The excessive roof temperature and its impact on phenol production

When coal is subjected to high-temperature dry distillation in the carbonization chamber of a coke oven, a series of physicochemical changes occur in the coal. 　　The coal is loaded, and the surface moisture is evaporated at temperatures below 200°C; simultaneously, gases such as carbon dioxide and methane adsorbed in the coal are released ； As the temperature rises to 250–300°C, the oxygen-containing compounds at the ends of the coal’s macromolecules begin to decompose, producing carbon dioxide, water, and phenols; these phenols are mainly higher-order phenols ； At around 500°C, the side chains of the large molecular aromatic polycyclic compounds in coal break and decompose, producing gases and liquids. The coal softens and melts, forming a viscous gel-like substance in which gas, solid, and liquid phases coexist; aliphatic hydrocarbons are also generated, along with the release of hydrogen. The steam and gases that emerge from the gel layer before 600°C, as well as those that come partially from the semi-coke, are known as primary decomposition products; they mainly contain methane, carbon dioxide, carbon monoxide, combined water, and initial tar, with a very low hydrogen content. 　　The main compositional groups of crude tar are as follows, in %: alkanes (paraffins), olefins, aromatics, acidic substances, basic substances, resinous substances, and others – 8.0, 2.8, 58.9, 12.1, 1.8, 14.4, 2 respectively. The main aromatics in crude tar include toluene, xylene, methylnaphthalene, methylbenzene, phenanthrene, anthracene, and their methyl derivatives; the acidic compounds are mainly cresol and xyleneol, with small amounts of trimethylphenol and methylindole present as well ； Both alkanes and olefins are compounds with carbon counts ranging from C5 to C32, while the bases are mainly dimethylpyridine, tolueneamine, etc. C-H bond cleavage induces dehydrogenation. The temperature at which the C–H bond breaks is between 400 and 550°C. Saturated hydrocarbons undergo cracking to produce olefins, with hydrogen being released as a byproduct. For example: CH3CH2CH2CH3 → CH2=CHCH2CH3 + H2 → CH2=CHCH=CH2 + 2H2. Dehydrogenation begins at 500°C; by 650°C, a significant amount of hydrogen is produced. At temperatures above 800°C, the olefins undergo further cracking – for instance, some ethylene breaks down into methane, hydrogen, and carbon

As COD decreases, the viscosity of tar increases significantly, resulting in reduced recovery of chemical products

Teacher, there’s a passage on Baidu Baike that seems a bit different from what you said. When coal is heated in an air-free environment, the general process is as follows: at temperatures below 100°C, the gases adsorbed in the coal and some of the water evaporate; by 110°C, all the water has evaporated; and at 200°C, the combined water molecules also evaporate ； The first pyrolysis begins at 250°C, with gas escaping ； Tar is produced at temperatures above 350°C ； 550–600 °C, tar evaporation ； The second pyrolysis begins at temperatures above 600°C, with gas escaping once again and condensing to form high-temperature coke; decomposition stops at 900–1000°C, leaving behind coke.

It’s possible that the types of coal are different, so I dare not call them teachers. . . I’m also studying*