Research On The Structure Analysis And Application Of Hailaer Brown Coal Pyrolytic Extract

The wide application of brown coal in industry has been limited by its characteristics,such as high moisture content,high ash yield,low calorific value and easy spontaneous combustion.Nevertheless,the high aromatic units and oxygen-containing functional groups and rich aliphatic structure of brown coal molecules make it possible to be considered as chemical raw material.It is generally acknowledged that the pyrolytic extraction is considered to be one of the effective methods for clean and efficient conversion of brown coal aiming at achieving the extract of brown coal with high calorific value,low ash content and good fluidity.It is thus of great significance to study the structure and composition of organic matter in the extract of brown coal for understanding the reaction characteristics and its clean and efficient utilization.On account of this,the structure analysis and application from micro to macro fields of pyrolytic extracts derived from Hailaer brown coal were studied as follows in this thesis:（1）The molecular structure of the Hailaer brown coal pyrolytic extract（CPE）was analyzed by ¹³C-nuclear magnetic resonance(¹³C-NMR),Fourier transform infrared spectroscopic（FT-IR）,X-ray photoelectron spectroscopy（XPS）and other characterization methods.It is deduced that the average molecular structure of CPE is an aromatic cluster structure which is connected by multiple monocyclic and bicyclic aromatic hydrocarbons through aliphatic chains and ether bonds.And,the average molecular weight of CPE is 1628 g/mol and the average molecular formula is C₁₁₄H₇₄O₉N₂.Based on TGA and TG-IR characterization,Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods were used to obtain the kinetic parameters of CPE pyrolysis.With the help of peaking fitting calculation model,the molecular structure information of CPE pyrolysis escape gas was obtained,and the mathematical model between the activation energy of CPE pyrolysis and the molecular structure parameters of pyrolysis escape gas was constructed.（2）Using CPE and HNO₃ as carbon and nitrogen sources respectively,brown coal-based carbon quantum dots（N-CQDs）were synthesized by one-step hydrothermal method for the detection of Cr（Ⅵ）in environmental water.The composition,structure and fluorescence properties of N-CQDs were studied.It was found that the N-CQDs could emit bright yellow-green fluorescence with a luminescence characteristic independent of excitation wavelength.The N-CQDs with the average particle size of 2.01±0.53 nm possesses uniform dispersion of C,N and O clinging to the surface,thus shows good water solubility,high stability and high fluorescence intensity as confirmed by transmission electron microscopy（TEM）,XPS and fluorescence spectrometer characterizations.Based on the fluorescence performance of N-CQDs that can be effectively quenched by Cr（Ⅵ）,a high sensitivity and selectivity Cr（Ⅵ）detection method is established.The detection range is 0～200μM the detection limit is 0.56μM,and the fluorescence quenching mechanism belongs to static quenching.It is realized as a simple,rapid and sensitive new method for the determination of Cr（Ⅵ）in environmental water.（3）Mesophase carbon microspheres（MCMB）were prepared from high-temperature coal tar pitch（HCTP）and CPE by means of co-condensation polymerization.The synergistic effects of two substances in co-carbonization were analyzed.The microstructure（including optical texture and carbon microcrystals）,surface morphology and impedance behavior of the MCMB were characterized by polarizing microscope,X-ray diffraction,Raman spectroscopy and electrochemical impedance spectroscopy（EIS）.The results show that the addition of CPE has a great influence on the reactivity of mixed pitches during the copolymerization process,on account of the C=O functional group in CPE providing the active sites for the copolymerization reaction.The appropriate amount of added CPE（3%of HCTP）can effectively increase the graphite microcrystalline content in MCMB,and reduce the amorphous carbon content and the charge transfer resistance.CPE is proved to be a good additive for the preparation of MCMB from HCTP,which can provide reference for the application of Hailaer brown coal pyrolytic extract.（4）With CPE as an additive for coal blending for coking,the influence of additive amount on CO₂ gasification reactivity（CRI）of Qingjian coke（QJ）,Daizhuang 1/3 coke（DZ）and Jiangsu Port coke（JS）was investigated.Thermogravimetric analysis,Raman spectroscopy,micro-strength and polarizing microscopy were used to study the effect of CPE addition on the microstructure and macroscopic properties of coke,and to explore the internal reasons and relations of the differences in the microstructure and macroscopic properties of coke.The results show that the co-carbonization effect of CPE and QJ coal is better than the other two.The specific aspects including the binding index of blended coal and the micro-strength of coke are improved and the gasification reactivity of coke is reduced.The work provides a new idea for improving the quality of brown coal and the saving of high-quality coking coal.