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

Abstract

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.