| The gaseous compound composition of coal-bed gas reservior showed that CH4, C2-C4, CO2, H2O and H2 were the main gasous products of the coalification process. The generation kinetics of these gaseous products had been studied greatly for the past several decades, based on which, three devolatilisation model had been established. But as the complexity of coal structure, further comprehending of the generation mechanism of these products still needed. As deeply understanding of sysmatic coalification theory must taken profound understanding of the mechanism of pyrolysis products as the basis, understanding mechanism of gaseous products and the relation of its kinetics and coal structure is one of the important research contents in coal geology,coal chemistry and organic geochemistry.As low rank coal situated at the lower stage of coalification, studying on the pyrolysis characteristics of low rank coal was benificial for understanding the whole coalification stage. The first coalification jump(TFCJ), which caused by bituminization, induced abrupt change of physical chemistry properties, but the essence and mechanism of TFCJ needs to be revealed on molecular scale, so HLH lignite, YM lignite, SH long flame coal, YZ, TF and PS gas coal and DT non-caking coal whose ROm ax were 0.33%, 0.47%, 0.51%, 0.62%, 0.65%, 0.70% and 0.81% were chosen as the research emphasis of this paper, the structural characteristics and its effect on the generation of gaseous products were analyzed systematically, and the molecular mechanism of TFCJ was expected to be deepen understood. Meanwhile, Because low rank coal has abundant side chains and various functional groups, systematically understanding of pyrolysis characteristics and mechanism on coal molecular project scale is the basis for developing and deepening coal molecular project.In this paper, the FTIR experiment was used to analyze coal macromolecular structure and various functional groups characteristics, and the XRD was used to obtain the aggregate structure. Meanwhile, NMR and RAMAN experiments were done for part of the samples. TG/MS experiment were done for the whole samples, and the generation kinetics of the pyrolysis products were analyzed. The main conclusions were as follows:1. Analysis of the FTIR structural parameters demonstrated that the relation of A(1703+1745)/A1618, A(1703+1745)/A(2800-3000), A1745/A1618 and Har/Hal with coal rank showed the minumin value at TFCJ, but the relation of A1618/A(1703+1618) and was opposite, the value of which showed the maximum at TFCJ. This revealed the characteristics and essence of the coalification jump and provided foundation for deeply realization of TFCJ.2. Analysis on the correlation between the different structural parameters showed that, La was positively linear related with A2924/A2964 and d002 was negative related with A(700-900)/A1460. The results demonstrated that La related not only with the aromatics, but also with the aliphatics, and the aliphatics in low rank coals presented directionality.3. Pyrolysis characteristics and generation kinetics of the gaseous products demonstrated that the maximum weight loss rate temperature was the lowest near TFCJ; the weight loss rate showed a turn near TFCJ; and the activation energy of the main pyrolysis stage(300-600℃) was the maximum near TFCJ; and the generation rate peak temperatures of CH4, CH3, C2-C4, C6H6 and H2 showed the minimum value and the initial generation temperatures of CO2 and H2O were the maximum value near TFCJ. So the pyrolysis characterisation and generation kinetic parameters all present transition near TFCJ, and this had proven further that transition change of the coal macromolecular structure near TFCJ, and this result provided foundation for fully and systematically realisation of TFCJ.4. The evolution curves of CH4, CH3, C3H6 ,C3H7, CO2 and C6H6 showed that they are not the results of one reaction but multi-reactions. Curve-fitting of these curves were done and the generation kinetics characteristics were analyzed, the mechanism of elementary reaction were analyzed. The main results are as below:(1) CH4, C3H7 and H2 is the result of 5 reactions, CH3 is the result of 4 reactions, and C6H6 is the result of 4-5 reactions.(2) the mechanism of CH4, reaction type 1: it has two reactions for HLH and YM coals, the first is the desorption of adsorption CH4 and the second is the decomposition of–OCH3. Desorption of methane occurred as adsorption and solid solution is the main reaction for the other 5 coals; Reaction type 2: it's the results of two reactions, one is decomposition of aliphatic side chain with oxygen-containing functional group, the other is decomposition ofβ-site of methylene; Reaction type 3: this reaction is formed through CH3 generated from secondary decomposition of long-chain aliphatics reacted with H generated from decomposition of toluene, meanwhile, rupture of Ar-C-C-Ar and hydroaromatic are also the main origin of this reaction; Reaction type 4: methane in this reaction is from decomposition of toluene and cyclization and aromatisation of aliphatic chain; Reaction type 5: methane in this reaction is the result of aromatisation.(3) the mechanism of benzene, Reaction type 1: decomposition of toluene; Reaction type 2: decomposition of macromolecular structure; Reaction type 3: rupture of Ar-C-C-Ar and hydroaromatic structure;Reaction type 4: cyclization of alkane and aromatisation of cycloalkane; Reaction type 5: condensation.(4) the mechanism of CO2: at low temperature, CO2 is generated from decomposition of–COOH and–OCH3,with the increase of temperature, CO2 is related with oxygen-heterocyclic, when the temperature higher than 700℃, CO2 is mainly from carbonate.(5) the mechanism of H2: Reaction type 1: for HLH, YM and DT coal, H2 is the result of cyclization of alkane, for TF,PS,YZ and SH coals, there are two reactions, one is from decomposition of toluene, the other is decomposition of aliphatic free adicals generated from secondary decomposition of long chain aliphatics; Reaction type 2: for HLH, YM and DT coal, H2 is mainly from aromatisation of cycloalkane, for TF, PS, YZ and SH coal, H2 is mainly from dehydrogenation of hydroaromatic cycle; Reaction type 3: H2 is from condensation of aromatic ring; Reaction type 4 and Reaction type 5: H2 is the result of condensation of aromatics.5. by the research of the structure evolution of low rank coal and the generation characteristic and kinetics of gaseous products during pyrolysis, the molecular scale of TFCJ reflects that it was the result of the competition between the decomposition and polymerization of hetero-atomic functional groups was found. Decomposition of heteroatom functional groups prevail before 0.60% of RmO ax, and polymerization reached the first peak near 0.60% of RO max, then with the progress of the coalification, aliphaitics side chains began to remove and polymerization was inhibited. So the essence of TFCJ was the result of the advantage of polymerization. However, this polymerization was not the polymerization of aromatics but the interaction between the rest oxygen-containing functional groups, then new functional groups formed and caused the increase of the molecular system.
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