(663d) Structural Analysis of Humins Formed in the Brønsted-Catalyzed Dehydration of Fructose
Humins are carbonaceous and polymeric by-products formed during acid-catalyzed hydrothermal processing of sugars to 5-hydroxymethylfurfural (HMF). These are formed via cross-polymerization of HMF with sugars in acidic solutions, and cause significant carbon loss and unfavorable process economics of biorefineries. The deposition of these solid particles on the reactors and processing equipment also increases the maintenance costs. Currently humins are combusted to supply heat in biorefineries. Minimization of humins formation or their valorization is essential for improving the process economics of the biorefineries. In this work, we developed methods to understand microstructure of humins through solubility experiments. First, we have conducted dissolution experiments in various solvents and correlated the solubility data to molecular properties of solvents to develop suitable descriptors. By doing this, we have identified solvents for high solubility of humins at room temperature and provided insights into the mechanism of humins dissolution. Next, Liquid Chromatography- Mass Spectrometry (LC-MS) was used to determine and compare the masses of components in the humins solubilized in different solvents. Finally, a six stage dissolution experiment was done to investigate the structural inhomogeneity of humins. Both Fourier Transform Infrared Spectroscopy (FT-IR) and LC-MS were used to characterize the solubilized and insoluble humins obtained at each stage. Based on our results, an inhomogeneous structure where macromolecular and molecular components are connected through weak forces, was proposed.