PRODUCTION OF MESOPHASE PITCH BY SUPERCRITICAL FLUID EXTRACTION

Supercritical fluid extraction is being investigated for the production of the mesophase pitch used to make high-performance carbon fibers. A heat-soaked, isotropic petroleum pitch has been fractionated with supercritical toluene in a region of liquid-liquid equilibrium at temperatures and pressures to 656 K and 140 bar, respectively. Since both phases are black and opaque at the conditions of interest, an AC impedance bridge technique was used to detect the liquid-liquid interface level in the equilibrium cell. For all tested experimental conditions, the bottom-phase fraction contained a high percentage of the mesophase necessary for producing anisotropic carbon fibers. Generalized correlations have been developed for the characteristic constants of the Peng-Robinson equation applicable to high molecular weight, aromatic hydrocarbons.