Organic Sulphur in Coal
AUTHOR: Robert M. Davidson
DATE: August 1993
Sulphur in coal is found in both inorganic and organic forms. The inorganic sulphur is mostly pyrite (FeS2). Besides pyrite there may be marcasite and sulphates. The sulphate content is usually low unless the pyrite has been oxidised. The forms of organic sulphur are less well established.
Organic sulphur cannot be removed by physical means and existing chemical process are generally high cost. If milder, cheaper desulphurisation processes are to be developed then a knowledge of coal's organic sulphur chemistry is a necessity.
This report examines the standard (ASTM) methods for determining the quantity of total organic sulphur in a coal sample; newer methods of accomplishing this; and the variations in sulphur content in the different macerals. The question of the presence of elemental sulphur in coal is addressed. Methods of identifying organic sulphur species present in coal are discussed these mainly involve the use of gas chromatography and mass spectroscopy. Chemical methods for quantifying organic sulphur forms involve flash pyrolysis, temperature programmed reduction, and temperature programmed oxidation. The data obtained by these means are assessed. Newer methods of instrumental analysis involving X-ray spectroscopy are considered and the results compared with those obtained from chemical analysis.
Finally, the application of our knowledge of organic sulphur chemistry to the assessment of desulphurisation stratagems is briefly examined. It is concluded that while there has been much progress there is scope for further study of the quantity and form of organic sulphur in coal.