New technique for the electrochemical analysis of coal-derived materials

Abstract

A new method of electrochemical analysis has been developed for polycyclic aromatic and heterocyclic structures in coal-derived liquids: electroactive species are adsorbed on hard, planar mercury electrodes, which can then be transferred to aqueous electrolytes for electrochemical studies. Previously obtained tabulations of reduction potentials for a wide range of model aromatic and heterocyclic compounds have been revised and extended for comparison with potentials observed for coal-derived liquids. Redox potentials for single compounds did not differ systematically from those measured for mixtures. Different structures with similar redox potentials could be distinguished by variations in adsorption potentials. A further means of distinguishing nitrogen compounds from hydrocarbons was afforded by the forms of the electrode adsorption isotherms and their different adsorption-time behaviour. A quantitative analytical method for mixtures was developed from measurements of the charge passed in reducing the adsorbed layer, using fluorimetry to measure the concentrations of dilute solutions, and the relation between the molecular structure and the apparent number of electrons transferred during reduction was investigated. A wide variety of representative coal-derived liquids was investigated; the principal aromatic groups present were identified and quantitative estimates were made of their concentration.