Free Radical Evolution And Structure Analysis Of Coal And Its Hydrogenated Liquefaction Intermediates

A new parameter standard curve for quantitative analysis of free radical content by EPR was established by using standard free radical samples.The new parameter standard curve was applied to analyze the free radical concentration of coal samples with different degree of coalification and coal hydrotreated asphaltene.13C CP/MAS/TOSS NMR was used to test different model compounds,and regression equation was established to quantitatively analyze different types of carbon structure.The regression equation was applied to modify the carbon structure parameters of coal and asphaltene,and then combined with element analysis,XPS,bond energy analysis to construct the macromolecular structure model of NMH coal and asphaltene.The changes of carbon structure of coal and asphaltene before and after hydrogenation were analyzed from the perspective of free radicals and molecular structure.The experimental results show that the relative error between the measured value and the theoretical value of the standard curve method is less than 5%,and the relative standard deviation of the repeatability and reproducibility experiments is less than 3%.The free radical concentration of coal samples with different coalification degree increases gradually with the deepening of coalification degree,from 0.853 1×1018/g of low rank lignite to 33.7899×1018/g of high rank anthracite.The concentration of free radicals in asphaltene obtained from NMH coal increased first and then decreased with the increase of liquefaction temperature,while in the process of HS coal liquefaction,the concentration of free radicals in asphaltene decreased gradually with the increase of liquefaction temperature.The change trend of asphaltene free radical concentration of NMH coal and HS coal is consistent with that of its yield,and the relationship between asphaltene yield and free radical concentration of HS coal is linear.The regression equations of the carbon structure of the measured value and the theoretical values of the different models were all correlated.The regression equations were verified by single model compounds and mixtures,after the modification,the H/C errors were all within 10%.The regression equation was used to calculate the corresponding carbon content of NMH coal and asphaltene,the H/C errors are all within 11%.The modified calculation method of carbon structure shows that the content of aliphatic carbon and aromatic carbon in NMH coal is 32.82%and 62.71%,compared with the aromaticity of 64.04%calculated by Van Krevelen’s empirical formula,the error between them is less than 2.2%;the content of aliphatic carbon in 370℃ asphaltene is 25.55%,aromatic carbon is 70.40%;the content of aliphatic carbon in 430℃asphaltene is 20.71%,aromatic carbon is 79.28%.NMH coal macromolecular structure constructed with modified carbon structure parameters is mainly composed of single ring and binary ring;370℃ asphaltene is mainly composed of binary ring and ternary ring;430℃asphaltene is mainly composed of ternary ring and quaternary ring.In the process of coal hydroliquefaction,the lower temperature asphaltene is mainly from the molecular structure cracking of raw coal,while the higher temperature asphaltenes are caused by the secondary reaction of free radical fragments in coal pyrolysis.