Valorisation of plastic waste: Waste-to-Chemicals processes vs. co-combustion in cement kilns

This work compares two options for the valorisation of non-recyclable plastic waste: gasification-based Waste-to-Chemicals (WtC) processes geared toward the production of hydrogen or methanol vs. co-combustion in the cement industry. In both cases the use of waste as fuel displaces the consumption of fossil sources that would be used to produce chemicals (hydrogen / methanol) or cement. The comparison adopts an LCA inspired approach and focuses on energy consumption and CO2 emissions. The performances of two WtC technologies close to commercial readiness have been estimated based on available data and detailed process simulation, whereas data on cement production have been provided by the Italian association of cement producers. Results demonstrate that the use of waste in the considered WtC processes is less effective in terms of energy savings and CO2 emissions than the use of waste for cement production. When waste is used as feedstock for hydrogen production through the Ebara-UBE gasification technology, about 14% more energy is needed and about 33% more fossil CO2 is emitted with respect to waste co-combustion in cement kilns. When waste is used to produce methanol through the ENERKEM gasification technology, about 5% more energy is needed and 30% more fossil CO2 is emitted with respect to waste co-combustion in cement kilns.