Graphitization mechanism of coal organic macromolecular carbon structure

Coalification and graphitization jointly control the formation and evolution of coal. Due to the complexity of coal composition, chemical structure and the particularity of graphitization, it is very difficult to study the thermal evolution process of coal macromolecular structure. In order to carry out an exploratory research from the perspective of macromolecular quantum chemical calculation, different rank coals and coal measure graphite samples were selected in this study. The organic macromolecular structure system of different rank coals was constructed by using industrial analysis, elemental analysis, solid-state nuclear magnetic resonance, high-resolution transmission electron microscope, gold tube thermal simulation and AMS quantum chemical calculation technology, and the evolution of macromolecular carbon structure and graphitization mechanism of coal organic matter were studied. The conclusions are as follows:(1) With the increasing maturity, the proportion of aromatic structure in coal macromolecular structure gradually increases, the content of fat structure gradually decreases, and the aromatic carbon ratio reaches more than 0.9 in anthracite stage.(2) The aromatic stripe content of 2×2 and 3×3 in the macromolecules of low grade coals and medium grade coals accounts for the largest proportion, and the stripe proportion in the dominant direction(75°,90° and 105°) increases from 26.47% to 50.10% with the increase of maturity. The stacking of aromatic stripes occurs in the anthracite and high anthracite stages.(3) The three-dimensional macromolecular structure model was used to carry out pyrolysis simulation calculation. It was found that with the increase of simulation temperature, the aromatic lamellar spacing decreases regularly from 0.400 nm to 0.318 nm, which is consistent with the result that the aromatic lamellar spacing from low rank coal to high rank coal decreases from 0.467 5 nm to 0.368 0 nm.(4) The change law of macromolecular structure system in the process of coal graphitization was analyzed and evaluated. It was preliminarily considered that the removal of heteroatom and fat structure is the reason for the transformation of coal aromatic structure to crystal cluster. The graphitization mechanism of coal macromolecule was discussed, and the change law and evolution mechanism of carbon structure in the process of coalification and graphitization were preliminarily revealed.