14 MeV INNA oxygen determinations in coal conversion liquids

Fast neutron activation analysis has been applied to the direct determination of oxygen in coal conversion liquids. The detection system consists of two solid 7.6 cm×7.6 cm NaI(T1) detectors connected to a summing amplifier and mounted at 180° with respect to a uniaxially rotated sample container. Differences have been observed in the gamma-ray self-absorption for the low average atomic number organic matrix in coal liquids as compared to the higher average atomic number standards such as USGS Standard Rock BCR-1 and NBS Standard Reference Mateiral 136b, K₂Cr₂O₇, which have commonly been used for oxygen determinations in silicate rocks. In order to minimize problems associated with self-absorption and variable irradiation and counting geometries, a set of organic liquids was selected and evaluated for use as oxygen standards in the analysis of coal-derived liquids. The standard liquids were selected using criteria of high boiling point, well-defined stoichiometry, high purity, non-hygroscopic nature and simple C−H−O elemental composition. The final set of liquid standards is shown to yield an experimental oxygen—stoichiometric oxygen correlation coefficient of 0.9995 with an intercept at the origin, for liquids with oxygen contents from 3.55 to 49.94%. Dilutions of standards from the set with n-hexane permit extension of the range to lower oxygen contents.