Hydrothermal liquefaction of different waste biomass using green solvent 2-methyltetrahydrofuran as extractant and co-solvent†

Hydrothermal processes, such as hydrothermal liquefaction (HTL), are widely used for converting biomass into fuel and chemicals using superheated water as the processing medium. However, conventional organic solvents are often utilized in these processes, raising potential concerns about their environmental impact. For example, dichloromethane (DCM) is commonly used in HTL processes due to its ability to effectively extract organic molecules from the aqueous phase. Alcohols such as ethanol, 1-butanol and non-renewable tetrahydrofuran (THF) have also demonstrated positive effects as a co-solvent with water in biomass conversion. 2-Methyltetrahydrofuran (2-MeTHF) is recognized as a green solvent and is often used as a bio-renewable substitute for DCM and THF in low-temperature transformations. In this comparison study, we explored the potential of 2-MeTHF as a recovery agent and co-solvent in the HTL of several major examples of waste biomass, namely herb residues, paper towel and sawdust. In this investigation, we compare 2-MeTHF with other solvents as extractant and co-solvent in HTL processes. Our research demonstrates that 2-MeTHF is an exceptional option for biocrude extraction, surpassing DCM and consistently producing considerably higher biocrude yields for HTL under several identical conditions (e.g. atmosphere and pH) without lowering the quality of the biocrude products to any significant extent. When utilized as a co-solvent, 2-MeTHF significantly improved biocrude yields, generally outperforming ethanol, 1-butanol and THF while maintaining or enhancing their quality.