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The implementation of flow-through (FT) systems in the lignin-first approach can be a strategic tool for increasing the proficiency of biorefineries. Herein, the reductive catalytic fractionation (RCF) of waste beech wood sawdust (BWS) was conducted in an FT system using Ni on a nitrogen-doped carbon catalyst (35Ni/NDC) in pellet shape and MeOH and MeTHF as solvents. Lignin extraction was maximized in the first 4 h of time on stream (TOS), yielding maximum cumulative monomers of 247 mg gKL−1 using MeOH as solvent, extraction temperature of 235 °C, and reduction temperature of 225 °C. Importantly, the catalyst was used for two cycles and total time on stream (TOS) of 14 h without losing initial activity. These findings show that FT systems represent a promising solution for applications in lignin-first biorefineries.

Liquid transportation biofuel production is a promising strategy to reduce greenhouse gas emissions. Hydrothermal gasification (HTG) has shown great potential as an effective method for valorizing wet biomass. The high-quality syngas produced using the HTG process can be chemically/biochemically converted to liquid biofuels. Therefore, this paper aims to comprehensively review and critically discuss syngas production from biomass using the HTG process and its conversion into liquid biofuels. The basics and mechanisms of biomass HTG processing are first detailed to provide a comprehensive and deep understanding of the process. Second, the effects of the main operating parameters on the performance of the HTG process are numerically analyzed and mechanistically discussed. The syngas cleaning/conditioning and Fischer-Tropsch (FT) synthesis are then detailed, aiming to produce liquid biofuels. The economic performance and environmental impacts of liquid biofuels using the HTG-FT route are evaluated. Finally, the challenges and prospects for future development in this field are presented. Overall, the maximum total gas yield in the HTG process is obtained at temperature, pressure, and residence time in the range of 450–500 °C, 28–30 MPa, and 30–60 min, respectively. The highest C5+ liquid hydrocarbon selectivity in the FT process is achieved at temperatures between 200 and 240 °C. Generally, effective conversion of biomass to syngas using the HTG process and its successful upgrading using the FT process can offer a viable route for producing liquid biofuels. Future studies should use HTG technology in the biorefinery context to maximize biomass valorization and minimize waste generation.