Modifications of standard methods for coal analysis for sulphur and nitrogen determinations in oil shales

Abstract

Investigations were made to determine if methods that are satisfactory for determining total sulphur and total nitrogen in coals are also suitable for determinations when using compounds that contain some organic structures to be expected in oil shale kerogens. Sulphur recoveries in an excess of 98%, and typically better than 99%, were obtained using modifications of ASTM method D3177 (75). It was found that the semi-micro Kjeldahl method in the BS 1016 : Part 6 : 1977 was not suitable for the determination of nitrogen in aromatic nitrogen compounds. For example, the recovery of nitrogen from 8-hydroxyquinoline was increased from approximately 30 to 96% by increasing the digestion time to a minimum of 2 h. Variation in the initial amount of sulphuric acid in the digestion mixture between 3 and 5 ml did not alter the recovery. The use of the modified semi-micro Kjeldahl method for an oil shale sample gave a higher nitrogen recovery and better precision of results than the unmodified standard method.