Coal desulfurization with sodium hypochlorite

Wet desulfurization of Pittsburgh No. 8 coal and Illinois No. 6 coal were conducted with sodium hypochlorite in the laboratory. Pittsburgh No. 8 coal was leached by hypochlorite at high pHs in one step only. The hypochlorite concentration varied from 0.2 M to 0.6 M, the sodium hydroxide (NaOH) concentration was 0.2-0.8 M, and temperature was 80 and 90 degrees C. The desulfurization of Illinois No. 6 coal was conducted in three consecutive steps of pretreatment in concentrated ammonia at room temperature, leaching with hypochlorite at room temperature and hydrolysis in a NaOH solution at 90 degrees C. In the leaching step, the hypochlorite concentration varied from 0.2 M to 0.8 M. The desulfurization method of Pittsburgh No. 8 coal was observed to reduce mainly pyritic sulfur. More than 70% of pyritic sulfur removal was achieved at the optimum conditions of 0.4 M hypochlorite, 0.4 M NaOH, and 90 degrees C. The desulfurization method for Illinois No. 6 coal was capable of reducing significant amounts of organic sulfur. The removal of organic sulfur achieved a 37.8% reduction at the optimum operation of leaching at 0.4 M hypochlorite and room temperature, followed by hydrolysis at 0.3 M NaOH and 90 degrees C. The chlorine content in the coal produced by the chlorination during leaching was kept below the threshold value of 0.3% under the optimum conditions of the desulfurization method for each coal.