Humins in Soil Chemistry
Soil consists of both mineral (inorganic) and organic components. The organic components can be subdivided into fractions that are soluble, largely humic acids, and insoluble, the humins. Humins make up about 50% of the organic matter in soil.
Humic substances, including humin, have not been observed in soils using modern analytical techniques.
Humins from Biomass Sources
Humins also produced during the dehydration of sugars, as occurs during the conversion of lignocellulosic biomass to smaller, higher value organic compounds such as 5-hydroxymethylfurfural (HMF). These humins can be in the form of either viscous liquids or solids depending on the process conditions used.
Humins Structure and Mechanism of Formation
Both the structure of humins and the mechanism by which they are synthesized is at present not well defined as the formation and chemical properties of humins will change depending on the process conditions used. Generally, humins have a polymeric furanic-type structure, with hydroxyl, aldehyde and ketone functionalities.
Humins are not considered to be a dangerous substance according to officially recognized hazardous material classification systems based on physical-chemical properties such as flammability, explosiveness, susceptibility to oxidation, corrosiveness or eco-toxicity.
Potential applications of Humins
In the past, humins from biomass sources have been mostly considered as combustible materials to supply heat for biorefinery processes. However, high value applications have started to receive more attention, notably the use of humins in the preparation of catalytic materials  and in material applications (e.g. plastic reinforcement and construction materials). Humins can also be subjected to thermal treatments in order to form interesting solid materials, such as lightweight and porous humin foams.
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