy [1]
A two-stage reaction system was reported by Wu and Williams [5] where pyrolysis of the plastics was followed by catalytic steam reforming of the pyrolysis gases and where the hydrogen production could be optimised by manipulating the process parameters of the two separate processes
Ni/zeolite catalysts were investigated in relation to hydrogen and syngas production from the pyrolysis-catalytic steam reforming of waste high density polyethylene in a two stage reactor system
Summary
Hydrogen is an environmentally-friendly and efficient clean energy with the attraction that its combustion only releases water and energy [1]. Hydrogen production from waste resources such as waste plastics and biomass instead of fossil fuels appears to be more favourable as it overcomes the environmental impact resulting from the overexploitation of non-renewable resources [2,3]. A two-stage reaction system was reported by Wu and Williams [5] where pyrolysis of the plastics was followed by catalytic steam reforming of the pyrolysis gases and where the hydrogen production could be optimised by manipulating the process parameters of the two separate processes. Dou et al [8] optimized hydrogen production from waste plastics by integrating the gasification of the plastics with a sorption-enhanced steam reforming system, where up to 88.4 vol.% of H2 gas concentration was achieved. The feasibility of the two-stage system for hydrogen production was demonstrated by Czernik et al [9], where a hydrogen yield of 34 g per 100 g polypropylene was obtained for a 10 h duration test
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