| The extraction of coal-based fulvic acid from lignite as raw material is an effective way to achieve high value-added utilization of lignite.Microwave-assisted hydrogen peroxide oxidation and sulfuric acid-ethanol purification method can obtain high yield of high purity fulvic acid.At present,the research on the molecular structure model of fulvic acid is less,the molecular structure model of Hulunbuir lignite fulvic acid was constructed based on molecular structure test data.The molecular structure was optimized by quantum chemical calculation and the rationality of model construction was determined.The optimum conditions of extracting fulvic acid from Hulunbeier lignite were determined by single factor and orthogonal experiment.The ratio of hydrogen peroxide solution to coal was 11,the concentration of hydrogen peroxide was 21%,the microwave power was 400 W,the reaction time was 10 min,and the optimal yield of fulvic acid was 31.7%.The primary products of fulvic acid contain much water-soluble ash is difficult to separate,so sulfuric acid-ethanol method was used to purify the fulvic acid,the ratio of sulfuric acid to FA1 was 0.09,the liquid to solid ratio was 10,the reaction temperature was 45 ?,and the reaction time was 45 min.Under the optimum reaction conditions,the yield of high purity fulvic acid was 76.6%.The ash content of the samples before and after purification were 10.8% and 2.2%,respectively,the sulfuric acid-ethanol method had better purification effect.The yield of fulvic acid reached the maximum value that is 24.1% when the secondary oxidation of the coal was carried out to strengthen the utilization value of lignite,the concentration of hydrogen peroxide was 9%,the ratio of hydrogen peroxide solution to coal was 12,the reaction time was 12 min and the microwave power was 800 W.The fulvic acid was characterized by FT-IR,TG/DTG,UV/Vis,13 C NMR,XPS,elemental analysis and fluorescence spectroscopy.The results showed that fulvic acid was mainly composed of small molecular benzene carboxylic acid,there was more carboxyl and carbonyl groups,which is the main reason for the high oxygen content and easy pyrolysis of fulvic acid.The UV/Vis spectrum of fulvic acid monotonically decreased with increasing wavelengths,and there was a strong fluorescence peak in the fluorescence spectrum,which is related to the presence of carboxyl and carbonyl structures.According to the FT-IR data,the distribution of various functional groups in the fulvic acid structure could be obtained.Hydrogen peroxide could oxidize the aliphatic structure to produce a large number of oxygen-containing functional groups,but it did not cause serious damage to the macromolecule skeleton structure of lignite.Analysis of 13 C NMR can give fat carbon,aromatic carbon and other kinds of carbon atoms attribution in the fulvic acid structure,which play important roles in the study of the composition and the structure of carbon skeleton of fulvic acid.The average molecular structure model of fulvic acid was established by the method of comprehensive element analysis,FT-IR,13 C NMR and other test results combined with experimental research.The molecular formula was C38H32NO24 and Mr=886.The parameters of the model were matched with the experimental test values well.The characteristics of the model: the aromatic compounds are predominantly benzene ring structures,including benzene ring tetrasubstituted and benzene ring triad.There are more oxygen-containing functional groups in the model,including carboxyl,carbonyl,hydroxyl,methoxy,quinone and so on.Most of the carboxyl groups exist in the end of the fat structure,the benzene ring was connected each other through the ether bond and fat structure.The Gaussian 09 W software was used to optimize the model structure and calculate the frequency to get the calculated infrared spectrum.The calculated spectrum is basically matched with the experimental test spectrum,and the model is constructed reasonably. |
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