Modified active carbons from precursors enriched with nitrogen functions: sulfur removal capabilities

Activated carbons were prepared by carbonization and steam activation of nitrogen-enriched low-rank coals. N-enrichment was performed by reaction of ammonia or its derivatives (ammonium carbonate, hydrazine, hydroxylamine, urea) with the carboxyl groups either naturally occurring in coal or artificially introduced by performic oxidation. Urea at an elevated temperature and pressure appeared to be the most efficient. The yields of the products and their nitrogen contents suggest the chemistry of these reactions involving not only urea itself but also its thermal transformation products. The activated chars obtained from the selected nitrogen-enriched precursors had considerable effective surface areas and displayed excellent sulfur removal. (C) 1998 Elsevier Science Ltd. All rights reserved.