Influence of temperature on the bio-oil production from biomass pyrolysis in a solar hybrid drop-tube/fixed-bed reactor

Aviation remains a critical climate challenge in Europe, with emissions stubbornly high due to fossil fuel dependence, rising demand, and the slow adoption of low-carbon alternatives. SAFs, currently under 1% of fuel use, face barriers like high costs and limited feedstocks. The EU's Fit for 55 package mandates SAF blending targets of 2% by 2025, scaling to 70% by 2050, including e-fuels. To address these challenges, CNRS-PROMES (France) developed a solar-assisted quartz hybrid drop-tube/fixed-bed reactor (DTR), optimized for low-temperature pyrolysis (500 - 700 °C) and bio-oil production from the pyrolysis of demolition wood. The aim was to evaluate and optimize bio-oil yields, analyze products distribution (bio-oil, char, and gases) and elemental composition, and identify potential improvements to the solar reactor. The results showed that the bio-oil yield peaked at 500 °C, reaching 56 wt% when accounting for the “mass lost” required to close the mass balance, assuming that the missing mass consisted exclusively of liquid products. When considering only the measured mass, the bio-oil yield peaked at 600 °C, at 50 wt%. It declined at higher temperatures due to secondary cracking, while gas yield increased (12.5 - 20.4 wt%) and char yield remained stable (∼32 wt%) before slightly dropping at 700 °C. Compared to a Bubbling Fluidized Bed (BFB) reactor, the DTR produced less bio-oil (43 wt% for DTR vs. 62 wt% for BFB) and less gas (12 wt% for DTR vs. 17 wt% for BFB), but more char (32 wt% for DTR vs. 15 wt% for BFB), highlighting trade-offs tied to heat transfer and residence time. The study concludes that moderate temperatures (500 - 600 °C) favor bio-oil and char, while higher temperatures promote gasification, demonstrating the potential of solar-driven pyrolysis for scalable, carbon-neutral SAF production and circular biomass valorization.