Desulfurization and Solubilization of High-Sulfur Coal by Superacid HF/BF3

Abstract

Anhydrous hydrogen fluoride (HF) alone or combined with a small proportion of boron trifluoride (BF3) desulfurized high-sulfur coal in the presence of hydrocarbons without H2 in mild reaction conditions. HF removed mainly sulfidic and oxidized sulfur at temperatures of 75−200 °C, but at 250 °C decreased thiophenic sulfur. HF/BF3 at 200 °C decreased thiophenic sulfur by ionic hydrogenation as well as decreased sulfidic and oxidized sulfur. The extent of desulfurization of coal was roughly correlated with solubilization. Lighter fractions (hexane insoluble−benzene soluble) in the treated coal had lower sulfur content, especially of sulfidic sulfur, indicating that removal of sulfidic sulfur in coal improves its extractability. In contrast, the heavier fraction in the treated coal had higher sulfur content, which consisted of reactive sulfidic and oxidized sulfur as well as thiophenic sulfur.