Hydrothermal humification mechanism of typical agricultural waste biomass: a case study of corn straw

The hydrothermal humification technology provides a novel route for the preparation of artificial humic substances (A-HS), while the mechanism underlying the hydrothermal humification reaction still needs to be deeply explored. In this study, corn straw is chosen as a raw material to conduct hydrothermal humification kinetics experiments, and characterization techniques such as ultra-performance liquid chromatography, nuclear magnetic resonance spectroscopy, and Fourier-transform ion cyclotron resonance mass spectrometry are carried out to monitor the intermediate products for determination of the formation mechanism. As observed, rapid dissociation of lignocellulose can occur in an alkaline environment; meanwhile, cellulose and hemicellulose were hydrolyzed into glucose and xylose, further dehydrated to form 5-hydroxy furfural and furfural, and then rehydrated to synthesize levulinic acid and other small molecular acids. Then these as-formed small precursors also combine with lignin fragments and are polymerized for the formation of fulvic acids, humic acids and even humin. In addition, we also use the purchased lignin and cellulose as model species for the preparation of A-HS in order to investigate the effect of raw material composition on the A-HS structure. The proposed mechanism of hydrothermal humification is of great significance for the design, synthesis and application of A-HS in sustainable agriculture. Hydrothermal humification kinetics experiments were carried out to determine the formation mechanism of artificial humus.