Examination of the role of CS2 in the CS2/NMP mixed solvents to coal extraction

The roles of CS2 in the CS2/NMP mixed solvent to coal extraction and solubilization were investigated in this study. There was little effect of removing of CS2 from the solutions on the solubilities of UF coal extract and pyridine insoluble (PI) of the extract in the NMP/CS2 mixed solvent, suggesting that NMP has high enough solubilities to the UF coal extract and PI. Six Argonne different rank coals were extracted with the CS2/NMP mixed solvent and NMP, respectively. It was found that the extraction yield difference between NMP and CS2/NMP mixed solvent for UF coal is largely deviated from the curve obtained for the other 5 coals, suggesting that the pre-swelling of CS2 in the mixed solvent may be one of important roles for high extraction yield of UF coal in the CS2/NMP mixed solvent. FTIR indicated that there was a strong interaction between CS2 and NMP in the CS2/NMP mixed solvent of 1 : 1 volume ratio, which made the strong absorbance at 2156 cm− 1 in the FTIR spectra, and this interaction may disrupt the dipole based association of NMP thus making the CS2/NMP mixed solvent lower viscosity, to penetrate more quickly into the network structure of coal, resulting in the larger solvent partner (NMP) to enter and break the stronger coal–coal interactions.