Structural characterization and molecular model construction of humic acid from Yimin lignite
Extraction of humic acid from lignite is of great significance in realizing the clean and efficient utilization of lignite.Exploring the structure of lignite humic acid and constructing the corresponding structural model in the eastern region of Inner Mongolia provides extensive guidance for the application of lignite in this region.In this paper,the humic acid of lignite from Yimin in eastern Inner Mongolia was extracted by alkali dissolution and acid precipitation method.The structural characteristics of humic acid were comprehensively analyzed using X-ray diffraction,13C nuclear magnetic resonance,and X-ray photoelectron spectroscopy.The results showed that the aromatic structure forms the basis of humic acid from Yimin lignite,while the aliphatic structure primarily exists in the form of cross-linking bonds and side chains.The aromatic clusters in lignite humic acid were relatively small in size,with a significant spacing between aromatic layers and a disordered arrangement.Based on the parameters related to structural characterization,a representative structural model of lignite humic acid from Yimin,East Inner Mongolia,China,was reconstructed.The calculated data of the structural model of humic acid from Yimin lignite is in good agreement with the experimen-tal data and can fully reflect the chemical structure of humic acid from Yimin lignite.In the model,the aromatic car-bons are primarily in the form of benzene and naphthalene rings,with a small amount of phenanthrene rings.The ali-phatic carbons mainly consist of shorter side chains and aliphatic rings,serving to connect the fundamental aromatic units.Oxygen mainly exists in the form of O—C=O,such as carboxyl groups and esters.It also includes a certain amount of ketones,aldehydes,quinones,phenols,alcohols,and ether oxygen.Carbonyl C=O and ether oxygen have a cross-linking effect.Nitrogen primarily exists in the form of a pyrrole ring,with a small amount found in pyri-dine rings and quaternary nitrogen.The samples in this study have a higher aromatic carbon content and a larger pro-portion of pyrrole nitrogen-containing functional groups compared to the structure of Yunnan lignite humic acid from the southwest region,which indicates regional differences.
humic acidstructural featuresmolecular modelYimin brown coalaromatic structurealiphatic carbonpyrrole ringcross-linking bond
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