Modification of Model Structures of Upper Freeport Coal Extracts Using 13C NMR Chemical Shift Calculations

Abstract

The extract from carbon disulfide/N-methyl-2-pyrrolidinone mixed solvent extraction of Upper Freeport coal at room temperature was fractionated with acetone and pyridine into three fractions, and solid-state 13C NMR measurements of these fractions were made. Model structures for the three extract fractions constructed by Takanohashi et al. (Energy Fuels 1998, 12, 1168) were estimated using the NMR chemical shift calculation method. By comparing the spectra calculated for the model structures with the observed spectra, some corrections were made to the chemical structures of the original models to fit their spectra. Compared with the observed spectra, for the acetone-soluble fraction (AS), the model structure was richer in nonprotonated aromatic carbon and β methylene carbon, and poorer in protonated aromatic carbon and methyl carbon, and, for the acetone-insoluble−pyridine-soluble fraction (PS) and pyridine-insoluble−mixed-solvent-soluble fraction (PI), the spectra calculated for the model structures showed higher fractions for nonprotonated aromatic carbon and methylene carbon, and lower fractions for methyl carbon. We proposed modified model structures based on NMR chemical shift calculations for the three fractions.