Hydrogen Production Came from Catalytic Reforming of Volatiles Generated by Waste-Plastic Pyrolysis Over Sepiolite-Based Catalysts

Abstract

Several sepiolite-based catalysts have been prepared and investigated for pyrolytic H₂ production from a post-consumer mixture of residual plastics. The experimental installation involved a two-stage reaction system: first, the plastic mixture was thermally pyrolyzed at 500 ºC; then, the generated volatiles were reformed by increasing the temperature to 700 ºC and 800 ºC in the presence of the sepiolite-based catalysts. The real mixture came from non-separate waste collection streams and contained post-consumer polypropylene (rigid and film), expanded polystyrene, high-impact polystyrene, and polyethylene. The results demonstrated that the two-stage pyrolysis technique using sepiolite-based catalysts successfully generated hydrogen. The effects of the type of polymer, temperature, and catalyst were analyzed. The higher production of hydrogen (27.2 mmol H₂/g) was obtained when the mixture of plastic waste was pyrolyzed and then the volatiles were reformed at 800 °C with the SN5-800 12 nickel-modified sepiolite. Additionally, the generation of hydrogen also increased after acidifying natural sepiolite (from 18.2 mmol H₂/g plastic for natural sepiolite to 26.4 mmol H₂/g for acidified sepiolite at 800 ºC with a plastic/catalyst ratio of 1:2). Finally, the carbon deposited in the catalysts was examined. Approximately, only 20% of the carbon that was deposited in the sepiolite-based catalysts was filamentous carbon; the majority was amorphous carbon.

The results have therefore shown that it is possible to obtain a hydrogen-rich gas from the reforming of the pyrolysis vapors of a mixture of plastic waste using a low-cost catalyst based on nickel-modified sepiolite.