Molecular probe chromatography of selected lignites

Abstract

The properties of selected lignites have been studied by a molecular probe technique using several probes. Following the sorption of air components and carbon dioxide at ambient temperature, interesting flow disturbance peaks were observed due to swelling and shrinkage of the packing mass. Both the retention and peak asymmetry of carbon dioxide increase significantly upon column conditioning. Irrespective of their chemical identity, the probe molecules are sorbed on the surface of lignite by an adsorptive mechanism alone up to 175 °C. The probes are retained in the column both by specific and non-specific interaction forces, the former being very large. Water and methanol sorbed in monolayer or submonolayer coverage can only be eluted easily at a temperature of ≈ 175 °C. As well as hydrogen bonding, dative linkages of polar ligands with transition elements associated with brown coal have also been considered to contribute to the observed retention behaviour. The column permeability may depend on the sulphur content of lignites. The very large stationary phase non-equilibrium coefficient for carbon dioxide mass transfer has been ascribed to the slow interfacial mass transport within the micropores.