The composition and structure of coal

The composition of coal
Coal is a combustible ore composed of a complex mixture of organic and inorganic compounds. The organic components are mainly composed of carbon, hydrogen, oxygen, and a small amount of sulfur and nitrogen. At the same time, other trace elements inherited from the original plants are also included in the organic components. The inorganic component is dispersed throughout the coal, and it is composed of different ash-forming compounds. Inorganic components are introduced into peat swamps through residues brought about by wind and water flow during coalification, or are obtained from primitive vegetation and fluids from cracks and caves (Mackowsky 1968). Coal mineralogy can change and remove minerals through coal washing, combustion and conversion processes (such as liquid fuels and chemicals).

Some elements also participate in the formation of discrete minerals, such as pyrite. The concentration of inorganic components varies widely, and may range from a few percent of coal to the order of a few parts per billion of coal. Although 120 different minerals have been identified in coal, only 33 of them are commonly found in coal, and only 8 of these 33 types (quartz, kaolinite, illite, montmorillonite, The content of chlorite, pyrite and calcite) is so large that it can be considered as the main component.

Structure of coal
The structure of coal is extremely complex and depends on the origin, history, age and rank of the coal. In the late 1920s, chemists believed that coal consisted of a mixture of carbon and hydrogen-containing impurities. Analysis methods using dry distillation (heating without air participation) and solvent extraction (reaction with different organic solvents) have revealed that coal contains a large amount of carbon and a small amount of hydrogen, oxygen, nitrogen, sulfur and ash containing inorganic compounds , Such as aluminum and silicon oxides. The dry distillation process will produce tar, water and gas. Among them, hydrogen is the main component of the escaping gas, and the gas also contains ammonia, carbon monoxide, carbon dioxide, benzene and other hydrocarbons.

Richard Wheeler of Imperial College London, Friedrich Bergius of Mannheim (a city in western Germany), and Franz Fischer of Mülheim (a city in Germany) made important contributions to revealing the existence of benzene ring compounds in coal. In 1925, William Bone of Imperial College London confirmed the existence of a benzene ring structure in coal. They obtained terphenyl mono-, tetra-biphenyl- and other high carboxylic acids in the oxidation products of coal, which showed that three- and four-member aromatic structures, five-membered fused ring structures, and single-benzene ring structures generally exist in coal. . The simplest benzene ring structure contains 8 or 10 carbon atoms, while the fused ring structure contains 15 or 20 carbon atoms.
By studying the molecular conformation of coal, we can determine its reactivity during combustion, pyrolysis and liquefaction.

There have been some publications on this subject (such as WCI, WEC2004, Smith&Smoot 1990, Bhatia1987, Xuguang 2005, Carlson1991, etc.). Carlson (1992) studied the three-dimensional structure of coal by means of computer simulation, and further analyzed the structure of coal proposed by Given (1960), Solomon (1981), Shinn (1984) and Wiser (1984).