Structural Analysis And Molecular Model Construction Of Lignite Humic Acid Based On PH Grading

Humic acid is a heterogeneous macromolecular organic matter with complex structure.Separating it into a narrow change in properties and relatively uniform humic acid is beneficial to better understand such organic macromolecular substances.In this paper,Zhaotong lignite was taken as the research object,and different humic acid fractions were prepared by continuous fractionation extraction method,and the basic structural characteristics of each fraction were characterized.Based on the results of gel chromatography,TG-FTIR-GC/MS analysis,elemental analysis,¹³C NMR,etc.,the molecular structure model of humic acid was constructed to further explore the combination of humic acid molecules and water and the fine utilization of humic acid.A certain theoretical research basis.Research indicates:?1?The total humic acid and free humic acid content in Zhaotong lignite were54.38%and 43.6%,respectively.The humic acid fractions extracted based on different pH were recorded as HA-4,HA-6,HA-8,HA-10,HA-12,and the corresponding yields were 4.32%,9.56%,8.71%,11.80%,14.70%.The total yield of the five humic acids was 49.09%.?2?The total acid group and carboxyl group content of each humic acid fraction decreased with the increase of pH value of the extract,and the phenolic hydroxyl content showed the opposite change trend;except the HA-6 fraction,along with the pH of the extract The value of C and N increased,while O and O/C decreased continuously.The results of UV-Vis,FITR,gel chromatography and other analysis showed that when the extract was acidic,the humic acid fraction contained more.Oxygen-containing functional groups and fat structures,wherein HA-4 contains more carboxyl and aliphatic structures,while HA-6 has more oxygen-containing functional groups;as the pH of the extract increases,the oxygen-containing functional groups in humic acid decrease,and the aromatic structure increases.The average molecular weight increases,which indicates that the method of fractionally extracting humic acid can reduce the heterogeneity of humic acid.?3?The results of TG-FTIR-GC/MS analysis show that the main pyrolysis process of humic acid is in the stage of 300⁵00°C,and the pyrolysis products can best reflect the structural composition of humic acid molecules.CO,CO₂ and CH₄ are humic acid heat.The main non-condensable gas products in the solution process;the pyrolysis products of different humic acid fractions have obvious differences,the oxygen-containing compounds are mainly phenol,and contain different proportions of esters,alcohols,aldehydes,ketones;As the pH of the extract increased,the total oxygenated compounds detected decreased gradually,and the detected aromatic compounds increased.The monocyclic compounds were mainly benzene and alkylbenzenes,and the content of monosubstituted benzene was higher,indicating that the The functional group or oxygen bridge on the benzene ring is unstable and easily broken;the polycyclic ring has biphenyl,naphthalene,furan,anthracene,anthracene and its derivatives;and the N-containing compound mainly exists in the form of pyridine and its derivatives.?4?Comprehensive elemental analysis,FITR analysis,gel chromatography analysis and ¹³C NMR analysis showed that the basic structural parameters of HA-6were obtained,and the molecular formula of HA-6 molecular structure model was C₄₁H₃₉NO₂₅,Mr=945.Structural model features:less aromatic compounds,only contains two benzene rings,nitrogen atoms mainly exist in the form of pyridine,fat structure exists in shorter branches,and oxygen-containing functional groups are mainly carboxyl groups,followed by phenolic hydroxyl groups With carbonyl.The Gaussian software is used to optimize the model and calculate the frequency.The model parameters are in good agreement with the experimental parameters,and the model is reasonable.?5?Comprehensive elemental analysis,FITR analysis,gel chromatography analysis and ¹³C NMR analysis showed that the basic structural parameters of HA-12were obtained.The final formula was C₁₅₅H₁₂₇N₃O₆₅,Mr=3069.The structural model was characterized by:benzene ring in HA-12 structure.In the eleven,the main substitution forms of the benzene ring are tetra-and tri-substituted,and the substituents on the benzene ring are mostly cleavable functional groups or bridges.The heterocyclic compounds mainly include naphthalene,benzofuran and 2-propyl-pyridine.The oxygen-containing functional group is mainly composed of a phenolic hydroxyl group,and an ester group,an ether bond,a carbonyl group or the like exists as a crosslinked structure of HA-12.The Gaussian software is used to optimize the model and calculate the frequency.The model parameters are in good agreement with the experimental parameters,and the model is reasonable.