Article ID: ISIJINT-2018-807
A subbituminous coal was treated with a wash oil or 1-methyl naphthalene (MN), for 1 hr or 2 hr at 673 K or 693 K under nitrogen, in order to chemically upgrade the low-rank coal. In case of wash oil as the treated solvent, the extraction yield at 673 K reached 66 mass%, daf after recovering the solvent, however, some of wash oil remained in the extract because the wash oil contained polar compounds of 8.5 masst%. The extraction yield with MN at 673 K was 41.2 mass%, daf and it decreased with an increase in the severity of the extraction condition; it was 36.3 mass%, daf at 693 K for 2 hr.
The more polar solvent which contained polar compounds of 21.7 mass%, called the Super-Solvent (SS), was successfully produced by separation of the wash oil with methanol/water (3:1 by weight) mixture. The extract obtained from the extraction with SS showed similar degree of the H/C and O/C atomic ratios as bituminous coals, indicating that chemically upgrading reactions might occurred by the solvent treatment.
After the solvent treatment with MN at 693 K for 2 hr, hexane was used as the washing solvent, resulting that the ratio of hexane soluble fraction was a few. Thus, the solvent upgraded coal originated from a low-rank coal was successfully produced in high yield. The H/C and O/C ratios of the solvent upgraded coal became the similar level as those of caking coals. Decarboxylation and aromatization reactions might occur during the solvent treatment.
