Extraction of Coal-tar Pitch by Supercritical Carbon Dioxide. Dependence of Chemical Composition of the Extracts on Temperature, Pressure and Extraction Time

Several extractions of coal-tar pitch were performed using supercritical fluid carbon dioxide. The relationships between extraction yield during supercritical fluid extraction (SFE) and the variables temperature, pressure and extraction time were investigated. For qualitative and quantitative identification of organic compounds, gas chromatography and gas chromatography-mass spectrometry were used. Each SFE experiment was performed at a specific pressure and temperature; the maximum yield was obtained at 200 bar and 125 ºC. In general, the yields of all compounds studied increased with increasing temperature, and reached their maximum values at 125 ºC; above this temperature, yields remained almost constant. Higher yields were also obtained with greater retention times or higher pressures. Partial selectivity could be achieved by extracting at different constant temperatures and constant pressures. South African Journal of Chemistry Vol.53(3) 2000: 179-19