Purposes As a by-product of coking enterprises in China, crude benzene commonly exhibits fluctuations and exceedances in chlorine content. The characteristics of coal significantly impact the migration and transformation behavior of chlorine. Methods On the basis of the structural characteristics of coal and the distributions of chlorine forms, release behavior of chlorine during coking coal pyrolysis was analyzed. The effects of secondary reaction temperature and residence time of volatile on the chlorine release process were also investigated. Results The results indicate that chlorine in organic forms in coal is released more readily. Coal samples with higher organic chlorine content have more complete chlorine release under the same pyrolysis conditions. The chlorine content of pyrolysis gas and tar from Liulin coal is 44.20% and 53.67%, respectively (with a chlorine release rate of 97.87%). This is because the organic chlorine in coal is primarily bound to the coal structure via covalent bonds and/or coordinations with alkaline and oxygen-containing functional groups. It is therefore easily decomposed and converted into HCl or organic chlorides. However, the chlorine release rate for Inner Mongolian coal is only 85.01%, which is due to the presence of metallic components, such as calcium and magnesium. These metallic components can react with HCl to form relatively stable inorganic chlorides. Compared with residence time, the secondary reaction temperature of volatiles has a more significant impact on chlorine release. Macromolecular compounds (e.g., C13H19Cl, C20H12Cl2) undergo cleavage to form chlorine-containing free radicals. Then,they are converted into HCl and lower-carbon-number chlorinated substances (e.g., C2H2Cl2O, C2H2Cl4) after combining with hydrogen-rich free radicals. There is interactive migration behaviour between these two forms of organic chloride and HCl.
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