Humin

Humins are carbon-based macromolecular substances, that can be found in

saccharide

-based biorefinery processes.

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.^[1]

Due to their very complex molecular structure, humic substances, including humin, do not correspond to pure substances but consist of a mixture of many compounds that remain very difficult to characterize even using modern analytical techniques.[2]

Humins from biomass sources

Humins also produced during the

5-hydroxymethylfurfural

(HMF). These humins can be in the form of either viscous liquids or solids depending on the process conditions used.

Humin 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.^[3] However, the structure is dependent on feedstock type (e.g. xylose or glucose) or concentration, reaction time, temperature, catalysts and many other parameters involved in the process.^[4] These parameters also influence the mechanism of formation which is still a matter of debate. Different pathways have been considered, including ring-opening hydrolysis of HMF (believed to be the key intermediate for the formation of humins),^[5] nucleophilic additions,^[6] or via the formation of an aromatic intermediate.^[7] While there is no clear evidence to substantiate or exclude the mechanisms, general consensus is on a series of condensation reactions that reduce the efficiency of biomass

conversion strategies.

Safety aspects

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,^[8] explosiveness, susceptibility to oxidation, corrosiveness or eco-toxicity.^[9] Heating of humins forms a macroporous material known as humins foams^[10] and also these materials did not present critical fire behaviour despite their highly porous structure.^[8]

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^[11] and in material applications (e.g. plastic reinforcement and construction materials).^[12]^[13]^[14] Humins can also be subjected to thermal treatments in order to form interesting solid materials, such as lightweight and porous humin foams.^[15]^[16] Overall, humins appear to improve the final properties of the materials although research is mainly at the proof-of-principle

stage (early).

References

doi:10.1097/00010694-200111000-00002

PMID 26595271

^ van Zandvoort, I., "Towards the Valorisation of Humin By-products: Characterisation, Solubilisation and Catalysis", 2015

ISBN 9789812877697

ISSN 0040-4039
.

S2CID 84984623
.

ISSN 0008-6215
.

^ ^a ^b Muralidhara, A., Tosi, P., Mija, A., Sbirrazzuoli, N., Len, C., Engelen, V., de Jong, E., Marlair, G., ACS Sustainable Chem. Eng., 2018, 6, 16692-16701

^ Muralidhara, A., Bado-Nilles, A., Marlair, G., Engelen, V., Len, C., Pandard, P., Biofuels, Bioproducts and Biorefining, 2018, 1-7

PMID 29956889
.

^ Filiciotto, L., Balu, A.M., Romero, A.A, Rodriguez-Castellon, E., van der Waal, J.C., Luque, R., Green Chemistry, 2017, 19, 4423-4434

doi:10.1016/j.conbuildmat.2016.11.019

doi:10.1016/j.compscitech.2018.12.008

^ Pin, J.M., Guigo, N., Mija, A., Vincent, L., Sbirrazzuoli, N., van der Waal, J.C., de Jong, E., ACS Sustain. Chem. Eng., 2014, 2, 2182-2190

^ Mija, A., van der Waal, J.C., van Klink, G., de Jong, E., Humins-containing foam, 2016, WO2017074183A8

^ Tosi, P., van Klink, G.P., Celzard, A., Fierro V., Vincent, L., de Jong, E., Mija, A., ChemSusChem, 2018, 11, 2797-2809

Further reading

Singer, Michael J., and Donald N. Munns (2005). Soils: An Introduction (6th Edition). Upper Saddle River: Prentice Hall.
ISBN 978-0-13-119019-1
.

Retrieved from "https://en.wikipedia.org/w/index.php?title=Humin&oldid=1199145888"

[1] doi:10.1097/00010694-200111000-00002

[2] PMID 26595271

[3] van Zandvoort, I., "Towards the Valorisation of Humin By-products: Characterisation, Solubilisation and Catalysis", 2015

[4] ISBN 9789812877697

[5] ISSN 0040-4039
.

[6] S2CID 84984623
.

[7] ISSN 0008-6215
.

[:0-8] Muralidhara, A., Tosi, P., Mija, A., Sbirrazzuoli, N., Len, C., Engelen, V., de Jong, E., Marlair, G., ACS Sustainable Chem. Eng., 2018, 6, 16692-16701

[9] Muralidhara, A., Bado-Nilles, A., Marlair, G., Engelen, V., Len, C., Pandard, P., Biofuels, Bioproducts and Biorefining, 2018, 1-7

[10] PMID 29956889
.

[11] Filiciotto, L., Balu, A.M., Romero, A.A, Rodriguez-Castellon, E., van der Waal, J.C., Luque, R., Green Chemistry, 2017, 19, 4423-4434

[12] doi:10.1016/j.conbuildmat.2016.11.019

[13] doi:10.1016/j.compscitech.2018.12.008

[14] Pin, J.M., Guigo, N., Mija, A., Vincent, L., Sbirrazzuoli, N., van der Waal, J.C., de Jong, E., ACS Sustain. Chem. Eng., 2014, 2, 2182-2190

[15] Mija, A., van der Waal, J.C., van Klink, G., de Jong, E., Humins-containing foam, 2016, WO2017074183A8

[16] Tosi, P., van Klink, G.P., Celzard, A., Fierro V., Vincent, L., de Jong, E., Mija, A., ChemSusChem, 2018, 11, 2797-2809

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