FRACTIONATION OF PETROLEUM PITCH BY SUPERCRITICAL FLUID EXTRACTION

Petroleum pitch has considerable potential as an inexpensive raw material for the economical production of high-performance carbon fibers and carbon-carbon composites. However, current methods for pretreatment of the pitch have several deficiencies that result in inferior fiber and composite properties. A better separation process is needed to improve the reproducibility and quality of the mesophase pitch precursor. A supercritical fluid extraction process is being investigated for this purpose. A flow apparatus is described for measuring phase equilibrium data for mixtures of solvent and pitch at temperatures up to 675 K and pressures to 350 bar. Equilibrium phase compositions are reported for the toluene/Ashland A-240 pitch system at temperatures of 595, 634, and 674 K and pressures ranging from 29 to 76 bar. The molecular weight distributions of the extracted fractions show that the process is effective in separating pitch fractions by molecular weight.