Structural characterization and pyrolysis behavior of humin by-products from the acid-catalyzed conversion of C6 and C5 carbohydrates

Humin, a solid by-product formed during the acid-catalyzed conversion of carbohydrate to platform chemicals, can be further utilized by pyrolysis technology. In this study, two humins derived from glucose (humin-g) and xylose (humin-x) were characterized by elemental analysis, FTIR and 13 C NMR. Both humins were polymers rich in furan rings, and their carbon contents were more than 66%. Thermogravimetry and pyrolysis kinetic analyses based on Flynn-Wall-Ozawa and Friedman methods suggested that the activation energies for both humins increased as their conversion rates increased. At low conversion rates, the activation energy of humin-x was higher than that of humin-g, but this was reversed at high conversion rates. The results suggest that humin-g has better thermal stability following the removal of weak linkages at low temperature. Finally, Py-GC/MS was employed to study the product distribution from humin pyrolysis. The mechanisms for formation of typical products and the influence of temperature on product distribution are discussed.