Structure Characteristic Of Yunnan Typical Lignites And Physico-chemical Properties Of Humic Acids

Low-rank coals,such as lignites,are abundant fossil resources in China.Nevertheless,conversion and utilization of lignite are limited,due to high water content and low calorific value,accompanied with environmental pollution.It is crucial to develop grading and quality utilization technology of lignites for the high value-added applications.Yunnan has the second largest lignite reserve in China,only behind of Inner Mongolia.The humic acid content of Yunnan lignites is high due to coal-forming period and environmental factors.Moreover,Zhaotong and Mile lignites are typical feedstock for the production of humic acid.Humic acid is commonly used as fertilizer,soil amendment,battery anode,drilling aids,and pharmaceutical products.It is an important performance of realizing the high value-added classification and utilization of Yunnan lignite,which taking high humic acid lignite as raw material for production to extract and develop humic acid productions.Due to the complexity of structural characteristics in coal,humic acid products prepared by different types of coal have obvious differences in properties.Therefore,Zhaotong and Mile lignites with high content of humic acid in Yunnan were chosen as the research object in this thesis,and the intrinsic correlation between the structural characteristic of coals and the extraction and physicochemical properties of humic acid were investigated,so as to provide theoretical guidance for the subsequent production,utilization and product development of humic acid.The major research contents and conclusions are shown as follows:?1?The properties of Yunnan lignites were obtained by series of methos,e.g.Fourier transform infrared spectroscopy?FTIR?,Raman,X-ray photoelectron spectrum?XPS?,solid state ¹³C and ¹H magic angle spinning nuclear magnetic resonance?MAS NMR?,X-ray diffraction?XRD?,electron paramagnetic resonance spectroscopy?EPR?,pyrolysis-gas chromatography-mass spectrometry?Py-GC-MS?,thermal gravity analysis-Fourier transform infrared spectroscopy?TG-FTIR?,thermal gravity/differential thermal gravity?TG/DTG?equipped with differential thermal analysis?DTA?,scanning electron microscopy?SEM?and high resolution transmission electron microscopy?HRTEM?.Basis on the evaluation of calorific value and transmittance,the degree of coalification in Zhaotong?ZT?lignite was lower than that of Mile?ML?lignite.According to the characterization of chemical structure,the free radical concentration of ZT lignite was lower,while the content of carboxyl group and the ratio of aromatic carbon were higher.The free radical concentration of ML lignite was higher,with more fat chains.The reason for textural difference may be contributed to the coal-forming factors.?2?According to methods for extraction of humic acid set by International Humic Acid Association?IHSS?,the basic properties of humic acids were tested.The results showed that the content of carboxyl group in Zhaotong lignite humic acid?ZTHA?were higher than that in Mile lignite humic acid?MLHA?.However,the content of hydroxyl group in MLHA was higher.As a result,the coagulation value and cation exchange capacity of ZTHA were higher than MLHA.It indicated that MLHA was easier to form the supramolecular structure than ZTHA.The results of fluorescence analysis indicated that the number of aromatic ring in ZTHA was more than that in MLHA.XRD analysis indicated that the aromaticity of ZTHA was higher than that of MLHA.In addition,both E₄/E₆ coefficient and GPC analysis indicated that the molecular weight of MLHA was larger than ZTHA,while XPS analysis showed that the content of aromatic carbon in ZTHA was higher than that in MLHA,and the content of aliphatic carbon was opposite.Subsequently,the thermostability of MLHA was better than ZTHA,and thermal oxidation of ZTHA was better than MLHA.?3?The effects of anthraquinone added to Na OH and Na₄P₂O₇ lie on the extraction and composition of humic acid were discussed.The response surface methodology was used to optimize the extraction process of ZTHA and MLHA.The results showed that under the condition of solid to liquid ratio of 0.2 g:100m L,the optimal process parameters for the extraction of humic acid from ZT lignite by Na OH were Na OH concentration of 0.10 mol/L,the temperature of90�C and the reaction time of 2.0 h.The optimal process parameters for the extraction of humic acid from ZT lignite by Na₄P₂O₇ were the Na₄P₂O₇concentration of 0.04 mol/L,the temperature of 90�C and the reaction time of 1.5h.The optimal process parameters for humic acid extraction from ML lignite by Na OH were Na OH concentration of 0.05 mol/L,temperature of 80�C and reaction time of 1.5 h.The optimal process parameters for extracting humic acid from ML lignite by Na₄P₂O₇ were Na₄P₂O₇ concentration of 0.03 mol/L,temperature of 90�C and reaction time of 1.5 h.For ML lignite,the yields of using Na OH or Na₄P₂O₇ are not much too different.But for ZT lignite,the humic acid yield of using Na OH is better than using Na₄P₂O₇.?4?The humic acid extracted from Zhaotong lignite?ZTHA?by the method of alkali dissolution and acid precipitation has small molecular weight,low content of phenolic hydroxyl?1.11 meq/g?,high aromaticity?51.4%,NMR result?,large size and coiled structure.Whereas,humic acid extracted from Mile lignite?MLHA?has larger molecular weight,higher phenolic hydroxyl content?2.94 meq/g?,lower aromaticity?47.8%,NMR result?and smaller size.Through the correlation research of coal characteristic and humic acid characteristic,thermal stability and thermal oxidation is closely related to the structure characteristics of coal,and the strength of the organic structure of the chemical bond is the key to influence the thermal stability;humic acid extracted from high aromaticity of lignite has good thermal stability,and thermal oxidation was also related to organic structure in addition to oxygen-containing groups,high content of oxygen groups help to improve thermal oxidation properties of humic acid.