Determination of carboxyl groups in Yallourn brown coal

Abstract

Air-dried run of mine Yallourn coal, when subjected to a technique for the determination of total carboxyl content that has previously been successfully applied to other brown coals, fails to respond fully to conditions found adequate for full exchange of the previously analysed brown coals. In this technique, the carboxyl groups, both acid and salt-form, are converted to the barium salt form by exchange in barium chloride/triethanolamine solution; this is followed by exchange with acid. Excess acid is determined by titration. The carboxyl content is then calculated from the amount of acid used in the exchange. When subjected to this procedure, only 72% of the Yallourn coal's carboxyl groups are exchanged. Complete exchange is achieved with Yallourn coal only after an extended period (≈ 64 h) or an initial acid-washing of the coal to convert all carboxyl groups to the acid form. The difficulty in the accessibility of the Yallourn coal's carboxyl groups appears to be linked to its petrographic composition. For general application, acid extraction is recommended prior to ion-exchange for the accurate determination of the total carboxyl content in brown coals.