Study On Characteristics Of Aromatic Rings In Unit Structure Of Coals

Coal consists of two major structural elements, aromatic clusters (condensed aromatic rings) and intercluster bridges (short alkyl bridges, ether linkages, and thioether linkages). In addition, aliphatic structures are also present in coal. The size of the aromatic ring structures in coal gradually increases with an increase in rank. There were some different knowledge on average size of aromatic ring per cluster and range of aromatic ring structures in coals. Traditional concepts focused on qualifying the structural units of aromatic ring structures to study coal structure. However, the number of aromatic ring structures of coals of different coalifications have not been reported by an experimental approach. Existing studies focused on in-depth quantization and analysis of aromatic nuclei in coal structures. Quantification of the aromatic ring structures in coals of different coalifications provides further knowledge of coal structure. Further, association is an important noncovalent interaction between aromatic clusters in coal structure. The investigation of association between aromatic cluster structures of different rank coals is necessary. This work aims to study characteristics of aromatic rings in unit structure of coals, quantifies these aromatic ring structures of coals of different coalifications using sequential oxidation with basic permanganate, dissects association between aromatic ring structures in coals of different coalifications by solid phase extraction. The main study as follows.1. The quantification of aromatic rings in unit structure of lignite was studied. By the sequential oxidation of a sample of lignite (C%, on a dry, ash-free basis,65.8), the filtrates and residues were analyzed and quantified by high-performance liquid chromatography, gel permeation chromatography, Gas Chromatography/Mass Spectrometry, and ultimate analysis. The types and amount of aromatic ring structures in lignite were determined. The results indicated the presence of three types of aromatic ring structures based on the oxidation characteristics of lignite. Type ? structure, which can be oxidized into benzene poly(carboxylic acid)s; (2) Type ? structure, in which the aromatic ring is appended by containing O/N/S groups such as benzofuran, indol, benzothiophene, phenol, and anisole and which can be over-oxidized into small molecular fatty acids; and (3) Type ? structure, in which the aromatic organic matter cannot be oxidized. The concentration of Type ? aromatic ring structures is 0.71 mmol/g of lignite (on a dry and free-ash basis). For type ? structures, the concentrations of aromatic heterocycles containing nitrogen and sulfur are 0.07 and 0.14 mmol/g, respectively, assuming that these aromatic heterocycles contain an average of one nitrogen or sulfur atom per heterocycle. For type III structures, the concentration of tetrahydrofuran soluble substances, which are primarily 2,5-cyclohexadiene-l,4-dione, 2,6-bis(1,1-dimethylethyl), dibutyl phthalate, di-n-octyl phthalate, and butylated hydroxytoluene, is 0.035 mmol/g.2. In this study, the aromatic rings in unit structure of middle-low rank bituminous coals were classified and quantified. Samples of coal 1 (C%,77.4), coal 2 (C%,81.7) and coal 3 (C%,85.0) were subjected to sequential oxidation. The filtrates and residues were quantified using high performance liquid chromatography, gel permeation chromatography and ultimate analyses. The concentrations of Type ? in coals 1-3 are 2.01,2.20, and 2.93 mmol/g, respectively. Type ? consists of aromatic hydrocarbons based on oxidation of representative model compounds (methylbenzene, naphthalene, tetrahydronaphthalene, and so on) and nuclear magnetic resonance analyses of raw coals. Moreover, the concentrations of nitrogen-containing aromatic nuclei of Type ? in coals 1-3 are 0.37,0.62, and 0.51 mmol/g, respectively. The concentrations of sulfur-containing aromatic nuclei of Type ? in coals 1-3 are 0.11 0.45 and 0.17 mmol/g, respectively. Type ? is composed of aromatic heterocycles (benzofuran, carbazole, indole, benzothiophene, and so on), phenol, and anisole. The content of Type ? is extremely low, and the concentrations of tetrahydrofuran (THF) extracts of Type ? in coals 1-3 are 0.096,0.004, and 0.057 mmol/g, respectively. THF extracts of Type ? consist of diphenyl, diphenyl ether, and diphenylene oxide, THF-insoluble substances of Type III consist of polycyclic aromatic hydrocarbons, such as rubicene, truxene, decacyclene, and so on. The polycondensation of polycyclic aromatic hydrocarbons gradually increases with increasing coalification of bituminous coal. The polycondensation of nitrogen-/sulfur-containing aromatic clusters rapidly increases when carbon content in bituminous coal reaches 81.7%. The average size of the aromatic ring structures in the coals (C%,77.4-81.7) contains 2-ring to 3-ring with a maximum of 5-ring in the higher-ranked coal (C%,daf,81.7-85.0).3. The rule of changes in characteristics of aromatic rings in unit structure of coals of different coalifications was demonstrated. The effect of the percentage of carbon (C%) (on a dry, ash-free basis, in the range of 65.2-89.4) in coal on the concentration of aromatic nuclei was shown as follows. The concentration of aromatic nuclei gradually increased to 2.99 mmol/g from 0.79 mmol/g with an increase in C%. After C% reached 85.0, the concentration of aromatic nuclei began to decrease to 1.89 mmol/g from 2.99 mmol/g. The results indicate that the concentration of aromatic ring structures in bituminous coal higher than that of other coals, the degree of polycondensation of aromatic ring structures begins to rapidly increase after C% in coal reaches 85.0.4. Association between aromatic clusters in unit structure of coals of different coalifications was studied. Influences of acid, alkali, and organics on solid phase extraction of coals of different coalifications were analysed using synchronous spectra, gel permeation chromatography, and electron spin resonance. The rules of change in extraction yield, aromatic size of extracts, range of molecular weight of extracts, and radical content of raw coals and residues were demonstrated to study the association between aromatic cluster structures of coals of different coalifications. During the extraction of coals of different coalifications using polar solvents, the association between aromatic cluster structures of high-volatile bituminous coals weaker than those of other coals. With the conditions of acid, alkali, and organics, there were significant differences in association between aromatic cluster structures of coals of different coalifications. The size of aromatic ring structures of extracts ranged from 1 ring to 5 rings. The range of molecular weight of extracts that came from coals of different coalifications was 162.40-290.73 amu.