Catalytic Biochar and Refuse-Derived Char for the Steam Reforming of Waste Plastics Pyrolysis Volatiles for Hydrogen-Rich Syngas

Abstract

High-density polyethylene (HDPE) was pyrolyzed in a fixed-bed reactor and the derived pyrolysis volatiles passed directly to a second-stage fixed-bed reactor for catalytic steam reforming with the aim to produce hydrogen-rich syngas. The catalysts used were biochar produced from the pyrolysis of waste biomass and solid waste char produced from the pyrolysis of processed municipal solid waste in the form of refuse-derived fuel (RDF). The influence of char catalyst temperature and steam input were used to optimize the production of H2 syngas. Other types of waste plastics (low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET)) were also investigated to compare with the production from HDPE. The highest yields of syngas (H2, CO) were produced at 3.83 g gplastic-1 for biochar as the catalyst and 2.73 g gplastic-1 for RDF char as the catalyst, when the steam input was 10 g h-1 gcatalyst-1 and catalyst temperature was 1000 °C. Increasing amounts of steam input also increased the syngas yield, but at high steam inputs, saturation of the catalyst reduced syngas yield. Of the different plastic types investigated, the polyolefin plastics (HDPE, LDPE, PP) produced the highest yield of syngas, whereas PS and PET yields were significantly lower in the presence of both biochar and RDF char catalysts. Hydrogen yields were ∼0.44 g gplastic-1 for the polyalkene plastics with the biochar catalyst but were only ∼0.32 g gplastic-1 with the RDF char catalyst. At 1000 °C, the H2 potential from the processing of plastic with RDF char as the catalyst was higher than with biochar as the catalyst, which was attributed to the higher presence of an inorganic metal in the RDF char possessing catalytic properties.