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

In order to eliminate the Nuclear Overhause Effect (NOE) of carbon nucleus in 13C CP/MAS/TOSS NMR experiment and to obtain more accurate carbon structure parameters, NOE intensities of different model compounds were examined. The results show that there is an obvious carbon structure error between the fitting test value and theoretical one for different model compounds. The aliphatic carbon error is 25%-125%, while the aromatic carbon is 4%-50%. Therefore, the nonlinear regression equation is obtained by regression analysis of the measured and theoretical values of aliphatic and aromatic carbon in model compounds. Moreover, this equation was used to calibrate the carbon structure of 9,10-dimethylanthracene. It is found that after calibration the error between measured and theoretical value for aliphatic is reduced from 119.60% to 7.84%. The error for aromatic carbon is reduced from −17.10% to 1.11%. And the error is within 10%. Then, the carbon structural parameters of different coals are calibrated by the regression equation. Compared with elements analysis, H/C error is 45%-53%, while the calibration error is only 4%-13%, which is consistent with the results of elemental analysis after calibration. It indicates that the nonlinear regression equation could easily and precisely eliminate the solid state NMR carbon nucleus NOE and also provide new technical support for carbon structure analysis in coal.