REMOVAL OF BASIC NITROGEN SPECIES IN COAL-TAR PITCH BY METAL SULFATES SUPPORTED ON SILICA-GEL

Removal of nitrogen species in the toluene soluble fraction of a coal-tar pitch using metal sulphates (NiSO4, CuSO4 and Al2(SO4)3) supported on silica gel (MB-3A and MB-4B) was studied with the objective of preparing a feedstock of low nitrogen content for needle coke production. The adsorbent of supported NiSO4 (10 wt% on MB-4B) reduced the content of nitrogen in the fraction from 0.91 to 0.45 wt% (methanol insoluble-toluene soluble (MI-TS)) and from 1.1 to 0.69 wt% (TS) at recovered pitch yields of 82 and 74 wt%, respectively at a pitch/adsorbent ratio of 0.5. The major portion of the adsorbed pitch was recovered by extraction with a mixed solvent of toluene, methanol and water. The nitrogen content of recovered pitches was enriched to 3.1 wt% (TS). Aluminium sulphate (10 wt% supported on MB-4B) exhibited the largest adsorption capacity of the sulphates examined. MB-4B with larger pores was the better support. The acidity of the sulphate, controlled by the extent of hydration, is the key for such adsorption and desorption of nitrogen species from coal-tar pitch. The support medium with larger pores dispersed the sulphate on the accessible surface to increase the number of accessible active sites for the large nitrogen-carrying species. The adsorption capacity of the sulphate and the nitrogen content of the purified pitch are balanced because the acidity of the former and basicity of the latter range from strong to weak.