Assessment of Co-Gasification Methods for Hydrogen Production from Biomass and Plastic Wastes

In recent decades, economic development and population growth has been accompanied by the generation of billions of tonnes of solid residues or municipal “wastes”, a substantial portion of which is composed of plastics and biomass materials. Combustion-based waste-to-energy is a viable and mature method of extracting calorific value from these end-of-life post-recyclable materials that are otherwise landfilled. However, alternative thermochemical methods, such as gasification, are becoming attractive due to the ability to synthesize chemical precursors for supply chain recirculation. Due to the infancy of gasification technology deployment, especially in the context of anthropogenic CO2 emission reduction, additional systems engineering studies are necessary. Herein, we conduct an attributional life cycle analysis to elucidate the syngas production and environmental impacts of advanced thermochemical gasification methods for the treatment of biomass and plastic wastes obtained from municipal solid wastes, using a comprehensive thermodynamic process model constructed in AspenTech. Feedstock composition, process parameters, and gasification methods are varied to study the effects on syngas quality, yield, power generation potential, and overall greenhouse gas emissions. Steam-based gasification presents up to 38% reductions in CO2 emissions when compared to conventional thermochemical methods. Using gasifier-active materials, such as metal hydroxides, can also further reduce CO2 emissions, and realizes a capture load of 1.75 tonnes of CO2 per tonne of plastic/stover feedstock. This design alteration has implications for reductions in CAPEX due to the mode of CO2 capture utilized (e.g., solid sorbent vs. liquid SELEXOL). The use of renewable energy to provide a method to generate steam for this process could make the environmental impact of such MSW gasification processes lower by between 60–75% tonnes of CO2 per tonne of H2. Overall, these results can be used to inform the guidance of advanced waste gasification methods as a low-carbon transition towards a circular economy.