Earlier studies show that co-pyrolysis of biomass and plastics can improve the quantity and quality of the produced pyrolysis oil compared to pyrolysis of the separate feedstocks. In this work three relevant plastic wastes; paper reject, shredder light fraction and cable plastics; were evaluated together with woody biomass (stem wood from spruce and pine) using analytical pyrolysis, Py-GC-MS/FID. One verification experiment was also conducted in a cyclone pyrolyser pilot plant at industrially relevant conditions.

The addition of plastic waste to woody biomass pyrolysis was found to significantly affect the composition and properties of the produced pyrolysis products. In analytical pyrolysis experiments, positive synergetic effects were observed in the co-pyrolysis of paper reject and cable plastics together with the stem wood. The yield of reactive oxygenated compounds (ketones, aldehydes and acids) was suppressed while more stable alcohols and esters were promoted. The formation of hydrocarbons was also promoted in the co-pyrolysis of plastics from paper reject and stem wood. The results from the analytical pyrolysis were partly verified in the pilot scale experiment by co-pyrolysing stem wood and paper reject. However, the co-pyrolysis also affected other parameters that cannot be detected in analytical pyrolysis such as higher acidity and viscosity of the oil which highlights the need for undertaking experiments at different scales. The product yields in pilot scale were about the same for the co-pyrolysis case as for pure stem wood. However, a high volatile content of the solid product indicated that the process conditions can be further optimized for co-pyrolysing cases.