Engineering functional hydrochar via digestate-mediated carbonization: Mechanistic insights into structural evolution...

Area of Science:

• Biomass conversion
• Materials science
• Sustainable chemistry

Background:

• Digestate liquid from food waste (DFW) is a promising medium for hydrothermal carbonization (HTC).
• DFW's impact on hydrochar's non-carbonized fraction and underlying mechanisms are not fully understood.
• Understanding these mechanisms is crucial for optimizing hydrochar production.

Purpose of the Study:

• To systematically investigate feedstock- and solvent-dependent mechanisms of HTC.
• To elucidate the role of DFW in hydrochar formation using model biomass precursors.
• To reveal solvent-specific pathways and their impact on hydrochar structure and composition.

Main Methods:

• Hydrothermal carbonization (HTC) of model biomass precursors (lignin, cellulose) in deionized water and DFW.
• Combustion analysis to determine hydrochar reactivity.
• Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) for surface and chemical analysis.
• Multiscale approach to analyze structural evolution.

Main Results:

• DFW enhanced hydrochar reactivity, reducing ignition temperatures for lignin (10%) and cellulose (13%).
• DFW promoted depolymerization and decarboxylation, increasing carbon content (~69%) and lowering O/C ratios (<0.2).
• DFW facilitated nitrogen doping (>3.0%) and enhanced structural integrity, while reducing feedstock variability.

Conclusions:

• DFW acts as an effective medium for HTC, promoting specific degradation pathways (keto-enol tautomerism) distinct from deionized water (furfural-type degradation).
• DFW significantly improves hydrochar quality by increasing carbon content, nitrogen doping, and structural integrity.
• This study offers a scalable strategy for producing tailored carbon materials from diverse biomass sources using real-waste media.