Humin Formation Pathways

Humins are undesired solids that form during the aqueous processing of cellulose-derived carbohydrates. Aldol addition/condensation involving intermediates with multiple keto groups is one mechanistic pathway by which humins can form. The Gibbs free energy changes for aldol addition/condensation reactions in the early stages of humin formation have been computed from first principles. On this basis, primary humin building blocks have been identified. The effect of the initial carbohydrate upon the structure of the humins formed, as characterized by infrared spectroscopy, can be rationalized in terms of these building blocks.