Thermal dissolution of Shenfu coal in different solvents

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The thermal dissolution (TD) behaviors of Shenfu (SF) coal, a kind of Chinese sub-bituminous coal at different temperatures in different solvents were investigated in this study. The results show that almost all of the ash in the raw coal was transferred into the TD residue. The TD soluble yield (TDSY) of SF coal increased with the raising of TD temperatures from 300 to 360°C for 60min with 1-methylnaphthalene (1-MN) as solvent, and the highest TDSY of 56% was obtained at 360°C. Further raising temperature to 380°C, the TDSY decreased rapidly. The highest TDSY obtained at 360°C can be attributed to the partial pyrolysis of SF coal.When N-methyl-2-pyrrolidinone (NMP) or methanol was added into 1-MN, the TDSY greatly increased. Especially, when 20% NMP was added, the TDSY reached up to 75%. Since NMP is a strongly polar solvent, it can dissociate the strong cross-links in the coal, resulting in the increase of the TDSY. However, when both of NMP and methanol were added into 1-MN, the TDSY dramatically decreased, indicating that there are some interactions between the two solvents.Crude methyl naphthalene oil (CMNO) was a more effective solvent for the TD of SF coal than 1-MN, and its TDSY achieved 66% at 360°C for 60min. Addition of various polar solvents into CMNO, the TDSY decreased, especially for the addition of methanol, the TDSY decreased by about 15%. The result indicated that methanol may react with some active fractions in CMNO, resulting in the decrease of the TD effect. When both of NMP and methanol were added into CMNO, the TDSY dramatically decreased due to the interaction between them. The TD soluble fractions (TDSFs) obtained from various solvents were characterized by elemental and FTIR analyses.