Premium
Formation of molecular nitrogen and hydrogen sulfide during high‐temperature pyrolysis of coals
Author(s) -
Tsubouchi Naoto
Publication year - 2014
Publication title -
asia‐pacific journal of chemical engineering
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.348
H-Index - 35
eISSN - 1932-2143
pISSN - 1932-2135
DOI - 10.1002/apj.1858
Subject(s) - char , pyrolysis , chemistry , sulfur , coal , nitrogen , crystallization , carbon fibers , hydrogen sulfide , particle size , sulfide , demineralization , chemical engineering , mineralogy , inorganic chemistry , organic chemistry , materials science , enamel paint , composite number , engineering , composite material
Nitrogen and sulfur release from eleven coals during pyrolysis at high temperatures (≥1000 °C) was studied in both fixed‐bed and free‐fall quartz reactors. Yields of N 2 , char‐N and H 2 S were found to depend strongly on the pyrolysis conditions, such that N 2 and H 2 S yields increased with increasing pyrolysis temperature and coal particle residence time, whereas char‐N decreased. There was also a strong inverse correlation between N 2 and char‐N yields, suggesting that the majority of N 2 is produced from char‐N through solid‐phase reactions. H 2 S formation had no clear relationship with the carbon and sulfur contents of the parent coal. Demineralization with HCl washing was observed to remove primarily Ca 2+ cations from four low rank coals examined and to increase the char‐N and H 2 S yields but decrease N 2 generation. In contrast, the addition of 3 wt% Ca to the four coals drastically enhanced N 2 formation and suppressed the formation of char‐N and H 2 S. The X‐ray diffraction analysis of the chars derived from Ca‐loaded coals revealed that the Ca was present primarily as CaO with an average crystallite size of 15–45 nm, and that the presence of the Ca promoted carbon crystallization. Small diffraction peaks due to CaS were also observed. Fine particles of CaO may not only promote N 2 formation through solid phase reactions of char‐N but undergo sulfur capture reactions. A mechanism for the Ca‐catalyzed N 2 formation was discussed in terms of solid–solid reactions between CaO particles and char‐N. © 2014 Curtin University of Technology and John Wiley & Sons, Ltd.