Supercritical fluid extraction and fractionation of high-temperature coal tar

The high-temperature coal tar sample was separated into 10 narrow oil fractions and one solid-phase pitch product by supercritical fluid extraction and fractionation using n-pentane as solvent at 220°C and pressure from 5 to 15 MPa. Results show that the accumulative yields increase with the extract pressure especially at the lower pressures, and the yield increase rate decrease gradually. The total yield of the oil extract is 78.36%, and the raffinate pitch yield is 21.64%, which is far below that of the conventional distillation. Elemental analysis and chromatograph-mass spectrometer analysis show that with the increase of the extraction pressure, the atomic ratio of carbon to hydrogen, the average ring numbers, as well as the average molecular weight of narrow oil fractions also increase gradually.