Characterization and behavior of water in lignocellulosic and microalgal biomass for thermochemical conversion

- Water in lignocellulosic and algal biomass was characterized by DSC and XRD.
- Water exists in biomass as freezable free water and non-freezable water.
- Unlike PS and PT, position of free water peak during DSC shifted in the case of MA.
- Relatively large amount of water exists in biomass as non-freezable water.
- Non-freezable water content in biomass was correlated with oxygen functionalities.

Behavior and nature of water in biomass significantly influence the thermochemical conversion processes. This study investigates the characteristics and behavior of water in lignocellulosic and microalgal biomass using differential scanning calorimetry (DSC) and low-temperature X-ray diffraction (XRD) methods. Pine sawdust (PS), peanut shell (PT), and microalgae (MA) samples with different water contents were used and analyzed systematically. Freezable free water was detected in all biomass samples through DSC analysis. Different from PS and PT, a shift in the position of freezable free water peaks was observed during freezing process of MA on DSC, which was attributed to the strong hydrophilicity of this biomass. No freezable bound water was observed in the biomass samples. However, significant amount of non-freezable bound water was detected in all biomass samples. The freezing enthalpies of freezable free water in PS, PT, and MA ranged between 319.04 and 297.7 kJ/kg which were in good agreement with that of bulk water. The boundary between freezable and non-freezable water in the biomass samples was clearly defined combining DSC and XRD analyses. The amount of non-freezable bound water in biomass samples directly correlated with the relative concentration of oxygen functional groups in biomass samples.