Experimental study on pyrolysis/gasification of biomass and plastics for H₂ production under new dual-support catalyst

Energy security and environmental pollution are two major concerns worldwide. H₂ from pyrolysis/gasification of biomass and waste plastics is a clean energy source. However, relatively low yield and composition of H₂ is produced using this technology, thus preventing its commercialisation. Catalyst is key to promote H₂ production. This paper aims to explore whether newly developed dual-support catalyst Ni-CaO-C can catalyse gasification of volatiles from pyrolysis of different plastics (e.g. high density polyethylene - HDPE, polypropylene – PP and polystyrene - PS) and biomass (e.g. pine sawdust) for H₂ production. Experiments with and without catalysts were performed to test the performance of catalyst Ni-CaO-C. Impact of changing operating conditions (i.e. feedstock ratio, reforming temperature and water injection flowrate) on H₂ production were also investigated. Results show that catalysts (Ni-Al₂O₃ or Ni-CaO-C) can effectively promote H₂ production. The H₂ production using catalyst Ni-CaO-C is much better than catalyst Ni-Al₂O₃. The catalytic effect of Ni-CaO-C rank in the sequence of HDPE > PP > PS. Plastic content in feedstock is suggested to be less than 40 wt% (for HDPE and PP) and 30 wt% (for PS) when mixing with biomass to reach high H₂ production. When the feedstock ratio is constant, high H₂ yield (i.e. 80.36 mmol/g) is achieved under relatively low reforming temperature at 700 °C and water injection flowrate at 5 mL/h for HDPE. However, under the same conditions, PP and PS only have H₂ yields at 59.35 mmol/g and 38.51 mmol/g. PS requires even higher temperature (800 °C) and water injection flowrate (10 mL/h) to ensure acceptable H₂ yields. The new findings presented in this paper can help large scale commercial application of pyrolysis/gasification technologies for biomass and waste plastics.