The microscopy of mesophase formation and of anisotropic cokes produced from solvent‐refined coals

Thermal processing of coal and coal products can lead to the formation of ordered carbons through the mesophase mechanism. The performance characteristics of metallurgical coke may be improved by the extent of this ordering; however, in the direct hydroliquefaction of coals the objective is to make species of low molecular weight, and coking is an undesirable retrograde reaction. This study is concerned with fundamental mechanisms of coke formation and their roles in these two processes. Most studies of mesophase formation have involved the heat treating of samples followed by quenching and examination at room temperature. This project has used hot‐stage microscopy and the production of a 16‐mm colour film to study the dynamics of mesophase growth and coalescence. Various solvent‐refined coal (SRC) and SRC fractions were carbonized in gold tubes at 450°C and 34.5 MPa, and the pyridine‐insoluble fractions (semi‐coke) examined microscopically. Greater molecular mobility, manifested by lower proportions of anisotropic carbon and larger domain sizes, was evident for SRCs which had undergone more extensive hydrogenation at the pilot plant, and for SRC fractions of lower functionality. The performance of metallurgical coke in the blast furnace can be related to its inherent carbonaceous structure. Coals which give cokes of marginal quality include low‐rank bituminous coals which form an optically isotropic coke. One method of improving the carbon ordering in these cokes is the use of a carbonizing additive. In this study SRC was used as the additive, giving improvements in the coke structure and microstructure. 1983 Blackwell Science Ltd