Characterization and Refining Pathways of Straight-Run Heavy Naphtha and Distillate from the Solvent Extraction of Lignite

Abstract

Coal liquids were produced by solvent extraction of Bienfait lignite at 415 °C and 4 MPa H₂ for 1 h with a hydrotreated coal tar distillate in a 2:1 solvent to coal ratio. Detailed characterization was performed on four straight-run distillation fractions of the coal liquids in the 120–370 °C boiling range. It was found that the coal liquids contained very little aliphatic material. Most of the compounds were aromatics, with aromatic compounds having no alkyl substituents dominating the composition. The aromatic carbon content increased with boiling fraction from 80 wt % in the 120–250 °C fraction to 94 wt % in the 343–370 °C fraction. Major compounds identified in the coal liquids were acenaphthene, phenanthrene, fluoranthene, and pyrene, which constituted 62 wt % of the total product. The coal liquids also contained heteroatom species. Interestingly, the nitrogen content did not monotonically increase with an increase in boiling point. The maximum nitrogen content was found in the 300–343 °C boiling fraction as a result of a high concentration of carbazole. The refining pathways for transportation fuel production were evaluated. It was found that the naphtha fraction could be upgraded to a motor gasoline blending component just by hydrotreating. No subsequent catalytic reforming was necessary because of the low aliphatic content of the naphtha. The kerosene required severe hydrotreating in order to be acceptable as a jet fuel blending component, mainly because of the high dinuclear aromatic content of the straight-run kerosene. The distillate made a poor feed material for diesel fuel and required severe hydrotreating to achieve an acceptable cetane number. In general, the coal-derived distillate would benefit from ring opening to reduce its density. The prognosis for transportation fuel production from the coal liquids was not favorable. The production of aromatic chemicals was a better fit with the properties of the coal liquids