Involvement of the organics in aqueous phase of bio-oil in hydrothermal carbonization of lignin

Aqueous phase of bio-oil (APBO) is water-rich but also contains some sugar-derivatives and phenolics. APBO has little potential as feedstock for producing biofuel, but can be potentially used as medium for hydrothermal carbonization (HTC) of biomass. In this study, the HTC of lignin in APBO was conducted, aiming to probe the influence of the organics in APBO on property of the hydrochar. The results indicated that the organics in APBO cross-polymerized with lignin derivatives, resulted in the yield of hydrochar to exceed 100%. In addition, APBO promotes the deoxygenation but does not promote dehydrogenation. More aliphatic structures are generated in the hydrochar, reducing its thermal stability. In addition, the hydrochar from APBO also shows the improved combustion performance by lowering the activation energy and the ignition temperature (180 vs 240 °C).