Petrographic Changes in Compaction Themal Treatment of Recent Plant Materials, Peat and Coals

Abstract

Recent plant materials, peat and coals were compressed and thermally treated at various temperatures (200-400°C) for 25 hours. The compaction pyrolysis products were observed with a microscope in both reflected and fluorescent lights, and their vitrinite reflectance (Ro) were also measured.
The Ro values of the original samples varied from 0.1 of peat to 0.7 of Miike bituminous coal. After the thermal treatment at 300, 350 and 400°C, the Ro values increased to 0.7-1.0, 1.2-1.4 and 1.7-2.1, respectively, in spite of the kind of the original material. The compaction pyrolysis products obtained from plant materials at 200°C showed specific textures which are often observed in natural low rank coals. Those textures became homogeneous with the increasing temperatures of the thermal treatment. Petrographic characteristice of the xylems of Morwell coal and red pine changed similarly during the thermal treatment. Because peat and humus soil contained a large amount of mineral matter, they provided the pyrolysis products with different textures from other materials.
The fluorescent material of leaf (metasequoia) after the thermal treatment at 200°C was considered as cutinite, and it started to melt around 250°C and disappeared around 300°C, whereas thet of Miike bituminous coal did not melt and disappear even around 300°C.
There still remain quite a few coal macerals of which origin and formation are unclear, and the artificial maturation followed by the microscopic investigation is one of effective approaches to elucidate them.