Abstract
Supercritical gas extraction of Taiheiyo coal has been investigated using toluene, toluene-tetralin mixtures, toluene-quinoline mixtures, and water as solvents with semi-batch type apparatus.
Regardless of the solvents used, extraction yield and conversion increased with an increase in extraction pressure and reached a maximum at about 20MPa. For toluene, a maximum in extraction yield occurred at a temperature around 350°C, and a nearly linear relation was observed between the conversions and temperature in the range of 330 to 380°C.
Extraction of coal gave three products: coal extract, tar, and gas. Small amounts of tetralin or quinoline added to the toluene solvent increased coal extract yield remarkably but conversion only increased slightly. Water gave a higher proportion of gas whereas toluene gave more tar. It was found that the distribution of these products could be controlled by changing the solvent species.
The coal extract was rich in volatile matter and was a pitch-like material having a softening point of about 100°C. The extracted material (coal extract and tar) was pyridine soluble matter and consisted of almost only asphaltene (>90wt%). The molecular structure of the coal extract became more condensed with increasing temperature, pressure and extraction time. The extraction mechanism could be explained using a two-component structure model.
