High temperature fast pyrolysis of waste biomass in a solar-assisted quartz drop-tube reactor

Solar-assisted pyrolysis is a sustainable process for converting biomass into syngas, bio-oil, and biochar using renewable solar thermal energy, with a potentially zero carbon footprint. It generates both high-value gaseous and liquid fuels while transforming the atmospheric CO2 captured in biomass in the form of solid carbon that can be long-term sequestrated or valorized. The EU's target of reducing net greenhouse gas emissions to at least 55% by 2030 sets the stage for effective measures to limit carbon emissions and achieve a sustainable future. This study presents the development of an innovative fast pyrolysis quartz drop-tube reactor using concentrated solar power and its performance for bio-waste valorization. Extensive raw material characterization was carried out, which provides valuable insights into demolition wood and rye straw feedstocks properties. Solar pyrolysis runs revealed key dependencies of product yields on operational parameters such as feedstock type, nitrogen gas flow rate (0.7-1.4 NL/min), and heating profile in the temperature range 800-900 °C. Operation at such high temperatures promoted gas production (>50% gas yield in mass) over liquid and solid products. In similar conditions, rye straw showed higher gas yield as compared to demolition wood. In addition, preheating or increasing the gas residence time favored gas production with negligible impact on gas composition. The solar drop tube pyrolysis reactor appears as a sustainable option to upgrade waste feedstocks into valuable products using concentrated solar energy with net zero CO2 emission.