Biobased bitumen binder through hydrothermal liquefaction of waste biomass: Impact of different feedstock and solvents

This work investigates the hydrothermal liquefaction (HTL) of several waste biomass feedstocks, including hemp shives, seaweeds, corn cob and barley straw, for the production of asphalt bio-binders. The HTL process employed sulphuric acid as a catalyst where the effects of the co-solvents ethylene glycol and glycerol were studied. To improve bio-oil yield and quality, essential operational parameters including catalyst concentration, biomass loading, and reaction temperature were investigated. It was observed that ethylene glycol outperformed glycerol in terms of bio-oil yield and stability. Using a 1:1 volumetric ratio of ethylene glycol to acidic aqueous solution and a 10% biomass loading at 280 °C produced a notable bio-oil yield. Among the assessed feedstock, seaweed and hemp shives showed the highest yield and stability for bio-oil production, suggesting their suitability for sustainable asphalt binder applications. The resulting oil and hydrochars were separated and characterised using SEM, DSC, TGA, EDX, and FTIR to evaluate their chemical composition and thermal properties. TGA and DSC results demonstrated excellent thermal stability of the bio-oils and chemical stability of the hydrochars. EDX analysis confirmed the effective conversion of organic feedstock into carbon-rich materials suitable for carbon storage. SEM images showed the hydrochars possessed a well-developed porous morphology with high surface area. Further testing is needed to assess the effect of incorporating varying dosages of HTL bio-oils on the mechanical and rheological properties of modified bitumen. Preliminary results indicate that bio-oils may serve as binder extenders, potentially replacing 10–20% of bitumen by mass, while hydrochars could act as physical anti-ageing additives.