NEW TECHNIQUE FOR THE ELECTROCHEMICAL ANALYSIS OF COAL-DERIVED MATERIALS

A new method of electrochemical analysis has been developed for polycy clic aromatic and heterocyclic structures in coal-derived liquids: ele ctroactive species are adsorbed on hard, planar mercury electrodes, wh ich can then be transferred to aqueous electrolytes for electrochemica l studies. Previously obtained tabulations of reduction potentials for a wide range of model aromatic and heterocyclic compounds have been r evised and extended for comparison with potentials observed for coal-d erived liquids. Redox potentials for single compounds did not differ s ystematically from those measured for mixtures. Different structures w ith similar redox potentials could be distinguished by variations in a dsorption potentials. A further means of distinguishing nitrogen compo unds from hydrocarbons was afforded by the forms of the electrode adso rption isotherms and their different adsorption-time behaviour. A quan titative analytical method for mixtures was developed from measurement s of the charge passed in reducing the adsorbed layer, using fluorimet ry 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 repre sentative coal-derived liquids was investigated; the principal aromati c groups present were identified and quantitative estimates were made of their concentration. (C) 1997 Elsevier Science Ltd.