Revalidation of measurement method of free radical concentration and its application in coal chemistry

The standard curve method established by predecessors to measure the concentration of free radicals in coal was optimized to take the quadratic integral area ratio of the DPPH standard sample to the reference sample as new parameters. The results show that the relative error between the measured and theoretical values of the new parameter standard curve method is less than 5%, and the relative standard deviations of repeatability and reproducibility are less than 3%. The new parameter standard curve method was used to analyze the free radical concentration of the coal with different coal ranks and the asphaltene of Xinjiang Heishan Coal (HS). It is found that with the increase of coal rank, the free radical concentration in the coal increases gradually, from 8.531×10¹⁷/g for low-rank lignite to 3.37899×10¹⁹/g for high-rank anthracite. In the process of HS coal liquefaction, with the increase of liquefaction temperature, the free radical concentration of asphaltene decreases gradually, from 1.5793×10¹⁸/g at 290℃ to 7.410×10¹⁷/g at 450℃. The change trend of free radical is concentration in the asphaltene consistent with that of asphaltene yield.