Experimental study on pyrolysis/gasification of biomass and plastics for H-2 production under new dual-support catalyst

Abstract

Energy security and environmental pollution are two major concerns worldwide. H-2 from pyrolysis/gasification of biomass and waste plastics is a clean energy source. However, relatively low yield and composition of H-2 is produced using this technology, thus preventing its commercialisation. Catalyst is key to promote H-2 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 H-2 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 H-2 production were also investigated. Results show that catalysts (Ni-Al2O3 or Ni-CaO-C) can effectively promote H-2 production. The H-2 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 H-2 production. When the feedstock ratio is constant, high H-2 yield (i.e. 80.36 mmol/g) is achieved under relatively low reforming temperature at 700 degrees C and water injection flowrate at 5 mL/h for HDPE. However, under the same conditions, PP and PS only have H-2 yields at 59.35 mmol/g and 38.51 mmol/g. PS requires even higher temperature (800 degrees C) and water injection flowrate (10 mL/h) to ensure acceptable H-2 yields. The new findings presented in this paper can help large scale commercial application of pyrolysis/gasification technologies for biomass and waste plastics.

TSC Opinion

Les matières plastiques actuelles sont difficilement recyclables sur le long terme par leur conception pour des produits à durée de vie courte. Il en résulte que des quantités très importantes de déchets plastiques s’accumulent partout dans le monde avec des modes de gestion plus ou moins adaptés. Une voie possible est la pyrolyse et en particulier pour la production d’hydrogène qui peut ensuite servir de source d’énergie. Cette étude montre que le mélange de déchets plastiques avec des déchets organiques de biomasse est possible et apporte des rendements de pyrolyse intéressants. Ceci permet de valoriser deux types de déchets dans une production d’énergie. Le point critique de cette technologie est la gestion des gaz autres que H2 et celle des résidus solides post combustion.