Calibration of solid state NMR carbon structural parameters and application in coal structure analysis

Carbon structure parameters were obtained accurately, if the NOE effect of carbon nucleus has been eliminated in¹³C CP/MAS/TOSS NMR test. This study has investigated different model compounds NOE effect intensity. And the results show that there is an obvious carbon structure error between the fitting test value and theoretical value in the different model compounds. The aliphatic carbon error is 25%-125%, and the aromatic carbon is 4%-50%, the NOE effect has great influence in solid state NMR. Therefore, the nonlinear regression equation was obtained by regression analysis of the measured and theoretical values of the model compound aliphatic and aromatic carbon. And this equation was used to calibrate the carbon structure of 9, 10-dimethylanthracene. It is found that after calibration the error between the measured value and the theoretical value of the modified aliphatic is reduced from 119.60% to 7.84%. The error of the aromatic carbon is reduced from -17.10% to 1.11%. And the error is within 10%. Then, the carbon structural parameters of different coal are calibrated by the regression equation. It is found that the H/C error of different coal is 45%-53% compared with elements analysis, and the calibration error is only 4%-13%, which is consistent with the results of elemental analysis. It indicated that the nonlinear regression equation could easily and precisely correct the solid state NMR carbon nuclear NOE effects and also provides new technical support for analysis of carbon structure in coal.