SUPERCRITICAL-FLUID EXTRACTION OF COAL-TAR PITCH .2. EXTRACTION OF THE LOWER MOLECULAR-WEIGHT SPECIES WITH ALIPHATIC SOLVENTS

Extraction of coal-tar pitches has been carried out with a number of aliphatic hydrocarbons at temperatures between 210-degrees-C and 300-degrees-C and pressure of 10 or 15 MPa resulting in extraction yields of up to 50%. The toluene-insoluble (TI) content, molecular weight and the rate of mesophase formation of the residual (refined) pitches increase as the extraction yield increases. The molecular weight of the extract also increases with extraction yield. The volatiles produced during mesophase formation from a supercritical hexane-extracted pitch were analysed by NMR and mass spectrometry and were similar to the hexane extract.