OPTICAL-PROPERTIES OF COALS AND LIQUEFACTION RESIDUES AS INDICATORS OF REACTIVITY

The trend of vitrinite fluorescence intensity within the bituminous rank range, peaking in high volatile A coals, is thought to be due mainly to the development of the mobile or molecular phase with thermal maturation. A strong parallelism exists between fluorescence intensity, solvent yield and the thermoplastic behaviour of coals and hydrogenated coals. Determination of the reflectance distribution of hydrogenated coals can provide a measure of competing hydrogenation and retrogressive reactions in catalysed and non-catalysed runs, conducted both dry and with a solvent vehicle. The type of vitroplast generated and the anisotropy of the unextracted products give further insight into the size and mobility of the molecules generated by hydroprocessing. The relative reactivities of vitrinite and sporinite were reversed at different rank levels. The alteration of fluorescence intensity with time is another rank-dependent property; the phenomenon is seen clearly to be due to photochemical oxidation on irradiation. Highly weathered bituminous coals respond in a unique manner, similar to those of low rank coals which lack the negative alteration component due to the presence of the mobile phase. This may be due to the creation of absorption centres and enhanced molecular rigidity through cross-linking reactions.