Hydrogen/Syngas Production from Different Types of Waste Plastics Using a Sacrificial Tire Char Catalyst via Pyrolysis–Catalytic Steam Reforming

Single plastics and mixed waste plastics from different industrial and commercial sectors have been investigated in relation to the production of hydrogen and syngas using a pyrolysis–catalytic steam reforming process. The catalyst used was a carbonaceous char catalyst produced from the pyrolysis of waste tires. Total gas yields from the processing of single plastics were between 36.84 and 39.08 wt % (based on the input of plastic, reacted steam, and char gasification) but those in terms of the gas yield based only on the mass of plastic used were very high. For example, for low-density polyethylene (LDPE) processing at a catalyst temperature of 1000 °C, the gas yield was 445.07 wt % since both the reforming of the plastic and also the steam gasification of the char contributed to the gas yield. The product gas was largely composed of H2 and CO, i.e., syngas (∼80 vol %), and the yield was significantly increased as the char catalyst temperature was raised from 900 to 1000 °C. Hydrogen yields for the processing of the polyolefin single plastics were ∼130 mmol gplastic–1 at a catalyst temperature of 1000 °C. The pyrolysis–catalytic steam reforming of the industrial and commercial mixed plastics with the tire char catalyst produced hydrogen yields that ranged from 92.81 to 122.6 mmol gplastic–1 and was dependent on the compositional fraction of the individual plastics in their mixtures. The tire char catalyst in the process acted as both a catalyst for the steam reforming of the plastics pyrolysis volatiles to produce hydrogen and also as a reactant (“sacrificed”), via carbon-steam gasification to produce further hydrogen.