The ASTM method for the analysis of sulphur forms in coal is applied to a hydrodesutphurized coal. Precautions necessary to prevent the calculation of erroneous high values of organic sulphur are illustrated. The reduction of sulphate ion to sulphite ion by the hydrogen is reported. A complete sulphur balance shows the amounts of each sulphur form reacting with hydrogen.
The large-scale use of high-sulphur coals poses many problems such as boiler deposits, corrosion, and large amounts of sulphur dioxide emissions.
With new air quality standards, the utilization of coals with sulphur contents greater than one percent may soon be essentially prohibited in large urban areas in the United States'. The above facts combined with the relative difficulty of obtaining enough low-sulphur coal has created a great interest and need in developing various processes to desulphurize coal. As these processes are developed, there is also a rapidly growing need for reliable analytical methods of analysis of both the raw and the desulphurized coal.
In this study, ASTM method D 2492* for the analysis of sulphur forms in natural (raw) coals is applied, with necessary modifications, to the analysis of sulphur forms in hydrodesulphurized coal samples.
It was applied to one particular coal sample which was then subjected to hydrogenation at high temperature and pressure.
When pyrite (Fe&) reacts with hydrogen, half of the sulphur is eliminated as hydrogen sulphide and half remains as sulphide sulphur, FeS. Richardson has confirmed the formation of FeS by using thermo-magnetic studies3. The conversion is essentially complete above 400ยฐC.
Because sulphide sulphur is present only in small amounts in most natural coals4, the above ASTM method does not analyse for it.
Shimp and coworkers have pointed out that if sulphide sulphur is present in natural coals analysed by this method, incorrectly high values for organic sulphur will result'.
In coals treated with hydrogen, sulphide sulphur is present in considerable quantities.
This sulphide sulphur is analysed as part of the total sulphur content of the sample but escapes during the first treatment with acid. As the organic sulphur content is determined by difference, it becomes incorrectly large owing to this loss.
A similar error occurs when sulphate sulphur (SO:-) is reduced to sulphite sulphur (SO:-) by the hydrogen treatment. It is Included in the total sulphur analysis but is lost as sulphur dioxide gas during the acid treatment and produces a calculated organic sulphur content that is also too high.