Stagewise fractionation of petroleum pitches with supercritical toluene

A stagewise fractionation technique employing sequential single-stage extractions with super-critical toluene was used to fractionate the heaviest portion of an isotropic petroleum pitch. Each stage was operated in a region of liquid-liquid equilibrium (LLE) at a temperature of 614 K and a solvent-to-pitch ratio of 2.0, and the pressure was sequentially reduced so as to precipitate out similar to5 wt % of the feed pitch in each stage. Five single-stage flashes could be carried out in the LLE region at pressures ranging from 138 to 52 bar, and five pitch fractions comprising the heaviest 28.8 wt % of the feed pitch were obtained. No flashes were performed below the onset of vapor-liquid equilibrium at 49 bar, because the vapor phase is a relatively poor solvent for pitches. Softening points, C/H ratios, and DRIFTS were all used too characterize the pitch fractions that were isolated. The heaviest three fractions had to be hydrogenated to increase their solubility in the mobile phase before molecular weight distributions could be determined by gel permeation chromatography. Results from the characterization techniques all indicate that stagewise fractionation is separating the pitch according to molecular weight.