Hydrogen from waste plastics by way of pyrolysis-gasification

A screw kiln continuous reaction system was used to investigate the production of hydrogen from a representative waste plastic (polypropylene). The reactor system consisted of two stages, with pyrolysis of the plastic in the firststage screw kiln, followed by catalytic gasification of the product pyrolysis gases in the second stage. Two catalysts (a laboratory prepared Ni-Mg-Al catalyst and a commercial nickel catalyst) were used and the process conditions of gasification temperature and water injection rate were investigated. The results showed that the introduction of catalyst into the gasification stage dramatically increased the hydrogen production. The gas and hydrogen production and amount of reacted water per hour were increased with the increase of the gasification temperature from 600 to 900°C for both the Ni-Mg-Al and the commercial nickel catalysts. The rate of water injection was also shown to be critical for hydrogen production. The maximum hydrogen produced was 52% of the maximum theoretical hydrogen available in the polypropylene, representing 22̇38 g of hydrogen per 100 g polypropylene, obtained with the Ni-Mg- Al catalyst, at 800°C gasification temperature and with 28̇46 g/h water injection rate.